Preparation,design And Properties Of Shuttle ZnO Nanocrystal Array Photoelectrode

Developing sustainable and green renewable energy is the fundamental way to solve the issues of the energy crisis and environmental pollution that the world is facing.Photoelectrochemical water splitting,which converts solar energy into the storable and transportable hydrogen,is regarded a promising rout to utilize the abundant,clean solar energy.Moreover,hydrogen with high energy density and eco-friendly characteristic is one of the ideal clean energy carriers.The semiconductor photoelectrode is the essence part of a photoelectrochemical cell,whose microstructrues and heterostructures play an important role in light absorption,bulk transport and surface transfer of photogenerated carriers,affecting the solar conversion efficiency of the entire photoelectrochemical cell.In this dissertation,high performance ZnO based photoelectrodes have been rationally designed and prepared through controlling the microstructures and constructing the heterostructures.ZnO films with varied morphologies have been synthesized by simply adjusting the temperature and voltage parameters during the electrochemical deposition process.It was found that the ZnO nano-shuttle flower arrays(ZnO NSFs),deposited at hign voltage(4.0 V)and low temperature(55?),has the best photoelectrochemical water splitting performance.Its shortcircuit photocurrent density(0.38 mAcm-2)is almost 2 times of that(0.2 mAcm-2)achieved in the ZnO nanorod arrays(ZnO NRs),and photocurrent onset potential cathodically shifts about 200 mV compared to that of ZnO NRs.Further investigation on the structural characterization and in-depth analysis,it was found that the excellent photoelectrochemical water splitting performance of ZnO NSFs could be attributed to the synergistic effect of the hierarchical structure(enhancing light absorption,enlarging electrochemical specific surface area and shortening photogenerated carrier transport distance),upshifted flat band potential(increasing open-circuit voltage)and abundant oxygen defects(enhancing photogenerated carrier transport ability by enlarging carrier concentration).To extend the light absorption range,ZnO/CdS/PDA and ZnO/PDA/CdS heterojunction photoelectrodes have been constructed based on the ZnO NSFs.Although the light absorbances and absorption ranges of ZnO/CdS/PDA and ZnO/PDA/CdS photoelectrodes are similar,the short-circuit photocurrent density of the ZnO/CdS/PDA photoelectrode is 1.66 times that of the ZnO/PDA/CdS photoelectrode under the whole light irradiation,and is 2.3 times that of the ZnO/PDA/CdS photoelectrode under visible light irradiation.The significant improvment is attributed to the formation of a matched energy band alignments among ZnO,CdS and PDA in the ZnO/CdS/PDA photoelectrode.Consequently,the photo-generated carriers can separate more effectively than that in the ZnO/PDA/CdS photoelectrode,which is beneficial to the full utilization of photogenerated carriers and the improvement of the solar to hydrgeng conversion efficiency.