Preparation And Photoelectrochemical Properties Of Hierarchical Nanoarray Materials Based Photo Anodes

With increasing concern on the reduction of global fossil fuels, considerable efforts have been committed to exploit alternative energy sources in the past several decades. Photoelectrochemical (PEC) water splitting provides a renewable and environmentally friendly energy conversion method. The conventional photoelectrodes is metal oxide semiconductors, such as ZnO, TiO2, WO3. However, these photoelectrodes usually suffers from the limited surface area, less efficiency in light capture and unsatisfied electron-hole separation. Based on the conventional photoelectrodes, this thesis realize the optimization of photoanode material by constructing ZnO core-shell hierarchical nanostructure, deposition of precious metals and introducing cocatalyst NiFe-LDH because of the increased active site exposure, inhibited electronic-hole recombination, expanded light absorptionas well as the improved water oxidation kinetics. Furthermore, the mechanism of the photoelectrochemical water splitting on the photoanode material has been studied by DFT theory calculation.The detailed content is as follows:1. ZnO nanorod@nanoplatelet (NR@NP) core-shell arrays have been synthesized via a facile hydrothermal method. The resulting ZnO NR@NP nanoarray exhibits promising behavior in photoelectrochemical water splitting, which can be attributed to the core-shell hierarchical nanostructures which facilitates the exposure of active sites. By a further modification using Au nanoparticles, the obtained Au-ZnO NR@NP demonstrates a largely enhanced photocurrent density of 1.47 mA-cm-2 at 0.6 V, much large than that of ZnO NR@NP core-shell arrays (1.17 mA-cm-2). Au nanoparticles as electron traps inhibit ZnO electronic-hole recombination. In addition, the surface-plasmon-resonance effect of Au nanoparticles facilitates utilization of visible light. Density functional theory (DFT) calculations further confirm that the photogenerated electrons of ZnO transfer to Au, which suppresses the recombination of electron-hole pairs. Therefore, this work provides a facile and cost-effective strategy for the construction of hierarchical metal/semiconductor nanoarrays, which can be potentially used in the field of energy storage and conversion.2. WO3@NiFe-LDH core-shell nanoarrays have been synthesized by electrochemical deposition method. The combination of these two photoelectrodes material significantly enhances the performance of photoelectrochemical water splitting. Typically, WO3 has photocatalytic properties, while NiFe-LDH shell acts as cocatalyst which increases water oxidation kinetics and suppresses the recombination of electron-hole pairs. This work provides a facile strategy for the construction of hierarchical core-shell nanoarrays, which can be potentially used in the PEC water splitting.