Screening and characterization for the optimization of CdS-based photocatalysts

Abstract

Scanning electrochemical microscopy (SECM) with an optical fiber was used to rapidly screen M–CdS (M = Cu, Fe, Zn, Co, Ni, Mn and In) photocatalyst arrays for efficient photoelectrochemical reaction. Among the discussed arrays, the spot with the precursor composition In_0.2–Cd_0.8S showed the highest photocurrent in 0.1 M Na₂SO₄/Na₂SO₃ solution under both UV-visible and visible light irradiation. The SECM screening results were also confirmed with bulk photoelectrode studies. The In_0.2–Cd_0.8S photocatalyst had the hexagonal phase of the wurtzite solid solution structure with an average crystallite size in the range of 13–37 nm. A red shift was observed in the UV-visible absorption spectrum of CdS upon the addition of In. The Mott–Schottky plots showed that the In_0.2–Cd_0.8S photoelectrode exhibited a flat band potential of −1.2 V vs. Ag/AgCl. The IPCE value at 450 nm radiation for the In_0.2–Cd_0.8S photocatalyst is 60%, which is three times higher than that of CdS. The superior photocatalytic activity of the In_0.2–Cd_0.8S photoelectrode is mainly attributed to its high crystallinity, which promotes separation of the photo-induced electrons and holes and also reduces the probability of recombination.