Electrochemical Oxidation of H2 and H2/CO Mixtures in Higher Temperature (Tcell > 100DDGC) Proton Exchange Membrane Fuel Cells: Electrochemical Impedance Spectroscopy

Electrochemical impedance spectroscopy (EIS) of the electrochemical oxidation of H2 and H2/CO mixtures on the proton exchange membrane fuel cell anode (Pt-Ru/C or Pt/C electrocatalysts) was performed at higher temperature (Tcell > 100DGC) and ambient pressure. Anode polarization studies were also conducted with the same H2/CO mixture-fed streams. Both impedance and anode polarization provide information on the mechanism of electrochemical oxidation of H2 and H2/CO mixtures. The impedance spectra are presented and compared at various CO concentrations (0-500 ppm, 1 and 2%), cell temperatures (80-120DGC), relative humidity conditions (35-100%), as well as different dc bias potentials for characterizing the CO tolerance of the electro-catalysts. CO poisoning is alleviated by increasing the cell temperature, and relative humidity plays a strong role in the EIS and anode polarization. The impedance spectrum of the CO poisoned anode is strongly dependent on the dc bias potential. Under certain dc bias potential conditions, pseudoinductive behavior appears in the complex impedance plots, corresponding to the onset oxidation of CO as indicated from anode polarization.