Electrochemical reduction of U(VI) in H2SO4 at gold nanoporous film electrode

Gold nanoporous film (AuNPF) was grown on gold substrate by electrochemical oxidation of the gold electrode at 5 V for 180 s in phosphate buffer (pH 7.4) followed by reduction of the oxidized gold with ascorbic acid solution. Atomic force microscopy (AFM) showed the porous nature of the prepared film. In cyclic voltammetric (CV) studies, anodic shift of 141 mV in the cathodic peak potential for the reduction of UO22+ in 0.5 M H2SO4 was observed at the AuNPF electrode, showing evidence of its enhanced electrochemical activity as compared to that of the bare Au electrode. The charge transfer studies done using electrochemical impedance spectroscopy indicated similar rates of the heterogeneous electron-transfer kinetics at the bare Au and the AuNPF electrodes. The Cottrell plots obtained from the chronoamperometric experiments showed the Cottrell linearity at the bare Au electrode. In contrast, the Cottrell plot of the AuNPF electrode showed deviation from the linearity at longer times and this is characteristic of the thin-layer diffusion coupled with the electron transfer. Therefore, the observed anodic shift at the AuNPF electrode for the reduction of UO22+ was attributed to the contribution from thin-layer diffusion within the gold nanoporous film.