CHARACTERIZATION OF THE LIMITING STRUCTURAL EFFECTS ON THE ELECTROCHEMICAL-BEHAVIOR OF POROUS GAS-DIFFUSION ELECTRODES

In this work, the limiting structural effects of porous gas diffusion electrodes on the oxygen reduction reaction were studied in 0.5 M sulfuric acid solutions. Cyclic voltammetry, steady state polarization curves and ac impedance methods were employed in the experimental investigation of electrodes with various polytetrafluoroethylene (PTFE) contents, platinum loadings and platinum-to-carbon composition ratios. The experimental results were analyzed in terms of the current models of gas diffusion electrodes, through which the following conclusions were established: (i) the increase of the PTFE content changes the behavior of the gas diffusion electrodes from an agglomerate diffusion toward a distributed resistance description of the limiting situation; (ii) the change of the platinum loading does not change the rate-determining step of the global electrode process; and (iii) both for electrodes which are too thin (high Pt/C ratio) and too thick (low Pt/C ratio), the polarization behavior is described by a limiting agglomerate diffusion condition.