ZnS/CdS/TiO2光陽極之製備及其在光電化學產氫之應用

Abstract

In this work, ZnS/CdS/TiO2 photoanodes were prepared by pulse electrodeposition from zinc chloride and sodium thiosulfate solutions. The influence of the electrodeposition condition on the composition and structure of photoanode was investgated. Furthermore, the photoelectrochemical activities and hydrogen production rates of the photoanodes were also studied. For the study of ZnS electrodeposition, the preparation conditions including applied voltage, electrolyte composition, pH, input electricity, deposition temperature, and calcination temperature were investigated. The characterizations of photoanodes were investigated by means of XRD, SEM, TEM, XPS and UV techniques. In order to measure the photoactivity of prepared photoanode, a photoelectrochemical (PEC) cell with an electrolyte of 0.25 M Na2S and 0.35 M Na2SO3 were used under illumination by Xe lamp (100 mW/cm2). Moreover, the hydrogen generation experiment was carried out in a two-compartment PEC reactor. The concentration of alkaline electrolyte and the stirring rate in the anode compartment were investigated as well. The results showed that deposition amount, particle size, defects, and surface charges of ZnS layer were strongly influenced by the deposition conditions, which would in advance manipulate the photoactivity of photoanode. It was found that the optimal deposition conditions were: reductive voltage of -0.8 V (vs. Ag/AgCl), the electrolyte of 0.03 M ZnCl2, 0.3 M Na2S2O3, pH3, input reductive electricity of 1 C, deposition temperature of 25 ℃ and calcination temperature of 300 ℃. From the results of hydrogen genetation experiment, it revealed that the hydrogen generation condition was optimized at rotating speed of 300 rpm and the electrolyte of 1 M NaOH, 0.35 M Na2SO3 and 0.25 M Na2S. When the ZnS/CdS/TiO2 photoanode equipped with the PEC cell were operated at the optimal conditions, a maximum photocurrent density (8.17 mA/cm2) and photoconversion efficiency (3.56%) could be achieved. Moreover, the hydrogen generation rate reached to 87.98 mol/cm2-h with a long-term stability. As compared with CdS/TiO2 photoanode, the studied ZnS/CdS/TiO2 photoanode exhibited not only a promotion in photoactivity but also an increase in the hydrogen production rate. The lifetime of photoanode was increased as well, owing to the reduction in photocorrosion of photoanode.