Square-pyramidal Fe-N4 with defect-modulated O-coordination: Two-tier electronic structure fine-tuning for enhanced oxygen reduction

Adjusting the electronic and geometric structures of the Fe-N-4 active site using axially coordinated ligands has been shown to be effective for improving the performance of the electrocatalytic oxy-gen reduction reaction (ORR). Any progress beyond that remains extremely challenging, however. Here, we demonstrate a two-tier electronic modulation strategy using defect-modulated O -coordina-tion to further optimize the electronic structure of the Fe center in iron phthalocyanine (FePc), which realizes greatly enhanced ORR performances. Such an atomically dispersed FePc-O-defect catalyst is achieved using a wet ball-milling process. The mechanochemically constructed active site is a square-pyramidal Fe-N4, with the Fe atom located out of the N4-plane toward an axially coordinated O that is singly bonded to graphene at vacancy defects. The FePc-O-defect catalyst delivers a half-wave potential of 0.929 V with mass specific activity of 76.2 A g(catalyst)(-1) at 0.9 V in alkaline media. These values are the highest among the reported non-precious metal electrocatalysts and exceed the baseline with bare O -coordi-nation.

Automated summary

This study demonstrates a two-tier electronic modulation strategy to optimize the Fe center in iron phthalocyanine (FePc) for improved performance in the oxygen reduction reaction (ORR). By using defect-modulated oxygen coordination, the researchers achieved an atomically dispersed FePc-O-defect catalyst with significantly enhanced ORR performances. The catalyst exhibited the highest reported values among non-precious metal electrocatalysts, exceeding the baseline with bare oxygen coordination.