Preparation And Photoelectrochemical Properties Of Metal Oxides Photoanodes

Energy shortage and environmental pollution are becoming a global concern in the21st century.Seeking renewable energy to replace fossil energy has attracted more attention in recent decades.Photoelectrochemical?PEC?cell is an environmental friendly and low-cost technique that converts solar energy to clean hydrogen energy.In PEC cell,metal oxides are often used as photoanodes since they have strong tolerance of oxidant conditions during oxygen evolution.In the past years,morphology control,loading cocatalysts,doping and incorporation of plasmonic metals have been widely adopted to improve their properties.However,little attention has been paid to both effects on the photocurrent response and onset potential of the photoanodes as well as the underlying mechanisms.To address these issues,Ti doped Fe₂O₃ and WO₃/Au photoanodes were prepared in this work.The Ti doping effects on PEC properties of hematite were investigated and PEC properties of WO₃ photoanodes modified with different sized Au nanoparticles were compared.Follwing works were carried out.Ti doped hematite nanorod arrays were prepared by a facile treatment of hematite with TiCl₃ solution and used as photoanodes for water oxidation.The results show that Ti doping has improved the photocurrent of hematite at higher potentials and shifted the onset potential positively.The underlying reasons for anodic shift of their photocurrent onset potentials were investigated through structural analyses and electrochemical measurements.Raman,CV and EIS data manifest more surface states are formed in Ti doped hematite than that in the undoped one.Consequently,Ti doped hematite presents lower water oxidation kinetics in the dark,more electron-hole recombination at low potentials under illumination.More surface states and larger charge transfer resistance from surface states to electrolyte result in more positive photocurrent onset potential of Ti doped hematite.Different sized Au nanoparticles were loaded on WO₃ nanoplates films by reduction by WO_3-x or photochemical reduction method.The sizes and dispersion of these nanoparticles on WO₃ films were characterized by SEM and TEM.Au nanoparticles of 10⁴5 nm were obtained through reduction by WO_3-x,while Au nanoparticles of 1² nm were loaded and uniformly dispersed on WO₃ film via photochemical reduction.The results show that the photocurrent of WO₃ films has been improved after loading of these larger Au nanoparticles due to plasmon-induced resonance energy transfer and hot electron injection.In contrast,the onset potential of WO₃ films shows a negative shift after incoporation with the smaller Au nanoparticles,indicating these small nanoparticles act as good catalyst for water oxidation.