Synergistic Interplay of Fe and Co Single-Atom Sites Spatially Separated on g-C3N4 for Enhanced Electrochemical Performance in Li-O2 Batteries.

Abstract

Developing single-atom catalysts (SACs) with efficient atomic usage and well-defined coordination environments is pivotal for addressing limitations in redox kinetics and durability in lithium-oxygen (Li-O2) batteries. Herein, an efficient yet broadly applicable ball-milling followed by pyrolysis approach for the synthesis of bi-metal Fe, Co SACs supported on a graphitic carbon nitride (g-C3N4) matrix is proposed. The synthesis involves a top-down approach, where Fe and Co metals are atomized and stabilized on g-C3N4 support, facilitating uniform distribution of isolated metal atoms while inhibiting aggregation. This approach promotes the formation of coexisting Fe-N4 and Co-N4 single-atom sites anchored on distinct triazine units within g-C3N4, where the Co-N4 sites serve primarily as electronic modulators of the Fe-centred active sites. The electronic interplay between the Co and Fe-N4 sites within the g-C3N4 framework modulates the local electronic structure and optimizes the adsorption energetics of LiO2 intermediates, thereby accelerating both the oxygen reduction reaction and oxygen evolution reaction. As a result, the resulting catalysts deliver enhanced discharge capacity, lower overpotential, and prolonged cycling stability in Li-O2 batteries. Overall, this work provides new insights into bi-metal synergistic catalysis on g-C3N4 and highlights the critical role of active-site engineering in governing Li-O2 battery performance.