EFFECT OF GELLING ON THE SURFACE-STRUCTURE OF A POROUS LEAD ELECTRODEIN SULFURIC-ACID

Effect of immobilizing the electrolyte using thixotropic agents such a s sodium silicate on the electrochemical behaviour of lead in sulfuric acid is studied using electrochemical methods such as cyclic voltamme try (CV), charging curve technique, Tafel polarization and surface spe ctroscopic methods including X-ray photoelectron spectroscopy (XPS) an d scanning electron microscopy (SEM). CV studies indicate a 700 mV cat hodic shift in the hydrogen evolution potential as a result of gelling while the well-known reversible Pb/Pb2+ couple is found to be thermod ynamically disfavoured (100 mV and 50 mV shifts for the Pb dissolution and Pb2+ reduction reactions respectively). In addition, a significan t change in the double layer capacitance by 600 mu F cm(-2) is observe d at the same potential probably due to the contribution of silicate a dsorption at the interfacial region. Exchange current density values f or hydrogen evolution reaction calculated from Tafel plots are 1.35 x 10(-6) A cm(-2) and 1.31 x 10(-8) A cm(-2) for free and gelled electro lytes, respectively, which reveal the kinetic suppression of HER. Howe ver, XPS studies give no evidence for the chemisorption of silicate on the lead surface, although SEM analysis shows appreciable change in t he surface morphology.