Effect of gelling on the surface structure of a porous lead electrode in sulfuric acid

Abstract

Effect of immobilizing the electrolyte using thixotropic agents such as sodium silicate on the electrochemical behaviour of lead in sulfuric acid is studied using electrochemical methods such as cyclic voltammetry (CV), charging curve technique, Tafel polarization and surface spectroscopic methods including X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). CV studies indicate a 700mV cathodic shift in the hydrogen evolution potential as a result of gelling while the well-known reversible Pb/Pb²⁺ couple is found to be thermodynamically disfavoured (100mV and 50mV shifts for the Pb dissolution and Pb²⁺ reduction reactions respectively). In addition, a significant change in the double layer capacitance by 600 μF cm⁻² is observed at the same potential probably due to the contribution of silicate adsorption at the interfacial region. Exchange current density values for hydrogen evolution reaction calculated from Tafel plots are 1.35× 10⁻⁶A cm⁻² and 1.31× 10⁻⁸A cm⁻² for free and gelled electrolytes, respectively, which reveal the kinetic suppression of HER. However, XPS studies give no evidence for the chemisorption of silicate on the lead surface, although SEM analysis shows appreciable change in the surface morphology.