Break-in and Performance Issues on a single cell PBI-based PEM Fuel Cell

Depending on the application in question and the load cycle of operation, fuel cell degradation can be a serious problem. Fuel cell degradation of PBI-based MEA's and fuel cells in general is quite complex. The rate of degradation depends on several parameters, where the operating temperature and the current drawn from the fuel cell are of great importance. One must therefore choose the point of operation carefully in order for the fuel cell to fulfil the requirements for lifetime perform-ance of the system.

Break-in of fuel cells is often done in scientific experiments to improve the performance of the fuel cell, even though break-in of a fuel cell implemented in a commercial application would most likely not be feasible. In the present work a commercially available PBI-based high temperature MEA is subject to a break-in procedure, as specified by the manufacturer. The cell was operated at 160 °C during the break-in procedure at a current density of 0.2 A/cm2. The performance of the cell was measured over the 100 hour break-in period and a polarization curve was recorded after completion of break-in. The performance change was minimal during the break-in cycle. However, in the first hour of op-eration a significant performance decrease of 30 mV was observed. Hereafter a performance in-crease started and the overall performance change during the break-in procedure was a voltage in-crease of 35 mV corresponding to a rate of 240 μV/hr. The performance increase was however fast-est in the first 50 hours of operation, corresponding to a rate of 370 μV/hr. It is believed that the general break-in process is occurring during the first 50 hours, which is assumed to be separation of excess phosphoric acid (H3PO4) from the over-doped PBI-membrane, the excess H3PO4 may block the electrochemical reactions at the active sites of the electrodes causing a more sluggish perform-ance.

Moreover, preliminary data is given on a long term degradation study, using Electrochemical Im-pedance Spectroscopy (EIS) measurements to analyze the degradation at high current densities (0.8 A/cm2).