Catalytic Roles and Synergetic Effects of Iron-Group Elements on Monometals and Alloys for Electrochemical Oxidation of Ammonia

Electrooxidation of NH3 has gained extensive attention for energy and environmental applications such as fuel cells and water purification. Pt-based precious metal alloy catalysts have been intensively studied as anode catalysts for the NH3 electrooxidation whereas applicability of earth-abundant transition metals to catalysts has not been sufficiently examined. In this study, we synthesized carbon-supported simple metal-nanoparticle, binary- and ternary-nanoalloy (NA) catalysts composed of Fe-group elements, i.e., Fe, Co and Ni, and systematically investigated catalytic performance of these catalysts for NH3 electrooxidation in alkaline media. We found that the affinity of constituent metals to nitrogen species controls overpotential and durability for the NH3 electrooxidation on Fe-group simple monometal and NA catalysts for the first time. Furthermore, each Fe-group element shows distinctive catalytic features for the NH3 electrooxidation, i.e., Ni ensures chemical stability, Fe effectively lowers overpotential and Co increases current density. The ternary FeCoNi/C shows excellent activities due to combination of all the catalytic features and synergetic effects exerted by the alloying.