Tailoring electronic environments of dispersed Ru sites for efficient alkaline hydrogen evolution

Abstract

Under the global initiative for carbon reduction, promoting alkaline hydrogen evolution reactions (HER) holds crucial significance. Ruthenium (Ru) demonstrates excellent hydrogen binding energy and offers a cost advantage over other platinum-group metals. However, the water dissociation capability of Ru sites in alkaline environments needs improvement, and the surface H* coverage is relatively low. In this work, a facile galvanostatic deposition strategy is employed to anchor Ru atoms onto a NiCo bimetallic oxide support (Ru–NiCoO₂/CC), enabling the modulation of the electronic environment of Ru sites. Benefiting from the optimized metal–support interactions, the prepared Ru–NiCoO₂/CC display excellent alkaline HER activity, requiring overpotentials of only 37 mV and 50 mV to achieve a current density of 10 mA cm⁻² in 1 M KOH and 1 M KOH + seawater, respectively. Meanwhile, it also has robust long-term stability. Importantly, the two-electrode electrolyzer with Ru–NiCoO₂/CC as the cathode requires only 1.71 V to achieve a current density of 50 mA cm⁻² for alkaline overall water splitting (OWS), and it also demonstrates potential for integration with intermittent energy systems. The synergy between hydrogen spillover and the phase transition induced by electrodeposited Ru improves the water dissociation capability and H* coverage on Ru sites. This work provides new insights for regulating Ru sites to achieve efficient alkaline hydrogen generation.

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1. Introduction

Hydrogen energy has exceptionally high energy density and significant environmental benefits open up a new pathway to achieving global carbon neutrality.^1–6 Water electrolysis for hydrogen production is simple to operate and yields high production rates, making it as an ideal preparation strategy.^7–12 The process involves two half-reactions: the two-electron hydrogen evolution reaction (HER) and the four-electron oxygen evolution reaction (OER).¹³ In industrial production, alkaline electrolyzers are commonly used for hydrogen generation due to their operational safety and high production efficiency.¹⁴ Therefore, developing and preparing efficient alkaline HER electrocatalysts is highly important.

Ruthenium (Ru) possesses a hydrogen bonding strength (65 kcal mol⁻¹) similar to platinum (Pt) and offers a cost advantage over other Pt-group metals, costing approximately one-fifth as much as Pt.^15,16 However, the water splitting capability of Ru sites during the alkaline HER process remains insufficient, leading to inadequate H* coverage on the active sites.^17,18 Numerous studies indicate that decreasing the size of metal sites can maximize atomic utilization, markedly boosting their intrinsic activity.^19–21 Traditional dipping and high-temperature calcination strategies often result in metal site agglomeration.²² Fan et al. used a two-step electrodeposition strategy to fabricate Ru nanoparticle-modified Co(OH)₂ nanosheet arrays on carbon cloth (Ru–Co(OH)₂/CC). The synergistic interaction between Ru and Co(OH)₂ generates abundant oxygen vacancies, significantly enhancing catalytic activity.²³

Li et al. developed a simple electrochemical deposition method to synthesize an efficient PtRu hydrogen evolution catalyst supported on carbon cloth (PtRu/CC1500) that operates effectively across a wide pH range.²⁴ Anchoring metals onto the support to construct heterogeneous catalysts allows for the regulation of adsorption and desorption of specific electrocatalytic reaction intermediates through metal–support interactions (MSI). Carbon-based supports exhibit instability under harsh conditions such as high-temperature oxidizing environments. In contrast, non-carbon supports are more stable and have adjustable physicochemical properties. They can provide diverse coordination bonds to metal atoms, enabling the construction of efficient electrocatalysts.^25,26 Bimetallic oxides are often used as supports to anchor metal sites. Yang et al. reported a heterogeneous Ru modification strategy to enhance the catalytic performance of porous NiCo₂O₄ nanosheets (Ru–NiCo₂O₄ NSs). The prepared porous Ru–NiCo₂O₄ NSs possess ideal active components and morphological structures. The presence of oxygen vacancies (O_v) endows the catalyst with lower charge transfer resistance and superior catalytic activity.²⁷ Wang et al. developed a Ru-modified bimetallic oxide catalyst (Ru–NiCo₂O₄) deposited on conductive nickel foam (NF). By adjusting the d-band center, the adsorption energy of H* are optimized, leading to a significant enhancement in hydrogen production efficiency.²⁸

In this study, a one-dimensional (1D) Ru-modified NiCo bimetallic oxide (Ru–NiCoO₂/CC) is synthesized on carbon cloth (CC) using a constant current deposition strategy. The prepared catalyst exhibits excellent HER activity and long-term stability in alkaline environments. Ru–NiCoO₂/CC requires overpotentials of only 37 mV (in 1 M KOH) and 50 mV (in 1 M KOH + seawater) to drive a current density of 10 mA cm⁻². Additionally, a two-electrode electrolyzer, using Ru–NiCoO₂/CC as the cathode, requires only 1.71 V to drive a current density of 50 mA cm⁻² for overall water splitting (OWS). This electrolyzer demonstrates high coulombic efficiency and has the potential for coupling with intermittent energy systems. Through electrochemical tests and physical characterization, we conclude that the Ru–NiCoO₂/CC synthesized using a constant-current deposition strategy effectively controlled the size and loading of the Ru sites, ensuring uniform distribution in the NiCo oxide O_v. By exploiting the strong MSI, the water dissociation is facilitated and the H* coverage on the Ru sites is optimized, thus conferring the excellent HER catalytic activity of Ru–NiCoO₂/CC under alkaline environment. Importantly, the catalyst shows excellent performance in seawater, addressing the issue of freshwater scarcity in water electrolysis. This study offers guidance for customizing Ru sites to achieve efficient hydrogen production in alkaline environment.

2. Results and discussion

2.1 Physical characterization

The synthetic process of Ru–NiCoO₂/CC is illustrated in Fig. 1a. Initially, NiCo–OH nanowires are grown on a conductive carbon cloth (CC) substrate via a hydrothermal method. As shown in Fig. S1a,† no significant peaks of NiCo–OH/CC are observed in the X-ray diffraction (XRD) patterns, possibly due to its low content.²⁹ Subsequent oxidative annealing transforms the NiCo–OH/CC into NiCo₂O₄/CC (Fig. S1b†). Finally, a facile galvanostatic deposition strategy is employed to decorate NiCo₂O₄ with Ru single atoms (Ru–NiCoO₂/CC). As illustrated in Fig. 1b, no peaks of Ru are observed due to its high dispersion. Meanwhile, the characteristic peaks of NiCoO₂ are visible. The diffraction peaks at 36.8° and 42.8° correspond to the (111) and (200) facets of NiCoO₂ (PDF # 10-0188), respectively. Additionally, Ru–NiCo₂O₄/CC and Ru/CC are prepared to analyze the impact of electrodeposition on the substrate. According to the XRD patterns (Fig. S1c and S1d†), it can be observed that the introduction of elemental Ru under constant current conditions triggered a reduction reaction, and this reaction in turn led to a significant phase transition of NiCo₂O₄ into NiCoO₂.

Fig. 1 (a) Schematic synthesis of Ru–NiCoO₂/CC. (b) XRD pattern of Ru–NiCoO₂/CC. SEM images of (c) bare CC and (d) Ru–NiCoO₂/CC. (e–g) HRTEM and (h) HAADF-STEM images of Ru–NiCoO₂/CC. (i–l) Corresponding EDS mapping of Ru–NiCoO₂/CC.

Scanning electron microscopy (SEM) is applied to characterize the morphology of the synthesized samples. As shown in Fig. 1c, the CC exhibits a smooth surface. In Fig. 1d, the morphology of Ru–NiCoO₂/CC shows a nanoflower composed of bundled one-dimensional (1D) nanowires. As shown in Fig. S2a–d,† the prepared NiCo–OH/CC and NiCo₂O₄/CC display a radial nanowire morphology. The 1D nanowire structure provides the catalyst with an extremely large specific surface area and will facilitate the full exposure of active sites, thereby enhancing the adsorption and desorption efficiency of intermediates.³⁰ Transmission electron microscopy (TEM) reveals that the surface of the Ru–NiCoO₂/CC nanowires exhibits abundant defects with distorted lattices (Fig. 1e). Furthermore, high-resolution TEM (HRTEM) shows the same results as XRD, and it can be observed in Fig. 1f that the lattice spacing of 0.244 nm correspond to the (111) crystal planes of NiCoO₂, respectively. In Fig. 1g, it confirms that Ru exists in the form of single atoms. The high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images clearly present the nanowire morphology (Fig. 1h). Fig. 1i–l show the energy-dispersive spectra (EDS) mapping, demonstrating that the elements in the synthesized sample are uniformly distributed. As indicated in Fig. S3 and Table S1,† the EDS elemental mapping reveals that the Ru content is extremely low, at only 0.07%.

In addition, we further analyze the chemical states of the catalyst constituent elements using X-ray photoelectron spectroscopy (XPS).³¹ In Fig. S4,† the XPS spectra of NiCo₂O₄ can be observed. The XPS analysis in Fig. 2a clearly demonstrates the presence of Ni, Co, O and Ru elements in the Ru–NiCoO₂/CC sample. In the XPS spectrum of Ni 2p, two pairs of peaks can be observed (Fig. 2b). The peaks at 852.5 eV and 854.9 eV of Ru–NiCoO₂/CC can be deconvoluted to the 2p_1/2 of Ni⁰ and Ni²⁺, respectively, and two satellite peaks (Sat.) are observed (866.6 and 879.2 eV). The peaks at 871.5 eV and 873.1 eV are attributed to the 2p_3/2 of Ni⁰ and Ni²⁺, respectively.³² In the high-resolution XPS spectrum of Co 2p (Fig. 2c), Ru–NiCoO₂/CC exhibit two pairs of characteristic peaks, with the peaks at 779.0 eV and 794.2 eV are deconvoluted to 2p_1/2 and 2p_3/2 of Co³⁺, and the peaks at 781.0 eV and 796.2 eV are attributed to Co²⁺. While the two Sat. of Co are also observed.³³ Surprisingly, combining XRD and XPS data, we can confirm that the transition of the support from NiCo₂O₄ to NiCoO₂ occurs in the Ru–NiCoO₂/CC sample. The transition from a spinel structure to a layer structure facilitates ion transport, while the increased Co²⁺ content further enhances water dissociation.³⁴ In Fig. 2d, the XPS spectrum of Ru is deconvoluted into two pairs of peaks. The peaks at binding energies around 463.9 eV and 486.3 eV are attributed to Ru³⁺, while the other pair are the Sat.^35,36 Compared with the binding energy of Ru³⁺ in standard RuCl₃, the higher binding energy in Ru–NiCoO₂/CC indicates electron loss at the Ru sites.³⁷ This binding energy shift confirms that the constant current deposition process modulates the electronic environment around the Ru sites.³⁸ The C 1s spectrum shows three characteristic peaks at 284.8 eV, 286.0 eV, and 288.0 eV, corresponding to graphitized sp² carbon (C=C), (C–O), and (C=O), respectively (Fig. S5†).^39,40 Additionally, the peak at 282.6 eV is attributed to Ru 3d. The O 1s spectrum is deconvoluted into three peaks: M–O (metal–oxygen bond), O_v (oxygen vacancy), and C–O (carbon–oxygen bond in oxygen-contained groups) (Fig. 2e).^41,42 Ru–NiCoO₂/CC shows a lower O_v content compared with NiCo₂O₄. This reduction is attributed to the transformation from NiCo₂O₄ to NiCoO₂ and the anchoring of Ru single atoms in O_v.⁴³ These Ru atoms form Ru–O–M species, promoting H–OH cleavage and accelerating the formation of H* and OH*. Electron paramagnetic resonance (EPR) analysis further verifies the existence of O_v in Ru–NiCoO₂/CC (Fig. 2f).⁴³

Fig. 2 (a) XPS survey spectrum of Ru–NiCoO₂/CC. High-resolution XPS spectra of (b) Ni 2p, (c) Co 2p, (d) Ru 3p and (e) O 1s. (f) EPR spectra of Ru–NiCoO₂/CC and NiCo₂O₄. (g) UPS spectra for Ru–NiCoO₂/CC and Ru/CC. CA test for (h) CC and (i) Ru–NiCoO₂/CC.

In addition, work function values (Φ) of the above two samples are investigated through ultraviolet photoelectron spectroscopy (UPS) to probe the effect of NiCoO₂ on electronic transmission. The corresponding work functions for Ru–NiCoO₂/CC and Ru/CC are 3.98 and 4.74 eV, respectively (Fig. 2g). The smaller Φ indicates that NiCoO₂ as a support effectively reduces the electron transfer barrier, contributing to enhanced catalytic activity.^27,44 Contact angle (CA) measurement is utilized to analyze the interaction force between the liquid and solid surfaces. The hydrophilicity of the prepared catalysts is shown in Fig. 2h and i. The excellent hydrophilic surface promotes the detachment of small-sized bubbles from the electrode and improves the contact between the electrolyte and the electrocatalyst surface, therefore accelerating charge transfer during the HER and improving catalyst performance.^45,46 From Fig. 2h, it can be observed that the CA of CC is approximately 150°, whereas in Fig. 2i, the CA of Ru–NiCoO₂/CC is 0°, which proves its superior hydrophilic property.

2.2. Alkaline electrochemical hydrogen evolution performance

A standard three-electrode system was employed to fully evaluate the HER catalytic activity of the prepared catalysts in an alkaline environment of 1 M KOH. As shown in Fig. 3a, the superior overpotential of Ru–NiCoO₂/CC at 10 mA cm⁻² is only 37 mV, which is lower than that of Pt/C (51 mV), Ru/C (52 mV), NiCo₂O₄/CC (165 mV), NiCo–OH/CC (323 mV), and CC (364 mV). Furthermore, Tafel slopes derived from the linear sweep voltammetry (LSV) curves are used to evaluate the reaction kinetics of the synthesized catalysts. As depicted in Fig. 3b, the Tafel slope of Ru–NiCoO₂/CC is 63.7 mV dec⁻¹, superior to Ru/C (89.0 mV dec⁻¹) and second only to Pt/C (45.8 mV dec⁻¹), indicating that the Ru–NiCoO₂/CC possesses more favorable kinetic for the HER process. Electrochemical impedance spectroscopy (EIS) measurements conducted at a constant potential show that Ru–NiCoO₂/CC exhibits minimal charge transfer resistance (Fig. 3c). It aligns with the UPS results, indicating the fastest charge transfer and enhancing electrocatalytic performance. To verify the contribution of Ru single atoms (Ru SAs) in promoting catalytic performance, KSCN is chosen as a poisoning agent (since KSCN can coordinate with Ru SAs).^47–49 In Fig. S6,† the activity of Ru–NiCoO₂/CC is significantly reduced in the presence of 0.5 mM KSCN, while Ru/CC only shows a slight reduction. The above results indicate that anchored Ru SAs in Ru–NiCoO₂/CC catalysts play a crucial role in catalyzing the HER under alkaline conditions.^47–49 In addition, stability is an important parameter for assessing the practical application of catalysts. As shown in Fig. 3d, the electrode can respond quickly and remain stable when the current density is constantly changing, and even after undergoing reverse cycling, it is still able to recover to the same overpotential level. Meanwhile, the current density of Ru–NiCoO₂/CC is maintained at about 96% after a 12 hour chronoamperometric test, showing negligible decay compared with Ru/C (Fig. 3e). Additionally, as observed in Fig. S7,† the catalyst retains nanowire morphology after the stability test. Furthermore, as shown in Fig. S8,† after 5000 cycles of cyclic voltammetry (CV) testing, the LSV curves almost overlap with the initial LSV curve, further proving its good stability. All of these results indicate that the prepared Ru–NiCoO₂/CC possesses excellent HER performance with satisfactory stability. Impressively, Ru–NiCoO₂/CC demonstrates HER performance comparable to recently reported Ru-based or Co-based catalysts (Fig. 3f and Table. S2†), confirming that the incorporation of Ru atoms enables the defect-rich NiCoO₂ to deliver excellent HER activity.

Fig. 3 HER performance in an alkaline environment: (a) LSV curves, (b) Tafel slopes, (c) EIS for the prepared samples. (d) Multi-step chronopotentiometry for Ru–NiCoO₂/CC. (e) Stability of Ru–NiCoO₂/CC and Ru/C. (f) Comparative performance of previously reported electrocatalysts.

2.3. Alkaline seawater electrochemical hydrogen evolution performance

Given the abundance of seawater resources on the earth, seawater electrolysis technology is increasingly becoming a focus of public and scientific attention as an emerging route for hydrogen production. In view of this, we further investigated the performance of the prepared catalysts in alkaline seawater (seawater obtained from Shilaoren Beach, Qingdao, Fig. 4a) environment. The LSV curves of the prepared catalysts are shown in Fig. 4b, demonstrating that Ru–NiCoO₂/CC requires only an overpotential of 50 mV to reach 10 mA cm⁻², which is superior to commercial Pt/C (54 mV) and Ru/C (57 mV). In comparison, the reference samples NiCo₂O₄/CC, NiCo–OH/CC and CC need 192 mV, 199 mV, and 210 mV respectively to achieve 10 mA cm⁻². As shown in Fig. 4c, Ru–NiCoO₂/CC demonstrates superior HER performance in both 1 M KOH and 1 M KOH + seawater environment compared with other catalysts. Additionally, Ru–NiCoO₂/CC exhibits the smallest Tafel slope (93.2 mV dec⁻¹) compared with Pt/C (96.6 mV dec⁻¹) and Ru/C (99.3 mV dec⁻¹) (Fig. 4d), indicating favorable HER kinetics. As shown in Fig. 4e, EIS measurements in 1 M KOH + seawater indicate that Ru–NiCoO₂/CC has favorable electron transport efficiency compared with the reference electrocatalysts. In addition, the Ru–NiCoO₂/CC catalyst shows excellent stability in alkaline seawater, the LSV curves remain almost unchanged after 5000 CV cycles (Fig. 4f), and the current density remain almost constant after a 12 hour long-term i–t test (Fig. 4g). The multi-step chronopotentiometry test also confirms the excellent stability in alkaline seawater (Fig. 4h). As seen in Fig. S9,† the nanowire morphology of the catalyst remains intact after the i–t test, verifying its robust structure. In addition, Ru–NiCoO₂/CC exhibits comparable HER performance to recently reported catalysts (Fig. 4i and Table. S3†).

Fig. 4 HER performance in an alkaline seawater environment: (a) Location of natural seawater extraction. (b) LSV curves and (c) comparison of Tafel slopes and overpotentials in alkaline environments at 10 mA cm⁻². (d) Tafel slopes for the prepared catalysts. (e) EIS for the prepared catalysts. (f) Comparison of LSV curves before and after 5000 CV cycles test. (g) 12 hour stability test. (h) Multi-step chronopotentiometry for Ru–NiCoO₂/CC. (i) Comparative performance of reported electrocatalysts at 10 mA cm⁻² in 1 M KOH + seawater.

2.4. Proposed reaction mechanism

In addition, in situ Raman spectra (Fig. 5a and c) are collected to reveal the HER mechanism of Ru–NiCoO₂/CC. The Raman peaks at 1345 and 1590 cm⁻¹ are attributed to the D-band and G-band vibrations, respectively.⁵⁰ In Fig. 5b, the Ni–O vibrational peak is observed in the range of 446–530 cm⁻¹, and its intensity increases with the applied potential, indicating the formation of Ni–OH* intermediates.^50,51 These two Raman vibrational peaks are observed to increase with the applied potential, indicating their involvement in the alkaline HER process. In addition, the Ru–H stretching vibration shows the potential continuously increases.⁵²In situ Raman results indicate that Ni and Co active sites promote the dissociation of water to form H*.^53,54 Simultaneously, H* is transferred to the Ru single atoms to form Ru–H. To depict the proton-transfer information, we further performed kinetic isotope effect (KIE) experiments. As shown in Fig. 5d, Ru–NiCoO₂/CC requires overpotentials of 37, 78, 107, and 131 mV to drive current densities of 10, 50, 100, and 150 mA cm⁻², respectively. Reaching the same current densities in 1 M KOH D₂O solution requires overpotentials of 82, 163, 229, and 283 mV, respectively. The corresponding KIE values are 2.21, 2.09, 2.14, and 2.16 (Fig. 5e). The KIE values obtained from all cases are greater than 1.5, implying that H transfer indeed participates in the rate-limiting step for all processes.⁵⁵Fig. 5f visually illustrates the flow of H*, highlighting the significant role of the NiCoO₂ support on inducing hydrogen spillover.

Fig. 5 (a–c) In situ Raman spectra of Ru–NiCoO₂/CC at different applied potentials vs. RHE. (d) LSV curves obtained from Ru–NiCoO₂/CC in 1.0 M KOH (H₂O) and 1.0 M KOH (D₂O). (e) Calculated KIE values under corresponding potentials of Ru–NiCoO₂/CC. (f) Proposed potential hydrogen spillover mechanism.

Based on comprehensive testing and characterization, we believe the significantly enhanced alkaline HER activity of Ru–NiCoO₂/CC can be attributed to the following reasons: (1) The electrodeposition process introduces Ru atoms, inducing the transformation of the support from NiCo₂O₄ to NiCoO₂ and modulating the electronic environment of Ru sites. This includes the transition from a spinel to a layered structure, an increase in Co²⁺ content, and the formation of Ru–O–M species, which significantly optimize water dissociation and ion transport processes. (2) NiCoO₂ facilitates the migration of H* to Ru sites, greatly improving the coverage of H* on active sites in an alkaline environment. (3) The constant current electrodeposition strategy confines the size of Ru sites, enhancing their dispersion and preventing agglomeration. (4) The superhydrophilic 1D morphology, in synergy with the CC substrate, provides abundant exposed active sites, excellent structural stability, and conductivity to the catalyst.

2.5. Overall water splitting performance

Considering the excellent HER performance and stability of Ru–NiCoO₂/CC in alkaline media, we also studied a two-electrode device for alkaline overall water splitting (OWS), using the prepared electrocatalyst as the cathode and RuO₂ as the anode. As shown in Fig. 6a, compared with the state-of-the-art RuO₂∥Pt/C, RuO₂∥Ru–NiCoO₂/CC drives OWS more favorably. In addition, as shown in Fig. 6b, RuO₂∥Ru–NiCoO₂/CC demonstrates excellent stability, with negligible decay over 50 hours of stability testing. In contrast, RuO₂∥Pt/C experiences significant decay after 20 hours. The stability is further confirmed by the multi-step chronopotentiometry shown in Fig. 6c. These results indicate that the prepared catalyst has practical applications for hydrogen production. A series of simulations are conducted to further evaluate its performance. The designed electrolyzer can be powered by individual AAA batteries, solar energy, wind energy, and Stirling generators. As seen clearly in Fig. S10,† numerous bubbles are generated on both electrodes, demonstrating the high catalytic efficiency of the prepared electrocatalyst. A device for collecting gas is constructed using the drainage method (Fig. S11†). The Faraday efficiency (FE) is evaluated by measuring the volume of gas generated at the anode and cathode over a given time. According to the calculations, the average FE after 800 seconds is about 99.2% (Fig. 6d). Additionally, Fig. 6e clearly shows that the volume ratio of O₂ to H₂ is about 1 : 2, indicating that the Ru–NiCoO₂/CC exhibite a high FE during the electrolysis of water. All the above results suggest that the prepared catalyst has potential for practical applications.

Fig. 6 OWS performance in 1 M KOH: (a) LSV curves for the RuO₂∥Ru–NiCoO₂/CC and RuO₂∥Pt/C. (b) Stability comparison of RuO₂∥Ru–NiCoO₂/CC and RuO₂∥Pt/C. (c) Mult-step chronopotentiometry of RuO₂∥Ru–NiCoO₂/CC. (d) The amount of H₂/O₂ experimentally measured versus time and Faraday efficiency. (e) Photographs of hydrogen and oxygen collected at different time.

3. Conclusion

In summary, this work employs a facile galvanostatic deposition strategy to anchor Ru atoms in the NiCo bimetallic oxide, resulting in a self-supporting 1D Ru–NiCoO₂/CC. The electrocatalytic activity is optimized by utilizing the MSI. The phase transition from NiCo₂O₄ to NiCoO₂ adjusts the Ru site electronic environment, enhancing its water dissociation capability. The hydrogen spillover effect induced by NiCoO₂ improves H* coverage on the Ru site surfaces in an alkaline environment. The meticulously engineered Ru sites display a high-efficiency alkaline HER catalytic activity. Ru–NiCoO₂/CC achieves low overpotentials of 37 mV in 1 M KOH and 50 mV in 1 M KOH + seawater to drive the current density of 10 mA cm⁻², demonstrating the potential for coupling with intermittent energy systems. This work provides valuable insights for tuning the alkaline HER activity of Ru sites in carbon-supported catalysts.

Author contributions

Mengyu Zhang and Bowen Zhou did the design and operation of the experiment, the collation of the data, the processing of the data, and the completion of the initial manuscript. Lingfei Guo completed the research of literature, the supplement of data and the research of theory. Hongdong Li, Weiping Xiao, Guangrui Xu, Dehong Chen, Caixia Li and Yunmei Du provided valuable guidance and writing assistance. Zexing Wu and Lei Wang did writing review, content editing, experimental supervision and financial support. All authors discussed the results and provided comments on the manuscript.

Data availability

The data supporting this article have been included as part of the ESI.†

Conflicts of interest

The authors declare that they have no conflicts of interest.

Acknowledgements

The authors thank funding support from the National Natural Science Foundation of China (52371227; 22002068; 52272222, and 52072197), Taishan Scholar Young Talent Program (tsqn201909114), Shandong Province “Double-Hundred Talent Plan” (WST2020003), Youth Innovation and Technology Foundation of Shandong Higher Education Institutions, China (2019KJC004), Outstanding Youth Foundation of Shandong Province, China (ZR2019JQ14), Taishan Scholar Talent Program (ts20190402), Major Basic Research Program of Natural Science Foundation of Shandong Province under Grant No. ZR2020ZD09, Major Scientific and Technological Innovation Project (2019JZZY020405), University Youth Innovation Team of Shandong Province (202201010318), Youth Innovation Team Development Program of Shandong Higher Education Institutions (2022KJ155).

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4qi01505c

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