Heterojunction engineering of NiC/NiPt promoting charge remigration on the Pt site with efficient acid hydrogen evolution

Abstract

Alloying with transition metals can effectively reduce the content of Pt and improve the intrinsic hydrogen evolution activity of the catalyst. However, the problems of low stability and activity decay in the acidic environment of proton exchange membrane water electrolysis (PEMWE) have become difficulties in the development of such catalytic materials. In this work, the deep optimization of the NiPt alloy was successfully achieved by high temperature carbonization treatment, and the acid-stable NiC/NiPt@C catalytic material was prepared. With a heterojunction structure, NiC/NiPt@C exhibited an overpotential of 36.7 mV at −10 mA cm⁻² with excellent stability. Density functional theory calculation and characterization revealed that the high performance was driven by the surface charge remigration of the Pt site and the re-optimization of H* adsorption strength. The performance (1000 mA cm⁻² at 1.68 V, 80 °C) and stability (1000 mA cm⁻², 12 h) of the NiC/NiPt@C electrode were further verified in PEMWE cells, demonstrating its great potential for practical hydrogen production applications.

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Xin-Yu Zhang

Prof. Xinyu Zhang is an academic professor at Shandong University of Science and Technology. He serves as a youth editor for EcoEnergy, Chinese Chemical Letters, MetalMat and Energy Lab journals. His research interests cover electro-catalysts for hydrogen production. To date, he has published 32 papers in SCI journals. He has presided over more than 6 projects including the Shandong Provincial Natural Science Foundation and Postdoctoral General Project. He also won the Second Prize for Qingdao Science and Technology Award and the First Prize for Science and Technology from the Chemical and Chemical Engineering Society of Shandong Province.

Introduction

Replacing traditional fossil fuels with renewable sources, particularly hydrogen, is of paramount significance in addressing issues such as air pollution, global warming, and energy crises faced by humanity. Electrochemical water splitting represents not only a novel clean energy technology with broad application potential but also an effective means of reducing over-reliance on fossil fuels, and it is considered a promising method for producing clean hydrogen fuel from renewable energy sources.^1–3 For the hydrogen evolution reaction (HER), which occurs on the cathode side of the electrolyzer, platinum (Pt) remains the leading precious metal electrocatalyst to date. However, the scarcity and high cost of Pt have emerged as impediments to the scalable and sustainable production of hydrogen.^4–7 Consequently, the development of inexpensive and efficient HER catalysts is of great necessity.

Non-precious metal catalysts exhibit advantages such as abundant reserves, low cost, and excellent hydrophilicity, however, they possess intrinsic activity limitations.^8–10 By integrating Pt with transition metals (such as Ni, Co, Fe) to augment intermetallic interactions (electron donation or withdrawal), the catalytic activity can be effectively enhanced while minimizing Pt loading.^11–14 For instance, Cheng et al. promoted the enrichment of enormous electrons on the Co surface with the alloying treatment of PtCo, thus reducing the energy barrier required for hydrolysis and improving the catalyst reaction activity.¹⁵ By alloying with NiCo, Zhang et al. reduced the load content of Pt to 15% (wt), and HER activity was improved by 3 times compared with commercial Pt/C.¹⁶ Nonetheless, despite the exceptional properties displayed by non-precious metal catalysts in alkaline solutions through coupling or alloying, their application in proton exchange membrane water electrolysers (PEMWEs) is constrained by the requirements for higher current densities and strong acid environments.

In PEMWE, protons produced on the anode side will be continuously transferred to the cathode catalyst surface through the proton exchange membrane, thus forming an acidic electrolytic environment.^17–20 When the current density is at a higher level (such as 1000 mA cm⁻²), the proton concentration near the HER catalyst will be higher, which will lead to the dissolution of some non-precious metal components in the alloy, and then the collapse and loss of the active site.^21–23 In the face of these problems, the use of high-temperature calcination to locally carbonize these nonmetals may be an effective way. On one hand, the carbon layer as a conductive support can provide more electrochemical active area and increase the number of active sites of the catalyst. On the other hand, the newly constructed carbides can form a heterostructure with Pt, promote the redistribution of electrons at the metal site, improve the activity of the catalyst, and enhance the acidic stability of the catalyst.^24–26

Based on the above analysis, herein, a NiC/NiPt@C heterojunction was successfully fabricated by combining traditional hydrothermal synthesis with high-temperature calcination. By reducing the Pt content while enhancing catalytic stability, this approach effectively improves the catalyst's performance, achieving a low overpotential of merely 36.7 mV to reach a current density of −10 mA cm⁻². Further density functional theory (DFT) calculations reveal that the construction of the NiC/NiPt@C heterojunction facilitates the accumulation of charge on the nickel surface and the dissipation of charge on the platinum surface. This effectively reduces the adsorption energy of reaction intermediates at the sites of platinum and nickel, thereby promoting the fast cleavage of the chemical bond between adsorbed hydrogen and the catalyst surface. The abundant Pt–H bonds at the NiC/NiPt@C interface site are ultimately released as H₂, enabling an efficient Volmer–Tafel mechanism. This provides a solid foundation for the efficient utilization of precious metal-based catalysts and the optimization of acidic HER performance.

Experimental section

Chemicals

Platinum(II) acetylacetonate (Pt(acac)₂, 97%), nickel acetylacetonate (Ni(acac)₂, 95%), benzoic acid (C₆H₅COOH, ≥99.5%), and N, N-dimethylformamide (DMF, ≥99.9%) were all purchased from Sinopharm Chemical Reagent Co., Ltd. Commercial Pt/C (Com Pt/C, Pt 20 wt%) was purchased from Science Materials Station Company. Vulcan XC72R carbon was purchased from River's Electric Co., Ltd. Chemicals were directly applied in their commercial form without further purification. Ultrapure water with a resistivity of 18 MΩ cm⁻¹ was used in all synthetic procedures.

Synthesis of NiPt@C

NiPt@C was prepared by means of a hydrothermal reaction process. Typically, 60 mg of XC72R, 36 mg of Pt(acac)₂, 24 mg of Ni(acac)₂ and 260 mg of benzoic acid were dispersed in 30 mL of DMF. After being vigorously stirred for 20 minutes, the solution was transferred into a 90 mL Teflon-lined stainless-steel autoclave and heated at 160 °C for 10 h. After allowing the reaction mixture to cool to ambient temperature, the precipitate was collected via centrifugation. The solid was sequentially washed with deionized water and ethanol, and then dried under vacuum at 60 °C for 12 hours to ensure complete solvent removal. Similarly, the synthesis process of Ni@C and Pt@C was like that of NiPt@C except that reagents of Pt(acac)₂ and Ni(acac)₂ were not added, respectively.

Synthesis of NiC/NiPt@C

A high-temperature calcination strategy was used for the facile synthesis of the target catalyst NiC/NiPt@C. Specifically, 50 mg NiPt@C was weighed and placed in a tube furnace. In an argon atmosphere, the sample was calcined at 900 °C for 8 hours at a heating rate of 5 °C min⁻¹. After the reaction was completed, NiC/NiPt@C could be obtained.

Materials characterization

X-ray diffraction (XRD) patterns were obtained using a JSM-7500F diffractometer to determine the crystalline structure of all catalysts. X-ray photoelectron spectroscopy (XPS) was carried out on a VG ESCALABMK II system to reveal the electronic structure. High-resolution transmission electron microscopy (HRTEM) images were obtained using an FEI Tecnai G2 F20 S-TWIN, and energy-dispersive X-ray spectroscopy (EDX) was carried out at 300 kV to explore the crystalline structure and elemental distribution of the catalysts.

Electrochemical measurements

All the electrocatalysts were evaluated in 0.1 M HClO₄ solution. Moreover, the prepared samples loaded on glassy carbon were used as the working electrodes. The silver chloride electrode and graphite were used as the reference electrode and the counter electrode, respectively. The preparation process for the working electrode was as follows: First, the glassy carbon electrode was polished on a polishing cloth until clean before use. 5 mg of the sample was accurately weighed into a 1.5 mL microcentrifuge tube. 0.5 mL of 5 wt% Nafion solution and 0.5 mL of deionized water were added sequentially. The dispersion was then sonicated for 30 minutes to ensure uniform distribution. We adjusted a 2–20 μl micropipette to 5 μl capacity and aspirated 5 μl dispersion. The dispersion was pipetted onto the glassy carbon electrode and allowed to dry naturally to form a film. All potentials were converted to the RHE scale using the equation:

E_RHE = E_Ag/AgCl + 0.059 pH + 0.197 V (1)

For HER tests, polarization curves were recorded between 0 and −0.7 V vs. RHE at a scan rate of 5 mV s⁻¹ with iR-correction. The Tafel slope was determined by plotting the overpotential versus the logarithm of current density. Electrochemical impedance spectroscopy (EIS) was conducted over a frequency range of 0.1–100 kHz to probe the interfacial properties of the electrochemical system. For the stability test, the target catalyst was supported onto the surface of the glassy carbon electrode through a Nafion solution. And chronopotentiometric measurements were performed at −10 mA cm⁻² for 20 h.

PEMWE measurements

A Nafion 115 membrane was sequentially washed with 5 wt% H₂O₂, 0.5 M H₂SO₄, and deionized water at 80 °C for 1 h, respectively. After cooling to room temperature, the treated membrane was preserved in 0.5 M H₂SO₄ electrolyte. The membrane electrode assembly was prepared using Nafion 115 by the catalyst-coated membrane method with a geometric area of 5 × 5 (25 cm²). Commercial IrO₂ was used as the anode for the oxygen evolution reaction, and the NiC/NiPt@C electrocatalyst was used as the cathode for the hydrogen evolution reaction. For the anode electrode, the mass loadings of NiPt@C and NiC/NiPt@C were 0.53 mg cm⁻². For the cathode electrode, the loading of the IrO₂ was 0.41 mg cm⁻². The anode and cathode plates were heated to 25 or 80 °C during the test. Besides, a flow of water preheated to 25 or 80 °C at 100 mL min⁻¹ was supplied to the anode side. The performance evaluation of the PEMWE using the NiC/NiPt@C⁽⁻⁾ ‖ IrO₂⁽⁺⁾ electrocatalyst was performed using a DC power device. Linear sweep voltammetry (LSV) measurements were performed at a scan rate of 5 mV s⁻¹, typically spanning the potential range of 1.1–2.0 V. The stability test was performed with a chronoamperometry method, in which the test current can reach a maximum of 50 A.

Computational methods

All density functional theory (DFT) simulations were executed via the Vienna Ab initio Simulation Package (VASP), implementing the Perdew–Burke–Ernzerhof (PBE) functional under the generalized gradient approximation (GGA) exchange-correlation functional. The projector-augmented wave (PAW) method was employed to describe electron–ion interactions, with wavefunctions expanded in a plane-wave basis set and applying an energy cutoff of 380 eV. Geometric optimization proceeded until atomic forces fell below 0.02 eV Å⁻¹ and energy convergence reached 10⁻⁵ eV, ensuring high-precision structural relaxation. Based on experimental evidence of enhanced catalytic activity, the NiPt (111) and NiC_x (204) surfaces were modeled. Each lithiation step exhibited a Gibbs free energy change (ΔG), which was defined as:

ΔG = ΔE + ΔZPE − TΔS (2)

where ΔE is the electronic energy difference directly obtained from DFT calculations, ΔZPE is the change in zero-point energy, T is the temperature (T = 298.15 K) and ΔS is the change in the entropy, respectively.²⁷

Results and discussion

Electrocatalyst preparation and characterization

NiC/NiPt@C was synthesized by means of the hydrothermal reaction process combined with calcination, in which the benzoic acid acted as a reducing agent for the transformation of nickel and platinum ions into an alloy. Furthermore, a composite structure consisting of NiC and NiPt@C was formed because of a reaction between NiPt@C and the carbon layer during the calcination process (Fig. 1a). Additionally, X-ray diffraction (XRD) analysis was performed to investigate the crystalline structure of the produced catalysts when the metal source was nickel or platinum alone, as shown in Fig. S1 In these cases, Ni (PDF no. 00-001-1258) and Pt (PDF no. 00-001-1190) with an alloying phase structure could be successfully synthesized. However, in the coexistence of both metal sources, a distinctive crystalline phase of the NiPt@C alloy was directly obtained (Fig. 1b). The NiPt sample (PDF no. 03-065-9446) exhibits characteristic diffraction peaks at 41.8°, 47.5°, and 69.5°, corresponding to its (111), (200), and (220) lattice planes, respectively. Following high-temperature carbonization, new peaks emerge at 39.9°, 43.2°, and 47.2°, corresponding to the (204), (205), and (123) crystal planes of NiC_x (PDF no. 00-045-0979), indicating the in situ formation of NiC on the surface of NiPt@C. Subsequently, transmission electron microscopy (TEM) analysis was performed on Pt@C (Fig. 1c), Ni@C (Fig. 1d), NiPt@C (Fig. 1e), and NiC/NiPt@C (Fig. 1f), respectively. It was evident that the morphology of Pt@C was irregular, while that of Ni@C was more regular and has a larger particle size. For NiPt@C, it has a relatively uniform octahedral structure with a size of about 5–10 nm. After further calcination at high temperature, it was found that the morphology and size of NiC/NiPt@C obtained remained basically unchanged and uniformly dispersed, indicating great thermodynamic stability of the catalyst. Fig. 1g presents the high-resolution TEM image of NiC/NiPt@C, clearly showing two different crystal structures. The lattice fringe spacing of 0.25 nm corresponds to the (114) plane of Ni@C_x, while the spacing of about 0.19 nm on the other side of the Ni@C_x was assigned to the (200) face of NiPt@C. This observation further confirmed the formation of the NiC/NiPt@C heterojunction, which was consistent with XRD results. In addition, TEM mapping also revealed that Pt and Ni elements were loaded on the surface of the carbon layer in aggregated form, and the mass fractions of Pt and Ni were 15.81% and 4.41%, respectively, both significantly lower than the commercial Pt loading of 20% (Table S1). Using X-ray photoelectron spectroscopy (XPS), the electronic states and compositional evolution of NiPt@C during its conversion to NiC/NiPt@C were systematically investigated. The survey spectrum (Fig. 2a and b) revealed that both NiPt@C and NiC/NiPt@C contained the elements of Pt, Ni, and C, which was in accordance with the above TEM mapping results. Fig. 2c and d exhibit the XPS spectra of the Ni 2p region, corresponding to the samples before and after carbonization, respectively. Compared to the binding energy of Ni 2p in NiPt@C prior to carbonization (852.96 eV), the binding energy of Ni 2p in NiC/NiPt@C (852.91 eV) showed a shift of by 0.05 eV towards lower values.^28,29 This indicated that the chemical valence of nickel decreases, accompanied by the increase of the corresponding peak area of Ni²⁺, which might be related to the formation of nickel carbide. Fig. 2e and f show the XPS spectra of Pt 4f at NiPt@C and NiC/NiPt@C, revealing that platinum still maintained a zero-valence state after calcination. However, in a subtle way, compared with the binding energy of Pt before carbonization (71.66 eV), the binding energy of Pt after carbonization (71.76 eV) moved to a higher value by 0.1 eV, indicating an increase in the chemical valence state of Pt.^30,31 This indicated that the charge achieved remigration in Pt atoms compared to the pure Pt electrode, and thus further optimized the adsorption effect of the reaction intermediate on its surface.

Fig. 1 (a) Scheme for the synthesis of the NiC/NiPt@C catalyst. (b) XRD patterns of the prepared NiPt@C and NiC/NiPt@C samples. TEM images of (c) Pt@C, (d) Ni@C, (e) NiPt@C and (f) NiC/NiPt@C. (g) HRTEM image of NiC/NiPt@C. (h) TEM mapping images of Pt, Ni, and C in the NiC/NiPt@C electrode.

Fig. 2 XPS survey of (a) NiPt@C and (b) NiC/NiPt@C. Comparison of Ni 2p for (c) NiPt@C and (d) NiC/NiPt@C. Comparison of Pt 4f for (e) NiPt@C and (f) NiC/NiPt@C.

Electrocatalytic performance

The acid HER performances of NiC/NiPt@C and its reference catalysts were evaluated in 0.1 M HClO₄ electrolyte. As evident from the linear sweep voltammetry (LSV) curves in Fig. 3a, NiC/NiPt@C exhibited the highest performance among all samples, achieving current densities of −10 mA cm⁻² at an overpotential of only 36.7 mV, significantly surpassing the other control catalysts (including Ni@C, Pt@C, NiPt@C, and Com Pt/C). Specifically, the trend of overpotentials required to achieve −10 mA cm⁻² followed the order: NiC/NiPt@C (36.7 mV) < NiPt@C (44.1 mV) < Com Pt/C (49.3 mV) < Pt@C (70.8 mV) < Ni@C (154.2 mV) (Fig. 3b). This phenomenon suggested that nickel alone was inert to the HER but played an important role in enhancing the catalytic activity of NiPt@C and NiC/NiPt@C. Tafel slopes were derived to provide insights into the HER kinetics (Fig. 3c), where NiC/NiPt@C exhibited the lowest Tafel slope of 16.6 mV dec⁻¹, underscoring its exceptional charge transfer efficiency and fastest reaction rate among the prepared samples. It was worth noting that the Tafel slopes of the NiPt@C and NiC/NiPt@C were both smaller than 30 mV dec⁻¹, suggesting that they followed the Volmer–Tafel hydrogen evolution mechanism. To gain further insights into the electrode kinetics during the HER, electrochemical impedance spectroscopy (EIS) analysis was conducted as shown in Fig. 3d. Under the same applied potential, the NiC/NiPt@C catalyst possessed the smallest radius and the lowest charge transfer resistance compared with the other catalysts, indicating faster electron transfer from the electrode to the catalyst surface, thereby enhancing HER kinetics. Subsequently, in situ EIS was utilized to conduct test analysis on the two samples of NiPt@C and NiC/NiPt@C. The Bode phase plots depicted the phase angle as a function of frequency under different applied voltages (Fig. 3e and f). It could be found that when the applied voltage gradually increased from −0.26 to −0.30 V vs. RHE, the peak position of NiPt@C decreased rapidly compared to that of NiC/NiPt@C, indicating that the dynamic process of NiC/NiPt@C was faster and it was consistent with the Tafel slope analysis (Fig. 3g).³² Furthermore, the durability of the NiC/NiPt@C electrocatalyst was examined by chronopotentiometry. When the current density of −10 mA cm⁻² was maintained steadily for 100 h, the voltage applied on the catalyst surface was basically unchanged, reflecting its great operating stability (Fig. 3h). TEM images of NiC/NiPt@C after the stability test were then characterized. As shown in Fig. S2, NiC/NiPt@C remained uniformly dispersed. Meanwhile, the size and morphology of NiC/NiPt@C have not changed significantly, demonstrating the excellent stability of the catalyst. The EDX data of NiC/NiPt@C after cycling are provided in Table S2, which shows that the mass and atomic ratio of Ni in NiC/NiPt@C were 4.41% and 1.12%. The decrease in nickel content, compared with initial NiC/NiPt@C, might be related to the nickel dissolution that occurred when the nickel species on the catalyst surface have not fully transformed into NiC.

Fig. 3 (a) Polarization curves of Ni@C, Pt@C, NiPt@C, NiC/NiPt@C and Com Pt/C catalysts in 0.1 M HClO₄. (b) Comparison of overpotentials for Ni@C, Pt@C, NiPt@C and NiC/NiPt@C at −10 mA cm⁻². (c) Tafel and (d) Nyquist plots of all electrodes. In situ EIS data of (e) NiPt@C and (f) NiC/NiPt@C collected over the potential range from −0.26 to −0.30 V vs. RHE. (g) Frequency trend curve with applied potential. (h) Chronopotentiometry curve of NiC/NiPt@C at −10 mA cm⁻².

Mechanism of improving the HER performance of NiC/NiPt@C

To gain a deeper understanding of the outstanding HER performance on NiC/NiPt@C at the molecular level, density functional theory (DFT) calculations were performed. Fig. 4a illustrates the electron configuration of NiC/NiPt@C from three perspectives, where yellow and blue represent the accumulation and consumption of electrons on the atomic surface, respectively. Based on this, the simulated valence analysis in Fig. 4b showed that after carbonization, the valence state of Pt in NiPt@C increased (from 0.33 to 0.34), indicating the loss of surface electrons. In contrast, the valence state of Ni in NiPt@C decreased (from 0.29 to 0.28), while the valence state of Ni in NiC increased by 0.37, revealing that the construction of the heterojunction promoted electron flow on the surface of platinum to the Ni site in NiPt and NiC_x. Fig. 4c depicts the density of states (DOS) plot of catalysts NiPt@C and NiC/NiPt@C before and after carbonization. Notably, the d-band center of the catalyst underwent a significant shift following carbonization, transitioning from NiPt@C with a d-band center at −3.51 eV to NiC/NiPt@C with a d-band center at −3.77 eV. Moreover, Gibbs free energy (ΔG) was used to investigate the existence state of the reaction intermediate H* at different sites. As shown in Fig. 4d, the ΔG of the Pt-active site in NiC/NiPt@C was −0.29 eV, which was smaller than that of the Pt-active site in NiPt@C (−0.49 eV) and other Ni-active sites. This result suggested that the decrease of Pt surface charge effectively weakened the interaction between Pt and H, thus significantly facilitating the desorption of adsorbed hydrogen and accelerating the progress of the Tafel process (Fig. 4e).^33–35

Fig. 4 (a) Charge density difference for NiC/NiPt@C. Blue and yellow contours mark electron depletion and accumulation areas, respectively. (b) Average metal valence of Pt and Ni elements in catalysts. (c) DOS curves of NiPt@C and NiC/NiPt@C. (d) Gibbs free-energy diagram for the two steps of the HER on NiPt@C and NiC/NiPt@C. (e) Schematic diagram of the evolution and precipitation mechanism of reaction intermediates on the catalyst surface.

Proton-exchange membrane water electrolyser testing

The NiC/NiPt@C-based catalyst demonstrated superior HER performance when compared to other similar catalysts reported in the literature (Table S3). To assess its practical application potential, simulations and tests on the activity of NiPt@C⁽⁻⁾//IrO₂⁽⁺⁾ and NiC/NiPt@C⁽⁻⁾//IrO₂⁽⁺⁾ pairs in a PEMWE were further conducted (Fig. 5a). The water electrolysis performance was evaluated through LSV measurements. As depicted in Fig. 5b, the performance of NiC/NiPt@C⁽⁻⁾//IrO₂⁽⁺⁾ was significantly better than that of the NiPt@C⁽⁻⁾//IrO₂⁽⁺⁾ couple at 25 °C. To simulate industrial applications, the water splitting property was further tested at higher temperatures. As depicted in Fig. 5c, the performance of the NiC/NiPt@C⁽⁻⁾//IrO₂⁽⁺⁾ couple was further enhanced at 80 °C, only requiring a potential of 1.68 V to achieve the current density of 1000 mA cm⁻² in pure deionized water solution. Given the importance of electrode durability for practical water splitting applications, NiC/NiPt@C⁽⁻⁾//IrO₂⁽⁺⁾ was tested under both laboratory conditions (25 °C) and simulated industrial conditions (80 °C). It was demonstrated (Fig. 5c) that the NiC/NiPt@C⁽⁻⁾//IrO₂⁽⁺⁾ cell maintained stable performance over 12 hours at 1000 mA cm⁻² (industrial current density), with negligible degradation. This observation strongly suggests that the prepared NiC/NiPt@C possessed tremendous potential in water electrolysis systems for the future hydrogen-economic society.

Fig. 5 (a) The proton-exchange membrane water electrolyser model. (b) Polarization curves of the NiPt@C⁽⁻⁾//IrO₂⁽⁺⁾ and NiC/NiPt@C⁽⁻⁾//IrO₂⁽⁺⁾ couples. (c) Chronopotentiometry curve of the NiC/NiPt@C⁽⁻⁾//IrO₂⁽⁺⁾ couple in pure water.

Conclusions

In summary, we have developed a NiC/NiPt@C catalyst for HER electrocatalysis in acid electrolytes, exhibiting ultralow overpotential and high efficiency. The NiC/NiPt@C catalyst prepared by high temperature carbonization of the NiPt alloy showed an ultra-small size of 5–10 nm and a heterojunction internal structure. The in situ construction of nickel carbide further improvement the HER performance of NiPt@C and only required a low overpotential of 36.7 mV to reach −10 mA cm⁻². Meanwhile, the PEMWE assembled with NiC/NiPt@C and IrO₂ realized 1000 mA cm⁻² at 1.68 V and could be stably operated for at least 12 h. Theoretical simulation and XPS characterization proved that the electrons on the surface of the Pt site were transferred to the adjacent Ni during the heterogeneous structure construction, and thus Pt and Ni served as the best active sites for H* adsorption and water dissociation, respectively. This result not only reduced the cost of catalyst preparation and the amount of Pt used, but also deepened the understanding of the mechanism by which heterojunction structures promote efficient water splitting.

Conflicts of interest

There are no conflicts to declare.

Data availability

Data will be made available on request.

The data supporting this article have been included as part of the SI. See DOI: https://doi.org/10.1039/d5ta03321g.

Acknowledgements

This work is financially supported by the Shandong Provincial Natural Science Foundation (ZR2024QB021) and Qingdao Natural Science Foundation (24-4-4-zrjj-21-jch).

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