Hydrogen production of ZnO and ZnO/Ag films by photocatalysis and photoelectrocatalysis

Abstract

This paper reports the hydrogen production of ZnO and ZnO/Ag films prepared by sol-gel method. All films were evaluated under solar light simulated using photocatalytic and photoelectrocatalytic systems. XRD results revealed that hexagonal crystal structure of ZnO is presented in all films and SEM micrographs indicate a well-defined sphere-shaped morphology. By increasing the amount of Ag, band-gap value is slightly shift in the absorbance spectra towards the visible light region. Besides the increase of Ag dopant, roughness is modified improving the light absorption due to the scattering on the surface of the films. ZnO and ZnO/Ag films were used as active materials in photocatalytic and photoelectrocatalytic system for H2 production. The presence of Ag favoured the existence of active sites (estimated by Turnover Frequency, TOF) and enhances the charge transfer avoiding the electron-hole pair recombination in ZnO films for H2 production as it was determined by photoluminescence and electrochemical measurements. In the photocatalytic system, the film containing 5% of Ag as dopant produces an amount of H2 of about 3.5-times higher than ZnO undoped film. While in the photoelectrochemical system, the density of donors increases in ZnO due to the presence of Ag, but also the charge transfer resistance decreases, which improves the electrical and charge transport properties of ZnO, making the PEC system more efficient.