Hydrogen evolution on Pt and polyaniline modified Pt electrodes—a comparative electrochemical impedance spectroscopy study

Kinetic of hydrogen evolution reaction, HER, at Pt and polyaniline, PANI, polymer film modified Pt electrodes in the sulphuric acid solution was investigated within the context of possible inhibition of HER by conducting polymers. Pt/PANI electrodes were prepared by electro-polymerization procedure with different quantities of PANI and electrochemically aged in the insulating state prior polarization and electrochemical impedance spectroscopy experiments. Polarization and impedance data obtained in the hydrogen (0.30 to 0.05 VRHE) and HER (0.00 to −0.155 VRHE) potential regions of bare Pt-poly electrode were compared with those of Pt/PANI electrodes. Significant differences of impedance spectra in the hydrogen region of potentials pointed toward domination of hydrogen under-potential deposition, H UPD, at Pt-poly surface and domination of PANI impedance at Pt/PANI electrodes, respectively. Quite similar impedance spectra obtained in the HER region of potentials and Tafel slopes of about 30 mV decade−1 evaluated from polarization measurements indicated that HER is proceeding by the same mechanism at Pt-poly and Pt/PANI electrodes, respectively. Analysis of respective impedance parameters showed that HER which is easily driven at Pt-poly electrode becomes inhibited to a certain extent at both Pt/PANI electrodes, but more for the one with higher quantity of PANI. These results can commonly be interpreted by HER that is taking place on the Pt substrate underlying more or less porous PANI film acting as a barrier toward electrolyte solution.