Precise Regulation of Iron Spin States in Single FeN₄ Sites for Efficient Peroxidase-Mimicking Catalysis

The catalytic activity and selectivity of single-atom sites catalysts is strongly dependent on the supports structure and central metal coordination environment. However, the further optimization of electronic configuration to improve the catalytic performance is usually hampered by the strong coordination effect between the support and metal atoms. Herein, it is discovered that enzyme-mimicking catalytic performance can be enhanced at the fixed coordination single-atom Fe sites by regulating the Fe spin states. The X-ray absorption fine structure, ⁵⁷ Fe Mössbauer spectrum, and temperature-dependent magnetization measurements reveal that the spin states of Fe in single FeN₄  sites can be well manipulated via changing the pyrolysis temperature. The intermediate-spin Fe sites catalyst (t_2g 4 e_g 1) demonstrates a much higher peroxidase-mimicking activity in comparison with high-spin structure (t_2g 3 e_g 2). More importantly, the based enzymes system realizes sensitive detection of H₂ O₂  and glucose by colorimetric sensors with high catalytic activity and selectivity. Furthermore, theoretical calculations unveil that the intermediate-spin FeN₄  promotes the OH* desorption process, thus greatly reducing the reaction energy barrier. These findings provide a route to design highly active enzyme-mimicking catalysts and an engineering approach for regulating spin states of metal sites to enhance their catalytic performance.