Wavelength-dependent photoactivity of Zn Cd1−S and ZnCo2O4/Zn Cd1−S for H2 and H2O2 production

Zinc cadmium sulfide (Zn x Cd 1− x S) is a good photocatalyst for hydrogen evolution reaction (HER), but an optimum x ( x m ) 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 H 2 in the presence of Na 2 S and Na 2 SO 3 , but also for oxygen reduction reaction (ORR) without addition of any sacrifices. For the HER under a 365 and 420 nm LED lamp, the x m were 0.9 and 0.7, respectively. For the HER under a 330 and 395–515 nm cut-off xenon lamp, the x m were 0.7 and 0.5, respectively. For the ORR under a 420 nm cut-off halogen lamp, a maximum production of H 2 O 2 was observed at x = 0.3. Furthermore, after 4% ZnCo 2 O 4 loading, Zn x Cd 1− x S 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 Zn x Cd 1− x S is determined by its light absorptivity and electron reactivity. The improved performance of n-type Zn x Cd 1− x S by p-type ZnCo 2 O 4 is due to formation of a p-n junction, promoting the HER (ORR) on Zn x Cd 1− x S, and the sulfide (water) oxidation on ZnCo 2 O 4 . This work highlights that Zn x Cd 1- x S is a promising photocatalyst for H 2 and H 2 O 2 production, respectively. • Zn x Cd 1- x S is more active than CdS and ZnS for H 2 and H 2 O 2 production. • Zn x Cd 1- x S activity depending on both x and light wavelength used. • Zn x Cd 1- x S activity and stability greatly increased by ZnCo 2 O 4 . • A p-n junction between ZnCo 2 O 4 and Zn x Cd 1- x S improving their charge separation.