Electrocatalytic hydrogen evolution in acidic media using electrodeposited Ag/PPy and Ni/PPy hybrid materials

Two types of hybrid films were prepared by electrolytic deposition of Ni or Ag nanoparticles on predeposited polypyrrole (PPy) layers to produce electrocatalytic materials for the hydrogen evolution reaction (HER). Porous PPy substrate was used to increase the surface area for active material deposition and accordingly to enhance the catalytic performance of hybrid electrodes. The influence of metallic nanoparticle loading on electrocatalytic activity of hybrid electrodes was studied. Surface morphology of electrodes produced was characterised by scanning electron microscope. It was found that the increasing number of deposition cycles resulted in increasing amount of Ni nanoparticles while rather in increasing size of Ag nanoparticles deposited on PPy substrate. The electrocatalytic activity of hybrid layers and bare metallic layers deposited at the same conditions was evaluated by linear Tafel polarization and electrochemical impedance spectroscopy in a 0.5 M H2SO4 solution. Hybrid layers showed enhanced catalytic activity as compared to bare metallic layers. The best HER performance was observed for electrodes with highest metallic nanoparticle loading. The comparison of values of overpotential needed to afford the cathodic current density of 10 mA/cm(2) has shown that hybrid layers containing Ag exhibited slightly higher catalytic activity towards the HER than Ni-containing layers. However, lower values of equilibrium potential were observed for Ni-containing hybrid layers as compared to Ag-containing layers. The Tafel analysis indicated that the HER was limited by the Volmer step for Ag-containing electrodes, while by the Heyrovsky step for Ni-containing electrodes. Electrochemical impedance spectroscopy revealed that the hybrid layers with highest metallic nanoparticle loading reduce the charge transfer resistance of the HER.