Sub-2 nm IrRuNiMoCo High-Entropy Alloy with Ir-Rich Medium-Entropy Oxide Shell to Boost Acidic Oxygen Evolution.

Ensuring high catalytic activity and durability at low Ir usage is still a big challenge for the development of electrocatalysts towards oxygen evolution reaction (OER) in proton exchange membrane water electrolysis (PEMWE). Here, a rapid liquid-reduction combined with surface galvanic replacement strategy is reported to synthesize the sub 2 nm high-entropy alloy (HEA) nanoparticles featured with Ir-rich IrRuNiMo medium-entropy oxide shell (Ir-MEO) and a IrRuCoNiMo HEA core (HEA@Ir-MEO), which exhibits a low overpotential of 243 mV at 10 mA cm -2 and high mass activity (261.5 A g Ir -1 ). Advanced spectroscopies reveal that the Ir-rich MEO shell inhibits the severe structural evolution of transition metals upon the OER, thus guaranteeing the structural stability. In-situ DEMS, activation energy analysis and DFT calculations unveil that the OER on HEA@Ir-MEO follows an adsorbate evolution mechanism pathway, where the energy barrier of rate-determining step is substantially lowered, interpreting the enhanced OER kinetics. The optimized catalyst is assembled into PEM electrolyzer with low Ir usage of ca. 0.4 mg cm -2 , and to give the excellent performance (1.85 V/3.0 A cm -2  °C), long-term stability (>500 h@1.0 Acm -2 ) and low energy consumption (3.98 kWh Nm -3 H 2 @1.0 A cm -2 ), realizing the dramatical reduction of hydrogen production cost to USD 0.88 per kg H 2 . This article is protected by copyright. All rights reserved.