Direct Synthesis of Low-Index Palladium Nanocrystals and Their Catalytic Activities Toward Formic Acid Oxidation

Palladium nanocrystals have attracted more and more interest due to their extraordinary hydrogen storage capability and high catalytic activity in various reactions. In direct formic acid fuel cell (DFAFC), Pd has much higher catalytic activity toward formic acid oxidation than Pt. Like many other reactions, formic acid oxidation is structure-sensitive and significantly affected by the size and shape of Pd nanoparticles. In this presentation we report a facile one-pot synthesis approach for selectively synthesizing single crystalline rhombic dodecahedral (RD), cubic and octahedral palladium nanocrystals. These nanocrystals are enclosed by twelve {110}, six {100}, and eight {111} low-index facets, respectively. By controlling the concentration of potassium iodide and ascorbic acid in the reaction mixture, all of three low-index palladium nanocrystals can be obtained with high yield and uniform size within thirty minutes. The high quality nanocrystals enable examining facet effects of Pd nanocrystals in various reactions. Here formic acid oxidation is used as an example to elucidate how the catalytic activity varies with particle shape.  The results show that cubic nanocrystals enclosed by {100} facets exhibited the highest catalytic activity, followed by RD and octahedra. This activity sequence differs from that found on bulk Pd single crystal electrodes. The obtained information is useful for designing high efficiency catalysts for fuel cell applications.