Experimental study and modelling of degradation phenomena in HTPEM fuel cell stacks for use in CHP systems

Degradation phenomena in HTPEM fuel cells for use in CHP systems were investigated experimentally and by modelling. It was found that the two main degradation mechanisms in HTPEM fuel cells are carbon corrosion and Pt agglomeration. On basis of this conclusion a mechanistic model, describing the degradation caused by these phenomena, is suggested. Using the proposed model, information about optimum operational temperatures is derived. To investigate how the degradation propagates on stack level, a simplified stack model is developed. The model is 1-dimensional, non-isothermal, and semi-transient (considering degradation with time). The model shows that the degradation in a stack will not progress uniformly, but occurs faster in the hot end of the stack. Furthermore, the model shows that the degradation is very dependent on stack temperature control scheme. Two experiments were conducted; a 500 hours single cell experiment and a long term stack experiment (around 800 hours so far). In the stack experiment two 1 kW stacks were operated at temperatures of 150oC and 170oC. Individual cell voltages were monitored during the experiment, along with stack voltage and temperature. The experiment support the model, by showing a skew degradation in the stack.