Elektrochemische Impedanzspektroskopie zur experimentellen Untersuchung des Betriebsverhaltens eines PEM-Brennstoffzellenstacks

Kurzfassung

This Master Thesis characterises the operational behaviour of low temperature fuel cell stacks with electrochmical impedance spectroscopy and the currunt interrupt method. The PEM-FC-Stack HD10, a fuel cell system by Hydrogenics, will be used for the investigations. The aim is to gather information about every cell in the stack by only measuring at one point over the whole stack. At first the test setup will be described and the modifications of the fuel cell stack needed for the measurements. Subsequently EIS measurements at stationary states of operation are conducted to quantify the moisture of the stack dependent on operating conditions and temperature. To accomplish that the fuel cell operation temperature is varied at different loads. The results of 16 generic single cell measurements are compared with measurements over the whole stack of cells. With the comparison of the single cell measurements with those of the whole stack it can be found that to quantify the state of the cells by a single measurement over the whole stack is not expressive enough. To use the full potential of the impedance spectroscopy measurements with different excitation frequencies have to be performed. Especially at low frequencies of oscillation the measurements take a lot of time. To shorten the length of the experiments, tests without the low frequencies are conducted. It can be shown that the time of the measurements can be lowered by 80%, but only the information about the electrolyte resistance can be gained from that. The current interrupt method is an other way to quantify the operational behaviour of a stack comparable to the EIS measurements. For that voltage measurements of the whole stack are made with a sample rate of 50 kHz while a sharp drop of the current is performed. The results show that the effort of the CI method is not less than that of the EIS measurments. In the evaluation of the CI-tests it is not possible to quantify the electrolyte resistance, the moisture or the operating condition of the stack.