Shape-dependent electrocatalysis: formic acid electrooxidation on cubic Pd nanoparticles

Abstract

The electrocatalytic properties of palladium nanocubes towards the electrochemical oxidation of formic acid were studied in H₂SO₄ and HClO₄ solutions and compared with those of spherical Pd nanoparticles. The spherical and cubic Pd nanoparticles were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The intrinsic electrocatalytic properties of both nanoparticles were shown to be strongly dependent on the amount of metal deposited on the gold substrate. Thus, to properly compare the activity of both systems (spheres and nanocubes), the amount of sample has to be optimized to avoid problems due to a lower diffusion flux of reactants in the internal parts of the catalyst layer resulting in a lower apparent activity. Under the optimized conditions, the activity of the spheres and nanocubes was very similar between 0.1 and 0.35 V. From this potential value, the activity of the Pd nanocubes was remarkably higher. This enhanced electrocatalytic activity was attributed to the prevalence of Pd(100) facets in agreement with previous studies with Pd single crystal electrodes. The effect of HSO₄⁻/SO₄²⁻ desorption–adsorption was also evaluated. The activity found in HClO₄ was significantly higher than that obtained in H₂SO₄ in the whole potential range.