Fast Kinetics of Hydrogen Oxidation Reaction on Single-Atom Ce-Alloyed Ru in Alkaline Electrolytes

The kinetics of anodic hydrogen oxidation reaction (HOR) in alkaline media, even catalyzed by the state-of-the-art Pt catalysts, is much lower than that in acidic electrolytes, which is a significant barrier for the development of high-performance anion-exchange membrane fuel cells (AEMFCs). Based on the difference in catalytic mechanism under alkaline and acidic conditions, we suggest that the sluggish HOR in alkaline media is due to the involvement of hydroxyl in Heyrovsky or Volmer steps, and this can be improved by forcing HOR on active sites via the mechanism like that in acidic media. Herein, we prepared a single-atom Ce-alloyed Ru catalyst (Ce₁Ru/C) in which Ce atoms could adsorb abundant OH^– owing to its much stronger oxophilicity compared to that of Ru. Therefore, the nearest neighbor Ru atoms around Ce atoms become the adsorption sites for H_ad which would react with the surrounding adsorbed water to form H₃O⁺_ad. A key H₃O⁺_ad intermediate on the surface of Ce₁Ru/C during HOR in alkaline media was detected by in situ Raman spectroscopy, providing direct evidence for the HOR in alkaline media occurring via steps similar to those in acidic media. Even at 30 mV overpotential, Ce₁Ru/C still displays rapid reaction kinetics with high mass and specific activity about 27/59 and 5/12 times higher than those of Pt/C and PtRu/C. The activity of our catalyst is the best among various alkaline HOR electrocatalysts reported so far. Moreover, Ce₁Ru/C demonstrates high electrochemical stability and CO tolerance, taking a giant step forward toward the commercialization of AEMFCs.