Sensitivity analysis of a polybenzimidazole-based polymer fuel cell and insight into the effect of humidification

Abstract

The present work describes a systematic investigation of the effect of operating temperature, cathode stoichiometry, anode stoichiometry and reactants humidification rate on the behavior of a polybenzimidazole-based high temperature polymer fuel cell. The effect of reactants humidification was also considered; actually, in real applications, the syngas holds great amounts of water. Furthermore, water diffuses through the membrane and reaches the cathode side where it adds to the water produced by the electrochemical reaction. The investigation is based on the analysis of polarization curves measured under different operating conditions. Anode stoichiometry has no impact on the fuel cell voltage, while cathode stoichiometry and fuel cell temperature are relevant. When the anode stream is humidified, negligible effects take place; conversely, when the cathode stream is humidified, a consistent drop in the fuel cell voltage is observed, with a consequent drop in the power output. When air is saturated at 70 °C, a power loss of 8% and 27% takes place at 0.55 A cm−2 and 0.9 A cm−2, respectively. Such a finding might represent an issue when high power densities are pursued. The effect of cathode humidification was further investigated by means of electrochemical impedance spectroscopy and cyclic voltammetry. Thanks to dedicated tests, the effect of water in the cathode feed stream was clarified. Cathode humidification increases the electrode catalyst active area due to the dilution of the phosphoric acid retained in the electrode. Conversely, the presence of water hinders the oxygen mass transport to the catalyst active sites. Copyright © 2013 John Wiley & Sons, Ltd.