Wavelength-dependent photoactivity of ZnXCd1_XS and ZnCo2O4/ZnXCd1_XS for H2 and H2O2 production

Zinc cadmium sulfide (ZnxCd1_xS) is a good photocatalyst for hydrogen evolution reaction (HER), but an optimum x (xm) at which a maximum HER rate is reached varies from one report to another. In this work, we examine the effect of light wavelength, not only for the HER to H2 in the presence of Na2S and Na2SO3, but also for oxygen reduction reaction (ORR) without addition of any sacrifices. For the HER under a 365 and 420 nm LED lamp, the xm were 0.9 and 0.7, respectively. For the HER under a 330 and 395-515 nm cut-off xenon lamp, the xm were 0.7 and 0.5, respectively. For the ORR under a 420 nm cut-off halogen lamp, a maximum production of H2O2 was observed at x = 0.3. Furthermore, after 4% ZnCo2O4 loading, ZnxCd1_xS had an increased activity and stability, either for the HER or for the ORR. Through a (photo)electrochemical measurement, it is proposed that the photocatalytic activity of ZnxCd1_xS is determined by its light absorptivity and electron reactivity. The improved performance of n-type ZnxCd1_xS by p-type ZnCo2O4 is due to formation of a p-n junction, promoting the HER (ORR) on ZnxCd1_xS, and the sulfide (water) oxidation on ZnCo2O4. This work highlights that ZnxCd1-xS is a promising photocatalyst for H2 and H2O2 production, respectively.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.