Polyaniline–Lead Composites as Inhibitors for the Hydrogen Evolution Reaction, Relevant for Lead-Acid Batteries

This work developed a composite of the conducting polymer polyaniline (PAni) with lead that has a high onset potential for hydrogen evolution in a high-concentration acid solution. The aim was to avoid hydrogen evolution from a carbon fiber current collector, considering its application in lead-acid batteries. In a 5 M H2SO4 solution, the onset potential was as high as −0.75 V vs Ag/AgCl. The study revealed that the Pb2+ ions strongly interact with the nitrogen present in the PAni structure. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy gave an insight into how the interaction between lead ions and the nitrogen takes place, which is described schematically. This composite is stable and keeps the high onset potential, while Pb2+ is associated with nitrogen, as evaluated in various potentials through chronoamperometry and cyclic voltammetry conditions. The Pb2+ desorbs for potentials higher than −0.65 V vs Ag/AgCl and degrades the composite onset potential. The desorption was reversible as long as the PbSO4 particles formed were nanometric and immersed in the PAni. Desorption for long periods forms large PbSO4 particles; consequently, the reduction of these particles becomes difficult. Without Pb2+ ions, it is not possible to restore the interaction between Pb2+ and PAni. Besides XPS and Raman spectroscopy, the material characterization was performed by field emission gun scanning electron microscopy and energy-dispersive X-ray spectroscopy. The electrochemical characterization involved cyclic voltammetry, linear sweep voltammetry, galvanostatic charge–discharge cycles, and chronoamperometry.