RF-sputtering preparation of gold-nanoparticle-modified ITO electrodes for electrocatalytic applications

The preparation of gold-nanoparticle (Au-NPs)-modified indium tin oxide (ITO) electrodes (Au-NPs/ITO) was performed by radio-frequency (RF) sputtering from Ar plasmas at temperatures as low as 60 degrees C, tailoring the Au-NP morphology and content as a function of the sole sputtering time. The latter parameter was varied from 5 to 20 min in order to investigate the influence of gold amount and distribution on the electrochemical performances of the resulting Au-NPs/ITO systems. The electrodes were characterized using field emission-scanning electron microscopy (FE-SEM), UV-vis absorption and x-ray photoelectron spectroscopies (XPS); moreover variable scan rate cyclic voltammetry (CV) studies were performed to examine their electrochemical behavior. The electrocatalytic activity of the nanostructured Au-NPs/ITO electrodes toward methanol oxidation was investigated and compared with a continuous gold film (Au-film/ITO). The catalytic efficiency of the Au-NPs/ITO systems was found to increase with the gold content and the Au-NPs-support boundary region in the corresponding samples. For the longest sputtering time (i.e. 20 min) the performances of the nanostructured electrode were better than the Au-film/ITO reference, despite the much lower catalyst amount. Furthermore, conversely from the Au-NPs/ITO samples, in the Au-film/ITO case the gold film displayed a poor adhesion to the substrate and the electrode could be used only for a limited number of electrochemical cycles.