Synthesis Of Pd-based Alloy Catalyst And Performance Investigation Of Formic Acid Electro-oxidation

Formic acid fuel cells have received extensive attentions all over the world with a number of advantages such as higher open circuit potential, better security, lower fuel crossover et al. In comparasion to platinum group metals, palladium nanocatalyst show better activity of formic acid oxidation（FAO）. However, it is very necessary to design new catalyst to improve the stability in formic acid solution. In this report, PdPt and PdFe alloy nanocatalyst were prepared respectively, which demonstrate much higher activity than commercial Pd/C towards formic acid oxidation.The PdPt alloy nanocatalyst was synthesized in poly（diallyldimethylammonium chloride）（PDDA） solution, which XC-72 R carbon was first dispersed into PDDA solution to form PDDA modified carbon. The trendy of activity for formic acid oxidation was Pd0.9Pt0.1/C > Pd0.85Pt0.15/C > Pd0.65Pt0.35/C > Pd0.45Pt0.55/C > Pd0.25Pt0.75/C > Pd0.15Pt0.85/C. The area current density of Pd0.9Pt0.1/C could research 22.67 A.m-2 with much negative anodic peak potential and lower onset potential towards formic acid oxidation. According to the experments, the “electric effects” and “thirdbody effects” play a key role in the enhancement of formic acid oxidation.The PdFe alloy nanoparticles were synthesized by NaBH4 reducing, using K4[Fe（CN）6].3H2 O and PdCl2 as precursor, which Pd²⁺ formed a complex with Fe（CN）64-, in sodium citrate solution. The superior performance of Pd50Fe50/C was prepared by controlling the proportion and heat-treated temperature. The improvement of FAO was acirbed to attributed to a downshift in the energy of metal d-band center and the decrease of Gibbs free energy for the electron transfer steps, which caused by the lattice strain and the d-orbital coupling effect.To further improve both catalytic activity and stability, the Ultra-low Pt（0.09% wt） decorated PdFe NPs with a PdPt shell and a PdFe core were prepared via the galvanic replacement reaction. Compared with Pd50Fe50/C, the core-shell PdFe@PdPt/C exhibited much 1.52 times higher catalytic and lower onset potential（-0.12V）. The significant enhancements above can be attributed to HCOOads oxidized to CO₂ on PdFe NPs, which the HCOOads spilled from Pt clusters. Moreover, the core-shell catalyst also demonstrated better tolerance to poisons during formic acid oxidation.