Interstitial C-Atom Insertion-Assisted High-Entropy Engineering Boosts Ultrastable Ampere-Level Oxygen Evolution

Active and stable noble metal-free oxygen evolution reaction (OER) electrocatalysts are required for high-performance water splitting using renewable energy. Here, we report that interstitial C atoms doping into high-entropy transition metal oxide nanosheets (IC-HETMO NSs) can extend the OER durability in alkalinity by approximately two orders of magnitude over that of HETMO NSs, along with excellent activity. IC-HETMO NSs deliver a low overpotential of 260 mV in 1.0 M KOH at 500 mA cm^-2 while maintaining 8000 h (over 11 months), demonstrating notable stability and activity under the tested conditions. Operando spectroscopy measurements, together with first-principles analyses, support that IC-HETMO NSs preferably follow a low-energy pathway involving direct ^*O─^*O radical coupling from adsorbed water, resulting in electrocatalytic stability. The calculations also confirm that C-doping can optimize metal-O covalency, thus allowing enhanced resistance to over-oxidation and demetallation. In practical anion-exchange membrane water electrolysis, IC-HETMO NSs-based electrolyzer exhibits a low voltage of 1.68 V and good stability at 1.0 A cm^-2 for 2950 h at 60°C.