Preparation Of Oxide Semiconductor Heterostructure Material And Their Photoelectrochemistry Water Splitting

There is a growing interest in the conversion of water and solar energy into clean and renewable H2 fuels using earth-abundant materials due to the depletion of fossil fuel and its serious environmental impact.The promotion and application of solar water splitting into usable hydrogen need to reduce the cost of the catalyst and improve the efficiency of water splitting.Photoelectrochemical(PEC)water splitting into H2,which combines solar energy and electricity,helps to improve the efficiency of water splitting.In order to further improve the efficiency of PEC water splitting,it is necessary to improve the light harvesting ability,photogenerated carriers' transport/separation efficiency and surface reaction kinetics of the anodes.The semiconductor heterostructure is very effective in improving the electron transport,improving the light trapping ability and improving the surface reaction efficiency.This paper focuses on the synthesis of the heterogeneous oxide semiconductor materials and applies it to PEC water splitting,The main research contents are as follows:(1)Three-dimensional TiO2/ZnO hybrid array as a heterostructure anode for photoelectrochemical water splitting.The TiO2 nanorod array was firstly grown on FTO conducting substrate via a hydrothermal process.Then,the ZnO nanorod were decorated on TiO2 nanorod array,and three-dimensional TiO2/ZnO heterostructure arrays were obtained by hydrothermal reaction in ZnO precursor.Afterwards we further studied the influence of TiO2/ZnO thin film morphology and PEC activity under different ZnO precursor concentration,hydrothermal time and temperature.The results indicated that TiO2/Zn O thin film prepared by 10 mM of ZnO precursor concentration,3h of hydrothermal time and 90 oC of hydrothermal temperature showed the best photoelectrochemical performance,the photocurrent density(1.13 mA/cm2)is about four times than that of pure ZnO nanorod array(0.3 m A/cm2),and about double than that of pure TiO2 nanorod array(0.6 mA/cm2)at 1.23 V vs RHE.Compared with ZnO and TiO2 nanorod array anode,the carriers' density and the electron lifetime of three-dimensional TiO2/ZnO heterostructure is obviously improved.The light absorption and kinetic test results indicated that the TiO2/ZnO heterojunction can enhance light harvesting ability,improve carriers' transport and separation efficiency and enhance carriers' density.Therefore,the TiO2/ZnO exhibited enhanced PEC activity.(2)Synthesis of WO3/ZnO heterostructure anode for photoelectrochemical water splitting.First,Zn O nanorods were grown on FTO conductive substrate by chemical bath method.Afterwards,we studied the influence of ZnO nanorods morphology and PEC activity under different reaction time.According to the results of photoelectrochemical test,reaction time as 3h can help to fabricate high quality Zn O nanorod,and the photoelectrichemical properties of this material reached the best.On the basis of this material,we successfully prepared the WO3/ZnO heterojunction via hydrothermal method.The photocurrent density of WO3/ZnO films was the highest(1.225 mA/cm2 at 1.23 V vs RHE)as much as 2 times improvement of bare ZnO nanorod photoanode(0.508 mA/cm2 at 1.23 V vs RHE).The enhanced photocurrent was attributed to the extension of visible light response,increased carriers density,effective carriers separation at the interface of heterojunction and better electron transport properties,which were con?rmed by Mott-Schottky and electrochemical impedance spectroscopy.(3)Synthesis of CuWO4/WO3 composite materials anode for photoelectrochemical water splitting.WO3 nanorod array with diameter around 50 nm were synthesis via a hydrothermal method,then a facile dipping-annealing process was employed to fabricate Cu WO4/WO3 ?lms.The bandgap of the composite structure is adjusted by the deposition of CuWO4 onto the surface of WO3,so that the light absorption of the material increases obviously.As-prepared CuWO4/WO3 composite materials achieved a photocurrent density of 1.73 mA/cm2 at 1.23 V vs RHE,which was almost 1-fold higher than that of the pure WO3 ?lm(1.4 mA/cm2)under illumination.The enhanced performance of Cu WO4/WO3 composite structure bene?t from the fast photogenerated charge carriers transmission.Electrochemical impedance and Mott Schottky test showed that the composite material could significantly enhance the carrier density and charge transport rate,and the material could exhibit better performance.