PdM nanoparticles (M = Ni, Co, Fe, Mn) with high activity and stability in formic acid oxidation synthesized by sonochemical reactions

Bimetallic alloy Pd_nM (n = 1 for M = Mn, Fe, and Co; n = 1, 2, and 3 for M = Ni) nanoparticles (NPs) are synthesized on carbon supports by sonochemical reactions of Pd(acac)₂ (acac = acetylacetonate) with M(acac)₂ (M = Ni, Co, Mn) or Fe(acac)₃ in ethylene glycol. The NPs are characterized by powder X-ray diffractometry, transmission electron microscopy (TEM), and inductively coupled plasma-atomic emission spectroscopy to determine their crystal structures, particle sizes, morphology, and elemental compositions. Alloy formation of the NPs is proven by energy dispersive X-ray spectroscopy line profiles using scanning TEM. The electronic structures and the surface compositions of NPs are analyzed using X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy, respectively. Pd _nM NPs are applied as electrocatalysts for formic acid oxidation. The incorporation of M in Pd reduces the poisoning by surface hydroxyl groups. Activities based on the current densities are in the order of PdNi > PdFe > PdCo > PdMn. Within the Pd_nNi series, the activity is in the order of PdNi > Pd₂Ni > Pd₃Ni. The Pd_nM NP electrocatalysts show higher activity by a factor of 2-3.5 and improved durability than similarly prepared Pd NP electrocatalyst.