DOI:
10.1039/D4SE00565A
(Review Article)
Sustainable Energy Fuels, 2024,
8, 3476-3495
Flatland materials for photochemical and electrochemical nitrogen fixation applications: from lab-door experiments to large-scale applicability
Received
28th April 2024
, Accepted 26th June 2024
First published on 27th June 2024
Abstract
Rational design of materials in a catalytic system is the main determinant of the efficiency of sustainable energy sources. Significant efforts have focused on the study and development of flatland two-dimensional (2D) materials (MXenes, MBenes, transition metal dichalcogenides/phosphides (TMDs/TMPs), phosphorene, graphene derivatives) towards energy-driven aspirations in consideration of their superior physiochemical properties as compared to their non-layered counterpart materials, surpassing their transport properties and conductivity. Herein, we aim to provide a detailed account of where the flatland materials currently stand to achieve the goal of sustainability in light of their photochemical and electrochemical nitrogen fixation applications. As of now, numerous challenges have limited the expansion of 2D-material derived nitrogen fixation operations for scalable applications. Therefore, we summarized techno-economic analysis and future perspectives of nitrogen fixation applications in relation to their practical ammonia applicability. We have briefly summarized the functionality of flatland materials and classified them on the basis of their photochemical and electrochemical efficiencies.
![image file: d4se00565a-p1.tif](/image/article/2024/SE/d4se00565a/d4se00565a-p1.gif) Syed Asim Ali | Syed Asim Ali completed his undergraduate and post-graduate studies at Jamia Millia Islamia, New Delhi. Subsequently, he joined the Nanochemistry Lab under the supervision of Prof. Tokeer Ahmad. His research interests include the design of nanocatalysts, energy conversion and sensing applications, computational chemistry and techno-economic analysis. He is currently working on the synthesis and characterization of molybdenum chalcogenides-based heterojunctions for their multi-functional applications. |
![image file: d4se00565a-p2.tif](/image/article/2024/SE/d4se00565a/d4se00565a-p2.gif) Iqra Sadiq | Iqra Sadiq graduated from K. R. Mangalam University and completed her post-graduate studies at G. D. Goenka University, Gurugram. She then joined Jamia Millia Islamia University, New Delhi, as a research scholar under the supervision of Prof. Tokeer Ahmad, and is currently working on the chemical synthesis and structural characterization of some functional nanostructures for environmental remediation and energy-based applications. |
![image file: d4se00565a-p3.tif](/image/article/2024/SE/d4se00565a/d4se00565a-p3.gif) Tokeer Ahmad | Prof. Tokeer Ahmad (graduated from IIT Delhi) is the full Professor of Chemistry at JMI Delhi. Prof. Ahmad has supervised 16 PhD's, 79 postgraduates, 10 projects, and published 194 research papers, one patent and three books with research citation of 7610, h-index of 52 and i10-index of 153. Prof. Ahmad is the recipient of the CRSI Medal, MRSI Medal, SMC Bronze Medal, ISCAS Medal, Inspired Teacher's President of India Award, DST-DFG award, Distinguished Scientist Award, Maulana Abul Kalam Azad Excellence Award of Education, Teacher's Excellence Award, and was elected as Member of the National Academy of Sciences, India. Prof. Ahmad is also an admitted Fellow of the Royal Society of Chemistry (FRSC), UK. |
Introduction
The present era of energy utilization has predominantly involved the extensive use of fossil-derived fuels dating back to the dawn of the industrial revolution. The last century paved the way for oil reserves, consolidating the fossils in strengthening economies across the globe.1,2 In the face of environmental challenges and the urgency to mitigate the effects of global warming, the pursuit of sustainable energy has emerged as a global imperative. Sustainable adaptability can be achieved by subscribing to those energy sources and maneuvers that meet the world's present needs and do not obstruct the scope of future generations for utilizing natural resources. Renewable energy resources such as hydrogen production via overall water splitting and hydrocarbon fuels originating from CO2 reduction reaction (CO2RR) are the front-runners aimed at alleviating carbon emissions and promoting a transition to a low-carbon economy.3–5 Despite significant progress in the research of hydrogen evolution reaction (HER) and CO2RR, both these processes have some disadvantages6 such as extraordinary costs associated with storage and transportation of the hydrogen carrier and separation of the desired product from the mixture of carbon-based products. Utilizing ammonia (NH3) as the source of renewable energy and as the transport medium for carrying H2 fuel comes with several benefits such as its compactness and higher efficiency in durable and longer distance energy endeavours.7,8 The market size of NH3 is expanding dramatically, which is substantially driven by its conventional use in agricultural and manufacturing sectors alongside its growing interest as a carbon-neutral energy carrier. Among the different routes of NH3 synthesis, one natural enzymatic reduction phenomenon is the conversion of nitrogen (N2) via nitrogenase that replenishes the N-cycle.9–11 Nevertheless, the lethargic kinetics of NH3 formation restrict the applicability of this pathway. Production of NH3 from photochemical and electrochemical N2 fixation processes at ambient conditions is an emerging area of research that has gained attention on account of the industrial significance of NH3 as the precursor to manufacturing many important chemicals and fertilizers.12–15 The efficiency of the photochemical and electrochemical nitrogen reduction reaction (NRR) for NH3 production relies upon the prudent choice of a catalytic system that can accelerate the reaction dynamics.16–21 A wide array of catalytic systems has been constructed by researchers to augment the yield of the targeted renewable energy carrier during energy-conversion applications. These systems include perovskites,22,23 mesoporous materials,24,25 transition metal oxides26/phosphides27/dichalchogenides28/carbonitrides/borides,29,30 single-atom catalysts (SACs),31,32 layered double hydroxides (LDHs),33,34 and carbon-based derivatives.35
Among these materials, the development of flatland materials has been a ground-breaking achievement in materials science and nanotechnology,36 offering unique properties and potential applications across interdisciplinary fields,37 including electronics,38 energy storage,39 catalysis,40 and biomedicine.41 In addition, the recent advances in flatland materials have ascertained their energy conversion applications.42 Chemical strategies, such as doping,43 surface modification,44 and heterostructure engineering,45 have been employed for tuning and engineering the properties of flatland materials for energy conversion applications. The functionalization and integration into a heterojunction formation have led to the development of novel devices with enhanced performance and functionality.46 The rise of graphene/graphitic nitride derivatives paved the doors of 2D compounds, as these materials possess remarkably higher surface area and tunable electronic properties that are highly sought after for catalytic transformations.47,48 As of now, different flatland materials have been designed and exploited in energy conversion applications, viz., hydrogen and oxygen evolution reactions (HER/OER)28,35 and CO2 sequestration.49 Nevertheless, the research of these layered materials toward NRR is still at its nascent stage, and researchers are showing immense interest in their applicability as state-of-art catalytic systems for the NRR process. Noteworthily, the origin of the catalytic excellence of several 2D materials is linked to their exposed edge facets and defect surfaces that also govern their NRR performance.49,50 Diverse modification attempts have been made by researchers to augment the catalytic efficiency of flatland materials, such as surface functionalization,51 intercalation,52 and incorporating porous materials or non-layered materials (such as porous organic polymers (POPs) or TiO2) to develop heterojunctions.28,53,54 These chemical strategies to tailor the physicochemical properties of flatland materials require optimized reaction conditions at the time of synthesis, such as the solvent selectivity, thermal conditions and exfoliating parameters, to extract monolayers of 2D materials.48 To achieve a higher yield during the NRR process, the enhancement of exposed surface sites is the primary factor. The ideal flatland material-based catalytic system is expected to provide an inherent basal plane activation, while possessing higher selectivity for N2-adsorption as compared to H-adsorption as an HER, making it a thermodynamically more viable process than NRR. The efficient synergetic relationship between the catalytic activity and long-term stability of 2D materials-based catalysts is necessary to have robustness during the NRR process. The stability and durability of flatland materials suffer from several bottlenecks, which restrict their performance. The 2D materials usually comprise defects, such as vacancies, grain boundaries, and edge irregularities, which ideally serve as active sites. However, they can also be prone to degradation, leading to the loss of catalytic activity. The 2D materials can undergo unwanted oxidation or reduction reactions, especially under extreme pH conditions or at high temperatures, which can alter their electronic structure and catalytic properties. When 2D materials are exploited during heterojunctions formation, weak interactions between the 2D material and the support can lead to detachment and loss of the active material. Fabricating 2D materials with consistent quality and physicochemical properties on a large scale is challenging. Variations in synthesis methods can lead to inconsistencies in the catalyst performance. Addressing these challenges involves synthetic advancements, enhancing the understanding of the material properties under operational conditions, and developing strategies to protect and stabilize 2D materials during catalytic transformations.
Synthetic advancements in the development of flatland materials
For the systematic exploitation of 2D materials to the maximum extent, the prudent choice of the synthetic protocol is necessary. Improved synthesis techniques lead to higher-quality 2D materials with tailored properties, addressing many of the challenges associated with their stability and durability. There are plenty of top-down and bottom-approaches that have been reported in the literature for the fabrication of functional and advanced materials, such as the facile hydrothermal route, sol–gel/polymeric citrate precursor method, reverse micellar, chemical vapor deposition, mechanical/chemical exfoliation, lithography techniques and many more.55–60 One of the most important routes of constructing MXene and MBene is their etching from the parental MAX/MAB phases, where A is basically the transition metal (such as Al, Ga or Sn). The MAX/MAB phase precursors are generally prepared via powder metallurgy techniques, followed by etching using stronger acid etchants such as HF/H2SO4 to selectively eliminate the A-layers. The etching routes expose the MXene/MBene layers, which are then washed and delaminated to obtain colloidal suspensions or films of MXene/MBene nanosheets.61 Exfoliation of bulk MXene/MBene materials involve breaking down the layered bulk MXene/MBene into individual nanosheets, which can then be dispersed in solvents to obtain colloidal suspensions or thin films.62,63 Another interesting method of designing MXenes and MBenes is the intercalation/delamination method, in which the concerned-intercalated precursors are subjected to chemical or electrochemical treatments to selectively eject the interlayer ions or nanoparticles, leading to the delamination of the layered structure into MXene/MBene nanosheets.64 Alongside these exfoliation and top-down methodologies, there is the growing interest of researchers toward designing MXenes and MBenes through bottom-up approaches, such as chemical vapor deposition (CVD)65 and facile hydrothermal method,66 without utilizing environmentally hazardous F-based etchants that are not economical for the scalable synthesis of MXene/MBene nanosheets.67 These methodologies offer versatile chemical strategies for developing MXene/MBene materials with tailored properties and structures to ensure their simplified integration into various energy-related applications. Recent attempts have focused on optimizing the synthesis parameters, scaling up the production and exploring novel MXene/MBene catalysts to expand their range of applications.68,69 For the development of TMDs, there are diverse fabrication routes that ensure morphological and structural tailoring to a larger extent, such as CVD, template-assisted synthesis, mechanical/chemical/liquid-phase exfoliation. CVD provides a simplified protocol to prepare high-quality TMDs nanosheets with higher specific surface areas.70 By tuning different reaction parameters like the temperature, pressure, precursor concentration, and substrate type, the rate of nucleation and growth can be modulated to design the desired morphology of TMDs materials required for targeted applications. Exfoliation techniques of synthesizing TMDs generally involve manually peeling off thin layers of bulk TMDs to acquire TMDs monolayers with great control over the thickness of the nanosheets. The facile hydrothermal route ensures the construction of TMDs having controlled size and desirable morphological and structural properties under 180–200 °C temperature range at higher pressure.26,28 These routes have been comprehensively discussed in reviews elsewhere.70 The fabrication routes of TMPs generally encompass different methods based on the precursors of P, such as elemental phosphorus, phosphorenes or organic phosphines. To achieve morphological tunability and higher specific surface area, P-pyrolysis with a C-based compound is an excellent method that hampers the aggregation of TMP nanosheets and improves its electrical conductance. Just like other 2D materials, there are different routes of TMPs fabrication, such as phosphorizing metal sources,71,72 CVD, solid state method, and hydrothermal synthesis, as detailed in reviews elsewhere.27 The fabrication routes of carbon-based derivatives are more or less similar to those of other 2D materials, such as CVD, exfoliation techniques for g-C3N4,73 and the Hummer's method for synthesizing graphene oxide (GO) and reduced-GO. These fabrication routes all fundamentally involve the utilization of different chemical reducing agents, such as hydrazine, hydroiodic acid, or thermal treatment under reducing atmospheres.47 Despite the success of these methods in designing flatland materials, the achievement of scalability in their synthesis is fundamental for realizing their industrial applications. State-of-art approaches such as high-throughput screening techniques can be exploited, which involve systematically screening a large number of reaction conditions and parameters to identify optimal conditions for the preparation of 2D materials.74 Reaction variables like the reactant concentrations, reaction temperatures, mixing rates, and reactor geometry can be optimized to attain an equilibrium between the maximized yield and minimized production costs.75–77 Pilot-scale operations and process modelling can be utilized to determine the critical factors affecting scalability and guide the design of large-scale 2D materials synthesis processes. The advancements in the fabrication routes are pivotal for the construction and application of 2D materials in NRR.
Nitrogen fixation
N2 fixation is regarded as one of the most significant processes to transform atmospheric N2 into NH3 and other value-added N-based compounds. This transformation can be achieved through a wide array of pathways, such as the conventional Haber–Bosch method, biological or microorganisms-assisted N2 fixation. Artificial photochemical N2 fixation is a sustainable route for developing nitrogenous compounds by utilizing photon energy and replicating the natural N2 fixation process. Similarly, electrochemical N2 fixation also should produce N-based chemical feedstock at the expense of electrical energy.78–81 Among the various nitrogenous compounds, NH3 holds relatively superior industrial significance and day-to-day applicability, as it serves as the fundamental precursor in manufacturing several fertilizers and purifiers.82 Alongside, condensed NH3 promises applications in the energy conversion on account of its greater gravimetric density and transportability as compared to H2 fuel. The recent trend of sustainable energy transition suggests an exponential growth in the demand of H2 fuel by 2050. However, there are challenges in achieving efficient transportation over a larger distance in compact containers. In contrast, NH3 is relatively easy to transport with the requirement of a less complicated infrastructure.83,84 Green NH3 synthesis relies upon the accelerated production of H2 simultaneously with the extraction of N2 from the environment via air separating techniques. Photochemical and electrochemical NH3 production routes are carbon-neutral pathways that aspire to generate NH3 efficiently and economically in the near future.85,86 NH3 is most commonly produced commercially via Haber–Bosch reactions, which require high temperatures (400–500 °C) and pressure (15–25 MPa). A simpler and environmentally benign protocol of NH3 is sought after to accelerate the pace of NH3 usage as an energy carrier.
NRR applications of flatland materials
Flatland materials have garnered significant attention for effective NH3 production due to their unique physicochemical features. These 2D materials offer a diverse range of properties and structures that can be tailored via different compositional and structural modifications, such as surface functionalization, heterostructure engineering, and optimization of electronic and catalytic properties.87 Perseverant advancements into the rational design, characterizations and applications of 2D materials affirm their scalability in sustainable nitrogen fixation technologies.
Photochemical applications
The reaction mechanism of photochemical NRR generally progresses via the formation of several reactive intermediate species like N-based radicals and adsorbed N-intermediates that have to effectively undergo the hydrogenation reaction, followed by desorption to generate NH3.88 The excellent optoelectronic and surface properties of 2D materials are of paramount importance in mediating the thermodynamic landscape of NRR by providing the favourable free energies and lower reaction barrier during the surface reactions on the active materials.
MXenes- and MBenes-based photocatalysts
MXenes and MBenes have emerged as two of the latest classes of flatland materials that hold a plethora of potential for heterogeneous catalysis, especially in energy-conversion applications, owing to their enormously higher exposed active sites and unusual layered structures.89 Current research has hinted that MXenes- and MBenes-based catalytic systems have advanced the enhancement in the rate of N2-adsorption/activation and its conversion into NH3 through photochemical and electrochemical NRR processes.90–92 As of now, the quantum yield of MXenes-led NRR remains lower as compared to the non-sustainable routes of NH3 synthesis. This is the main reason that a deeper understanding of the mechanism is requisite to optimize the activity of MXenes. Gao et al.93 fabricated a unique MXene-based heterostructured photocatalyst composed of Co-decorated Ti3C2/TiO2 for effective nitrogen fixation. The group demonstrated that the tailoring of the surface activity of N2 was due to the presence of Co-atoms, as the extent of chemisorption was altered. The optimized photocatalyst achieved as high as 110 μmol g−1 h−1 NH4+ yield in the absence of any sacrificial hole acceptor species. Hao et al.94 hydrothermally constructed a RuO2-incorporated TiO2–Ti3C2Tx photocatalytic system to examine its nitrogen fixation performance at ambient conditions. The group revealed that the augmented activity of the as-developed catalytic system was due to the symbiotic effects between the MXene/metal oxides, and to the efficient N2-activation over light exposure. Liao et al.95 showcased the role of Ti3C2 in augmenting the NRR activity of the P25 (TiO2) photocatalyst, attributed to its higher exposed active sites and marvelous electrical conductance. In addition to that, the improved N2-adsorption over the Ti3C2-P25 photocatalyst resulted in its 5-fold higher NRR performance as compared to pristine P25. The close-knit relationship between Ti3C2-P25 was realized by X-ray photoelectron spectroscopy (XPS), as illustrated in Fig. 1(a)–(d). The photochemical results inferred enhanced NH3 selectivity over H2 evolution on account of the relatively higher chemisorption of N2 over the H-atoms. Furthermore, the lower conduction band position of Ti3C2 also favoured the NRR, as can be seen in Fig. 1(e). Shen et al.96 engineered a ligand-bridged Ti3C2Ox/MIL-125(Ti)-based MXene/MOF photocatalyst to favourably couple the O-terminal groups (MXene) with the COO-groups (MOF). This type of coordination linkage facilitated the charge migration via heterojunction formation during the NRR process. The as-prepared photocatalyst displayed a remarkable NH3 production rate as high as ∼103 μmol gcat−1 h−1, which was ascribed to the monodirectional channelization of electron carriers from MOF to MXene. Intermediary species formed during the course of the NRR experiment over the optimized Ti3C2Ox/MIL-125(Ti) photocatalyst were assessed via DRIFTS technique, which proved the N2-adsorption and activation due to the advent of peaks corresponding to N-based intermediates, as illustrated in Fig. 2(a). These observations indicated the probable symmetric side-on mechanistic route for the NH3 production. The authors utilized density functional theory (DFT) calculations to investigate the impact of ligand-bridging on the dynamics of N2-activation. Bader charge analysis and the corresponding 2D curve of the Ti3C2Ox/MIL-125(Ti) photocatalyst revealed the extensive charge migration occurring through the ligand molecular bridge (LMB). Based on the hydrogenation reaction step of adsorbed-N2 over Ti3C2Ox/MIL-125(Ti), NRR could have proceeded via two different distal and alternating pathways, as shown in Fig. 2(b). Both reaction mechanisms exhibited varying energy barriers, where the alternating route inferred a relatively lesser uphill energy barrier. In addition, the authors analyzed the modifications in the N–N bond order in the span of the reaction mechanism to further supplement their identification of the probable NRR route. Based on the bond length values of the N–N bonds in both pathways, the pronounced bond elongation in the alternating route provided the evidence that it was the predominant course of NRR. Just like their MXenes counterparts, MBenes have also recently emerged as active materials for the photocatalytic NRR process. Zhang et al.97 developed the unique Ni3B-incorporated N-vacant g-C3N4 (VN-CN) to augment the N2 fixation efficiency for NH3 generation. The group ascertained the Schottky junction-formation between MBene and VN-CN, which led to the improved light harvesting and higher exposed sites availability for adsorbing and activating N2 molecules. The optimized Ni3B/N-vacant g-C3N4 photocatalyst revealed a rate of NH3 production as high as 7.68 mM g−1 h−1, which was nearly 7-fold higher than bare g-C3N4. These recent achievements in MXenes and MBenes infer the potential of these 2D-materials toward NRR applications.
![image file: d4se00565a-f1.tif](/image/article/2024/SE/d4se00565a/d4se00565a-f1.gif) |
| Fig. 1 Core-level spectra of (A) C 1s, (B) Ti 2p, (C) O 1s of bare P25(TiO2), Ti3C2 and the optimized Ti3C2-P25 heterostructure. (D) Chemical interactions between TiO2 and Ti3C2. (E) Reaction mechanism of the photochemical NRR for NH3 formation over the Ti3C2-P25 heterostructure. Reproduced with permission.95 Copyright 2020, Elsevier. | |
![image file: d4se00565a-f2.tif](/image/article/2024/SE/d4se00565a/d4se00565a-f2.gif) |
| Fig. 2 (a) In situ infrared spectra of the optimized Ti3C2Ox/MIL-125(Ti) heterojunctions analyzed at the time of photochemical NH3 generation. (b) Thermodynamic landscape for alternating and distal reaction mechanisms over Ti3C2Ox/MIL-125(Ti). Reproduced with permission.96 Copyright 2024, Elsevier. | |
TMDs-based photocatalysts
TMDs have attained significant benchmarks in the field of photochemical NRR on account of their uncommon electronic properties, higher specific surface area, lower band energy and facilitated visible light absorption. TMDs possess active sites with favourable free energies that accelerate the adsorption/activation of nitrogen molecules, leading to efficient NH3 conversion.98,99 Alongside their unique physicochemical properties, two important chemical strategies to enhance the NRR activity of TMDs are structural and compositional modifications. The ability of TMDs to accommodate various dopants and functional groups, in addition to their ability to form heterojunctions with other conducting materials, remarkably augment their NRR response. Nevertheless, TMDs suffer from several bottlenecks, such as their limited chemical and thermal stability during photochemical environment, which consequently lead to the oxide formation and photo-corrosiveness of TMD-photocatalysts. Moreover, a profound understanding of the underlying NRR mechanisms is requisite to optimize the catalytic efficiency and stability of TMDs for practical applications. By developing novel TMDs-based heterojunction photocatalysts for energy conversion applications,26,28 researchers have made satisfactory progress in the past few years, especially for realizing their potential in NRR applications. Recently, Ma et al.100 illustrated the unique interfacial chemical bonding between MoS2/In-Bi2MoO6, which resulted in the enhancement of the NRR performance of the as-developed heterostructured photocatalyst fabricated via electrostatic self-assembly route. The group ascertained the advent of the Mo–S intermolecular chemical bonding between the heterostructured photocatalyst to be the primary influencing factor that facilitated the charge-transfer dynamics at the interfacial contact. The theoretical investigations inferred the transfer of electron carriers from MoS2 to the antibonding orbitals of N2-molecules for its activation. The optimized MoS2–In-Bi2MoO6 heterostructured photocatalyst exhibited ∼90 μmol gcat−1 h−1 rate of NH3 production. Based on the experimental observations, the authors revealed the significant role of MoS2 in impeding the generation of NO3− species, which is an offshoot of the oxidation reaction of the NH3/NH4+ present in the aqueous solution. Therefore, this study clearly depicted the role of the TMDs-based photocatalyst for the selective N2 photo-reduction reaction. To further highlight the role of MoS2 in achieving higher photocatalytic NRR performance, Hu et al.101 proposed an excellent study where they regulated the edge sites of MoS2 to augment the NRR performance. The S-rich edge sites of MoS2 are relatively exposed active sites that are responsible for the reduction reaction as compared to the S-atoms present on the basal planes. It was revealed that Mn-doping effectively enhanced the NRR activity of MoS2 by improving its edges. This led to the modulation of S-edges that facilitated the adsorption of N2 molecules and lowered the NRR energy barrier. Hydrothermally-derived optimized Mn-doped MoS2 depicted an NH3 yield as high as ∼213 μmol gcat−1 h−1 without using any sacrificial electron donor species, which was found to be nearly 5-fold higher than that for the bare MoS2 photocatalyst. Recently, Yao et al.102 constructed a TMDs/metal organic framework (MOF) heterostructured photocatalyst composed of WS2/ZIF-8 to examine its photochemical NRR activity using tap water in real/simulated solar energy. The optimized photocatalyst revealed an NH3 production rate as high as ∼191.6 μmol gcat−1 h−1, as can be seen in Fig. 3(a). The accelerated NRR performance was attributed to the enhanced light harvesting and higher separation of photo-excited charge carriers. In addition, the close-knit interfacial contact between WS2/ZIF-8 led to the pronounced weakening of the N2 bond and facilitated its activation dynamics during photochemical NRR. Fig. 3(b and c) demonstrates the Bader charge analysis and photocatalytic NRR mechanism for the generation of NH3. The transfer of electron-carriers from ZIF-8 to WS2 led to the facilitated reduction of N2, which was ascribed to the higher availability of electrons on the conduction band of WS2. Qin et al.104 explored the reaction mechanism of N2 adsorption/activation over the hexagonal-triclinic biphasic Mo1−xWxS2 photocatalyst for advancing the rate of NH3 production. The optimized Mo1−xWxS2 photocatalyst exhibited an NH3 evolution rate of ∼111 μmol gcat−1 h−1, which was found to be 3.7- and 3-fold higher than that of bare MoS2 and WS2. Experimental investigations manifested the favourable doping of W-atoms, which caused the exploitation of electron density states from the W 5d-orbital for the polarization of the adsorbed-N2 species. This report highlighted the significance of fabricating intramolecular TMDs to achieve an efficient NRR process. These recent advancements in TMDs-led NRR experiments reveal the scope of MoS2, MoSe2 and WS2 in accelerating the NH3 production efficiency by acting either as an active material or as the cocatalyst in heterostructured materials during photochemical transformations.
![image file: d4se00565a-f3.tif](/image/article/2024/SE/d4se00565a/d4se00565a-f3.gif) |
| Fig. 3 (a) Photochemical efficiency of the WS2/ZIF-8 catalytic system towards NRR in varying sources of photon energy. (b) Bader charge analysis and optimized crystal structure of WS2/ZIF-8. (c) Photochemical NRR mechanism over WS2/ZIF-8. Reproduced with permission.102 Copyright 2024, Elsevier. (d) Recyclability test of the optimized Ni2P/Cd0.5Zn0.5S photocatalyst under visible light irradiation. (e) Photochemical NRR mechanism over Ni2P/Cd0.5Zn0.5S for NH3 production. Reproduced with permission.103 Copyright 2017, Elsevier. | |
TMPs and phosphorene-based photocatalysts
TMPs are an emerging class of 2D materials that offer potential eminence when employed as a photocatalyst during the NRR process on account of their unique physicochemical properties that accelerate the transformation of N2 into NH3 under light irradiation. These flatland materials possess an edge over other photocatalysts in terms of their improved activity, selectivity, and stability during photocatalytic transformations.105,106 The excellent optoelectronic properties of TMPs assist in achieving higher efficiency in photochemical NRR processes, ascribed to the improved light absorption and their layered structure that promote the separation and migration of photo-induced charge carriers during photocatalysis. Alongside, TMPs exhibit exceptional surface properties with mesoporous exposed active sites that favour the adsorption/activation of N2 molecules during NRR. Recently, researchers have attempted to design the heterostructured photocatalytic systems by exploiting the remarkable physicochemical properties of TMPs. TMPs exhibit superior stability, robustness and prolonged lifetime during photochemical runs, which particularly make them viable photocatalysts for durable NRR experiments. To demonstrate the higher stability of the TMP-based photocatalysts, Gao et al.107 recently reported on the construction of a g-C3N4/Ni2P/Ni-3D reticulated foam photocatalytic system (CNNPF) for visible light-driven NRR application. The as-designed CNNPF photocatalyst displayed excellent NRR activity as high as ∼373 μmol gcat−1 h−1 rate owing to the synergetic relationship of g-C3N4/Ni2P, which resulted in the ameliorated charge-transfer dynamics. The group revealed that the 3D-scaffold was responsible for providing the exposed surface-sites availability for N2 capture. The CNNPF photocatalytic system has shown advanced stability and recyclability after 5 consecutive cycles without significant loss in the activity toward the NRR process. This study demonstrates the significance of designing a stable photocatalytic system for durable NRR application. To highlight the simultaneous HER and NRR applications of TMP-based photocatalysts, Wang et al.108 recently came up with an interesting study where they reported the simple route of designing a unique Ohm–Schottky heterostructured photocatalytic system by utilizing Co–Ni2P nanosheets. The as-designed modified-CdS/Co–Ni2P/O-rich Ti3C2 photocatalyst revealed a H2 yield as high as 1.72 mmol h−1 and NH4+ yield of ∼656.8 μmol L−1 h−1 with 59.81% AQE. The enhanced HER and NRR performances were ascribed to the improved interfacial charge transfer via Ohm–Schottky heterojunctions. Theoretical investigations ascertained the positive impact of decorating the Co–Ni2P nanosheets over CdS/MXene by providing favourable N2 adsorption energy and by increasing the conductivity of photocatalyst. Ye et al.103 fabricated a unique Ni2P/Cd0.5Zn0.5S photocatalyst. The TMP incorporation into Cd0.5Zn0.5S incredibly ameliorated the charge-transfer dynamics during the photochemical NRR process. In the visible-light driven photocatalysis, the NRR activity to achieve NH3 was found to be ∼101.5 μmol L−1 h−1 with 4.32% AQE. The heterostructured photocatalyst depicted no loss of activity after four consecutive cycles, as can be seen in Fig. 3(d). Moreover, the advanced performance of the TMP-based Cd0.5Zn0.5S photocatalyst was realized by the modulations of the conduction band (CB) positions after Ni2P loading, which tuned the photo-reduction efficiency during NRR, as shown in Fig. 3(e). As compared to Cd0.5Zn0.5S, the relatively higher CB position of the heterostructured photocatalyst facilitated the N2 reduction and lowered the dynamics of oxidation of NH3 into NO3−, which was confirmed by the low yield of the latter (∼0.35 μmol L−1 h−1). Phosphorene is the P-analog of graphene that is composed of a honeycomb lattice composed of P-atoms. Phosphorene has gained significant research interest owing to its unusual physicochemical properties, such as its higher specific surface area, and its peculiar electronic properties that favour its energy conversion applications.109 The effectiveness of phosphorene materials in the photochemical NRR application is supported by its recent reports. Wang et al.110 designed the unique non-metallic B-decorated phosphorene (BP) photocatalytic system for investigating its photochemical NRR performance. The group revealed that in the case of P-phosphorene, the adsorption limit of the photocatalyst towards N2 remains limited. However, the BP-photocatalyst has shown its structural superiority to enhance the rate of N2 capture by the utilization of vacant and filled sp2- and p-orbitals, respectively. This ensured the better electron-acceptance and -donation between the σ–π* orbitals for efficiently adsorbing N2, as illustrated in Fig. 4(a). On account of the boron-decoration, the band structure of phosphorene was considerably tailored and the electrical conductance of the photocatalyst was uplifted to favour the NRR performance, as revealed in Fig. 4(b). The B-sites played a crucial role in transmitting electron-carriers from BP to N–H composites during N2 activation.
![image file: d4se00565a-f4.tif](/image/article/2024/SE/d4se00565a/d4se00565a-f4.gif) |
| Fig. 4 (a and b) Mechanistic sketch of the photo-reduction of N2via the B-decorated phosphorene catalyst. Reproduced with permission.110 Copyright 2021, Elsevier. (c) Photochemical NH3 production performance of g-C3N4 and boron-decorated g-C3N4. Reproduced with permission.111 Copyright 2020, John Wiley and Sons. (d) Photochemical NRR activities of bulk g-C3N4 and carbon-vacant g-C3N4. Reproduced with permission.112 Copyright 2019, Elsevier. | |
This study provided insight into the reaction mechanism for improving the NRR activity of phosphorene due to the anchoring effect of the Boron atoms. Cheng et al.113 theoretically anticipated the NRR efficiency of the B-incorporation and oxidation of black/blue phosphorene. Their study also included the lowering of the band energy due to boron atoms, which enhanced the light absorption range in the visible-IR region. The thermodynamic screening also indicated the favourable formation energy of the B-introduction into phosphorene at ambient temperature. Furthermore, it was ascertained that the oxidation of the black/blue phosphorene augmented the NRR response via end-on/side-on modes during the reaction mechanism.
Carbon derivatives-based photocatalysts
Carbon-based derivatives have shown enormous growth in their catalytic applicability, which is ascribed to their peculiar layered structure and advanced stability. Graphitic-carbon nitride (g-C3N4) has been most frequently exploited for photochemical NRR application among the different carbon derivatives, as it is cost-efficient, easy to fabricate, and possesses visible light band energy. Experimental characterization techniques indicate its adequate band positions of conduction and valence bands to fulfil the thermodynamic criteria for the reduction of N2.114,115 To highlight the catalytic efficiency of g-C3N4, Liu et al.116 designed an Fe2O3/g-C3N4 photocatalytic system for NH3 synthesis through NRR. The Z-scheme type heterojunction formation facilitated the interfacial charge transfer. Furthermore, it was ascertained that g-C3N4 was the reduction photocatalyst responsible for the NRR, whereas Fe2O3 was the oxidation photocatalyst. The higher specific surface area with mesoporous active sites favoured the extensive N2 adsorption/activation as an optimized Fe2O3/g-C3N4 photocatalyst with an NH3 generation rate of 47.9 mg L−1 h−1, which was 6-fold higher than that of pristine g-C3N4. In order to activate the N-atom active sites in g-C3N4 such as edges/amino-N sites during NRR, Wang et al.111 came up with a unique study in which, by anchoring B-atoms over g-C3N4, the N-atom active sites were stabilized via the development of B–N–C bonding that ultimately boosted the photochemical activity of g-C3N4 towards NH3 production. The limited loading of boron into g-C3N4 enhanced the range of light absorption, and also impeded the recombination dynamics of photo-excited e−–h+ pairs. This was confirmed by the higher activity of the optimized photocatalyst for NH3 evolution (∼314 μmol g−1 h−1), which was found to be 10-fold higher than bare g-C3N4, as can be seen in Fig. 4(c). Dong et al.117 investigated the role of the nitrogen vacancy (Nv) in ameliorating the photochemical NRR performance of g-C3N4. As the shape and size of Nv was found to be identical to N-atoms of N2 molecules, it thus promoted the adsorption and activation of the reactant N2 during the reaction mechanism. Similar to this study, for the utilization of the carbon-vacancies (VC), Zhang et al.112 developed an ultrathin g-C3N4 having a higher VCvia thermal peeling technique that augmented the NRR efficiency. The group ascertained that the NRR activity of the carbon-based materials can be substantially increased by structural control at the atomic level and by the introduction of VC in g-C3N4. A photochemical NRR activity test was performed in N2 and Ar gases to determine the origin of the N-precursor for N2 fixation, as the catalyst in itself was composed of N. The control test inferred the fixed amount of NH4+ release in both catalytic systems, as can be seen in Fig. 4(d). The VC-rich g-C3N4 showed nearly 2.25-fold higher NRR efficiency as compared to bulk-g-C3N4, thus manifesting the significance of VC in augmenting the photocatalytic activity of g-C3N4. Other carbon-based derivatives such as graphene also exhibited a propensity to be utilized as a photocatalyst for NRR application owing to their ability to induce a higher hot electron density in the presence of visible light irradiation.118 To support this claim, Lu et al.119 demonstrated the induction of hot electrons from an Fe-decorated 3D-graphene photocatalyst to accelerate its activity and selectivity for NH3 production at ambient conditions in the presence of a simulated light source. The as-prepared Fe@graphene photocatalyst exhibited remarkable stability without losing its activity up to 50 h. Based on the aforementioned recent advances in the photochemical NRR process via flatland materials, we have highlighted the strategies of ameliorating the scalability of this carbon-neutral vector in Fig. 5.
![image file: d4se00565a-f5.tif](/image/article/2024/SE/d4se00565a/d4se00565a-f5.gif) |
| Fig. 5 Chemical strategies for advancing the photochemical NRR efficiency of catalytic systems. | |
Electrochemical applications
Aiming to supplant the energy-intensive Haber–Bosch method, the electrochemical NRR to form NH3 takes place under ambient conditions and can be propelled by renewable energy comprising solar energy, wind energy, etc. Thermodynamically, it has been considered that electrocatalytic NRR holds the advantage of 20% greater energy efficiency in comparison to the Haber–Bosh process.120 However, an effective electrochemical NRR has been evinced to be exceptionally challenging due to the need of a considerable amount of energy to break the N2 triple bond.121 Additionally, HER is the competitive process in electrocatalytic NRR as its theoretical reductive potential is less than NRR.122 It is widely known that one of the most crucial parameters in electrochemical NRR is the conductivity of materials; hence, the search for novel electrocatalysts to surpass the challenging issues is necessary for the electrocatalytic NRR industrial applications.123 In general, noble metal catalysts display significant activity, but their scarcity and high cost limit their far-reaching applications. As a result, research studies have changed focus to non-noble metals-derived catalytic systems, such as carbon derivatives, MXenes, TMDs, TMPs. Electrochemical NRR is a typical heterogeneous reaction that comprises the adsorption of N2 molecule at the catalytically active surface of the catalyst, hydrogenation and desorption of NH3 molecule or other intermediates. According to reduction and protonation sequences and the breaking of N
N bonds, electrochemical NRR can be classified into dissociative and associative mechanisms. In the dissociative mechanism, the N
N bond is broken at the time of adsorption, resulting in the adsorption of discrete N atoms separated by a defined distance. In the successive step, hydrogenation takes place on each N atom, leading to the construction of NH3 that is released in the last step. In the associative mechanism, the N
N bond stays intact after the adsorption of N2 and breaks at the time of hydrogenation. Consequently, the associative pathway is more complex than the dissociative route, and can be further simplified according to the hydrogenation sequences into distal, alternating, and enzymatic pathways. In the distal route, the hydrogenation preferentially takes place on the N atom that is away from the catalytic surface, inclining to the adsorption of one nitrogen atom after the release of the first NH3 on the catalytic surface. In the following steps, the successive hydrogenation of the remaining N atoms leads to the construction of a second NH3 molecule. In the alternating route, the hydrogenation takes place on two N atoms alternatively and N
N bond breaks with the generation of the first NH3 at the last step, which leaves one NH3 molecule behind.124 In contrast to the alternating route, N2 adsorbs at the catalytic surface in the very first step in the enzymatic route. The subsequent steps are similar to those in the alternating route.125 Recently, the Mars-van Krevelen mechanism was developed by Abghoui and Skulason. In this mechanism, the lattice N atoms are reduced to NH3 on the surface of transition-metal nitrides (TMNs) and N vacancies are thus created.126 These vacancies chemically adsorb N2 molecules for electrochemical NRR to occur continuously. Therefore, a suitable electrocatalyst for effective NRR is rather critical that can ensure the convenient reaction mechanism in order to attain higher NH3 efficiency.
MXenes and MBenes-based electrocatalysts
MXenes are a novel type of 2D materials possessing a high specific surface area, good electrical conductivity, stability and hydrophilic behaviours, making these flatland materials potential candidates for electrocatalytic NRR applications. Shi et al.127 fabricated the N-doped-TiV-Ti3−xC2Ty-1.2 MXene for electrocatalytic NRR. The introduction of Ti vacancies improved the adsorption and activation of N2. Furthermore, the N-dopant species enhanced the desorption of NH3. The optimized level of the N doping content and Ti vacancy density in the as-synthesized MXene boosted the electrocatalytic NRR with the rate of 24.33 μg h−1 mgcat−1 of NH3 and around 10% faradaic efficiency (FE) through the promotion of kinetic desorption and activation barriers of NH3. Ba et al.128 designed Ti3AlC2 MAX/Ti3C2 MXene electrocatalysts for N2 fixation. The difference of the surface potential between MXene and MAX was around 40 mV, indicating that the electron can be easily migrated from MAX to MXene over the interfaces. This was beneficial for N2 fixation, resulting in a remarkable FE of ∼40% and rate of 2.73 μg h−1 cm−2 of NH3. The outstanding NRR activity was ascribed to the unique MXene/MAX heterostructure framework that offered suitable and rich active centers to assist in the N2 adsorption billiard sequence, hydrogenation and N
N bond breaking. Guo et al.129 altered the surface of Ti3C2Tx (MXene) by introducing Fe to attain high surface reactivity for the NRR. The optimized MXene/TiFeOx-700 electrocatalyst exhibited remarkable performance with an NH3 production rate of 2.19 μg cm−2 h−1 and FE of 25.44% for the NRR. The improved catalytic activity was credited to the high surface reactivity of as-prepared optimized electrocatalyst generated through the reduction of inactive F*/OH* terminals and the rational decrement in the surface work function, which revealed the higher number of active sites to bind N2 and accelerated the electron migration from the catalytic surface to the intermediates of the reaction, enhancing the NRR. Du et al.130 incorporated Ni nanoparticles on V4C3Tx MXene (Ni/MX) for effective electrocatalytic N2 fixation that performed exceptionally well by achieving ∼21.3 μg h−1 mgcat−1 yield of NH3. The enhanced performance was credited to the synergistic pathway by the O vacancy of V4C3Tx and the Ni sites in the nanoparticles, achieving excellent enhancement of the NRR performance on the MXene based nanocomposites. Niu et al.131 examined the transition metal atom-assisted Ti3C2T2 MXene along with O/OH terminals for electrocatalytic NRR. The catalytic activity of the transition metal single atoms was investigated by their capability of adsorption on MXene, and also their potential to bind and desorb N2 and NH3, respectively. The OH termination in the as-synthesized electrocatalyst improved the N2 adsorption and suppressed the adsorption of NH3. The results displayed that Ni/Ti3C2O0.19(OH)1.81 showed rational kinetics and thermodynamics for electrocatalytic NRR. Another class of flatland materials having unique characteristics and structure, transition metal borides termed as MBenes have recently shown immense potential in energy-driven applications. The exotic nature of B in MBenes in terms of bonding and conductivity has led to growing research interest in these 2D materials. Zhang et al.132 demonstrated FeB2 as a novel catalytic system for electrochemical nitrate reduction into NH3. The synergetic relationship between Fe and the B atomic-sites augmented the rate of activation of nitrate and the rate of hydrogenation of the intermediary species to achieve higher NH3 selectivity. As high as 96.8% FE was obtained with 25.5 mg h−1 cm−2 rate of NH3 generation at −0.6 V overpotential. Recently, Feng et al.133 carried out a high-throughput screening of hexagonal-MBene electrocatalysts to determine their NRR efficiency. The authors ascertained that the catalytic response of MBenes can be tuned by bimetallic anchoring effects. It was concluded that this compositional modification leads to the regulation of the orbital energy redistribution in MBenes, and ultimately ameliorates the binding limit of the N-based intermediate species over the MBene-active sites. Gao et al.134 examined the electrochemical NRR activity of hexagonal-Zr(Hf)2B2O2 nanosheets-decorated SAC. The theoretical simulations inferred the low overpotential value of −0.10 V with higher NRR selectivity against the competitive HER process. These recent studies endorse the MXenes and MBenes tandem electrocatalysts as the state-of-art catalytic systems for efficient electrochemical NRR application.
TMDs-based electrocatalysts
TMDs have been extensively examined for a number of electrochemical reactions such as HER, oxygen reduction reaction (ORR), CO2RR, and OER because of their tunable electronic structures to attain high catalytic performance.135 It is quite obvious that the revealed edge defects of TMDs are the favourable active sites for HER catalysis. Therefore, decreasing edge defects can activate their capability for NRR catalysis applications. Chen et al.136 fabricated a series of transition metal (TM)/WS2 and examined their electrocatalytic performance for NRR. The results illustrated that Os/WS2, Tc/WS2 and Cr/WS2 showed the best catalytic performance. The adsorbed N2 can be efficiently transformed into NH3 following the distal mechanism pathway together with −0.33, −0.27 and −0.37 V limiting potentials, respectively, as a consequence of the suppressed dynamics of the HER competing process. Yang et al.137 synthesized hollow MoSe2 nanospheres as an effective electrocatalyst for NRR. The results exhibited the rate of 11.2 μg h−1 mgcat−1 of NH3 production and 14.2% FE that was credited to the greater number of active sites, higher surface area and the longer retention time of N2 in the shells due to the hollow structure of the as-prepared electrocatalyst. Chu et al.138 investigated the MoS2/C3N4 heterostructure for electrochemical NRR via in situ growth of MoS2 on C3N4 nanosheets utilizing the solvothermal method, as represented in Fig. 6(a). The proton nuclear magnetic resonance (1H NMR) spectrum showed a doublet chemical shift upon providing 15N2 gas after electrochemical NRR. A triplet chemical shift was also displayed upon providing 14N2 gas. Meanwhile, the peaks of 15NH4+ and 14NH4+ were undetectable in Ar gas, as shown in Fig. 6(b). The current density for 2 hours at various potentials is displayed in Fig. 6(c). The as-synthesized electrocatalyst exhibited enhanced NRR activity with the yield of 18.5 μg h−1 mg−1 of NH3 and FE of 17.8%, which was much better than that of pristine MoS2 and C3N4, as illustrated in Fig. 6(d) and (e). DFT calculations showed that the interfacial charge migration from C3N4 to MoS2 can improve the NRR activity of MoS2/C3N4 by boosting the stability of the intermediate and simultaneously reducing the reaction energy barrier. Ling et al.139 reported the WS2/WO2 electrocatalyst for efficient NRR that exhibited the rate of 8.53 μgNH3 h−1 mgcat−1 for NH3 production with 13.5% FE, which was better than that of pristine WS2. The enhanced activity was ascribed to the incorporation of WO2 that efficiently suppressed the HER due to the blocking of the edge defects in WS2 and concurrent formation of planar defects at the heterostructure as active sites for effective NRR. Liu et al.140 reported an interesting study in which synergetic effects between bridged-S atoms and metallic sites over the 1T-MoS2 phase were exploited in achieving higher electrochemical NRR performance. S-rich metallic MoS2 yielded as high as ∼99 μg h−1 mgcat−1 NH3 with nearly 23% FE, which was found to be one of the highest among the MoS2-based reports of NRR as of now. Theoretical studies also corroborated the favourable adsorption energy and lowered energy barrier during the reaction mechanism. The as-designed electrocatalyst also depicted the higher NH3 selectivity and remarkable competitiveness during NRR.
![image file: d4se00565a-f6.tif](/image/article/2024/SE/d4se00565a/d4se00565a-f6.gif) |
| Fig. 6 (a) Schematic representation of the MoS2/C3N4 heterostructure fabrication. (b) NMR depiction of MoS2/C3N4. (c) Current densities of MoS2/C3N4 at different potentials. (d) Yield and FEs of NH3 at various potentials. (e) NRR activities of MoS2, C3N4 and MoS2/C3N4. Reproduced with permission.138 Copyright 2020, American Chemical Society. | |
TMPs and phosphorene-based electrocatalysts
Much attraction has been garnered by TMPs due to their low cost, distinct physical and chemical features, controllable components, in addition to TMPs specifically exhibiting remarkable results as electrocatalysts. Integrating phosphorus (P) into the transition metal lattices can alter the internal electronic structure of metals, thus enhancing the intrinsic catalytic performance. Although the utilization of TMPs in NRR has not been explored more, Rytelewska et al.141 reported Fe2P for electrochemical NRR. The as-prepared electrocatalyst showed inhibition for HER, providing around 60% FE and an NH3 production rate of 7.5 μmol cm−2 h−1. The improved results were attributed to the interfacially reduced iron in the presence of P network sites that activated and reduced N2. Su et al.142 designed RhPx and a N, P-doped carbon framework as a highly efficient electrocatalyst for NRR. The catalytic behaviour and electronic structure of RhPx were altered by tuning the P contents in the composites. DFT calculations illustrated that the incorporation of P into Rh eased the intermediate process of the catalytic reaction and reduced the catalytic reaction barrier. The results exhibited 7.64% FE and 37.6 μg h−1 mgcat−1 NH3 production in accordance with the higher stability and selectivity possessed by the optimized electrocatalyst. Luo et al.143 engineered Mo/FeP through the thermo-assisted hydrolysis method, as shown in Fig. 7(a), for the electrochemical transformation of N2 to NH3. The chronoamperometry results displayed steady current densities at various potentials under 2 hours electrolysis, indicating the outstanding stability (Fig. 7(b)). Also, the ultraviolet visible (UV-vis) spectra at the potential range from −0.2 V to −0.6 V is shown in Fig. 7(c). The as-synthesized nanosphere possessed remarkable catalytic activity with the rate of 13.1 μg h−1 mg−1 for NH4+ yield and ∼7.5% FE, as illustrated in Fig. 7(d) and (e). The enhanced results stemmed from the Mo doping that was beneficial for the adsorbed N2 molecule polarization, facilitating the easier dissociation of the N
N bond.
![image file: d4se00565a-f7.tif](/image/article/2024/SE/d4se00565a/d4se00565a-f7.gif) |
| Fig. 7 (a) The synthesis method of the Mo–FeP nanosphere. (b) Current density plots of Mo–FeP at distinct applied potentials. (c) UV-vis absorption spectra tinted with the indophenol indicator for the electrolytes after electrochemical NRR from −0.2 V to −0.6 V. (d) Yield of NH4+ and (e) FEs of Mo–FeP and FeP at various potentials. Reproduced with permission.143 Copyright 2020, American Chemical Society. | |
Wu et al.144 examined the NRR taking place on the monolayers of iron-based phosphides. The Mo-doped Fe3P and Fe2P monolayers effectively boosted the electrocatalytic NRR with −0.17 and −0.30 V onset potential. Additionally, the Fe and Mo atoms served as bimetallic active sites that corroborated the linear relationship at the time of the NRR pathway. Wang et al.145 highlighted the anchoring effects of bimetallic Cu–Ru atoms over N-loaded phosphorene (NP) in enhancing the rate of the electrochemical NRR. The results manifested the lower overpotential value of 0.3 V of the as-designed electrocatalyst for N2 reduction into NH3. The electron donor–acceptor relationship of π–d electrons facilitated the activation of N2 that is fundamental for its hydrogenation into NH3. The symbiotic relationship between Cu–Ru and NP was further confirmed by the lowering of the NH3-desorption energy ascribed to the higher availability of the exposed active sites.
Carbon derivatives-based electrocatalysts
At present, graphene and its derivatives have become propitious metal-free electrocatalysts possessing several distinctive features, such as tunable porosity, high surface area, outstanding stability, and conductivity and abundant defects. These merits of mass transfer and reinforcing electrons and higher active sites offer efficient NRR. Wang et al.146 synthesized broken holey graphene oxide (BHGO) for electrocatalytic NRR, and compared the activity of the optimized electrocatalyst with holey graphene oxide (HGO) and graphene oxide (GO). The BHGO displayed higher active sites and greater electron migration capability. Therefore, it showed outstanding NRR activity and stability with an NH3 yield of 22.27 μg h−1 mg−1 and ∼11% FE at ambient conditions, as shown in Fig. 8(a) and (b). Also, the yield and FE of NH3 almost remained constant for 10 cycles, as displayed in Fig. 8(c). The source of the N element had also been examined by carrying out the experiment in blank and control environments. The results demonstrated that there was no NH3 detected except for when N2 was used as the feed gas, as shown in Fig. 8(d). Moreover, DFT simulations showed that the insertion of multi-dimensional coordinated defects improved the adsorption of N2, decreased the energy barrier at the rate-determining step, and profoundly redistributed the charge. Zhang et al.147 designed reduced graphene oxide (rGO) consisting of tuned defects for NRR. The as-synthesized rGO having defect sites (including unsaturated carbon) displayed enhanced NH3 selectivity because of the robust binding of N2 in place of the H+ ions. The as-prepared dopant-free electrocatalyst showed the FE as high as 22% and an NH3 production yield of ∼7.5 μg h−1 mg−1. Liu et al.148 fabricated a MoS2/rGO electrocatalyst for N2 fixation. The homogeneous distribution of MoS2 on rGO and the C–S–C linking bonds among them benefitted the electrocatalyst and offered abundant active sites, boosting the electron migration in the reaction that galvanized an outstanding FE of ∼28% and nearly 16.5 μg h−1 mgcat−1 yield of NH3. Moreover, the as-prepared electrocatalyst displayed high electrochemical stability and selectivity.
![image file: d4se00565a-f8.tif](/image/article/2024/SE/d4se00565a/d4se00565a-f8.gif) |
| Fig. 8 (a) FEs and yield of NH3 at distinct potentials for BHGO. (b) Current density curve of BHGO for 80 000 seconds. (c) Ten electrocatalytic cycles at −0.6 V for BHGO. (d) Yield of NH3 of blank and after 2 hours electrolysis at different conditions. Reproduced with permission.146 Copyright 2020, Elsevier. | |
Wang et al.149 synthesized an Fe3O4/rGO electrocatalyst for NRR having remarkable stability, selectivity and activity, with an achieved NH3 rate of ∼28 μg h−1 mg−1 and FE of ∼19% at ambient conditions. The enhanced NRR activity stemmed from the chemical coupling impact between the Fe3O4 particles and rGO that resulted in the improvement of the binding affinity of N2 molecules, decreasing the free energy of the reaction and notably ameliorating the conductivity. Wang et al.150 engineered In2O3/rGO, and determined the experimental and theoretical evidences to support the remarkable NRR activity of the heterostructured electrocatalyst. DFT studies manifested that the exposed facets of In2O3 favoured the efficient N2 adsorption, which ultimately led to the improved cleaving of N–N bonds and following hydrogenation steps during NRR. This ultimately restricted the HER kinetics and resulted in a lower NRR overpotential. Therefore, the as-synthesized electrocatalyst showed excellent NRR activity with ∼8% FE and the rate of NH3 yield was found to be 18.4 μg h−1 mg−1.
Techno-economic assessment of NRR
It is known that nearly 50% of the H2 evolved globally is consumed as one of the primary reactant feeds of the NH3 preparation process via Haber–Bosch technique. Therefore, sustainable NH3 production holds great significance, which is very much achievable due to the lowering prices of renewable electricity across the globe and because of the abundant solar energy.151 For the determination of the economic viability of the NH3 synthesis via NRR process, techno-economic analysis (TEA) is an important indicator that encompasses the various segments of the proposed technology and its market size globally. It is a methodology that can be employed to estimate the economic feasibility of NRR, as it combines the engineering principles with economic analysis to assess the cost of green NH3 fuel, benefits, and risks associated with it.151–154 To obtain the balanced equilibrium between the cost and production of NH3, the photochemical and electrochemical NRR should be more efficient than the conventional Haber–Bosch process for its industrial competitiveness. As of now, the production cost of the latter technology is estimated to be nearly 600 dollars per ton by comprising different costs of transporting and storing NH3.155,156 Pozo et al.157 evaluated the viability of green NH3 production as a carbon-neutral energy vector. The group carried out cash flow investigations, which inferred that based on the gas-switching reforming, a levelized cost of ∼332 € per ton is achievable as compared to traditional NH3 production plants (∼385.5 € per ton). Pawar et al.154 examined the TEA of NH3 generation by employing renewable resources of wind, solar and electrical energies. The group revealed that India can achieve the higher NH3 efficiency with cost as low as 723 and 765 EUR per tNH3 towards national and international usage. Progress in TEA of green NH3 will play a vital role in channelizing the NRR technology to a scalable platform. However, TEA alongside life-cycle assessments (LCA) have certain disadvantages which limit their effectiveness in providing a complete scenario of green NH3 generation refinery, such as resource intensiveness, limited scope of analysis, and assumption sensitivity. Nevertheless, TEA remains a valuable technique for providing detailed insights into the economic viability and risks of NH3 production via NRR. It is essential to recognize and address these limitations to ensure that the TEA results are robust, reliable, and actionable.
Conclusions
Photochemical and electrochemical NRR have emerged as potential alternative pathways of the energy-exhaustive conventional Haber–Bosch (HB) route to produce NH3 efficiently at lower cost. The generation of green NH3 alongside HER and CO2RR is the environmentally benign energy carrier that promises to achieve a carbon-neutral society. Herein, we have discussed photochemical and electrochemical NRR applications in light of the ever-evolving flatland materials by taking into consideration their remarkable physicochemical properties. Recent advances in 2D-materials-utilized photochemical NRR operations have been described with the main preference given to those materials which have achieved decent progress in green NH3 synthesis in the past few years, such as MXenes and MBenes, TMDs, TMPs, carbon derivatives and phosphorene. In addition, the electrochemical NRR applications of 2D materials have been summarized to highlight their experimental achievements in achieving higher faradaic efficiency and NH3 selectivity. Different types of reports have been discussed to bolster the catalytic design of flatland materials for efficient photochemical and electrochemical NRR performance. The catalytic efficiency of flatland materials can be augmented by engineering unique heterostructured catalysts and introducing surface defects to improve the optoelectronic and surface properties in order to ameliorate the charge-transfer dynamics and electrical conductance of 2D materials. Techno-economic assessment of NH3 has also been surveyed to indicate the current status of NRR, and where this technology stands as the contender of a sustainable energy resource.
Future outlook
Photochemical and electrochemical pathways of NRR offer promising perspectives for sustainable NH3 synthesis, providing opportunities to address environmental challenges and transition towards a greener and more energy-efficient nitrogen fixation process. Here, we have aimed to discuss the most important factors that should be taken into consideration for an efficient NRR process via flatland materials-based catalytic systems, as shown in Fig. 9.
![image file: d4se00565a-f9.tif](/image/article/2024/SE/d4se00565a/d4se00565a-f9.gif) |
| Fig. 9 Significant variables to enhance the effectiveness of flatland materials-based catalytic systems for NRR. | |
(1) As compared to the exploitation of 2D materials in other energy conversion applications of HER and CO2RR, the literature of NRR is still in its nascent stage. This is attributed to several contributing factors, such as the complexity of the reaction mechanism, low yield, sluggish dynamics, and its lower thermodynamic feasibility as compared to the competitive HER process.158–160
Nevertheless, various chemical strategies are in the developing phase for impeding the rate of the competitive HER during nitrogen fixation, such as: (1) designing catalysts with tailored surface properties and active sites that selectively promote the NRR over the HER by providing favourable free energies for N2 capture in contrast to the H+-adsorption. In this quest, Liao et al.95 provided the superior chemisorption of N2 over H-atoms during photochemical NRR process, as also discussed in aforementioned reports. Furthermore, engineering flatland materials with controlled surface morphology/hierarchical structure are the other prospects of ameliorating the NRR efficiency. (2) Decoration of exposed facets of 2D-materials can also lead to the modification of their electronic properties, thus assisting in improving the selectivity towards NRR. For instance, the incorporation of metallic/non-metallic dopants (as highlighted by Wang et al.108) by utilizing Co-dopant in Ni2P nanosheets. (3) Surface modification of 2D materials in such fashion that functionalizes their catalytic surface with ligands/functional groups for preferential binding of N2 molecules and facilitates their activation and reduction, such as introduction of heteroatoms (N, P, B) into the catalyst. For instance, Wang et al.110 ascertained the anchoring effects of B-atoms in augmenting the N2 adsorption ability of P-phosphorene on account of exploiting vacant and filled sp2- and p-orbitals during the NRR process. In a similar manner, Dong et al.117 examined the role of the nitrogen vacancy (Nv) in improving the N2 capture ability of g-C3N4 by exploiting the identical geometry of Nv and N-atoms. This report uncovered an excellent surface engineering strategy to augment the NRR activity by enhancing the N2 binding. (4) Optimization of the operational reaction conditions (such as temperature, pressure, pH, electrolyte composition) and utilization of sacrificial electron donor species to improve the NRR performance over its HER counterpart. Moreover, in electrochemical processes, the applied potential can be equilibrated to shift the reaction dynamics towards NRR, while minimizing the rate of HER. For instance, utilization of electrolytes with high ionic conductivity and low HER overpotential can suppress the HER and enhance the NRR. (5) Hampering the HER-active sites by introducing inhibitors that selectively block or deactivate sites on the catalyst surface is another strategy of promoting the rate of NRR. This can be achieved by employing strategies that can passivate or modify specific exposed sites on the surface of flatland materials that otherwise are favourable for HER activity. For instance, the edge sites of TMDs are naturally inclined towards the adsorption of H+ ions, ascribed to their favourable free energies. Therefore, modifying these edge sites in such fashion that NRR active sites are exposed can lead to an efficient NRR process. These are some of the most significant chemical strategies that can mitigate the rate of the competitive HER process during NRR, and enhance the selectivity and efficiency of the NH3 production.
(2) Another important factor that governs the NRR efficiency is the stability of the catalyst and separation of NH3 from the side reactions that take place simultaneously during the photo/electro fixing of N2 through reductive pathways. As of now, the catalytic activity of the flatland materials is limited towards NRR with stability up to hardly hundreds of hours only. Based on this, the scalable applicability of these 2D materials is still far away and requires the addressing of factors that restrict their activity, such as robustness, recyclability during NRR, separation of NH3 and its oxidation into nitrite/nitrate species via activated O-radicals.161
(3) To fully optimize the catalytic performance of flatland materials, a comprehension of the mechanistic sketch is requisite during photochemical and electrochemical NRR applications. Owing to the complex reaction mechanism of NRR, machine learning tools and theoretical modelling should be employed to investigate the surface-active sites that involve favourable free energies for N2 adsorption/activation. The role of non-covalent interactions, chemical modifications and chemical environment effects during surface reactions should be extensively scrutinized using different experimental techniques to determine the kinetics of intermediates that are formed during the reaction mechanism of N2 fixation.3 Existing computational models are able to ascertain the formation energies of different intermediates. However, the anticipations of theoretical data should be confirmed via experimental tools. Therefore, researchers should focus on developing theoretical-experimental problems to accelerate the pace of NH3 formation via NRR process.10 The state-of-art atomic-level characterization and in situ techniques can play a crucial role in obtaining scalability in NH3 synthesis.
(4) One of the most significant approaches of enhancing the quantum efficiency during NRR operations is the fabrication of catalytic systems that exhibit an ideal band structure with visible light-driven band energy, as the driving potential involved in N2 reduction is 1.17 V. However, the role of other half-oxidation reactions should not be undermined as the produced NH3 is prone to the oxidation reaction. For identifying the reactions that take place at the valence band of the photocatalyst, high-throughput screening of HER can be utilized, which has been discussed in detail in reviews elsewhere.162
Data availability
No primary research results, software or code have been included, and no new data were generated or analysed as part of this review.
Conflicts of interest
The authors declare no financial competing interest.
Acknowledgements
T. A. thanks the SERB sponsored research scheme (CRG/2023/000480) and UGC, Govt. of India for Research Grants for In-service Faculty Members for financial support. S. A. A. and I. S. acknowledge UGC for research fellowships.
References
- S. A. Ali and T. Ahmad, Mater. Today Chem., 2023, 29, 101387 CrossRef CAS
.
- S. C. Peter, ACS Energy Lett., 2018, 3, 1557–1561 CrossRef CAS
.
- S. A. Ali, I. Sadiq and T. Ahmad, Mater. Today Sustain., 2023, 24, 100587 CrossRef
.
- J. Fu, K. Jiang, X. Qiu, J. Yu and M. Liu, Mater. Today, 2020, 32, 222–243 CrossRef CAS
.
- A. Mehtab, S. A. Ali, I. Sadiq, S. Shaheen, H. Khan, M. Fazil, N. A. Pandit, F. Naaz and T. Ahmad, ACS Sustainable Resour. Manage., 2024, 1(4), 604–620 CrossRef CAS
.
- A. Mehtab and T. Ahmad, ACS Catal., 2024, 14, 691–702 CrossRef CAS
.
- Z. Huang, M. Rafiq, A. R. Woldu, Q. X. Tong, D. Astruc and L. Hu, Coord. Chem. Rev., 2023, 478, 214981 CrossRef CAS
.
- S. A. Ali and T. Ahmad, Inorg. Chem., 2024, 63, 304–315 CrossRef CAS PubMed
.
- H. Liu, J. Timoshenko, L. Bai, Q. Li, M. Rüscher, C. Sun, B. R. Cuenya and J. Luo, ACS Catal., 2023, 13, 1513–1521 CrossRef CAS
.
- G. Zhang, Y. Li, C. He, X. Ren, P. Zhang and H. Mi, Adv. Energy Mater., 2021, 11, 2003294 CrossRef CAS
.
- J. Lim, C. A. Fernández, S. W. Lee and M. C. Hatzell, ACS Energy Lett., 2021, 6, 3676–3685 CrossRef CAS
.
- F. Rehman, S. Kwon, M. D. Hossain, C. B. Musgrave III, W. A. Goddard III and Z. Luo, J. Mater. Chem. A, 2022, 10, 23323–23331 RSC
.
- J. Hou, M. Yang and J. Zhang, Nanoscale, 2020, 12, 6900–6920 RSC
.
- O. A. Ojelade, S. F. Zaman and B. J. Ni, J. Environ. Manage., 2023, 342, 118348 CrossRef PubMed
.
- L. Kang, W. Pan, J. Zhang, W. Wang and C. Tang, Fuel, 2023, 332, 126150 CrossRef CAS
.
- B. Sun, S. Lu, Y. Qian, X. Zhang and J. Tian, Carbon Energy, 2023, 5, e305 CrossRef CAS
.
- H. Song, D. A. C. Haro, P. W. Huang, L. Barrera and M. C. Hatzell, Acc. Chem. Res., 2023, 56, 2944–2953 CrossRef CAS PubMed
.
- D. Hao, Y. Liu, S. Gao, H. Arandiyan, X. Bai, Q. Kong, W. Wei, P. K. Shen and B. J. Ni, Mater. Today, 2021, 46, 212–233 CrossRef CAS
.
- Y. Kong, X. Li, A. R. P. Santiago and T. He, J. Am. Chem. Soc., 2024, 146, 5987–5997 CrossRef CAS PubMed
.
- G. Ren, J. Zhao, Z. Zhao, Z. Li, L. Wang, Z. Zhang, C. Li and X. Meng, Angew. Chem., Int. Ed., 2024, 63, e202314408 CrossRef CAS PubMed
.
- X. Wei, C. Chen, X. Z. Fuand and S. Wang, Adv. Energy Mater., 2024, 14, 2303027 CrossRef CAS
.
- H. Khan, S. E. Lofland, J. Ahmed, K. V. Ramanujachary and T. Ahmad, Int. J. Hydrogen Energy, 2024, 58, 717–725 CrossRef CAS
.
- U. Farooq and T. Ahmad, Int. J. Hydrogen Energy, 2024, 64, 290–300 CrossRef CAS
.
- Y. He, M. Wang, L. Zhang, Q. Cheng, S. Liu, X. Sun, Y. Jiang, T. Qian and C. Yan, Adv. Funct. Mater., 2024, 2315548 CrossRef CAS
.
- Y. Xiong, B. Li, Y. Gu, T. Yan, Z. Ni, S. Li, J. L. Zuo, J. Ma and Z. Jin, Nat. Chem., 2023, 15, 286–293 CrossRef CAS PubMed
.
- S. A. Ali, S. Majumdar, P. K. Chowdhury, N. Alhokbany and T. Ahmad, ACS Appl. Energy Mater., 2024, 7, 2881–2895 CrossRef CAS
.
- S. Shaheen, S. A. Ali, U. F. Mir, I. Sadiq and T. Ahmad, Catalysts, 2023, 13, 1046 CrossRef CAS
.
- S. A. Ali and T. Ahmad, Int. J. Hydrogen Energy, 2023, 48, 22044–22059 CrossRef CAS
.
- A. L. Marinho, C. Comminges, A. Habrioux, S. Célérier, N. Bion and C. Morais, Chem. Commun., 2023, 59, 10133–10136 RSC
.
- Y. Ruan, Z. H. He, Z. T. Liu, W. Wang, L. Hao, L. Xu, A. Robertson and Z. Sun, J. Mater. Chem. A, 2023, 11, 22590–22607 RSC
.
- N. Sathishkumar and H. T. Chen, ACS Appl. Mater. Interfaces, 2023, 15, 15545–15560 CrossRef CAS PubMed
.
- Y. Pang, C. Su, L. Xu and Z. Shao, Prog. Mater. Sci., 2023, 132, 101044 CrossRef CAS
.
- M. Arif, G. Yasin, L. Luo, W. Ye, M. A. Mushtaq, X. Fang, X. Xiang, S. Ji and D. Yan, Appl. Catal., B, 2020, 265, 118559 CrossRef CAS
.
- F. Du, J. Yao, H. Luo, Y. Chen, Y. Qin, Y. Du, Y. Wang, W. Hou, M. Shuai and C. Guo, Green Chem., 2024, 26, 895–903 RSC
.
- A. Mehtab, S. A. Ali, P. P. Ingole, Y. Mao, S. M. Alshehri and T. Ahmad, ACS Appl. Energy Mater., 2023, 6, 12003–12012 CrossRef CAS
.
- P. Y. Chen, M. Liu, Z. Wang, R. H. Hurt and I. Y. Wong, Adv. Mater., 2017, 29, 1605096 CrossRef PubMed
.
- Z. Dai, L. Liu and Z. Zhang, Adv. Mater., 2019, 31, 1805417 CrossRef CAS PubMed
.
- M. C. Lemme, D. Akinwande, C. Huyghebaert and C. Stampfer, Nat. Commun., 2022, 13, 1392 CrossRef CAS PubMed
.
- H. Tao, Q. Fan, T. Ma, S. Liu, H. Gysling, J. Texter, F. Guo and Z. Sun, Prog. Mater. Sci., 2020, 111, 100637 Search PubMed
.
- F. R. Fan, R. Wang, H. Zhang and W. Wu, Chem. Soc. Rev., 2021, 50, 10983–11031 RSC
.
- N. Rohaizad, C. C. Mayorga-Martinez, M. Fojtů, N. M. Latiff and M. Pumera, Chem. Soc. Rev., 2021, 50, 619–657 RSC
.
- H. Wang, J. Chen, Y. Lin, X. Wang, J. Li, Y. Li, L. Gao, L. Zhang, D. Chao, X. Xiao and J. M. Lee, Adv. Mater., 2021, 33, 2008422 CrossRef CAS PubMed
.
- X. Hui, X. Ge, R. Zhao, Z. Li and L. Yin, Adv. Funct. Mater., 2020, 30, 2005190 CrossRef CAS
.
- C. Feng, Z. P. Wu, K. W. Huang, J. Ye and H. Zhang, Adv. Mater., 2022, 34, 2200180 CrossRef CAS PubMed
.
- G. Swain, S. Sultana and K. Parida, Nanoscale, 2021, 13, 9908–9944 RSC
.
- Y. Meng, J. Feng, S. Han, Z. Xu, W. Mao, T. Zhang, J. S. Kim, I. Roh, Y. Zhao, D. H. Kim and Y. Yang, Nat. Rev. Mater., 2023, 8, 498–517 CrossRef
.
- I. Sadiq, S. Asim Ali and T. Ahmad, Catalysts, 2023, 13, 109 CrossRef CAS
.
- M. Zhao, C. Casiraghi and K. Parvez, Chem. Soc. Rev., 2024, 53, 3036–3064 RSC
.
- P. D. Pedersen, T. Vegge, T. Bligaard and H. A. Hansen, ACS Catal., 2023, 13, 2341–2350 CrossRef CAS
.
- H. Jin, L. Li, X. Liu, C. Tang, W. Xu, S. Chen, L. Song, Y. Zheng and S. Z. Qiao, Adv. Mater., 2019, 31, 1902709 CrossRef PubMed
.
- W. Y. Chen, S. N. Lai, C. C. Yen, X. Jiang, D. Peroulis and L. A. Stanciu, ACS Nano, 2020, 14, 11490–11501 CrossRef CAS PubMed
.
- J. Zou, J. Wu, Y. Wang, F. Deng, J. Jiang, Y. Zhang, S. Liu, N. Li, H. Zhang, J. Yu and T. Zhai, Chem. Soc. Rev., 2022, 51, 2972–2990 RSC
.
- S. A. Ali, I. Sadiq and T. Ahmad, Langmuir, 2024, 40, 10414–10432 CrossRef CAS PubMed
.
- Y. Liu, Y. H. Li, X. Li, Q. Zhang, H. Yu, X. Peng and F. Peng, ACS Nano, 2020, 14, 14181–14189 CrossRef CAS PubMed
.
- T. Ahmad, G. Kavitha, C. Narayana and A. K. Ganguli, J. Mater. Res., 2005, 20, 1415–1421 CrossRef CAS
.
- T. Ahmad and A. K. Ganguli, J. Am. Ceram. Soc., 2006, 89, 1326–1332 CrossRef CAS
.
- T. Ahmad, M. Shahazad, M. Ubaidullah, J. Ahmed, A. Khan and A. M. El-Toni, Mater. Res. Express, 2017, 4, 125016 CrossRef
.
- M. Fazil, S. M. Alshehri, Y. Mao and T. Ahmad, Catalysts, 2023, 13(5), 893 CrossRef CAS
.
- T. Ahmad, S. Khatoon, K. Coolahan and S. E. Lofland, J. Alloys Compd., 2013, 558, 117–124 CrossRef CAS
.
- R. Phul, C. Kaur, U. Farooq and T. Ahmad, Mater. Sci. Eng. Int. J., 2018, 2(4), 90–94 Search PubMed
.
- M. S. Javed, X. Zhang, T. Ahmad, M. Usman, S. S. A. Shah, A. Ahmad, I. Hussain, S. Majeed, M. R. Khawar, D. Choi and C. Xia, Mater. Today, 2024, 74, 121–148 CrossRef
.
- K. R. G. Lim, M. Shekhirev, B. C. Wyatt, B. Anasori, Y. Gogotsi and Z. W. Seh, Nat. Synth., 2022, 1, 601–614 CrossRef
.
- N. Miao, Y. Gong, H. Zhang, Q. Shen, R. Yang, J. Zhou, H. Hosono and J. Wang, Angew. Chem., 2023, 135, e202308436 CrossRef
.
- O. Mashtalir, M. Naguib, V. N. Mochalin, Y. Dall'Agnese, M. Heon, M. W. Barsoum and Y. Gogotsi, Nat. Commun., 2013, 4, 1716 CrossRef PubMed
.
- D. Wang, C. Zhou, A. S. Filatov, W. Cho, F. Lagunas, M. Wang, S. Vaikuntanathan, C. Liu, R. F. Klie and D. V. Talapin, Science, 2023, 379, 1242–1247 CrossRef CAS PubMed
.
- F. Han, S. Luo, L. Xie, J. Zhu, W. Wei, X. Chen, F. Liu, W. Chen, J. Zhao, L. Dong and K. Yu, ACS Appl. Mater. Interfaces, 2019, 11, 8443–8452 CrossRef CAS PubMed
.
- C. Wang, H. Shou, S. Chen, S. Wei, Y. Lin, P. Zhang, Z. Liu, K. Zhu, X. Guo, X. Wu and P. M. Ajayan, Adv. Mater., 2021, 33, 2101015 CrossRef CAS PubMed
.
- T. Najam, S. S. A. Shah, L. Peng, M. S. Javed, M. Imran, M. Q. Zhao and P. Tsiakaras, Coord. Chem. Rev., 2022, 454, 214339 CrossRef CAS
.
- E. T. Akgul, O. C. Altıncı, A. Umay, P. Aghamohammadi, A. A. Farghaly, P. Ma, Y. Chen and M. Demir, J. Energy Storage, 2024, 84, 110882 CrossRef
.
- S. A. Ali and T. Ahmad, Int. J. Hydrogen Energy, 2022, 47, 29255–29283 CrossRef CAS
.
- Z. Liu, S. Yang, B. Sun, X. Chang, J. Zheng and X. Li, Angew Chem., Int. Ed., 2018, 57, 10187–10191 CrossRef CAS PubMed
.
- L. Xiong, B. Wang, H. Cai, H. Hao, J. Li, T. Yang and S. Yang, Appl. Catal., B, 2021, 295, 120283 CrossRef CAS
.
- A. Mehtab, Y. Mao, S. M. Alshehri and T. Ahmad, J. Colloid Interface Sci., 2023, 652, 1467–1480 CrossRef CAS PubMed
.
- N. Mounet, M. Gibertini, P. Schwaller, D. Campi, A. Merkys, A. Marrazzo, T. Sohier, I. E. Castelli, A. Cepellotti, G. Pizzi and N. Marzari, Nat. Nanotechnol., 2018, 13, 246–252 CrossRef CAS PubMed
.
- S. H. Choi, S. J. Yun, Y. S. Won, C. S. Oh, S. M. Kim, K. K. Kim and Y. H. Lee, Nat. Commun., 2022, 13, 1484 CrossRef CAS PubMed
.
- T. M. Boland and A. K. Singh, Comput. Mater. Sci., 2022, 207, 111238 CrossRef CAS
.
- S. Milana, Nat. Nanotechnol., 2019, 14, 919–921 CrossRef CAS PubMed
.
- H. Jin, S. S. Kim, S. Venkateshalu, J. Lee, K. Lee and K. Jin, Adv. Sci., 2023, 10, 2300951 CrossRef CAS PubMed
.
- T. T. Liu, D. D. Zhai, B. T. Guan and Z. J. Shi, Chem. Soc. Rev., 2022, 51, 3846–3861 RSC
.
- X. Chen, Y. Guo, X. Du, Y. Zeng, J. Chu, C. Gong, J. Huang, C. Fan, X. Wang and J. Xiong, Adv. Energy Mater., 2020, 10, 1903172 CrossRef CAS
.
- B. Yang, W. Ding, H. Zhang and S. Zhang, Energy Environ. Sci., 2021, 14, 672–687 RSC
.
- N. Morlanés, S. P. Katikaneni, S. N. Paglieri, A. Harale, B. Solami, S. M. Sarathy and J. Gascon, Chem. Eng. J., 2021, 408, 127310 CrossRef
.
- C. Kurien and M. Mittal, Int. J. Hydrogen Energy, 2023, 48, 28803–28823 CrossRef CAS
.
- S. Sun, Q. Jiang, D. Zhao, T. Cao, H. Sha, C. Zhang, H. Song and Z. Da, Renewable Sustainable Energy Rev., 2022, 169, 112918 CrossRef CAS
.
- D. Ye and S. C. E. Tsang, Nat. Synth., 2023, 2, 612–623 CrossRef
.
- Y. Wei, W. Jiang, Y. Liu, X. Bai, D. Hao and B. J. Ni, Nanoscale, 2022, 14, 2990–2997 RSC
.
- Y. Pang, C. Su, G. Jia, L. Xu and Z. Shao, Chem. Soc. Rev., 2021, 50, 12744–12787 RSC
.
- A. N. Singh, R. Anand, M. Zafari, M. Ha and K. S. Kim, Adv. Energy Mater., 2024, 2304106 CrossRef
.
- M. Ozkan, K. A. Quiros, J. M. Watkins, T. M. Nelson, N. D. Singh, M. Chowdhury, T. Namboodiri, K. R. Talluri and E. Yuan, Chem, 2024, 10, 443–483 CAS
.
- R. Zhao, Y. Chen, H. Xiang, Y. Guan, C. Yang, Q. Zhang, Y. Li, Y. Cong and X. Li, ACS Appl. Mater. Interfaces, 2023, 15, 6797–6806 CrossRef CAS PubMed
.
- Y. Ruan, Z. H. He, Z. T. Liu, W. Wang, L. Hao, L. Xu, A. Robertson and Z. Sun, J. Mater. Chem. A, 2023, 11, 22590–22607 RSC
.
- S. A. Ali and T. Ahmad, Langmuir, 2024, 40, 10835–10846 CrossRef PubMed
.
- W. Gao, X. Li, S. Luo, Z. Luo, X. Zhang, R. Huang and M. Luo, J. Colloid Interface Sci., 2021, 585, 20–29 CrossRef CAS PubMed
.
- C. Hao, Y. Liao, Y. Wu, Y. An, J. Lin, Z. Gu, M. Jiang, S. Hu and X. Wang, J. Phys. Chem. Solids, 2020, 136, 109141 CrossRef CAS
.
- Y. Liao, J. Qian, G. Xie, Q. Han, W. Dang, Y. Wang, L. Lv, S. Zhao, L. Luo, W. Zhang and H. Y. Jiang, Appl. Catal., B, 2020, 273, 119054 CrossRef CAS
.
- Z. Shen, F. Li, L. Guo, X. Zhang, Y. Wang, Y. Wang, X. Jian, X. Gao, Z. Wang, R. Li and C. Fan, Appl. Catal., B, 2024, 346, 123732 CrossRef CAS
.
- Q. Zhang, Q. Li, H. Li, X. Shi, Y. Zhou, Q. Ye, R. Yang, D. Li and D. Jiang, Inorg. Chem., 2023, 62, 12138–12147 CrossRef CAS PubMed
.
- H. Guo, H. Zhang, J. Zhao, P. Yuan, Y. Li, Y. Zhang, L. Li, S. Wang and R. Song, J. Phys. Chem. C, 2022, 126, 3043–3053 CrossRef CAS
.
- Z. Li, N. H. Attanayake, J. L. Blackburn and E. M. Miller, Energy Environ. Sci., 2021, 14, 6242–6286 RSC
.
- T. Ma, R. Li, Y. C. Huang, Y. Lu, L. Guo, M. Niu, X. Huang, R. A. Soomro, J. Ren, Q. Wang and B. Xu, ACS Catal., 2024, 14, 6292–6304 CrossRef CAS
.
- B. Hu, B. H. Wang, Z. J. Bai, L. Chen, J. K. Guo, S. Shen, T. L. Xie, C. T. Au, L. L. Jiang and S. F. Yin, Chem. Eng. J., 2022, 442, 136211 CrossRef CAS
.
- L. Yao, Y. Yu, X. Xu, Z. Du, T. Yang, J. Hu and H. Huang, J. Colloid Interface Sci., 2024, 654, 189–200 CrossRef CAS PubMed
.
- L. Ye, C. Han, Z. Ma, Y. Leng, J. Li, X. Ji, D. Bi, H. Xie and Z. Huang, Chem. Eng. J., 2017, 307, 311–318 CrossRef CAS
.
- J. Qin, W. Zhao, X. Hu, J. Li, P. Ndokoye and B. Liu, ACS Appl. Mater. Interfaces, 2021, 13, 7127–7134 CrossRef CAS PubMed
.
- K. Sun, M. Liu, J. Pei, D. Li, C. Ding, K. Wu and H. L. Jiang, Angew. Chem., 2020, 132, 22937–22943 CrossRef
.
- Y. Shi, M. Li, Y. Yu and B. Zhang, Energy Environ. Sci., 2020, 13, 4564–4582 RSC
.
- X. Gao, B. Zhang, L. Cao, F. Liu, H. Fan, C. Wang and J. Xu, J. Environ. Chem. Eng., 2024, 12, 112276 CrossRef CAS
.
- Z. Wang, L. Xu, X. Yin, Y. Liu, Y. Chen, Q. Wang and W. Yang, Int. J. Hydrogen Energy, 2024, 51, 809–819 CrossRef CAS
.
- S. Rana, A. Kumar, P. Dhiman, G. Sharma, J. Amirian and F. J. Stadler, Fuel, 2024, 356, 129630 CrossRef CAS
.
- M. Wang, Z. Xu, X. Zhang, J. Yang, J. Liu, G. Qiao and G. Liu, Appl. Surf. Sci., 2021, 554, 149614 CrossRef CAS
.
- W. Wang, H. Zhou, Y. Liu, S. Zhang, Y. Zhang, G. Wang, H. Zhang and H. Zhao, Small, 2020, 16, 1906880 CrossRef CAS PubMed
.
- Y. Zhang, J. Di, P. Ding, J. Zhao, K. Gu, X. Chen, C. Yan, S. Yin, J. Xia and H. Li, J. Colloid Interface Sci., 2019, 553, 530–539 CrossRef CAS PubMed
.
- Y. Cheng, Y. Song and Y. Zhang, Phys. Chem. Chem. Phys., 2019, 21, 24449–24457 RSC
.
- M. Majumder, H. Saini, I. Dedek, A. Schneemann, N. R. Chodankar, V. Ramarao, M. S. Santosh, A. K. Nanjundan, S. Kment, D. Dubal and M. Otyepka, ACS Nano, 2021, 15, 17275–17298 CrossRef CAS PubMed
.
- W. J. Ong, L. L. Tan, Y. H. Ng, S. T. Yong and S. P. Chai, Chem. Rev., 2016, 116, 7159–7329 CrossRef CAS PubMed
.
- S. Liu, S. Wang, Y. Jiang, Z. Zhao, G. Jiang and Z. Sun, Chem. Eng. J., 2019, 373, 572–579 CrossRef CAS
.
- G. Dong, W. Ho and C. Wang, J. Mater. Chem. A, 2015, 3, 23435–23441 RSC
.
- D. Brida, A. Tomadin, C. Manzoni, Y. J. Kim, A. Lombardo, S. Milana, R. R. Nair, K. S. Novoselov, A. C. Ferrari, G. Cerullo and M. Polini, Nat. Commun., 2013, 4, 1–9 Search PubMed
.
- Y. Lu, Y. Yang, T. Zhang, Z. Ge, H. Chang, P. Xiao, Y. Xie, L. Hua, Q. Li, H. Li and B. Ma, ACS Nano, 2016, 10, 10507–10515 CrossRef CAS PubMed
.
- S. L. Foster, S. I. P. Bakovic, R. D. Duda, S. Maheshwari, R. D. Milton, S. D. Minteer, M. J. Janik, J. N. Renner and L. F. Greenlee, Nat. Catal., 2018, 1, 490 CrossRef
.
- X. Chen, Y. Guo, X. Du, Y. Zeng, J. Chu, C. Gong, J. Huang, C. Fan, X. Wang and J. Xiong, Adv. Energy Mater., 2019, 10, 1903172 CrossRef
.
- J. H. Montoya, C. Tsai, A. Vojvodic and J. K. Nørskov, ChemSusChem, 2015, 8, 2180 CrossRef CAS PubMed
.
- Y. Huang, D. D. Babu, Z. Peng and Y. Wang, Adv. Sci., 2020, 7, 1902390 CrossRef CAS PubMed
.
- Y. Wang, W. Zhou, R. Jia, Y. Yu and B. Zhang, Angew Chem., Int. Ed., 2020, 59, 5350 CrossRef CAS PubMed
.
- K. C. MacLeod and P. L. Holland, Nat. Chem., 2013, 5, 559 CrossRef CAS PubMed
.
- P. Mars and D. W. van Krevelen, Chem. Eng. Sci., 1954, 3, 41 CrossRef CAS
.
- Y. Shi and Y. Liu, Appl. Catal., B, 2021, 297, 120482 CrossRef CAS
.
- K. Ba, D. Pu, X. Yang, T. Ye, J. Chen, X. Wang, T. Xiao, T. Duan, Y. Sun, B. Ge and P. Zhang, Appl. Catal., B, 2022, 317, 121755 CrossRef CAS
.
- Y. Guo, T. Wang, Q. Yang, X. Li, H. Li, Y. Wang, T. Jiao, Z. Huang, B. Dong, W. Zhang and J. Fan, ACS Nano, 2020, 14, 9089–9097 CrossRef CAS PubMed
.
- C. F. Du, L. Yang, K. Tang, W. Fang, X. Zhao, Q. Liang, X. Liu, H. Yu, W. Qi and Q. Yan, Mater. Chem. Front., 2021, 5, 2338–2346 RSC
.
- K. Niu, L. Chi, J. Rosen and J. Bjork, J. Phys. Chem. Lett., 2022, 13, 2800–2807 CrossRef CAS PubMed
.
- G. Zhang, X. Li, K. Chen, Y. Guo, D. Ma and K. Chu, Angew. Chem., Int. Ed., 2023, 62, e202300054 CrossRef CAS PubMed
.
- S. Feng, Y. Yao, J. C. Charlier, G. M. Rignanese and J. Wang, Chem. Mater., 2023, 35, 9019–9028 CrossRef CAS
.
- Y. Gao, E. Wang, Y. Zheng, J. Zhou and Z. Sun, Energy Mater. Adv., 2023, 4, 0039 CrossRef
.
- C. R. Zhu, D. Gao, J. Ding, D. Chao and J. Wang, Chem. Soc. Rev., 2018, 47, 4332–4356 RSC
.
- Y. Chen, X. Zhang, J. Qin and R. Liu, Appl. Surf. Sci., 2022, 571, 151357 CrossRef CAS
.
- L. Yang, H. Wang, X. Wang, W. Luo, C. Wu, C. A. Wang and C. Xu, Inorg. Chem., 2020, 59, 12941–12946 CrossRef CAS PubMed
.
- K. Chu, Y. P. Liu, Y. B. Li, Y. L. Guo and Y. Tian, ACS Appl. Mater. Interfaces, 2020, 12, 7081–7090 CrossRef CAS PubMed
.
- Y. Ling, F. M. Kazim, S. Ma, Q. Zhang, K. Qu, Y. Wang, S. Xiao, W. Cai and Z. Yang, J. Mater. Chem. A, 2020, 8, 12996–13003 RSC
.
- R. Liu, H. Fei, J. Wang, T. Guo, F. Liu, Z. Wu and D. Wang, Appl. Catal., B, 2024, 343, 123469 CrossRef CAS
.
- B. Rytelewska, A. Chmielnicka, T. Chouki, M. Skunik-Nuckowska, S. Naghdi, D. Eder, A. Michalowska, T. Ratajczyk, E. Pavlica, S. Emin and Y. Fu, Electrochim. Acta, 2023, 471, 143360 CrossRef CAS
.
- J. Su, H. Zhao, W. Fu, W. Tian, X. Yang and H. Z. Y. Wang, Appl. Catal., B, 2020, 265, 118589 CrossRef CAS
.
- Y. X. Luo, W. B. Qiu, R. P. Liang, X. H. Xia and J. D. Qiu, ACS Appl. Mater. Interfaces, 2020, 12, 17452–17458 CrossRef CAS PubMed
.
- J. Wu, J. H. Li and Y. X. Yu, Catal. Sci. Technol., 2021, 11, 1419–1429 RSC
.
- M. Wang, R. Song, Q. Zhang, C. Li, Z. Xu, G. Liu, N. Wan and S. Lei, Fuel, 2022, 321, 124101 CrossRef CAS
.
- F. Wang, H. Wang and J. Mao, Colloids Surf., A, 2020, 605, 125345 CrossRef CAS
.
- M. Zhang, C. Choi, R. Huo, G. H. Gu, S. Hong, C. Yan, S. Xu, A. W. Robertson, J. Qiu, Y. Jung and Z. Sun, Nano Energy, 2020, 68, 104323 CrossRef CAS
.
- Y. Liu, W. Wang, S. Zhang, W. Li, G. Wang, Y. Zhang, M. Han and H. Zhang, ACS Sustain. Chem. Eng., 2020, 8, 2320–2326 CrossRef CAS
.
- F. Wang, L. Xia, X. Li, W. Yang, Y. Zhao and J. Mao, Energy Environ. Mater., 2021, 4, 88–94 CrossRef CAS
.
- P. Wang, Q. Q. Li, Y. H. Cheng and K. Chu, J. Mater. Sci., 2020, 55, 4624–4632 CrossRef CAS
.
- L. Wang, M. Xia, H. Wang, K. Huang, C. Qian, C. T. Maravelias and G. A. Ozin, Joule, 2018, 2, 1055–1074 CrossRef CAS
.
- J. R. Gomez, J. Baca and F. Garzon, Int. J. Hydrogen Energy, 2020, 45, 721–737 CrossRef CAS
.
- O. Osman, S. Sgouridis and A. Sleptchenko, J. Cleaner Prod., 2020, 271, 121627 CrossRef CAS
.
- N. D. Pawar, H. U. Heinrichs, C. Winkler, P. M. Heuser, S. D. Ryberg, M. Robinius and D. Stolten, Int. J. Hydrogen Energy, 2021, 46, 27247–27267 CrossRef CAS
.
- B. M. Comer, P. Fuentes, C. O. Dimkpa, Y. H. Liu, C. A. Fernandez, P. Arora, M. Realff, U. Singh, M. C. Hatzell and A. J. Medford, Joule, 2019, 3, 1578–1605 CrossRef CAS
.
- G. Hochman, A. S. Goldman, F. A. Felder, J. M. Mayer, A. J. Miller, P. L. Holland, L. A. Goldman, P. Manocha, Z. Song and S. Aleti, ACS Sustain. Chem. Eng., 2020, 8, 8938–8948 CrossRef CAS
.
- C. A. Del Pozo and S. Cloete, Energy Convers. Manage., 2022, 255, 115312 CrossRef
.
- X. Zhao, G. Hu, G. F. Chen, H. Zhang, S. Zhang and H. Wang, Adv. Mater., 2021, 33, 2007650 CrossRef CAS PubMed
.
- C. Ling, Y. Zhang, Q. Li, X. Bai, L. Shi and J. Wang, J. Am. Chem. Soc., 2019, 141, 18264–18270 CrossRef CAS PubMed
.
- Y. Ren, C. Yu, X. Tan, H. Huang, Q. Wei and J. Qiu, Energy Environ. Sci., 2021, 14, 1176–1193 RSC
.
- H. Hirakawa, M. Hashimoto, Y. Shiraishi and T. Hirai, ACS Catal., 2017, 7, 3713–3720 CrossRef CAS
.
- M. Umer, S. Umer, M. Zafari, M. Ha, R. Anand, A. Hajibabaei, A. Abbas, G. Lee and K. S. Kim, J. Mater. Chem. A, 2022, 10, 6679–6689 RSC
.
|
This journal is © The Royal Society of Chemistry 2024 |