Investigation of the Effect of Humidity Level of H₂ on Cell Performance of a HT‐PEM Fuel Cell

Abstract

High temperature polymer electrolyte membrane (HT‐PEM) fuel cell is often integrated with a light fossil fuel reformer to improve the fuel flexibility. Although the operation of HT‐PEM fuel cell does not rely on the humidification of the inlet gas, water vapor is found in the reformate gas which is fed to the HT‐PEM fuel cell. In this work, the influence of water content in the H2 to the cell performance of a HT‐PEM fuel cell is studied under different operating temperatures. Under lower operating temperature of 140 °C, the HT‐PEM fuel cell shows the best performance with low water content in the H2. With increasing water content, the cell performance decreases. Under the operating temperature of 160 °C, the best cell performance is achieved with an intermediate water content in the H2. While under high operating temperature of 180 °C, the cell performance shows an increasing trend with the increase in the water content. By measuring the impedance spectra of the HT‐PEM fuel cell, the reasons for the different influence of anode humidification in cell performance at different operating temperatures were investigated.

Effects of Impurities on Pre-Doped and Post-Doped Membranes for High Temperature PEM Fuel Cell Stacks

“…The effects for both cases are the highest in the beginning of test and there is a slight recovery, especially at higher current densities at the end of the 24 h tests. This is inline with certain reports that, even though the net effect of N 2 dilution on the thermodynamic, kinetic, and mass-transport driving forces is approximately independent of the relative humidity, both the relative humidity and N 2 dilution affect the anode potential in the same way that water vapor also causes dilution effects [13,48,49]. Similar effects can be seen from the Nyquist polts in Figure 6b, which were recorded at the higher current density end of the polarization curves at 0.4 A/cm 2 .…”

“…However, the fact that there was a significant performance recovery with the pure H 2 operation at the end of the tests indicates that the reason for the losses during the wet reformate operation were not related to acid loss. Acid loss is reported to mainly happen at lower operating temperatures and during shutdown/startup cycles due to the condensation of water that can wash out the acid [13,15]. This is not the case in the current work, as there were only a limited number of shutdown/startup procedures, and the operating temperature was kept constant at 160°C.…”

“…Studies suggest both positive and negative effects of humidification in HT-PEMFCs, where some propose that the interaction of water with phosphoric acid improves the proton conductivity and fuel cell performance and others reported negative effects of water vapor, including dilution and acid loss, especially at lower temperatures [11,13,47]. Therefore, it can be said that water vapor in an HT-PEMFC has the dual opposite effects of dilution and that of maintaining the equilibrium concentration of phosphoric acid.…”

“…Water has positive effects in low temperature PEM fuel cells, where it is used as a proton transport medium. Nonetheless, its effects on an HT-PEMFC are not fully understood, with some reporting advantages [47] and others recommending that it is avoided under certain operating conditions [13].…”

“…On the other hand, Zhou et al [13] proposed that the water content in the anode gas should be minimized to avoid the performance loss when the HT-PEMFC is operated at lower operating temperatures (i.e., 140-160°C), and researchers reported that this may also cause faster degradation due to increased acid loss [11]. According to Park et al [14], the performance loss due to a humidified atmosphere can be reversed by precise acid-dosing of the degraded membrane electrode assemblies (MEA).…”