Storage and evolution of hydrogen in acidic medium by polyaniline

Emeraldine salt of polyaniline-coated copper substrate was used as a cathode to study hydrogen evolution reaction in 1M H2SO4. Hydrogen evolution reaction in acidic medium followed Grotthus mechanism, where proton hops randomly on the surface of polyaniline. With Randles-Sevcik equation, the average value of diffusion coefficient for H+ on polyaniline was calculated to be 2.66 times higher than that in the literature data. This higher value explicitly supported the rapid diffusion of H+ on polyaniline surface from the bulk electrolyte solution. With the help of a phenomenological thermodynamic approach demonstrated elsewhere, the solvent-modified work function of polyaniline-coated copper in acidic medium was calculated. The plot of exchange current density versus solvent-modified work function of different metals and polyaniline-coated copper indicated that at lower work function polyaniline-coated copper showed higher exchange current density and the rate of hydrogen evolution was much higher on polyaniline-coated copper than on copper. This was further confirmed by gas chromatography, and C-13 and H-1 nuclear magnetic resonance studies supported the mechanism proposed. From linear sweep voltammetry analysis, it was observed that the total capacity of hydrogen stored on polyaniline-coated copper was approximately 1.85 times higher than that on copper.