Influence of the nonionic surfactant Triton X-100 on electrocrystallization and electrochemical performance of lead dioxide electrode

Effects of the nonionic t-octyl phenoxy polyethoxyethanol (Triton X-100) on electrocrystallization of lead dioxide were investigated on titanium substrates in the bath containing nitric acid solutions and lead nitrate. Two series of samples were produced in the presence (modified samples: PTX) and in the absence of Triton X-100 (unmodified samples: PT) at bath temperatures ranging from 25–100 °C. Higher current efficiencies, mechanical strength and more adhesion to Ti substrates were found for modified samples. Results confirm an increase in the overpotential for oxygen evolution during electrodeposition process in the presence of Triton X-100. It is suggested that the accumulation of oxygen species and the growth of crystals could be affected through the aqueous network of the self-assembled surfactants on the electrode surface. A higher overpotential for oxygen evolution reaction was also observed for electrodes made of PTX samples in sulfuric acid solution. Results of the voltammetric experiments and those from laboratory-designed test cells have confirmed a higher charge/discharge performance of modified samples towards the PbO2/PbSO4 transformation in aqueous sulfuric acid solutions. Scanning electron microscopy (SEM) has shown reduced morphological defects of PTX samples at all bath temperatures. This was in agreement with X-ray diffractograms, showing more crystalline appearance and regularity, compared to those of unmodified samples. The sample obtained under optimized conditions (synthesis in the presence of Triton X-100 at a bath temperature around 100 °C), had a higher degree of crystallinity and electrochemical activity. The enhanced characteristics of this sample is attributed to its special morphology due to creation of large number of small micropores, strong incorporation of hydrogen species and enhanced proton diffusivity as confirmed by SEM, thermogravimmetric analysis (TGA) and Electrochemical Impedance Spectroscopy (EIS).