Composition-Dependent Electrocatalytic Activity of Palladium− Iridium Binary Alloy Nanoparticles Supported on the Multiwalled Carbon Nanotubes for the Electro-Oxidation of Formic Acid

ACS Appl. Mater. Interfaces 2015, 7, 15223−15229

Jianming Bao, Meiling Dou, Haijing Liu,* Feng Wang,* Jingjun Liu, Zhilin Li, and Jing Ji

ABSTRACT: Surface-functionalized multiwalled carbon nanotubes (MWCNTs) supported Pd₁₀₀-xIrx binary alloy nanoparticles (Pd₁₀₀-_xIr_x/MWCNT) with tunable Pd/Ir atomic ratios were synthesized by a thermolytic process at varied ratios of bis (acetylacetonate) palladium(II) and iridium- (III) 2,4-pentanedionate precursors and then applied as the electrocatalyst for the formic acid electro-oxidation. The X-ray diffraction pattern (XRD) and tran**ission electron microscope (TEM) ****ysis showed that the Pd100-_xIr_x alloy nanoparticles with the average size of 6.2 nm were uniformly dispersed on the MWCNTs and exhibited a single solid solution phase with a face-centered cubic structure. The electrocatalytic properties were evaluated through the cyclic voltammetry and chronoamperometry tests, and the results indicated that both the activity and stability of Pd₁₀₀-_xIr_x/MWCNT were strongly dependent on the Pd/Ir atomic ratios: the best electrocatalytic performance in terms of onset potential, current density, and stability against CO poisoning was obtained for the Pd₇₉Ir₂₁/MWCNT. Moreover, compared with pure Pd nanoparticles supported on MWCNTs (Pd/MWCNT), the Pd₇₉Ir₂₁/MWCNT exhibited enhanced steady-state current density and higher stability, as well as maintained excellent electrocatalytic activity in high concentrated formic acid solution, which was attributed to the bifunctional effect through alloying Pd with transition metal.