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

Herein, spin regulation of the low-spin Ir⁴⁺ in Ca₂IrO₄ is realized via a novel spin balance strategy through a Janus Ir-Co structure using high-spin Co³⁺ 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 HClO₄, 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_g¹ 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.