Evaluation of oxygen transport parameters in H2SO4-CH3OH mixtures using electrochemical methods

The effects of the addition of methanol on the diffusion coefficient and solubility of oxygen in different solutions of 0.5 M H2SO4 and 1.0 M CH3OH were studied for a wide range of methanol to sulfuric acid concentration ratios using platinum and Sold microelectrodes. The studies were performed at room temperature and atmospheric pressure using cyclic voltammetry and potential step techniques. Solutions with a given methanol to sulfuric acid ratio were prepared, acid the limiting currents vs. time were measured for the different electrodes. By using a planar geometry approximation to the microelectrodes, the values of diffusion coefficient and solubility were determined for the different solutions. The transport parameters and reduction potentials of oxygen were affected by the concentration of methanol in 0.5 M H2SO4. Although the transport parameters measured by the gold and platinum electrodes were in qualitative agreement, their actual values were found to be different. The dissolved oxygen concentration in 0.5 M H2SO4 solution was determined to be 1.22 x 10(-6) mol/cm(3) with the platinum electrode and 1.16 x 10(-6) mol/cm(3) with the gold electrode, while the O-2 diffusion coefficient was determined to be 1.04 X 10(-5) cm(2)/s for platinum and 1.34 x 10(-5) cm(2)/s for gold. The reasons for the observed differences in the transport parameters determined with the two electrodes are discussed. (C) 2000 The Electrochemical Society. S00 13-4651(99)06-040-1. All rights reserved.