The characterisation of PbO2-coated electrodes prepared from aqueous methanesulfonic acid under controlled deposition conditions

A series of PbO2 coatings on planar carbon substrates has been prepared by anodic deposition in aqueous methanesulfonic acid (MSA) under galvanostatic conditions. The effect of four experimental parameters, i.e., lead(II) methanesulfonate and MSA concentrations, current density, and temperature was analysed. Surface characterisation by XRD, SEM-EDX, and AFM has provided information about the structural (phase distribution, degree of crystallinity, and crystallite size), morphological (crystallite shape, degree of porosity), and tribological (surface roughness) properties of the PbO2 coatings, respectively. Electrochemical studies based on linear and cyclic voltammetry allowed comparison between electrodes prepared in MSA and classical electrodes prepared in HNO3. Pure α- or β-PbO2 and α + β mixtures were obtained depending on the conditions, being temperature the most influential deposition parameter. A temperature rise caused a transition to pure β-PbO2 and led to a higher degree of crystallinity with a progressive increase of crystallite size, always within the range of 10–30 nm, as well as to a remarkably higher roughness, from smooth (35–50 nm rms) to rough (up to 500 nm rms) surfaces. Low MSA and high lead(II) methanesulfonate concentrations were required to avoid the formation of excessively porous powdery coatings, as well as cracks, pits, and holes. Most of the coatings obtained in MSA were uniform, nanocrystalline, and moderately rough. Their electrocatalytic behaviour was comparable to that of the electrodes prepared in HNO3, showing an O2-overpotential of +0.66 V in 0.05 M Na2SO4 at pH 3.0. Such coatings can then be envisaged as suitable anodes for energy and water treatment applications. Prolonged electrolysis has shown their stability against leaching.