Facile and rapid synthesis of spherical porous palladium nanostructures with high catalytic activity for formic acid electro-oxidation

摘要

Highly uniform, spherical porous palladium nanostructures (SPPNs) with rough surfaces were prepared by a facile and rapid ultrasound assisted reduction. The synthesis involves sonicating a solution of K _2PdCl _4 and ascorbic acid for only 7min at 40°C without any additives. The products are isolated structures with a narrow size distribution, and their average diameters are controllable in a range from 40 to 100nm via the K _2PdCl _4 concentration. Typical products have a diameter of 52nm and consist of loosely packed grains of 23nm. They are thus very porous, with a specific surface area of 47m ~2g ~1. The growth mechanism of SPPNs is discussed on the basis of varying relevant reaction parameters and characterizations from different microscopy techniques, nitrogen absorption analysis, and time-dependent UVvis spectra. The electrocatalytic performance of the SPPNs was evaluated by electro-oxidation of formic acid. The mass current density per mass of SPPNs (1.88Amg ~1) exceeds that of commercial Pd black (1.69Amg ~1) and is more than twice that of commercial Pd/C catalyst (0.79Amg ~1). Long-term stability of the activity makes this material a promising anode catalyst for direct formic acid fuel cells.