Study Of Non-noble Metal Catalysts On Si Photocathodes For Solar Water Splitting

Nowadays humans are encountering two global problems:the increasingly serious environmental pollution and the expected depletion of fossil fuels.Access to clean new energy by solar water splitting is probably one of the most effective solutions to solve the two global problems.Among numerous electrode materials,Si is an important photocathode material for the reason of not only abundant reserves but also narrow band gap well matched to the solar spectrum and the appropriate band structure for the hydrogen production.However,it is hard for us to get efficient photocathode due to its slow surface kinetics for hydrogen production.In order to overcome this difficulty,many researchers have been making a lot of efforts to seek suitable catalysts.Although efficient noble metal catalyst platinum?Pt?has been proved to be the best,it is expensive so that looking for non-noble metal catalysts is the inevitable choice.The purpose of this paper is to solve the slow surface kinetics of the Si photocathode during hydrogen production and therefore study the non-noble metal catalysts.The main research contents are as follows:?1?It is unlikely that a non-noble metal alone can compete with Pt.One strategy to improve the activity of non-noble metal catalysts is to investigate the mixed-metal or alloy catalysts.In this study,we loaded the NiMo alloy on a stable 2 nm Al₂O₃ protected n⁺p-Si photocathode using electrodeposition method to explore its photoelectrochemical?PEC?catalytic effect.We determined the best amount of NiMo through interrupted electrodeposition and testing of PEC properties.We also analyzed the morphology and composition of NiMo by SEM,TEM,and XPS and compared the catalytic performance of NiMo and Pt.Finally,we studied the PEC stability of NiMo when different electrolytes are used,which have different PH values.We found that the performance of the catalyst NiMo is close to Pt when their work environment is alkaline electrolyte.The NiMo/Al₂O₃/n⁺p-Si photocathode is in the most stable state in alkaline electrolyte while it is unstable in acidic solution.?2?Metal sulfide is also a promising catalyst besides alloy catalysts among non-noble metal catalysts.Simulation based on density functional theory?DFT?on catalyst-hydrogen binding energy has shown that molybdenum disulfide?MoS₂?is located close to the top of volcano curve.The capability of MoS₂ for serving as a catalyst for H₂ production was subsequently verified by electrochemical measurements.Tungsten disulfide?WS₂?is similar to MoS2 in electron energy structure.Herein WS2 is investigated as a non-noble metal catalyst for Si.We combined WS₂ with Al₂O₃/n⁺p-Si photoelectrode by dip-coating and post-annealing.Subsequently,we analyzed the surface morphology,composition and PEC properties of WS₂/Al₂O₃/n⁺p-Si photoelectrode and found that the open-circuit voltage of the WS₂/Al₂O₃/n⁺p-Si photocathode increases nearly 0.6V compared to the pure Al₂O₃/n⁺p-Si.In addition,its performance is more outstanding in acid environment.