ZnO nanorod arrays (NRAs) grown on the Zn foil substrate in the dual alkaline solution by hydrothermal method were first successfully utilized for photoelectrochemical (PEC) water splitting. ZnO NRAs were sufficiently covered on the Zn foil substrate via the reasonable match of the pH value, reaction temperature and reaction time through intensive experimental works. To enhance PEC performance, ZnS was coated on the surfaces of ZnO NRAs by ion exchange. The morphological, structural, optical and PEC characteristics of as-grown ZnO NRAs and ZnO/ZnS heterostructures were investigated. Compared with the pristine smooth and hexagonal ZnO NRAs, the surfaces of ZnO/ZnS heterostructures become rough and rounded in shape. Through the sulfidation treatment, some ZnO/ZnS heterostructures with a diameter of no more than 60 nm break and fade away, leading to a decrease in number density of ZnO/ZnS heterostructures. The texture coefficients of (002) diffraction peaks of ZnO decrease from 2.32 to 2.158. ZnO/ZnS heterostructures exhibit efficient separation rate of electron-hole pairs and enhanced visible light absorption, and thus have higher photocurrent density and photoconversion efficiency. In the polysulfide electrolyte solution , ZnO/ZnS heterostructures show good stability.
Changlin Li,Shangrong Chen,Xiangxiang Gao,Wei Zhang,Yanfang Wang
The photoelectrochemical (PEC) performance of ZnO is restricted by its low light absorption ability and high recombination rate of photogenerated carriers. In order to overcome these drawbacks, ZnO/CdS/CdSe heterostructures are prepared on Zn foil substrate using facile three-step methods containing hydrothermal growth, successive ionic layer adsorption reaction (SILAR) and modified chemical bath deposition (CBD). The effects of process parameters containing the number of SILAR cycles of CdS, sensitization sequence of CdS and CdSe, and precursors of CdSe on PEC performance of ZnO/CdS/CdSe heterostructures, and ZnO NRAs on PEC performance of CdS/CdSe co-sensitizer have been scrutinized. Through CdS and CdSe co-sensitization, a layer of CdS/CdSe nanofilm is conformally deposited on ZnO nanorod arrays (NRAs) observed by transmission electron microscopy (TEM). Both the visible-light absorption ability and separation efficiency of photogenerated carriers of ZnO NRAs are significantly enhanced evidenced by UV–vis diffuse reflectance absorption spectra , photoluminescence (PL) spectra and electrochemical impedance spectra. Due to the synergistic effect of ZnO NRAs and CdS/CdSe co-sensitizer, the ZnO/CdS/CdSe heterostructures with five SILAR cycles and one modified CBD cycle (ZnO-CdS5-CdSe) show efficient PEC properties with photocurrent density of 6.244 mA/cm 2 at −0.2 V vs Ag/AgCl under light illumination of 100 mW/cm 2 , which are 57.28 and 4.73 times higher than those of pristine ZnO NRAs and CdS/CdSe clusters, respectively. Moreover, the photoconversion efficiency and incident photon to current conversion efficiency (IPCE) of the ZnO-CdS5-CdSe photoanode reach 4.381% and 80.92%, respectively. The heterostructures based on Zn foil substrate in this study can be a promising candidate for practical PEC application and other applications such as photocatalytic degradation and solar cell due to its low manufacturing cost, large-scale production and efficient PEC ability.
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