In-Situ Generated High-Valent Iron Single-Atom Catalyst for Efficient Oxygen Evolution

Oxygen evolution reaction (OER) plays an important role in renewable energy supplies as the anodic reaction for electrochemical transformation of various chemicals. Iron-based OER catalysts are potential candidates due to their abundance but suffer from poor activity. Here we demonstrate that a single-atom iron catalyst with in-situ generated Fe4+ centers is highly active toward OER. Only an overpotential of 320 mV was needed to reach 10 mA cm–2. The catalyst exhibited an ultrahigh turnover frequency of 0.62 s–1 at an overpotential of 0.35 V, which is comparable to currently reported transitional-metal based OER catalysts. Experimental and theoretical studies revealed that the valence state of the metal center transferred from Fe3+ to highly active Fe4+ prior to the OER process. This transformation was originated from the strong interaction between atomic Fe and carbon support via C–O–Fe bonding, leading to a lower energy barrier of the rate-limiting *OOH formation.