Improving Electrocatalytic Oxygen Evolution through Local Field Distortion in Mg/Fe Dual‐site Catalysts

Abstract Transition metal single atom electrocatalysts (SACs) with metal‐nitrogen‐carbon (M−N−C) configuration show great potential in oxygen evolution reaction (OER), whereby the spin‐dependent electrons must be allowed to transfer along reactants (OH − /H 2 O, singlet spin state) and products (O 2 , triplet spin state). Therefore, it is imperative to modulate the spin configuration in M−N−C to enhance the spin‐sensitive OER energetics, which however remains a significant challenge. Herein, we report a local field distortion induced intermediate to low spin transition by introducing a main‐group element (Mg) into the Fe−N−C architecture, and decode the underlying origin of the enhanced OER activity. We unveil that, the large ionic radii mismatch between Mg 2+ and Fe 2+ can cause a FeN 4 in‐plane square local field deformation, which triggers a favorable spin transition of Fe 2+ from intermediate (d xy 2 d xz 2 d yz 1 d z2 1 , 2.96 μ B ) to low spin (d xy 2 d xz 2 d yz 2 , 0.95 μ B ), and consequently regulate the thermodyna‐mics of the elementary step with desired Gibbs free energies. The as‐obtained Mg/Fe dual‐site catalyst demonstrates a superior OER activity with an overpotential of 224 mV at 10 mA cm −2 and an electrolysis voltage of only 1.542 V at 10 mA cm −2 in the overall water splitting, which outperforms those of the state‐of‐the‐art transition metal SACs.