Performance Degradation Tests of Phosphoric Acid Doped Polybenzimidazole Membrane Based High Temperature Polymer Electrolyte Membrane Fuel Cells

Degradation tests of two phosphoric acid (PA) doped PBI membrane based HT-PEM fuel cells were reported in this paper to investigate the effects of start/stop and the presence of methanol in the fuel to the performance degradation of the HT-PEM fuel cell. Continuous tests with pure dry H2 and methanol containing H2 which was composed of H2, steam and methanol as the fuel were performed on both single cells. After the continuous tests, 12-h-startup/12-h-shutdown dynamic tests were performed on the first single cell with H2 as the fuel and on the second single cell with methanol containing H2 as the fuel. Along with the degradation tests, electrochemical techniques such as polarization curves and electrochemical impedance spectroscopy (EIS) were employed to study the degradation mechanisms of the fuel cells. The results of the tests showed that both single cells experienced an increase in the performance during the H2 continuous tests, because of a decrease in the reaction kinetic resistance mainly in the cathode due to the redistribution of PA between the membrane and electrodes. The performance of both single cells decreased in the following tests, with highest performance decay rate in the methanol continuous test, followed by that in the H2 start/stop test and the lowest performance decay rate in the H2 continuous test. EIS measurements for the first fuel cell during the start/stop test showed that the mass transfer resistance and ohmic resistance increased which could be attributed to the corrosion of carbon support in the catalyst layer and degradation of the PBI membrane. During the continuous test with methanol containing H2 as the fuel the reaction kinetic resistance and mass transfer resistance of both single cells increased, which may be caused by the adsorption of methanol decomposition products (CO mainly) on the catalyst surface and dilution of H2 because of the presence of water vapor and methanol in the gas stream. The performance of the second single cell experienced a slight decrease during the start/stop test with methanol containing H2 as the fuel. It is revealed from all the tests that the presence of methanol and start/stop can accelerate the degradation of HT-PEM fuel cell, and the effect of presence of methanol is more significant.