Rh and Rh Alloy Nanoparticles as Highly Active H2 Oxidation Catalysts for Alkaline Fuel Cells

When moving from acidic to alkaline media, non-Pt-group metal catalysts can be used as the oxygen reduction catalyst, because of their high activity and stability. However, in alkaline electrolytes, we meet another challenge: slower H2 oxidation kinetics on platinum group metals, relative to acidic electrolytes. We require new robust anode catalysts to enhance H2 oxidation kinetics in alkaline anion exchange membrane fuel cells (AEMFCs). In this Letter, carbon-supported Rh and Rh alloy nanoparticles such as Pt7Rh3/C, Ir9Rh1/C, Rh9Ru1/C and Rh9Pd1/C were found to be highly active hydrogen oxidation and evolution catalysts in alkaline media. A size effect was observed for Rh/C, i.e., the hydrogen oxidation reaction (HOR) activity significantly increased on Rh nanoparticles, relative to bulk Rh. A synergistic effect was noted for the hydrogen oxidation on PtRh and IrRh alloy catalysts. These Rh and Rh alloy nanoparticles outperformed Ir/C and Pt/C as electrocatalysts. In particular, Rh/C with an average particle size of ca. 2 nm was identified to be the best HOR catalyst among all catalysts studied, in terms of its mass activity, while Pt7Rh3/C outperformed other studied catalysts, in terms of its specific activity and exchange current density. Ir9Rh1/C was found to be the most effective electrocatalyst among all studied Ir alloy nanoparticles. These Rh and Rh alloy catalysts could be employed as highly active H2 electrocatalysts in anion exchange membrane fuel cells.