Unraveling the Transformation of Cobalt Sulfide in the Hydrogen Evolution Reaction at a High Overpotential: A Step Toward Deciphering the Mechanism

Abstract

The hydrogen evolution reaction (HER) plays a crucial role in various renewable energy technologies, and its efficiency is contingent upon the utilization of effective catalysts. Cobalt disulfide (CoS2), like platinum, is utilized as an HER electrocatalyst. Nevertheless, CoS2 has the advantage of being sourced from elements that are abundantly available on Earth, compared to platinum, for the HER. In this study, the stability of a commercially accessible nanostructured CoS2 powder is investigated. To achieve this aim, analytical techniques, including scanning electron microscopy, transmission electron microscopy, energy-dispersive spectrometry, X-ray diffraction, X-ray absorption spectroscopy, electron paramagnetic resonance, and in situ Raman spectroscopy, are employed to characterize CoS2 both prior to and subsequent to HER treatment. Our results indicate that when subjected to a high overpotential of 400 mV for 10 days, CoS2 transforms into an alternative Co species, likely metallic Co, and subsequently into Co (hydr)oxide (CoHyOx) under air exposure. These discoveries provide valuable insights into the development of state-of-the-art catalysts for the HER and elucidate the underlying mechanisms that contribute to efficient water splitting for energy storage applications.