Manipulation of\nd‑Orbital Electron Configurations\nin Nonplanar Fe-Based Electrocatalysts for Efficient Oxygen Reduction

Manipulation of the spin state holds great promise to\nimprove the\nelectrochemical activity of transition metal-based catalysts. However,\nthe underlying relationship between the nonplanar metal coordination\nenvironment and spin states remains to be explored. Herein, we report\nthe precise regulation of nonplanar Fe atomic d-orbital energy level\ninto an irregular tetrahedral crystal field configuration by introducing\nP atoms. With the increase of P coordination number, the spin magnetic\nmoment decreases linearly from 3.8 μB to 0.2 μB, and the\nhigh spin content decreases linearly from 31% to 5%. Significantly,\na volcanic curve between the spin states of Fe-based catalysts (Fe–N<sub><i>x</i></sub>P<sub><i>y</i></sub>) and oxygen\nreduction reaction (ORR) activity has been unequivocally established\nbased on the thermodynamic results. Thus, the Fe–N<sub>3</sub>P<sub>1</sub> catalyst with a 19% medium spin state experimentally\nexhibits the optimal reaction activity with a high half-wave potential\nof 0.92 V. These findings indicate that regulating electron spin moments\nthrough coordination engineering is a promising catalyst design strategy,\nproviding important insights into spin catalysis.