Spin Balance Over Janus Ir-Co Magnetic Atoms for Efficient Acidic Water Oxidation

Abstract Herein, spin regulation of the low-spin Ir 4+ in Ca 2 IrO 4 is realized via a novel spin balance strategy through a Janus Ir–Co structure using high-spin Co 3+ dopants, achieving the intermediate-spin state of Ir and Co atoms and enhancing the acidic oxygen evolution reaction (OER) performance of the obtained catalysts (Co–CIO). The optimized 0.2Co–CIO catalyst, with a nominal Co/(Co + Ir) metal atom percentage of 20%, displays exceptional electrochemical water oxidation activity with an ultrasmall overpotential of ~ 200 mV at 10 mA cm −2 , ultralarge mass activity of 1110 A g Ir −1 , and high turnover frequency of 2050 h ‒1 under an overpotential of 300 mV in 1 M HClO 4 , outperforming most recently reported Ir–based oxides catalysts. Molecular and atomic characterizations via in situ X-ray absorption near-edge and Raman spectroscopy demonstrate the acceleration of bridged O‒O formation over the Janus Ir–Co units, indicating a preference for the superoxide path mechanism for Co–CIO. Furthermore, density functional theory calculations rationalize the promotion of the superoxide *O‒O intermediate over the spin-regulated Ir‒O‒Co units, thanks to optimized e g 1 orbital and reduced t 2g orbital occupancy. The study presents a rare example of Ir spin regulation via a Janus Ir–Co magnetic structure, thereby promoting acidic OER activity.