Understanding the role of surface oxygen-containing functional groups on carbon-supported cobalt catalysts for the oxygen evolution reaction

Supported Co-based catalysts exhibit promising catalytic activities in the oxygen evolution reaction (OER) during alkaline water electrolysis. Surface functionalization of the support modulates the dispersion of the catalysts and their interaction with the support, consequently tuning their catalytic properties. This study thoroughly investigates the role of surface oxygen-containing groups (OFGs) during the synthesis of carbon-supported Co-based catalysts and their contribution to the OER catalytic activity of the material. Following the dispersion of Co onto four different carbon supports, X-ray photoelectron spectroscopy, N2 adsorption-desorption, and transmission electron microscopy were used to analyze the dispersion degree of cobalt and the concentration of surface OFGs. The results reveal that high concentrations of acidic OFGs over the surface of the carbon support lead to the fine dispersion of Co nanoparticles. Raman spectroscopy further demonstrates that the homogeneous dispersion of Co nanoparticles results in the formation of additional surface OFGs and defects in the carbon structure. By adjusting the Co loading onto the support, it is verified that the small and finely-dispersed Co nanoparticles, rather than the large agglomerates, contribute significantly to the introduction of additional surface carboxyl groups (COOH) resulting from strong metal-support interaction. The excellent mass activities that exceeded 8 A mg-1 can be predominantly attributed to these small and finely-dispersed Co nanoparticles and the corresponding high surface concentration of COOH groups, which were found to participate directly in the OER by serving as O2 spillover sites. A high content of acidic surface OFGs on a carbon support enables the fine dispersion of Co-based nanocatalysts, enhancing its OER mass activity, while also inducing additional COOH surface groups that act as O2 spillover sites.