Experimental determination of HOR and ORR kinetic parameters in an AEMFC by the distribution of relaxation times method

The need for realistic inputs in computational fluid dynamics (CFD) models motivated this research. Anodic and cathodic charge transfer resistances were identified and measured directly from a typical anionic exchange membrane fuel cell (AEMFC) assembly, which also provided the data for a performance analysis of such a cell. The proposed technique employs electrochemical impedance spectroscopy (EIS) and the deconvolution of its signal through the distribution of relaxation times (DRTs). The DRT method identified specific electrode reactions, either oxidation or reduction, in the AEMFC with identical Pt/C electrodes in a membrane-electrode assembly (MEA) fed with H2 and O2. The reliability of the detected specific signals was confirmed by modifying the gas-fed mode, using the same gas type in both compartments to isolate the specific hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). This technique demonstrated the ability to detect the signals for the HOR and ORR and those related to the ion and mass transport in the MEA components. The charge, ion, and mass transport processes were followed within the cell potential condition between open circuit potential and 0.3 V, with a frequency interval of 0.5-1000 Hz. The charge transfer resistance showed an exponential decrease as the cell potential lowered, with a 90 and 97 % reduction in resistance for the HOR and ORR, respectively, from the OCP condition to 0.3V. For the Pt/C electrodes in the AEMFC, the anodic charge transfer resistance (0.29 S2 cm2) was 62 times lower than the cathodic one (18.02 S2 cm2) at the open circuit potential. With these data, the exchange current density for the HOR and ORR were 9.89 x 10- 2 and 1.59 x 10-3 A cm- 2, respectively, in an operating AEMFC at 60 degrees C, 68.9 kPa, and gas-fed stoichiometry of 1:2 for anodic and cathodic humidity-saturated flow rates.