Efficient atomically dispersed Fe catalysts with robust three-phase interface for stable seawater-based zinc-air batteries

Abstract

The use of seawater-based electrolytes in zinc-air batteries (S-ZABs) presents significant economic and social benefits and mitigates the demand for scarce freshwater resources. However, it is challenging to achieve a metal–nitrogen–carbon (M–N–C) catalyst that exhibits high resistance to corrosive Cl^– in seawater-based electrolytes and possesses a strengthened binding affinity with O₂, which enables catalysts with an optimized oxygen reduction reaction (ORR) and enhances the applicability of S-ZABs. Herein, we propose a combined wet chemistry-pyrolysis strategy to obtain atomically dispersed Fe-decorated nitrogen-doped mesoporous carbon spheres (N-MCS-Fe-900). Benefiting from the capacity of the Fe decorations to form the edge-hosted aerophilic FeN₄-O₂ sites at the optimized three-phase interface, N-MCS-Fe-900 affords the enhanced resistance of the active Fe sites to corrosive Cl^–, as well as improved interaction with O₂, thereby facilitating the ORR process. As expected, the N-MCS-Fe-900 delivers high half wave potential of 0.90 V and kinetic current density of 18.61 mA cm⁻² at 0.85 V in seawater-based 0.1 M KOH. More importantly, the S-ZABs equipped with N-MCS-Fe-900 exhibited long-term stability under a high current density for over 140 h without voltage decay. Theoretical calculations and electrochemical performance evaluations collectively revealed the superior catalytic efficacy and genesis of this activity in N-MCS-Fe-900, which features edge-hosted FeN₄-O₂ sites at the stable three-phase interface in seawater electrolytes. This study provides new insights for the advancement of ORR catalysts in sustainable energy conversion technologies for seawater-based electrolytes.