The Impedance Analysis for Cathode Gas Diffusion Electrode of High Temperature Pemfc by Distribution of Relaxation Times

In the membrane electrode assembly (MEA) of high temperature polymer electrolyte membrane fuel cells, many types of resistance existed but they couldn’t be separated clearly in other previous research. The distribution of relaxation times (DRT) method was used in this study with the electrochemical electrode analysis system (EEAS) made by ourselves to figure out the impedance of the cathode gas diffusion electrode (GDE) only. The impedance analysis by the DRT method was carried out at different temperatures and current densities. The four peaks (designated as Peak 0 – 3) were shown at DRT plots of cathode GDE and they were defined as four resistances by comparing DRT plots according to analysis conditions and considering EEAS structure. Comparing the DRT plots of the cathode GDE with those of MEA, another peak (Peak 4) was elucidated to the resistance of the anode. Based on these assignments of the DRT peaks, the DRT method was applied in our previous research which is about polymer binders including phosphonic acid functional groups, such as PPO-MPA and PPO-HPA, in the cathode catalyst layer. Using these binders, Peak 1 which is related to the mass transport of oxygen and charge transfer of oxygen reduction reaction was separated by two peaks due to the phosphonic acid functional group.