Influence of the metal loading on the electrocatalytic activity of carbon-supported (100) Pt nanoparticles

The influence of the metal loading (i.e. interparticle distance) of shape-controlled Pt nanoparticles on their electrocatalytic properties is evaluated for the first time. For this purpose, carbon-supported cubic Pt nanoparticles (-17 nm) with different metal loadings were prepared, characterized and electrochemically tested. To avoid differences in particle size and shape/surface structure of the Pt nanoparticles between samples, all samples used in this work were prepared from a single batch. The surface structure of the Pt nanoparticles was evaluated through the so-called hydrogen region and showed a preferential (100) orientation. Interestingly, the electroactive surface area of the samples, estimated both from the H or CO stripping processes, was directly proportional to the total Pt mass, independently of the metal loading. The CO stripping profile was also found to be unaffected by the metal loading. However, for ammonia and formic acid electrooxidation, the activity obtained was dependent on the metal loading. For ammonia oxidation, the optimal loading was found to be about 20-30 wt%. Nevertheless, this trend may be altered by different factors including (i) active surface area, (ii) metal loading and (ii) thickness of the catalytic layer. For formic acid electrooxidation, the results obtained showed a clear decrease of the activity for increasing metal loadings which is explained in terms of formic acid consumption on the top layers of the catalyst.