Recent Progress in Strategies for Ruthenium-Based Electrocatalysts for Alkaline Hydrogen Evolution and Oxidation Reactions

To establish clean and environmentally friendly energy systems, hydrogen-based electrochemical energy storage and conversion devices must be developed. Fuel cells and electrolyzers based on the anion-exchange membrane have attracted a lot of interest owing to their utilization as efficient earth-abundant catalysts for oxygen electrode reactions. However, sluggish hydrogen electrode reactions under alkaline conditions still rely on expensive platinum group metals as electrocatalysts, hindering widespread commercialization. For the hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR), ruthenium (Ru) has emerged as a possible replacement for platinum (Pt) in alkaline conditions. This is explained by its adequate hydrogen-binding energy and oxyphilic property, which enables it to achieve low hydrogen electrode potentials while being more cost-effective than Pt. Therefore, a comprehensive analysis and understanding of the HER and HOR mechanisms, along with the development of rational designs for Ru-based HER catalysts with desirable activity and stability, have been performed for cost-effective energy storage and conversion devices. This review provides a detailed introduction and discussion of the fundamental reaction mechanisms involved in the alkaline HER/HOR. Additionally, it provides a comprehensive summary of the effectiveness of four advanced strategies (composition engineering, phase engineering, support engineering, and atomic-scale engineering) aimed at enhancing the performance of Ru-based electrocatalysts. Finally, to direct future research in this area, the obstacles and perspectives are underlined.