Study of the long-term operation of a vanadium/oxygen fuel cell

A vanadium/oxygen fuel cell (VOFC) with a geometrically active area of 51 cm2 and two membranes was discontinuously operated over a period of over 676 h with 47 successive tests at room temperature with a current density of 19.6 mA/cm2 in order to investigate signs of ageing. As well as measuring cell voltages, the test setup was also used to measure anode and redox potentials as well as cell and half-cell impedances. The performance data of the VOFC fluctuated widely over the course of the test period, due to different V2+ concentrations and instabilities of the starting solutions on the one hand and complex changes in cathode conditions on the other. The desired behaviour of the anode reactions was achieved primarily through improved methods for producing the V2+ solutions, and remained stable at the end of the experiments. The kinetics of the cathode reactions were temporarily increased by purging with 2 M H2SO4, however their performance decreased over time. The VOFC had symptoms of ageing by complex and overlaid changes in the cathode's triple phase boundary layer and in the special conditions between the two electrodes and membranes.