A Facile Preparation of Hollow Palladium Nanosphere Catalysts for Direct Formic Acid Fuel Cell

A facile and low-cost preparation of a polypyrrole-modified Vulcan XC-72 carbon-supported Pd/PPy-XC-72 hollow nanosphere catalyst was introduced in this paper. To increase the stability and utilization ratio of the catalyst, a two-step strategy was employed, which included the synthesis of a polypyrrole-carbon composite and the preparation of a hollow nanosphere catalyst. Co nanoparticles as sacrificial templates were deposited on the prepared polypyrrole-carbon composites by chemical reduction, and then Pd hollow nanospheres formed through the surface replacement reaction between the surface of Co nanoparticles and PdCl2 at room temperature. The novel Pd/PPy-XC-72 hollow nanosphere catalyst was 30-40 nm in diameter and 3-4 nm in shell thickness. FT-IR and TGA characterizations confirmed the existence and content of polypyrrole in the catalysts. The catalysts with 40 and 20% Pd showed a very high electrochemically active surface area and significant increase in electrocatalytic activity toward formic acid oxidation, which make them the preferable catalysts for direct formic acid fuel cells.