Júlio César Martins Silva)Highlights Direct ammonia fuel cell (DAFC) performance using PtRh/C electrocatalysts as anode.Ammonia oxidation evaluation by electrochemical experiments. An optimization study of the NH 4 OH and KOH concentrations used as fuel in a DAFC.Using PtRh/C 90:10 were obtained the highest power density and open circuit voltage.Using 3 mol L -1 KOH and 3 mol L -1 NH 4 OH the best result in a DAFC was obtained. AbstractThis study reports on the use of PtRh/C electrocatalysts prepared by the borohydride reduction method with different Pt:Rh atomic ratios: (90:10, 70:30 and 50:50) which was investigated toward the ammonia electro-oxidation considering electrochemical and also direct ammonia fuel cell (DAFC) experiments. The DAFC experiments were conducted using different proportions of NH 4 OH and KOH as fuels.X-ray diffraction showed the formation of PtRh alloy while transmission electron micrographs showed the particles sizes between 4.1 and 4.5 nm. Among the different NH 4 OH and KOH concentrations the combination of 3 mol L -1 NH 4 OH and 3 mol L -1 KOH was the most favorable due to the higher KOH concentration, which increased the electrolyte conductivity, thus improving the ammonia oxidation. Moreover, among the PtRh/C electrocatalysts the Pt:Rh ratio of 90:10 showed to be the best suited one since it showed a power density almost 60 % higher than Pt. X-ray photoelectron spectroscopy results revealed for this catalyst that the nanoparticles contain a high proportion of metallic Pt and Rh phases, supporting the alloy formation between Pt and Rh. The improved fuel cell efficiency can be related to the combination of different effects: the alloy formation between Pt and Rh (electronic effect), suppressing the adsorption strength of poisonous intermediates, and a synergic effect between Pt and Rh at this composition.

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