Butylphenyl-functionalized palladium nanoparticles as effective catalysts for the electrooxidation of formic acid

摘要

Monodisperse butylphenyl-functionalized palladium (Pd-BP, dia. 2.24 nm) nanoparticles were synthesized through co-reduction of butylphenyldiazonium and H2PdCl4 by NaBH4. Because of this unique surface functionalization and a high specific electrochemical surface area (122 m2 g-1), the Pd-BP nanoparticles exhibited a mass activity ~4.5 times that of commercial Pd black for HCOOH electrooxidation. Direct formic acid fuel cells (DFAFCs) are a promising power source for portable electronic devices due to their high energy density, modest operating conditions, relatively low toxicity and the low crossover rate of formic acid through Nafion membranes.1-5 The anodic reaction of DFAFCs is formic acid electrooxidation to CO2 on Pt- or Pd-based catalysts. Pt catalysts typically exhibit a high intrinsic activity. However, they are vulnerable to surface poisoning by adsorbed CO (COad), a reaction intermediate.6,7 In contrast, Pd is free of COad poisoning in the short term, and formic acid is mainly oxidized via the direct pathway.8,9 Yet, the electrooxidation of HCOOH on Pd catalysts in general requires a substantially high overpotential (~0.3 V), which significantly impedes the large-scale commercialization of DFAFCs.