Atomically thin high-entropy oxides via naked metal ion self-assembly for proton exchange membrane electrolysis

Designing efficient Ruthenium-based catalysts as practical anodes is of critical importance in proton exchange membrane water electrolysis. Here, we develop a self-assembly technique to synthesize 1 nm-thick rutile-structured high-entropy oxides (RuIrFeCoCrO₂) from naked metal ions assembly and oxidation at air-molten salt interface. The RuIrFeCoCrO₂ requires an overpotential of 185 mV at 10 m A cm^-2 and maintains the high activity for over 1000 h in an acidic electrolyte via the adsorption evolution mechanism. We discuss the role of each element in the RuIrFeCoCrO₂ and find that the Cr, Co, and Ir sites contribute to the catalytic activity, while the Cr atoms weaken the Ru-O bond covalency and improves the catalyst stability. The assembled proton exchange membrane electrolyzer operates stably for more than 600 h at a large current of 1 A cm^-2. The naked ion assembly demonstrated in this work may provide an effective pathway for the controlled synthesis of a diversity of high-entropy materials.