Cell voltage analysis of a 6 kW polymeric electrolyte fuel cell stack designed for hybrid power systems

A polymeric electrolyte Fuel Cell System (FCS) was experimentally studied for application as power generator in hybrid power systems. The electrochemical device was based on 96 individual cells and produced a maximum power of 6.2 kW. A dedicated DC-DC converter was inserted between the FCS, a Pb battery pack used as storage system, and a resistive variable electric load. The whole system was preliminarily characterized to evaluate FCS and DC-DC converter efficiency in the whole power range. The FCS operated at low pressure, without external humidification and in anode recirculation mode. As irregularities of cell voltages could be a sign of draining conditions for catalyzed electrodes and electrolytes, the cell voltage uniformity analysis was effected in both steady state and dynamic conditions. The coefficient of variation (C-v), was used as a measure of dispersion of cell voltage around the mean value. The experimental data evidence a satisfactory behavior of all cells in steady-state conditions in the entire power range (1-6 kW), with FCS+DC-DC converter efficiencies close to 50% and very low C-v values (<1.6%). Stack and cell performance remained high and reliable during most of transient phases of a dynamic test characterized by a high frequency of load variation steps. Power variation rates higher than 300 W/s determined C-v values close to 3-3.5%. These load ramp rates could be considered as a threshold range for the management of a low pressure self-humidified FCS in hybrid power system configurations. (C) 2019 Elsevier Ltd. All rights reserved.