Preparation and electrochemical properties of a gallium-doped zinc oxide electrode decorated with densely gathered palladium nanoparticles

A novel method for chemically preparing densely gathered palladium nanoparticles (PdNPs) on a gallium-doped zinc oxide (GZO) electrode is reported. We found that PdCl₄^2- could be captured directly on a bare GZO electrode surface simply by immersing a piece of GZO in an aqueous solution of K₂PdCl₄, resulting in a GZO electrode color change from transparent to yellow. The subsequent reduction of the composite electrode in an aqueous solution of NaBH₄ produced a further color change to blackish-violet even after the PdCl₄^2--captured GZO had been washed and dried. X-ray photoelectron spectroscopy analysis confirmed the presence of Pd as PdCl₄^2- and Pd⁰ on the GZO before and after reduction with NaBH₄, respectively. The surface images collected using field emission scanning electronic microscopy revealed that the PdNPs were densely gathered and connected to one another. Although bare GZO electrodes have not been used extensively in voltammetric analysis, the present modification using densely gathered PdNPs shows promise as a new approach to constructing Pd-functionalized electrodes as confirmed by measuring voltammetric responses. The simple capture of metal complex precursors and nanostructuring followed by a simple reduction reaction on GZO is promising as a new and efficient fabrication method that conserves precious starting materials.