(272f) Palladium Nanocrystals for Formic Acid Electro–Oxidation: The Effects of Facet and Twin Defect

Palladium has been extensively studied as a catalyst for the formic acid electro–oxidation (FAO) in direct formic acid fuel cells (DFAFCs) due to its high catalytic ability. Since the FAO activity on single crystal surfaces increases in the order of Pd(110) < Pd(111) < Pd(100), controlling the shape of Pd nanocrystals has been explored with great interest. This presentation introduces a comprehensive study of the FAO on Pd nanocrystals with a variety of different shapes (which preferentially expose different facets) including cubes, right bipyramids (RBPs), octahedra, tetrahedra, decahedra, and icosahedra. The FAO on the various shapes of Pd reveals that the Pd nanocrystals enclosed by {100} facets have higher specific activities than that on the nanocrystals enclosed by {111} facets, with respect to the observations on the Pd single crystals. When comparing nanocrystals which are predominantly enclosed by a particular facet, (e.g., mostly {100} or {111}), the twinned nanocrystals (those having a twin defect) show higher FAO activity than the single nanocrystals. To rationalize these experimental results, we performed density functional theory (DFT–GGA) calculations on model single–crystal surfaces of Pd. The calculations suggest that the enhancement in FAO could be attributed to enhanced flux on Pd(211) sites, a model representation of the twin defects, compared to that on Pd(100) and Pd(111).