Preparation And The Performance Study Of TiO₂-based Triple Photoanode For Photoelectrochemical Water Splitting

In recent years,with the dual pressures of environmental pollution and energy crisis,considerable efforts have focused on exploiting clean and efficient photoelectrochemical?PEC?devices,as to PEC devices,the performance of photoanode play an important role during water splitting.In general,TiO₂ nanowires or TiO₂ nanotube as a promising candidate of the photoanode which could provide a direct and fast transport channel for electrons.Based on the ideal geometry,the rapid transport of electrons in photoanode was able to realize.TiO₂ nanowire arrays photoanode are extensively studied of PEC devices due to the simple synthesis methods,low cost and good stability.However,the large bandgap of TiO₂ limits its light absorption within the UV part of the solar spectrum,which strictly prevents the efficient utilization of the solar energy in the visible region.In order to enhance the visible light harvesting ability of TiO₂,lots of core/shell nanowire arrays photoanodes was fabricated by combining short bandgap semiconductors such as ZnSe,CdS with TiO₂,which could greatly promote the visible light harvest ability.But,the poor stability caused by hole-induced self-oxidative of photocatalysts is a fatal flaw existed during practical PEC hydrogen generation application as to the metal sulfide photoanodes.To cope with the poor PEC stability,we manufacturing the triple photoanode by combining TiO₂/ZnSe and TiO₂/CdS core/shell nanowire arrays with Co-Pi and Ni-FeLDH oxygen evolution reaction?OER?catalysts,respectively.As a result,the Co-Pi and Ni-Fe LDH OER catalysts acts as the hole transfer relay to accelerate the surface water oxidation reaction,which suppresses the ZnSe and CdS self-oxidative decomposition as well as improves the photocatalytic activity.Here,we report the TiO₂/ZnSe/Co-Pi and TiO₂/CdS/Ni-FeLDH triple photoanodes for solar-driven water splitting,respectively.The details are as follow:1.Firstly,the TiO₂/ZnSe/Co-Pi triple photoanode successfully fabricated on FTO substrates via hydrothermal,physical vapor deposition and photo-assisted electrodeposition.The size and geometry of TiO₂ nanowires can be well controlled by changing the conditions of hydrothermal,it will determine the efficiency of electron transport in TiO₂ nanowires photoanode.The physical vapor deposition and photo-assisted electrodeposition can precisely regulate the thickness of ZnSe layer as well as the amount of Co-Pi OER catalysts,which affects the visible-light absorptionproperties and PEC stability of the triple photoanode directly.It is found that a remarkable enhancement of PEC performances was achieved by comparing TiO₂/ZnSe/Co-Pi triple photoanode with TiO₂ and TiO₂/ZnSe photoanodes,respectively.Especially for PEC stability,the TiO₂/ZnSe/Co-Pi photoanode retains⁵6% of the initial photocurrent value after the 4000 seconds persistent light irradiation,which is much higher than that in TiO₂/ZnSe photoanode?²5% of the initial value?.2.In addition,the TiO₂/CdS/Ni-FeLDH triple photoanode also assembled on FTO substrates for water splitting.Firstly,the TiO₂ nanowire arrays were grown on FTO substrate by the facile hydrothermal.Then,the above-synthesized TiO₂ nanowire arrays was coated with CdS layer via physical vapor deposition,followed by loading the Ni-FeLDH OER catalysts on the surface of TiO₂/CdS nanowire arrays by the photo-assisted electrodeposition.Electrochemical analysis indicates that the Ni-FeLDH OER catalysts serve as the hole transfer relay to accelerate the surface water oxidation reaction meanwhile suppresses the CdS self-oxidative decomposition.More importantly,the TiO₂/CdS/Ni-FeLDH photoanode shows a remarkable enhancement of the PEC stability compare with TiO₂/CdS nanowire array photoanode,which retains⁸0%?TiO₂/CdS/Ni-FeLDH?and³5%?TiO₂/CdS?of the initial photocurrent value after the 1500 seconds persistent light irradiation at 0.6V versus Ag/AgCl,respectively.