Transition metal sulfides for electrochemical applications: Controlled chemical conversion of CuS to Ag2S

Abstract

Transition metal sulfides have received great attention as electrocatalysts for electrochemical sensors and water electrolysis. In the present study, a facile and rapid chemical conversion route was used for the synthesis of partially and fully converted $Ag_{2}S$ from tube-like CuS. The morphology of the obtained materials was investigated by scanning electron microscopy (SEM) and transition electron microscopy (TEM), revealing that the complex shape of CuS was maintained after the conversion. Information about phase and elemental composition was obtained by X-ray diffraction (XRD), Raman spectroscopy, X-ray fluorescence spectrometry (XRF), and inductively coupled plasma optical emission spectrometry (ICP-OES). The surface composition was analyzed utilizing X-ray photoelectron spectroscopy (XPS). The results indicated that it was possible to precisely control the contribution of each sulfide by varying precursors ratio. Moreover, the conducted experiments enabled to schematically illustrate the $CuS-Ag_{2}S$ junction and propose a conversion mechanism. The electrochemical behavior of the materials was examined using cyclic voltammetry (CV) in the potential range of biomolecules electrooxidation as well as water splitting. Special attention was devoted to reactions occurring on $Ag_{2}S$-modified electrodes in alkaline and neutral media. It was found that the formation of subsequent oxides, their reduction, and the recovery of $Ag_{2}S$ are diffusion-controlled processes.