An oxalate anion-assisted strategy mediated densely edge-hosted atomic FeN4 sites for enhanced oxygen reduction reaction in Zn-air batteries

The construction of edge-hosted Fe N sites presents a promising way to boost catalytic performance of typical Fe N sites for the oxygen reduction reaction (ORR). However, the controllable synthesis of densely accessible edge-hosted Fe N sites remains challenging. Herein, an oxalate anion-assisted strategy is developed for precise preparation of densely edge-hosted Fe N 4 atomic sites for ORR. The strong coordination between oxalate anions and Fe 3+ ions facilitates the formation of dense edge-hosted Fe N 4 atomic sites. The subsequent decomposition of oxalate anions creates a hierarchically porous structure. Remarkably, the obtained e -FeNC exhibits improved ORR activity in acidic (0.79 V) and alkaline (0.89 V) electrolytes, a higher site density (SD), and an enhanced turnover frequency (TOF, 3.71 s −1 ). Density functional theory calculations reveal that edge FeNC sites exhibit a lower energy barrier for ORR than center FeNC sites. The downward shift of the d-band center weakens the adsorption of ORR intermediates, accounting for the high intrinsic activity of edge FeNC sites. Additionally, the assembled Zn-air battery displays a high specific capacity of 781 mAh g −1 , a large energy density of 999 Wh kg Zn −1 , and outstanding cycling performance over 550 h with minimal voltage gap of 0.84 V.