Ethanol Oxidation on Electrocatalysts Obtained by Spontaneous Deposition of Palladium onto Nickel-Zinc Materials

Ni-Zn and Ni-Zn-P alloys supported on Vulcan XC-72 are effective materials for the spontaneous deposition of palladium via redox transmetalation. The materials obtained, Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C, have been characterized by a variety of techniques, including HRTEM, EXAFS, EDS, ICP-AES, XANES and XRPD. Incorporation of the analytical and spectroscopic data allowed us to conclude that the surface of Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C contain very small (0.5-1 nm), highly dispersed and highly crystalline palladium clusters as well as single palladium sites, likely stabilized by interaction with oxygen atoms from Ni-O moieties. As a reference material, a nanostructured Pd/C material was prepared by reduction of an aqueous solution of PdCl2/HCl with ethylene glycol in the presence of Vulcan XC-72. In Pd/C, the Pd particles were larger, less dispersed and much less crystalline. Glassy carbon electrodes coated with the Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C materials, containing very low Pd loadings (22-25 ?g cm-2), have been scrutinized for the oxidation of ethanol in alkaline media in half cells providing excellent results in terms of both specific currents (as high as 3600 A (gPd)-1 at room temperature) and onset potentials (as low as -0.6 V). The electrochemical performance exhibited by the Pd/C catalyst was slightly inferior to those obtained with Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C, but chronopotentiometric tests showed higher overpotentials with time.