Investigation of PdIr/C electrocatalysts as anode on the performance of direct ammonia fuel cell

Abstract

This work investigates the ammonia electro-oxidation considering electrochemical and direct ammonia fuel cell (DAFC) experiments. The working electrodes/anodes are composed of Pd/C, PdIr/C (90:10, 70:30, 50:50, 30:70 and 10:90 atomic ratios) and Ir/C. Solutions of 1 mol L−1 NH4OH and 1 mol L−1 KOH were used for electrochemical experiments while 1.0, 3.0 and 5.0 mol L−1 NH4OH in 1.0 mol L−1 KOH were used in DAFC. X-ray diffraction analysis of PdIr/C electrocatalysts suggests the formation of PdIr alloy, while transmission electron micrographs show the average particle diameters between 4.6 and 6.2 nm. Electrochemical experiments indicate PdIr/C 30:70 as the best electrocatalyst in accordance with DAFC. The maximum power densities obtained with PdIr/C 30:70 as anode using 5 mol L−1 NH4OH and 1 mol L−1 KOH at 40 °C are 60% and 30% higher than the ones obtained with Pd/C and Ir/C electrocatalysts, respectively. The enhanced synergic effect in this specific composition may be assigned to an optimal ratio of palladium sites that dehydrogenates ammonia at lower overpotential with the lower surface coverage of Nads on iridium. Furthermore, electronic effect between palladium and iridium might also contribute to the decrease of poisoning on catalyst surface by Nads.