Suppressing the oxidation of active-Ir(III) in IrOₓ catalysts is crucial for efficient and durable oxygen evolution reaction (OER) in water electrolysis. This study demonstrates that an excess electron reservoir (EER), consisting of charged oxygen species incorporated into antimony-doped tin oxide (ATO) supports, effectively controls Ir oxidation states by enhancing charge donation to IrOₓ catalysts. Computational and experimental analyses show that the EER promotes charge transfer, stabilizing active-Ir(III). In a polymer electrolyte membrane water electrolyzer (PEMWE), the Ir catalyst on the EER-incorporated support exhibited 75 times higher mass activity than commercial catalysts and outstanding long-term stability (250 h with marginal degradation at 1 A cm²). A remarkably high Ir-specific power (74.8 kW g⁻¹) suggests significant potential for gigawatt-scale H₂ production.

Gyu Rac Lee, Jun Kim, Doosun Hong, Ye Ji Kim, Hanhwi Jang, Hyeuk Jin Han, Chang-Kyu Hwang, Donghun Kim, Jin Young Kim, Yeon Sik Jung