// Dynamic operation of PEM fuel cells

Examination of the degradation behaviour during dynamic operation of a polymer electrolyte membrane fuel cell (PEMFC)

PEMFCs are a suitable alternative drive concept for vehicles due to their flexible operating characteristics and their high energy efficiency. A high power density and a sufficiently long lifetime must be ensured for automotive applications. In particular, the conditions of local undersupply of reactant gas that occurs during dynamic operation can cause accelerated degradation and thereby shorten the service life of the PEMFC.

The method for examining dynamic operation has been further developed in one finalised and one ongoing funded project and was tested on specific components by carrying out single-cell load variation (see the chart below) and dynamic driving cycle experiments on laboratory fuel cells. Using non-dispersive infrared (NDIR) sensors, carbon dioxide emitted as a result of local undersupply states was detected in the gas released by the cathode and anode. Furthermore, these undersupply states were investigated during dynamic operation by means of local current density measurements (see the chart above) and supported by further characterisation studies (UI characteristics and CV and EIS measurements).

A significant decrease in cell performance due to the critical operating conditions was identified during dynamic operation. This can, on the one hand, be explained by a reduction of the electrochemically active surface area of the catalyst and, on the other, by an increase in mass transfer resistance and cell resistance due to degradation. This illustrates the necessity of an adequate control strategy to avoid such critical operating conditions in order to ensure the required lifetime of PEMFCs, for example for automotive applications.