Acidic water oxidation with ultralow 131 mV overpotential over surface-reconstructed RuIr nanoalloy: Chloride-driven high performance

Abstract

The oxygen evolution reaction (OER) in kinetics is sluggish but a key electrode reaction for various energy storage and conversion devices, such as green hydrogen from water electrolysis, rechargeable metal-air battery, sustainable carbon dioxide electroreduction, synthetic ammonia, etc. However, it still remains a major and cutting-edge challenge to pioneering catalysts with simultaneously ultrahigh activity and stability for OER, even with diverse performance enhancement strategies, such as complex composition designs, surface chemical reconstructions, and multiphase engineering have been implemented to accelerate this key electrochemical process. Herein, we proposed a chloride-triggered activation and stabilization strategy for the branched RuIr alloy coated by thin IrO2 layer to achieve unparalleled high-performance toward OER in acidic water. The ultralow overpotential of the activated catalyst is reduced to about 131 mV at 10 mA cm−2, with 79-fold enhancement of mass-activity than commercial IrO2. Moreover, a modified proton exchange membrane water electrolysis (PEMWE) device was first constructed by introducing NaCl into recyclable electrolyte. It run a stably and low cell potential (1.514 V) for 170 h, having no obvious performance decay at 50 mA cm−2 in 0.5 M H2SO4 with 1.6 M NaCl, which far exceeding traditional IrO2||Pt/C PEMWE. The outstanding performance stems from that Cl- ions enable a faster lattice oxygen evolution mechanism. The novel catalyst activates asymmetric O-Ir-Cl structure induced by Cl- filled oxygen vacancies, which modify the electronic and geometric properties, improving OER activity. Moreover, these adsorbed ions can also efficiently patch and refill the oxygen vacancies that ensure the long-term structure stability. Therefore, tailoring the chloride-activated Ir-based catalysts with simultaneously improved activity and stability may be a valuable guide to achieve surprisingly high-performances for acidic water splitting.