Observing N in Co-Nx-C during cathodic reaction via operando X-ray spectroscopy

Abstract

Single atom catalysts (SACs) anchored to N-carbon (M-Nx-C) have been extensively investigated owing to their impressive catalytic activity and relatively low cost. In contrast to the bulk catalysts, M-Nx-C almost maintain their oxidation states even under the cathodic potentials, displaying only minor adjustments in its pristine electronic structure. In this context, we have examined the electronic structure of nitrogen through in-situ/ operando NEXAFS to unveil the origin of the distinct electronic configuration of M-Nx-C. We were able to observe the behavior of N, which significantly influences the state of SACs. When exposed to conditions resembling hydrogen evolution reactions, the electronic structure of cobalt exhibited slight changes, while the electronic configuration of the nitrogen ligands remained largely intact. Through a combination of in-situ/ operando NEXAFS investigation and insights from prior literature, we hypothesized that the sustained electronic structure of M-Nx-C can be attributed to the inherent stability of the nitrogen ligands under the cathodic potentials. Moreover, any subtle shifts in the cobalt state appeared to result from chemical adsorption rather than modifications to the nitrogen ligands, such as protonation. Our study contributes valuable insights into the functional role of nitrogen ligands in M-Nx-C, thereby bolstering the findings of previous theoretical and experimental studies.