Electrochemical Impedance Spectroscopy (EIS) Characterization of Reformate-operated High Temperature PEM Fuel Cell Stack

This paper presents an experimental characterization of a high temperature protonexchange membrane fuel cell (HT-PEMFC) short stack carried out by means of impedance spectroscopy. Selected operating parameters; temperature, stoichiometry and reactant compositions were varied to investigate their effects on a reformate-operated stack. Polarization curves were also recorded to complement the impedance analysis of the researched phenomena. An equivalent circuit model was used to estimate the different resistances at varying parameters. It showed a significantly higher low frequency resistance at lower stoichiometry. Both anode and cathode stoichiometric ratios had significant effects on the stack performance during the dry hydrogen and reformate operation modes. In both cases the effects faded away when sufficient mass transport was achieved, which took place at λanode= 1.3 for dry hydrogen, λanode= 1.6 for reformate operation and λcathode= 4.The work also compared dry hydrogen, steam reforming and autothermal reforming gas feeds at160 ◦Cand showed appreciably lower performance in the case of autothermal reforming at the same stoichiometry, mainly attributable to mass transport related issues. In a CO poisoning analysis the stack showed good tolerance to concentration up to 1% CO in the fuel stream.