Self-assembled Platinum-iridium Alloy Aerogels and Their Efficient Electrocatalytic Ammonia Oxidation Performance

Ammonia with low cost, easily liquefied and high volumetric energy density is an attractive carbon-free fuel. Utilizing ammonia as anodic fuel, direct ammonia fuel cells are showing great interests to researchers. However, such amazing fuel cell device is limited by the sluggish anodic ammonia oxidation reaction. In this work, PtIr alloy aerogels with a three-dimensional porous network structure were prepared by nanoparticles (NPs) self-assembled under a simple and surfactant-free conditions. This structure provided a rich open interconnected proton transport channel and additional catalytically active sites which contributed to the dehydrogenation process of NH3 molecules in ammonia electrocatalytic oxidation. An optimal AOR activity was achieved at the 80/20 molar ratio of Pt/Ir. Effects of NH3 concentration and operating temperature on catalyst's ammonia oxidation performance were studied, which revealed that the AOR performance of Pt80Ir20 alloy aerogel was improved with the increase of ammonia concentration or operating temperature. For example, the mass specific activity, at 0.50 V of the Pt80Ir20 alloy aerogel, was estimated to be 44.03 A center dot g(-1), which was about 4 times as that of the ammonia concentration at 0.05 mol/L. In the case of operating temperature effect, the mass activity was estimated to be 148.73 A center dot g(-1), which was almost 12 times as that of the temperature rising (from 25 degrees C) to 80 degrees C. Encouragingly, the onset potential of the optimal Pt80Ir20 alloy aerogel catalyst displayed about 40 mV reduction during such a temperature change. Further calculations using the Arrhenius equation showed that its activation energy was reduced by about 9.43 kJ center dot mol(-1) as compared with commercial Pt/C. Moreover, its AOR stability was improved as evidenced by a loss of similar to 50.6% mass activity after 2000 potential cycles when compared with commercial Pt/C (similar to 74.9%).