New Process for the Formation of Mixed-Valence Platinum Sulfide Thin Films from Bulk CdS Layer: Characterization of Physical and Electrochemical Properties

Abstract

A thin film (60−90 nm) of mixed-valence platinum sulfide (PtSM) has been successfully deposited on a fluorine-doped tin oxide substrate. An innovative method was developed to synthesize this film in which Cd atoms were replaced by Pt atoms within the bulk of a CdS layer prepared by chemical bath deposition. The PtSM films were analyzed by various characterization techniques, such as Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The analyses revealed that PtSM films are mainly composed of PtS, PtS 2 , and a small amount of CdS. The surface composition of PtSM films was determined by XPS analysis, which indicated that the composition consists of 73.8% PtS and 26.2% PtS 2 . The detailed sequence and mechanism of PtSM film formation were investigated by electrochemical, photoelectrochemical, and Mott−Schottky analysis. The hydrogen evolution reaction (HER) properties of these films were also investigated. In a 1.3 M lactic acid and 0.25 M Na 2 SO 4 solution at pH 2, the best PtSM film and Pt metal electrode showed HER electrocatalytic performance with overpotentials of −0.317 and −0.267 V, respectively, at a current density of −10 mA cm −2 . A long-term stability test was used to demonstrate that the film is stable and not subject to degradation. The practical application of the PtSM coating was demonstrated by photoelectrochemically induced HER on PtSM-coated p-Si wafers.