ABSTRACT Water oxidation is crucial for energy conversion and storage technologies, but its efficiency is limited by the spin‐flip characteristics of the oxygen evolution reaction (OER). Here, we present a chemical approach to spin control of trinuclear ferric clusters (Fe 3 O) as the catalytic sites for the OER, by incorporating radical molecules into a metal‒organic frameworks (MIL‐T). The spin catalyst MIL‐T provides spin‐parallel electrons for triplet O─O bonding, and exhibits a low overpotential of 238 mV@10 mA cm −2 for the OER and a long‐term stability at 500 mA cm −2 for 100 h in an electrolyzer device. The spin crossover of one Fe site from low spin (LS, s = 1/2) to high spin (HS, s = 5/2) breaks the symmetry of the spin electron distribution in triangular Fe 3 O and thus promotes the local spin interaction of two Fe(LS) sites in Fe(HS)Fe(LS) 2 O. The spin catalysis in MIL‐T is validated by the absence of a magnetic field effect on the OER, paving the way for practical spin catalytic technologies.
Wang et al. (Sat,) studied this question.