Hydrogen evolution reaction on electrodes coated with conducting-polymer films

Abstract

The cathodic hydrogen evolution reaction has been studied on gold electrodes coated with poly(N-methylpyrrole)(PMPy), and with a polymer mixture of PMPy and poly(4-styrenesulfonate)(PMPy–PSS). In all cases, H⁺ ions were found to permeate the film and react at the metal-electrode surface. In particular, for low concentrations of HCl, the PMPy film hinders significantly the movement of the depolarizer to the electrode. On the other hand, in the case of PMPy–PSS the H⁺ transport across the film proceeds readily, because the H⁺ ions constitute counter-ions to the immobilized sulfonate groups, present at a concentration of ca. 1 mol dm^–3. The effect of the partitioning equilibria and the Donnan potential on the observed potential dependence of the charge-transfer rate is discussed in detail. It is shown that the presence of the cation-exchanger coating (PMPy–PSS) enhances the rate of electrochemical H⁺ reduction (relative to the uncoated electrode) when the concentration of H⁺ in the electrolyte is small. The diffusion coefficient of H⁺ ions in the PMPy–PSS matrix was determined: D= 1 × 10^–6 cm² s^–1.