The synergistic effect in a CoNiTaRuMn high-entropy alloy regulates Ru valence state for efficient hydrogen evolution

Abstract

High-entropy alloys (HEAs) exhibit a vast compositional space. Developing high-performance HEA catalysts with low precious metal content holds significant industrial application potential. Identifying catalytic centers and exploring novel strategies besides traditional methods such as element selection and lattice distortion to enhance the performance of HEA catalysts are of paramount importance. In this study, through designing CoNiTaRuMn HEA catalysts with varying compositions, we revealed that Ru⁴⁺ serves as the primary catalytic center for the hydrogen evolution reaction (HER). We introduced a new strategy by harnessing the synergistic effect among elements to drive the transition of Ru to Ru⁴⁺, effectively improving the performance of HEA catalysts. The synergistic effect of Co, Ni, Ta, and Mn with Ru facilitates this transformation, with Mn and Ni better promoting this transformation. The CoNiTaRuMn HEA catalyst exhibited overpotentials of 43 and 30 mV under acidic and alkaline conditions, respectively, at a current density of −10 mA cm⁻². This performance significantly outperforms that of the 20% Pt/C catalyst and most recently reported HER electrocatalysts. Moreover, in acidic solutions, the mass activity reached 94 times that of the single-Ru catalyst at −100 mV. This catalyst achieved over 1200 hours of continuous operation without degradation at an industrial current density of −1000 mA cm⁻² in an acidic environment and stable operation for over 900 hours in an alkaline environment, highlighting its potential for economically viable industrial applications. This strategy offers new insights and directions for the development of efficient and stable HEA-based HER catalysts.