Deciphering the impact of Zn-incorporation on M–NC (M = Fe, Co, Ni, Cu) type catalysts for enhanced HER and OER performance

Abstract

The catalytic activity is mainly controlled by the local environment of the active site, where the chemical reaction occurs. Through selective inter-mixing of different elements, it is possible to fine-tune the electronic and geometric properties of the active site with precision leading to significant enhancement of both catalytic activity and selectivity. This research work focuses on modeling efficient catalysts for electrocatalytic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) based on bimetallic MNC type materials. Introducing zinc into single-atom catalysts like Fe–N–C, Co–N–C, Ni–N–C, and Cu–N–C allows us to develop dual-atom MNC catalysts. The HER and OER activities of M–Zn–N–C type catalysts show that zinc significantly improves catalytic performance. A comprehensive orbital interaction analysis of Zn-containing and Zn-free MNC catalysts reveals that the incorporation of zinc has a profound impact on the electronic structure of the transition metals at the active site. Specifically, zinc activates the low-lying d_x²−y² and d_z² orbitals of the transition metals, positioning them near the valence band maximum (VBM) enhances their interaction with the p_z orbitals of oxygen in adsorbed species, leading to a significant reduction in overpotential values for the oxygen evolution reaction (OER). In the case of the hydrogen evolution reaction (HER), zinc incorporation modifies the interaction between the d_z² orbital of the transition metals and the s-orbital of hydrogen. This modification reduces the in-phase overlap, optimizing the interaction and resulting in a lower reaction barrier. This detailed analysis provides insight into the mechanisms by which zinc incorporation enhances the catalytic activity of MNC catalysts for both OER and HER. Therefore, our findings explain the intrinsic reaction mechanism of MNC catalysts and provide insights into designing dual-atom catalysts for electrochemical applications.