Kinetics Analysis of the Electrocatalytic Oxidation of Methanol inside a DMFC working as a PEM Electrolysis Cell (PEMEC) to generate Clean Hydrogen

The electrochemical decomposition of methanol for hydrogen production has been carried out at several temperatures (25 to 85 °C) and different methanol concentrations (0.1 to 10 M in 0.5 M H2SO4) using a DMFC hardware working as a Proton Exchange Membrane Electrolysis Cell (PEMEC). Conversely to most of recent studies which investigated the effect of working parameters (cell voltage, methanol concentration, flow rate of reactants, temperature, etc.) on the hydrogen evolution rate, this work is focussed on the analysis of the kinetics of methanol oxidation at the anode using the hydrogen cathode as a reference electrode. In this way it was possible to plot the cell voltage (corrected from the ohmic drop) as a function of the logarithm of the imposed current density. A Tafel analysis of these plots allowed us to estimate the kinetics parameters of methanol oxidation, i.e. the charge transfer coefficient α of the rate determining step and the heat of activation Δ of the overall process. The values obtained for these parameters (α ≈  0.5 to 0.6, Δ̑H̆* ≈ 50–60 kJ mol−1) are similar to those published in the literature as deduced from the analysis of methanol oxidation both on smooth Pt-Ru electrodes and on Pt-Ru nanoparticles supported on carbon powders.