Study on Preparation and Properties of Nanoarray Photoanodes
Author:Wang Ru Yi
Solar power is the only renewable energy source to replace fossil fuels on a large scale and meet with growing environmental needs.Hydrogen is the cleanest energy source and has many potential applications.Using solar energy to produce hydrogen by photoelectrocatalysis is one of the most promising ways to use solar energy.Although the current researches have made significant progress in this area,there are still some problems such as high probability of electron-hole recombination,low conversion efficiency and low absorption and utilization of sunlight.One-dimensional semiconductor nanostructures have the potential to overcome these challenges and achieve large-scale conversion of solar energy.In this paper,the microstructure and morphology of carbon nitride(g-CN),titanium oxide(TiO2)and zinc oxide(ZnO)nanoarray materials were controlled,and heterojunction was constructed to improve the photocatalytic performance effectively.The details are summarized as follows:(1)Meter-scale uniform g-CN nanorod arrays(NRs)were directly grown on FTO glass using an unprecedented vacuum magnetic filtered arc ion plating system for enhanced photoelectrochemical(PEC)performance.The construction of the g-CN film is based on the substrate deposition of the direct reaction of ionized carbon and nitrogen species,a gas-based bottom-up approach,distinctly different from traditional powder deposition and thermal vapor pathways.The g-CN film exhibits obvious advantages over conventional ones in the application of PEC.The gas-based bottom-up approach enables the g-CN to facilely couple with including but not limited to TiO2 NRs to form heterostructures to further improve charge separation.(2)A highly efficient Al-ZnO/CdS photoanode system for solar water oxidation has been constructed.A current density 10.4 mA/cm2 at 1.23 V versus RHE and conversion efficiency of 5.75%at 0.38 V versus RHE was obtained,which is derived from the high electron transport of the Al-doped ZnO NRs and the appropriate bandgap of CdS absorption photon.More impressively,the stability of Al-ZnO/CdS photoanode was extensively prolonged with coating of AI2O3 protective layer through a DC magnetron sputtering(DCMS)process.The strengthen photostability is benefited from the oxidation of fresh metal aluminium at the surface layer of the photoanode treated with DCMS to aluminium oxide,which have liquid-like superplasticity and seamless features.(3)A highly efficient Al-ZnO/CdS/TiO2 photoanode system was demonstrated.Deriving from the high electron transport of the Al doped ZnO NRs,the appropriate bandgap of CdS absorption photon and TiO2 serving as passivation layer,a high efficiency photoanode system was achieved.More impressively,the lifetime of Al-ZnO/CdS photoanode was extensive prolonged after ALD TiO2 protective layer.The strengthen photostability is benefited from the triple functions of ALD TiO2 layer,that is,isolating the direct contact between the photoanode and the surrounding liquid environment,passivating the surface state of the CdS,capturing and storing the photogenerated hole.