Leveraging Co Spin State in Metal–Organic Frameworks for Efficient Water Oxidation

The design and development of highly efficient, stable, and low-cost electrocatalysts for the oxygen evolution reaction (OER) is crucial for green hydrogen production. Metal–organic frameworks (MOFs), with the merits of structural diversity and tunable organic ligand nature, have significant potential. Herein, a Co-based MOF (CoMnFcMOF) electrocatalyst was fabricated under hydrothermal conditions using Mn as a dopant and a ferrocene-based dicarboxylate linker. The as-prepared CoMnFcMOF enables a current density of 100 mA·cm–2 with an overpotential of 238 mV under an alkaline condition. The well-addressed OER activity is attributed to the spin state modulation of Co induced by Mn incorporation, as verified experimentally and from density functional theory calculations. The total effective magnetic moment (μeff) considerably decreases from 3.992 μB/f.u. in CoFcMOF to 1.974 μB/f.u. in CoMnFcMOF, indicating a spin transition from a high spin (HS) to an intermediate spin (IS) state. This spin modulation facilitates the adsorption of the O* intermediates, thereby accelerating the reaction kinetics. This work establishes a design paradigm for high-performance transition metal-based catalysts through spin state engineering.