Regulating The Surface And Interface Of Silicon Photocathode For Photoelectrochemical Carbon Dioxide Reduction

Photoelectrochemical(PEC)carbon dioxide(CO2)reduction reaction into highenergy fuels is one of the creative strategies for storing solar energy and achieving carbon neutrality,in which the core is the semiconductor photocathodes.Silicon(Si)is emerging as an attractive candidate for a photocathode,due to its nearly ideal band structure,excellent charge carrier transport properties,and relatively low cost.However,the rational design of catalytic architectures to selectively and efficient produce a target product such as carbon monoxide(CO)has remained a grand challenge.In this thesis,we introduced the basic principles and research processes of Si photocathodes for CO2 reduction,and then put forward several approaches to design highly efficient and stable Si photocathodes,including the built-in PN junction,catalyst,transition layer and the local surface plasmon resonance.By regulating the surface and interface of Si photocathodes,a high activity and high-efficiency selective CO2 reduction finally realized.Our mainly work is as follows:(1)High effective and selective Si photocathode for CO production is fulfilled by utilizing a TiO2 interlayer to bridge the Au nanoparticles and n+p-Si.Through microstructure characterization,PEC testing,incident photon-to-current conversion efficiency and charge transfer performance analyses,change of illumination mode and density functional theory calculations,etc.it was found that the TiO2 interlayer could not only effectively protect and passivate Si surface,but also exhibit an outstanding synergy with Au nanoparticles during the adsorption and activation of CO2 molecule.Specifically,the TiO2 layer and Au nanoparticles worked concertedly to enhance the separation of hot electrons and holes in Au nanoparticles,contributing to the improved activity and selectivity for CO production by utilizing the hot electrons generated in Au nanoparticles during the CO2 reduction.Finally,the Au/TiO2/n+p-Si photocathodes exhibited a faradaic efficiency of 86%,a partial light current density of-5.52 mA/cm2 at-0.8 VRHE for CO production and a stability of 20 hours under simulated AM 1.5G one sun illuminating.(2)The n+pp+-Si solar cells integrated with silver grid line were used as photocathode for CO2 reduction.Silver sulfide(Ag2S)nanowires structure can be prepared on the surface of silver gridlines by a facile sulfurization treatment.Through microstructure characterization and PEC testing,etc,We found that the sulfurization treatment could regulate the electronic structure of silver and increase the specific surface area,leading to the enhanced activity and selectivity of Si photocathodes for CO2 reduction.Finally,the Ag2S/n+pp+-Si photocathodes achieved a CO selectivity of up to 92%,a photocurrent density of-9.03 mA/cm2(at-1 VRHE)and a stability of 20 hours.