Twinned and Single-Crystal Palladium Nanocrystals for the Electrooxidation of HCOOH

Palladium has been widely used to catalyze formic acid (HCOOH) electrooxidation, and the catalytic behaviors were structure-sensitive based on fundamental studies on the single-crystal plane. Would the structure sensitivity still exist and what should it be when the size of single-crystal plane decreases to nanosize? In this work, by utilizing O2/I– etching and the capping effect of I– ions, we have successfully synthesized a series of Pd nanocrystals enclosed with different crystal facets, such as 5-fold twinned nanorods, decahedra, cuboctahedra, and octahedra. The twinned defects on the surface of these nanocrystals and the different crystal facet ratios provide a good basic model for us to study the relationship between the surface structure of Pd nanocrystals and their electrocatalytic performance to HCOOH oxidation. The electrocatalytic tests showed that nanorods with twinned structures and abundant (100) facets exhibited the highest electrocatalytic activity among all of the nanocrystals as synthesized. The peak current density (jP) of the nanorods was 2.2, 2.9, 9.1, and 15.7 times that of the cuboctahedron, decahedron, octahedron, and commercial Pd/C, respectively. The results were well consistent with those obtained from a fundamental study on single-crystal planes and, therefore, could provide a good bridge between the basic and applied research.