Ultra-small RuO₂/NHC nanocrystal electrocatalysts with efficient water oxidation activities in acidic media

Designing highly active and durable oxygen evolution reaction (OER) electrocatalysts is indispensable for promoting the sluggish reaction kinetics of OER to achieve low overpotential. RuO₂ is one of the representative oxygen evolution electrocatalysts in acid electrolytes, but it still faces the problem of poor stability. Herein, RuO₂ nanocrystal with an ultra-small size of approximately 3.5 nm loaded on N-doped hierarchical porous carbon (NHC) is successfully synthesized by RuCl₃ dipping, followed by an annealing process. It is found that NHC is assembled of porous nanosheets with a high specific surface area (BET up to 2107 m² g^-1), which could provide more active sites for RuO₂ loading and enable decorated catalysts to be effectively utilized. Combining the advantages of porous NHC and the high electrocatalytic activity of RuO₂, the optimized electrocatalyst RuO₂/NHC³ achieves a low overpotential of 186 mV at 10 mA cm^-2 for acidic water oxidation with a Tafel slope as low as 60 mV dec^-1 and maintains excellent long-term stability throughout the 27 h chronopotentiometry test in 0.5 M H₂SO₄. The elevated acidic OER activity and stability can be attributed to the diminutive size, abundant oxygen vacancies, and enlarged electrochemically active surface area of RuO₂/NHC³. This work could provide opportunities to explore efficient anodic electrocatalysts in acidic media.