Iterative oxidation and sulfidation reactions: revival of bulk cobalt sulfide into an active electrocatalyst for the oxygen evolution reaction

Nanostructuring of catalytically active materials has been an important research topic to identify robust yet cost-effective electrocatalysts. Despite the many benefits of nanostructured catalysts, their use in practical systems has not yet been fully realized due to their many technical challenges. A great deal of effort has been made to overcome the hurdles of nanomaterials, but we postulate that the solution to these problems may not necessarily result from technology based on nanomaterials. In this work, we demonstrate this by demonstrating a new thermal route that can produce an electrocatalytically active material for the oxygen evolution reaction from its bulk form that has a very low catalytic activity. In our synthesis protocol, the oxidation and subsequent sulfidation of bulk cobalt sulfide (CoSx) are delicately exploited so that its composition and porous structure are manipulated to make bulk CoSx as active as the state-of-the-art IrO2 catalyst. Given the simplicity and mass productivity, this re-engineering strategy based on sulfur/oxygen exchange reactions will pave a new avenue for designing cost-effective, active electrocatalysts. We also anticipate this method to provide an opportunity to reassess the potential of bulk materials for electrocatalysis.