X-ray Spectroscopy Characterization of Cobalt Stabilization within a Monolayer Carbon Nitride in Oxygen Evolution Reaction

Abstract

Carbon nitride-based catalysts containing earth-abundant metals such as Co have gained attention for the oxygen evolution and reduction reactions (OER and ORR). The catalytic activity of such materials is known to be sensitive to metal dispersion and coordination, which again may depend on reaction conditions, but exact information on the active state and the possible coordination state changes of Co in these materials induced by electrocatalytic conditions are in general lacking. Here, we study the redistribution of Co during OER in a composite planar model system consisting of a well-defined single-atom Co-doped carbon nitride monolayer and Co nanoparticles on Au(111). Through a combination of electrocatalytic activity measurements and analysis of the catalyst surface pre- and post-electrochemical operation using X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy, we investigate the induced changes to Co species and the carbon nitride network. Our findings indicate significant mobility during OER of Co atoms originating from the Co nanoparticles, with the presence of the carbon nitride stabilizing Co in a dispersed form. The dispersion of Co leads to a steady increase in OER activity over time, which is only observed when both Co nanoparticles and Co-doped carbon nitride co-exist. We attribute this phenomenon to the carbon nitride's role in dispersing and stabilizing highly mobile cobalt species on the surface, thereby enhancing electrochemical stability.