Multifunctional Electrocatalysts: Ru-M (M = Co, Ni, Fe) for Alkaline Fuel Cells and Electrolyzers

Moving from proton exchange membrane fuel cells to anion exchange membrane fuel cells (AEMFCs) enables the use of non-Pt-group (NPG) metals as cathodes for the oxygen reduction reaction, since the oxygen reduction kinetics on NPG metals is significantly enhanced in alkaline media. These NPG metal catalysts are also stable under alkaline conditions and cost much less than Pt-group metals. However, in alkaline media, H-2 oxidation on Pt anodes is much more sluggish than in acidic media, and thus, more active H-2 oxidation catalysts are required to enable AEMFCs. Here we report on a family of H-2 oxidation catalysts: Ru alloys with Co, Ni, or Fe. A series of RuCo/C, RuNi/C, and RuFe/C alloy nanoparticle catalysts have been synthesized via an impregnation method and characterized by atomic-scale scanning transmission electron microscopy. We find that Ru alloys with small amounts of Co, Ni, or Fe can significantly enhance H-2 oxidation (HOR), H-2 evolution (HER), O-2 reduction (ORR), and oxygen evolution (OER) reactions in alkaline media. They are much more active than pure Ru catalysts for the HOR, HER, ORR, and OER, and even more active than pure Pt catalysts for the HOR and HER, but they cost much less. In particular, Ru-0.95/Co-0.05/C is the most active among all studied Ru alloys catalysts for the HOR, HER, and ORR. Thus, they are promising catalysts for alkaline fuel cells and electrolyzers. The enhancement mechanism of Ru alloys has been elucidated by density functional theory calculations.