Synergy of mixed chromium species on NiFe layered double hydroxides for promoting alkaline water oxidation

Abstract

Water electrolysis in an alkaline medium is technically mature and shows current density comparable to that of proton exchange membrane water electrolysis while requiring no noble metal, thereby holding promise for the industrial production of high-purity green hydrogen. However, electrocatalysts at the anode, which triggers the oxygen evolution reaction (OER), suffer from high overpotential and unsatisfactory stability. This study systematically investigates the effect of the chromium species: Cr³⁺ within the laminates, CrO₄²⁻ in the interlayer space, and free CrO₄²⁻ in the electrolyte on the OER performance of benchmark NiFe layered double hydroxides (NiFe-LDHs). Our findings demonstrate that the strategic combination of these chromium species significantly improves catalytic activity and offers long-term stability, achieving overpotentials of 236 mV and 280 mV at current densities of 10 and 100 mA cm⁻², respectively. Moreover, with our strategy, the catalyst demonstrates 50 hours of stability at 800 mA cm⁻², and the dissolution levels of Ni and Fe were reduced to 31.3% and 38.6%, respectively, relative to the control group. The results presented herein provide a universal strategy for the design of effective alkaline water electrolysis anodes.