Unveiling the Activity Origin of M–N–C Supported Nanoparticles for Efficient Electrocatalytic Water Oxidation

Optimizing the electronic structures of metal sites is desirable for high intrinsic activity. Incorporated metal atoms in a carbon substrate can establish strong electronic interaction with loaded metal oxides. However, this structure may be unstable in a harsh oxygen evolution reaction (OER) environment. Herein, we take the NiSAFe sample of Ni-N-C supported Fe₂O₃ nanoparticles (NPs) as an example. Both in situ and ex situ characterizations show that the OER activation process facilitates the transformation of Ni single atoms into atomically dispersed NiOOH active species while retaining Fe₂O₃ NPs. Accordingly, abundant structural defects are formed in the carbon support, enhancing electron transfer and upshifting the d-band center of the NiFe catalyst. As a result, the catalyst exhibits accelerated OER kinetics and optimized adsorption energies for reaction intermediates, delivering outstanding intrinsic activity. A low overpotential of 230 mV at 10 mA cm⁻² and a turnover frequency (TOF) more than 9 times higher than that of commercial RuO₂ are achieved.