Research On The Preparation And Photoelectrochemical Performance Of Composite Thin Film Photoelectrodes

Due to the serious problems caused by energy crisis and environmental pollution,more and more attention have been focused on developing clean renewable energy in the society.Photoelectrochemical?PEC?hydrogen production based on photoelectrodes,a promising and environmentally benign method for solar hydrogen generation,has attracted significant attention.However,hydrogen production efficiency still can not reach the level of commercial application.Developing a highly efficient water splitting semiconductor therefore becomes an important research direction.The main research content of this article is the design and preparation of composite structure thin film photoelectrodes and the investigation on their photoelectrochemical hydrogen production performances.Hematite??-Fe₂O₃?has received considerable attention due to its abundance,low cost,excellent chemical stability,and favorable band gap energy of 2.1 eV.Unfortunately,pure-phase hematite has an intrinsically poor conductivity,which limits its quantum efficiency in photoelectrochemical reaction.We presented a facile preparation of the Ti-doped?-Fe₂O₃ultra-thin photoanode by a simple atmospheric pressure chemical vapor deposition method?APCVD?based on ferrocene pyrolysis on Ti foil substrate.The Ti-doped?-Fe₂O₃photoanode shows superior photoelectrochemical performance to the thin film prepared on FTO glass and pre-oxidized Ti substrate under the same conditions.The photocurrent of the Ti-doped?-Fe₂O₃ photoanode annealed at 450?reaches 80?A/cm² and 0.9 mA/cm² at0.6 V vs.Hg/Hg₂Cl₂ under 9 mW/cm² and 100 mW/cm² illumination,respectively.The IPCE of 15.4%and 7.2%were at 360 nm and 400 nm,respectively.The atomic concentration of Ti in the hematite thin films is 8.4%.Silicon is the second most abundant element in the earth's crust with a narrow band gap?Eg=1.1 eV?,which is widely applied as photovoltaic materials and proved to be efficient as photoelectrodes for solar hydrogen production.However,the surface reflection of solar radiation and the potential photocorrosion during PEC reaction,especially under concentrated radiation,remains an issue for Si photoelectrodes.Introduction of surface nanostructures and surface passivation layers significantly improve the solar absorption efficiency and chemical stability of many photoelectrodes.Si nanowire?SiNW?arrays decorated with Pt nanoparticles are passivated with TiO₂ surface layer using atomic layer deposition?ALD?.Pt nanoparticles separated from aqueous electrolyte by TiO₂ layer of more than 15 nm still well catalyze the surface photoelectrochemical hydrogen production reaction without direct contact to the electrolyte.This structural configuration shows remarkable chemical stability and anodically shifted the onset potential,suggesting a great promise for applications in solar hydrogen production.It shows superior photoelectrochemical performance to the planar Si,Pt/planar Si,and TiO₂/Pt/planar Si photoelectrodes in terms of chemical stability and photoresponse under 1 sun and concentrated illumination.The maximum cathodic photocurrent of the TiO₂/Pt/SiNW is^-27 mA/cm² under 100 mW/cm² illumination.The onset potential on the TiO₂/Pt/SiNW sample is 0.35 V_RHE and the maximum photon-to-energy conversion efficiency of the TiO₂/Pt/SiNW sample is 15.6%.Pt nanoparticles are the most frequently used catalyst for Si photocathode.Alternative catalyst based on transition metal or metal oxide as cathode catalyst is greatly desired to replace Pt.A mesoporous?-Fe₂O₃ thin film was deposited on the surface of planar p-Si using a facile atmospheric pressure chemical vapor deposition?APCVD?method through pyrolysis of ferrocene.The?-Fe₂O₃/Si photoelectrode produces a much higher photocurrent than the planar Si photoelectrode and Pt/planar Si photoelectrode.The cathodic photocurrent of the?-Fe₂O₃/Si photoelectrode reaches^-34 mA/cm² under 100 mW/cm²illumination at-1.5 V_RHE.The onset potential of?-Fe₂O₃/Si photoelectrode is anodically shifted by 0.5 V relative to the bare planar Si.The maximum IPCE of?-Fe₂O₃/Si photoelectrode is 70%at 600 nm.The photoelectrochemical hydrogen production was proposed to be catalysed by surface hematite nanoparticles on the interface of hematite and silicon.