Codeposition of Palladium and Gold on Nickel Wire Electrodes via Galvanic Replacement Reactions for Ethanol Oxidation

Codeposition of Pd and Au on a Ni wire was explored using a simple treatment of Ni wire electrodes in aqueous solutions containing both K2PdCl4 and HAuCl4, and the electrochemical properties of the thus-prepared electrodes were evaluated by recording cyclic voltammograms (CVs) of 1.0 M ethanol in 1.0 M NaOH aqueous solutions. Compared with the Pd-deposited Ni wire electrodes prepared by treatment in aqueous solutions of K2PdCl4, a remarkable increase in the electrocatalytic current of ethanol oxidation was observed when both the concentrations of K2PdCl4 and HAuCl4 were as low as 0.10 mM and after the treatment for 10 min at 30 °C. The results of the EDS elemental mapping analysis show that the distributions of Pd and Au on the Ni surface were not identical and that Au deposited preferentially on Ni. By observing the changes in the CV responses depending on the concentrations of K2PdCl4 and HAuCl4 and performing stepwise modifications, the promotion or acceleration of the codeposition of PdAu was found to be achieved due to the coexistence of K2PdCl4 and HAuCl4 in aqueous solutions. Because the codeposition of PdAu revealed in the present work was significant, it was found that PdAu-modified or PdAu-coated Ni materials could be prepared via simple galvanic replacement reactions without using any reducing reagents and additives.