The effect of overpotentials on the transient response of the 300 W SOFC cell stack voltage

This paper presents the results of an experimental investigation of transient characterizations of 300 W planar type Solid Oxide Fuel Cell (SOFC) cell stack during load change. It indicates the transient characterization obtained during a ramped electric current with a Current-Based Fuel Control (CBFC) strategy. The fuel utilization factor is chosen for a reference of the CBFC strategy and is kept constant to the ramping electric current. The fuel utilization factor can be described as a ratio of consumed fuel (expressed as a function with an applied electric current) to supplied fuel. For the simplification of discussion, hydrogen was used as fuel by mixing it with nitrogen in order to satisfy the constant gas residential time in all cases and instances. The transient response of the cell voltage obtained under several thermal conditions was shown for discussion. The effect of overpotentials, associated with the cell's operating temperature, on the transient response of the cell voltage is primarily discussed. The paper indicates that reducing the fuel flow rate, namely, setting a higher set-point for the fuel utilization factor, may decrease the OCV, increase concentration polarization and finally degrade cell performance. This paper also pointed out the importance of operating temperature management on both improving the steady-state cell performance and eliminating the negative effect of the overpotentials that appear on the transient response of the cell voltage. (C) 2013 Elsevier Ltd. All rights reserved.