ANALYSIS AND CHARACTERIZATION OF NONUNIFORMITY IN PHOSPHORIC-ACID FUEL-CELLS

A numerical simulation tool has been developed to map out three dimens ional distributions of current densities, gas concentrations, temperat ures, etc., in phosphoric acid fuel cell (PAFC) stacks. The analysis i s based on measured voltage-current output characteristics of a PAFC w ith an area of 3 cm(2). We have verified the validity of the simulatio n by comparing the temperature distribution and gas concentrations wit h the experimental results. In our analysis for the case of cross flow with an average current density of 240 mA/cm(2) at a hydrogen utiliza tion of 80%, the current density was found to range from 195 to 309 mA /cm(2) over the electrode of 4900 cm(2). The hydrogen concentration in the fuel decreased down to 11.4% in the fuel outlet/air inlet region, where gradual electrochemical corrosion is possible, The low hydrogen concentration was actually detected with a quadrupole mass spectromet er system for an experimental fuel cell. The possible corrosion will b e suppressed by adopting a return flow for the fuel.