Revealing the Potential of Ternary Medium-Entropy Alloys as Exceptional Electrocatalysts toward Nitrogen Reduction: An Example of Heusler Alloys.

With less energy consumption and environmental pollution, electrochemical ammonia synthesis is regarded as the most promising way to replace the industrial Haber-Bosch process, which greatly contributes to global energy consumption and CO emission. At present, the best metal electrocatalyst for N fixation is ruthenium although its performance still suffers from a low Faradaic efficiency and a high overpotential. Alloy engineering is a promising way to discover more metal-based electrocatalysts for dinitrogen reduction reaction (N2RR), and almost all reported alloy catalysts so far are binary alloys. In this work, we proposed a large group of ternary alloy electrocatalysts (Heusler alloys) for N2RR and demonstrated their superior catalytic performance. As an example, alloying Ru with Mn and Si led to a reduced Ru-Ru distance on the surface, which facilitates an uncommon horizontal adsorption mode of N and results in effective activation of N molecules. The theoretical overpotential of N2RR on RuMnSi(100-Ru) is only around 0.28 V, which ranks among the best reported results, and the usage of precious Ru is greatly reduced. Meanwhile, the adsorption of N on RuMnSi(100-Ru) was much stronger than that of protons, and it also took less energy to drive N2RR than the hydrogen evolution reaction (HER), making HER less competitive on this catalyst. Considering the successful synthesis of numerous Heusler alloys including the six members mentioned here, our work provided a wider range of practical and excellent N2RR electrocatalysts in terms of both catalytic performance and economical cost.