Electrochemical Modeling of the Current-Voltage Characteristics of an SOFC in Fuel Cell and Electrolyzer Operation Modes

A zero-dimensional and isothermal stationary model demonstrably predicting the current-voltage (C/V) characteristic of an anode supported SOFC single cell is for the first time verified for C/V characteristics measured in electrolysis mode. The accuracy of the presented model was increased by including the actual cell temperature under current load, determined by an impedance-based temperature measurement routine. C/V characteristics measured at 800°C in the range from 0.66 V to 1.6 V for H2O:H2 compositions 70:30 and 30:70 reveal a pronounced asymmetric operation of the fuel electrode supported cell in electrolysis mode. This experimentally observed behavior is accurately reproduced by the model and is explained by (i) increasing polarization losses related to Knudsen diffusion and (ii) decreasing reaction rate in dry conditions at the fuel electrode at high current densities in electrolysis mode.