Palladium Deposition on Nickel Wire Electrodes by a Galvanic Replacement Reaction

Practical aspects of the modification of palladium on nickel wire electrodes were explored for the electrocatalytic applications of palladium-modified nickel (Pd/Ni) composite materials. In principle, Pd/Ni wire electrodes could be prepared via a simple galvanic replacement reaction, e.g., between tetrachloropalladate (PdCl42–) and Ni by simply immersing a piece of Ni wire into an aqueous solution of PdCl42–. However, our preliminary trials at room temperature indicated that the reproducibility of the preparation is not good: in fact, Pd could not be modified on Ni in some cases even though we conducted the same preparation procedures. To improve the reproducibility of the modification, we studied the effects of pretreatments of Ni wire and the temperature of aqueous solutions. Consequently, it was found that the pretreatment with 1.0 M HCl aqueous solution and increased temperature, such as 50 °C, were effective to improve the Pd modification. The control of the modified states of Pd on Ni was found to be possible under the improved conditions by controlling the immersion time. For the comprehensive understanding of galvanic replacement reactions for preparing noble-metal-modified common metal wires, the results obtained using Pt precursors on Ni and the Pd modification on other metal wires, Fe, Cu, and Co, are shown and discussed compared with the case of Pd/Ni wire.