Comparative study on formic acid electro-oxidation by shape-controlled platinum@palladium nanocrystals

Abstract

Searching for high-performance electrocatalysts for the electro-oxidation of formic acid is essential for the widespread application of direct formic acid fuel cells. Herein, three types of core-shelled Pt@Pd nanoarchitectures were prepared via an epitaxial growth process using Pd cubes, dodecahedra, and icosahedra as seeds. The structures of the Pt@Pd nanocrystals were characterized by transmission electron microscopy, energy dispersive X-ray spectroscopy, and electrochemical measurements. Using formic acid as a model substrate, the electrocatalytic performance and underlying mechanism of the resulting samples were studied. The Pt@Pd showed better activity and stability in both acidic and alkaline electrolytes compared to the commercial Pt/C and Pd/C. In particular, the Pt@Pd icosahedra showed the best activity in acidic electrolytes, leading to a current density of 4.18 mA cm−2, which is 3 times that of the Pt/C. In alkaline electrolytes, the Pt@Pd dodecahedra showed the best activity, yielding a current density of 2.5 mA cm−2, which is 11.9 times that of the Pt/C. The mechanisms of formic oxidation were studied by potential sweeps and the facet-dependent activity was correlated with the adsorptions of the formate and intermediates. The Pt@Pd cubes exhibited the superior stability in the alkaline electrolytes, resulting in a current decay by only 19 % after 1000 cycles, which is much smaller than that of the Pt/C.