Asymmetric Ru–O–Cr active units trigger oxygen radical coupling for efficient oxygen evolution reaction across the entire pH range

Efficient and durable anodic electrocatalysts for the oxygen evolution reaction (OER) are crucial for water electrolysis. In this study, a binary solid-solution oxide Ru x Cr 1-x O 2 , enriched with asymmetric Ru-O-Cr active units, was synthesized by introducing Cr as an active site into RuO 2 . We demonstrate that the appropriately spaced asymmetric active sites facilitate the direct coupling of *O − *O radicals during the OER process, thereby circumventing the formation of *OOH intermediates. The optimized Ru 0.7 Cr 0.3 O 2 exhibits high activity and exceptional stability across the entire pH range, achieving an overpotential of only 213 mV at 10 mA cm −2 in 0.1 M HClO 4 , with negligible voltage degradation after continuous operation for 800 h. This makes it one of the most acid-stable OER catalysts reported to date. Notably, Ru 0.7 Cr 0.3 O 2 demonstrates effective performance as an anode catalyst under practical operating conditions in both proton exchange membrane water electrolyzers (PEMWE) and anion exchange membrane water electrolyzers (AEMWE). DFT calculations and DEMS analysis confirm that the Ru Cr dual-active sites' asymmetry triggers the oxide pathway mechanism (OPM), overcoming the activity-stability trade-off in OER. This work offers a new strategy for optimizing OER catalyst design and insights into the use of asymmetric units in other electrocatalytic systems. • Ru 0.7 Cr 0.3 O 2 is enriched with asymmetric Ru − O − Cr active units. • Ru − O − Cr with optimal spacing promotes OER via the OPM pathway. • Ru 0.7 Cr 0.3 O 2 shows 213 mV overpotential at 10 mA cm −2 with 0.069 mV h −1 decay. • OPM-driven OER on Ru 0.7 Cr 0.3 O 2 bypasses the RDS via *O − *O radical coupling. • Ru 0.7 Cr 0.3 O 2 is a high-performance anode for industrial PEMWE and AEMWE.