Abstract: Single-metal site catalysts have exhibited high-efficient electro-catalytic performance due to their unique coordination environments and adjustable local structures for reactant adsorption and electron transfer. They have been widely studied for many electro-catalytic reactions, including oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, it remains a significant challenge to realize high-efficiency bi-functional catalysis (ORR/OER) with single-metal-type active sites. Herein, we report atomically dispersed Fe-Co dual metal sites (FeCo-NC) derived from Fe and Co co-doped imidazolate frameworks (ZIF-8s), aiming to build up multiple active sites for bifunctional ORR/OER catalysts. The atomically dispersed FeCo-NC catalyst shows excellent bi-functional catalytic activity in alkaline media for both ORR activity (E_1/2 = 0.877 V) and OER activity (E_j=10 = 1.579 V). Moreover, its outstanding stability during the ORR and the OER is comparable to noble-metal catalysts (Pt/C & RuO₂). The atomic dispersion state, coordination structure, and the charge density difference of the dual metal site FeCo-NC were characterized and determined using advanced physical characterization and density functional theory (DFT) calculations. The FeCo-N₆ moieties are likely the mainly active sites simultaneously for the ORR and the OER with improved performance relative to traditional single Fe and Co site catalysts. We further incorporated the FeCo-NC catalyst into an air electrode for fabricating rechargeable and flexible Zn-air batteries, generating a superior power density (372 mW cm^-2) and long-cycle (over 190 h) stability. This work would provide a simple method to design and synthesize atomically dispersed multi-metal site catalysts for advanced electro-catalysis.

Keywords: Atomically dispersed metal sites; oxygen reduction; oxygen evolution; aqueous batteries; flexible batteries; Zn-air batteries.

https://doi.org/10.1021/acscatal.1c04550