Precise construction and activation of Fe-N2O2 single atom catalysts from amidoxime-Fe complex for oxygen reduction reaction

Nitrogen coordinated single iron sites embedded in carbon materials (Fe-N-C) have emerged as cost-effective alternatives to Pt-based electrocatalysts for the oxygen reduction reaction (ORR). Optimizing the coordination environment of single metal sites to enhance ORR performance is a highly desirable but challenging task. Herein, an innovative single metal coordination structure featuring unique nitrogen and oxygen symmetrically coordinated iron sites (Fe-N 2 O 2 ) is presented. The synthesis involves fabricating a monolithic porous amidoximated polyacrylonitrile precursor, which chelates Fe 3 + ions to form well-defined Fe-N 2 O 2 moieties. Pyrolysis of the precursor conformally transforms these moieties into atomically dispersed Fe-N 2 O 2 sites embedded within a porous carbon matrix. Experimental and theoretical analyses reveal that a simple thermal activation step can shorten the Fe-N(O) bond distance, thereby enhancing the intrinsic ORR activity by weakening the adsorption of oxygenated intermediates. The optimized Fe-N-C catalyst (Fe 3 NC-900) exhibits an exceptionally high active site density (2.00 ×10 19 sites g −1 ) and turnover frequency (6.11 e site −1 s −1 ), placing it among the top-performing ORR catalysts in both acidic and alkaline electrolytes . This work introduces a novel active site structure and activation strategy for the ORR, highlighting the potential of rationally tuning the coordination environment of single metal sites to improve catalytic efficiency.