Screening of ZnS-Based Photocatalysts by Scanning Electrochemical Microscopy and Characterization of Potential Photocatalysts

M-ZnS (M = Cr, Cu, Ni, Mo and Ag) photocatalyst arrays were rapidly screened for photoelectrochemical water oxidation using scanning electrochemical microscopy (SECM) with an optical fiber. Among the various arrays, the spot with the precursor composition Ni0.1-Zn0.9S showed the highest photocurrent in 0.1 M Na2SO4/Na2SO3 solution under both UV-visible and visible light irradiation. X-ray diffraction analysis revealed that the Ni0.1-Zn0.9S photocatalyst possessed both cubic zincblende and heazlewoodite structures corresponding to ZnS and Ni3S2 with an average crystallite size in the range 22-28 nm. The theoretical quantity of ZnS, Ni3S2 and Ni phases in this composite was 94.8, 2.6 and 2.6 mol%, respectively. A red shift was observed in the UV-visible absorption spectrum of ZnS upon the addition of Ni. The Mott-Schottky plots showed that the Ni0.1-Zn0.9S photoelectrode exhibited a more positive flat band potential and higher donor density than that of the ZnS photoelectrode. The SECM screening results were also confirmed with bulk film studies.