High-Entropy Ruthenium-Based Oxides with Rich Grain Boundaries for Efficient Oxygen Evolution

Developing efficient and stable oxygen evolution reaction (OER) electrocatalysts is essential for the production of hydrogen from water electrolysis. Here, we successfully synthesized a high-entropy ruthenium-based oxide (RuMnFeCoNiO-HEO) with rich grain boundaries using a fast and nonequilibrium molten salt method. The RuMnFeCoNiO-HEO with significantly reduced ruthenium dosage could exhibit much higher OER performance with a low overpotential of 190 mV at 10 mA/cm 2 and long-term durability of 100-h continuous operation under 100 mA/cm 2 in alkaline solution. The mass activity and turnover frequency of RuFeCoNiMn-HEO are significantly enhanced by nearly 1 order of magnitude compared to those of commercial RuO 2 . Microstructural characterizations reveal that the incorporation of four extra 3d transition metals into ruthenium oxides results in the formation of Ru-based high-entropy materials with a rich grain boundary structure and unsaturated coordination Ru active centers, which optimize both the electrocatalytic activity and electrochemical durability of RuMnFeCoNiO-HEO during the OER process.