Oxygen electroreduction on carbon-supported Pd nanocubes in acid solutions

• Carbon-supported Pd nanocubes of three different size and varied loading were prepared.
• The specific activity for oxygen reduction reaction is independent of Pd content.
• Pd nanocubes possess higher specific activity for ORR than spherical Pd nanoparticles.
• The ORR on carbon-supported Pd nanocubes proceed mainly via 4-electron pathway.
• Tafel behaviour of ORR on carbon-supported Pd nanocubes is similar to that of bulk Pd.

The oxygen reduction reaction (ORR) was studied on carbon-supported cubic palladium nanoparticles of different sizes (∼30 nm, ∼10 nm and ∼7 nm). Cetyltrimethylammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) were used as capping agents to prepare the nanocubes and Pd content in the catalyst samples was 20 and 50 wt%. The surface morphology of the prepared materials was studied by transmission electron microscopy (TEM). The catalyst materials were electrochemically characterised by cyclic voltammetry and CO stripping experiments. The rotating disk electrode (RDE) method was employed for ORR studies in 0.5 M H2SO4 and 0.1 M HClO4 solutions. The ORR results revealed that the specific activity of cubic Pd nanoparticles is higher than that of spherical Pd particles and does not depend on the Pd content in the catalyst, but decreases with decreasing the size of Pd nanocubes. Mass activity of Pd nanocubes increased with decreasing the particle size. The ORR proceeds mainly via 4-electron pathway and the reaction mechanism is similar to that on bulk Pd.