Spin‐State Engineering of Single‐Atom Nickel Catalysts for Acidic Electrosynthesis of Hydrogen Peroxide

Abstract Electrosynthesis of hydrogen peroxide (H 2 O 2 ) via the two‐electron oxygen reduction reaction offers a sustainable method for chemical manufacture. However, catalysts in acidic media still face inherent trade‐offs between activity and selectivity. Herein, a ligand‐field–tailoring strategy is introduced that uses a nickel‐porphyrin molecular precursor and a pyrolysis‐driven competitive coordination process to precisely program the local environment of single‐atom Ni sites. The introduction of Ni─O bonds weakens the ligand field and increases electron pairing, promoting a transition from low‐spin to intermediate‐spin states at the Ni center. Density functional theory (DFT) calculations reveal a negative correlation between the magnetization and both OOH adsorption energy (ΔG OOH ) and orbital interaction strength. In the intermediate‐spin state, incompletely occupied dz 2 orbitals facilitate moderate OOH binding, facilitating H 2 O 2 production. Furthermore, spin polarization accelerates electron transfer to OOH, reducing the energy barrier of the rate‐determining step and optimizing reaction kinetics. The catalyst exhibits an exceptional H 2 O 2 production rate (6.4 mol g −1 h −1 ) and selectivity (>95%) under acidic conditions, outperforming most transition metal‐based catalysts and even many noble metal systems. This study unveils the role of spin‐state modulation in optimizing electrocatalysis, opening new avenues for designing high‐performance catalysts for H 2 O 2 synthesis and other catalytic reactions involving oxygen intermediates.