Silicon Photoanode Modified By Ni@Co Core-Shell Particles For Water Oxidation

At present,the energy crisis and environmental problems caused by excessive use of fossil fuels are becoming increasingly prominent.The water splitting reaction that generates hydrogen by capturing sunlight is widely regarded as one of the most promising solutions.The photoelectrochemical water splitting cell is a device capable of directly converting solar energy into clean hydrogen energy,and thus has been favored by researchers.However,the oxidation reaction kinetics reaction rate occurring on the photoanode is relatively slow and the reaction overpotential is relatively high.Therefore,the development of an efficient and low cost semiconductor photoanode material is the focus of current photoelectrochemical water splitting hydrogen production research.Among the semiconductor photoanode materials widely studied at present,n-type silicon(n-Si)photoanode materials are widely used by researchers because of their rich content on the earth,long diffusion distance of photogenerated carriers,and large light absorption range.Therefore,it is widely used in photoelectrode materials for efficient solar water decomposition.However,the n-Si photoanode currently has a problem of relatively positive onset potential,low separation and injection efficiency of photogenerated carriers,and light absorption loss due to modification of the catalyst.In this dissertation,the several problems existing in photoanodes are studied.The metal-insulator-semiconductor(MIS)n-Si photoanode is prepared by two-step electrochemical deposition successfully.The photoanode is modified by Ni@Co island-shaped distribution nanoparticles,wherein the island-like distribution of the Ni@Co catalyst reduces the light absorption loss caused by the catalyst.The Ni@Co core-shell structure can effectively extract photo-generated holes from the space charge layer for the oxidation of Co,which in turn improves the separation and injection efficiency.At the same time,the onset potential of the photoanode is effectively reduced,and the factors affecting the photochemical water splitting of n-type silicon photoanode are discussed from the mechanism.The main research contents include:We successfully prepared the core-shell nanostructures of crystalline Ni@amorphous Co by two-step electrochemical deposition.We found that the island-like distribution of Ni@Co catalyst particles can effectively reduce the light absorption loss caused by the catalyst,and since the work function of Co(5.0 eV)is slightly higher than Ni(4.6 eV),n-Si/SiOx/Ni@Co The photoanode can exhibit a greater degree of band bending to improve charge separation efficiency.The MIS structure prepared at the same time has a high work function Ni@Co core-shell structure nanoparticles and a CoOOH catalyst layer formed in situ during the oxygen evolution reaction(OER)process,which can effectively reduce the OER kinetics of the reaction.The Ni@Co core-shell structure nanoparticles and a CoOOH catalyst layer can effectively extract the charge from the Si-based photoanode,improve the injection efficiency of the carrier,and the CoOOH formed in situ also significantly improves the charge separation efficiency.Therefore,the n-Si photoanode-coupled Ni@Co core-shell nanocatalyst particles can effectively enhance the photoelectrocatalytic activity compared to the n-Si/SiOx/Ni photoanode,and the saturation photocurrent density is 36.7 mA cm-2.The onset potential of n-Si/SiOx/Ni@Co photoanode reached 1.02 V vs.RHE and maintained good stability in the K-Bi buffer solution.This interfacial regulation of the core-shell structure enables efficient and easy separation of photogenerated carriers and increases carrier injection efficiency to nearly 100%over a wide potential window.