Heterostructure boosts a noble-metal-free oxygen-evolving electrocatalyst in acid

Developing noble metal-free electrocatalysts (NMFEs) for the oxygen evolution reaction (OER) is tremendously challenging in acid. Despite extensive research efforts, few reported NMFEs can compete with Ru/Ir oxides for acidic OERs. Here, we report a heterostructure-engineering method to break the activity-stability limit of OER electrocatalysts and yield a noble-metal-free oxide that competes with RuO₂ in terms of OER specific activity and stability in acid. Via a set of correlative operando characterization techniques, heterostructured Co₃O₄/MnO₂ suppressed the in situ reconstruction of Co₃O₄ and MnO₂, and mitigated the electrochemical cycling-accelerated catalyst leaching, thus improving the acidic OER stability. Moreover, first-principles calculations supported that the synergy of Co and Mn in Co₃O₄/MnO₂ lowered the theoretical OER overpotentials. The optimized Co₃O₄/MnO₂ achieved an activity of 10 mA cm⁻² at 319 ± 1.2 mV overpotential, and it demonstrated low degradation during the varying-current stability test (up to 200 mA cm⁻²) for 100 hours, making it among the best NMFEs for acidic OERs. Moreover, the promising performance of Co₃O₄/MnO₂ as the anodic catalyst was also validated in a proton-conducting membrane water electrolysis cell.