Investigation On The Preparation And Modification Of One-Dimensional Photoanodes Made Of Zinc Oxide And Iron Oxide

Among the various processes for solar to hydrogen,photoelectrochemical water splitting stands out in terms of conversion efficiency and potential for application.Among the oxide semiconductors with n-type,ZnO is cheap,nontoxic with high electron conductivity and provides the richest anisotropic crystal growth.However,ZnO suffers from a wide band gap,high charge recombination rate and the problem of instability in aqueous solution.Otherwise,Fe₂O₃ shows the advantages of a narrow band gap,nontoxicity,good aqueous stability,and natural abundance.However,the charges in Fe₂O₃ show a short lifetime with a low carrier mobility and short holes diffusion length.Additionally,Fe₂O₃ surfers a sluggish surface reaction with a high turn-on voltage as well.By compositing g-C₃N₄ with ZnO as well as incorporating Pt nanoclusters in between,a tricomponent C₃N₄/Pt/ZnO photoanode is adapted.g-C₃N₄ and ZnO constitute a heterojuction,while the Pt serves as the cocatalyst to facilitate the transfer of the photogenerated electrons from g-C₃N₄ to ZnO.In addition,a ZnO:Ga/ZnO isostructural nanojunction photoanode is prepared by Ga doping and pure ZnO composting.Ga doping improves conductivity and makes ZnO available to visible light.The ZnO:Ga/ZnO composite achieves obviously enhanced photocurrent and better photostability than ZnO.However,the onset potential of ZnO:Ga/ZnO is relatively high due to the low position of the conduction band of Zn:Ga.The conduction band of carbon quantum dots?CQDs?is very high.A dual-junction composite photoanode is established with CQDs and ZnO:Ga/ZnO.The CQDs@ZnO:Ga/ZnO photoanode exhibits a negative shift of the onset potential and a significant increase in the photocurrent density.The CQDs modification benefits to remarkably enhancing the conductivity and decreasing the interfacial charge transfer resistance in the ZnO:Ga/ZnO.The cooling rate during the annealing process is discovered to be a considerable factor affecting the photoelectrochemical performance of Fe₂O₃.The rapidly cooled hematite nanowires show decreased diameter,reduced surface disorder,Fe partial reduction,decreased amount of surface OH groups simultaneously with red shifted light absorption.Both the charge separation and injection efficiencies are improved.However,rapid cooling treatment shows little impact on the onset potential of Fe₂O₃.To decrease the onset potential of Fe₂O₃,a FeCoW oxy-hydroxide gel is introduced as cocatalyst.The FeCoW acts as a hole storage layer,resulting in efficient hole extraction from Fe₂O₃ for water oxidation.In addition,the surface state of FeCoW/Fe₂O₃ shifts to higher position,thus allows for a lower onset potential of the photocurrent.The composite anode exhibits a dramatic increase of the photocurrent a good stability.