Investigation of water transport and its effect on performance of high-temperature PEM fuel cells

The phosphoric acid doped polybenzimidazole (PBI) membrane is the most commonly used electrolyte in high-temperature PEM fuel cells (HT-PEMFCs). The aims of this study are to investigate the transport of water vapour from the cathode to the anode and the effect of water vapour on the performance of a single cell HT-PEMFC using a commercial PBI-based membrane-electrode-assembly (MEA). The amount of water vapour transportation is determined by weighing the water vapour condensed from the fuel off-gas stream located at the anodic outlet of HT-PEMFC under a flow-through mode. Experimental results show that up to 31.7% of the generated water vapour is transported from the cathode to the anode. To study the effect of water on the cell performance, the polarization curves, transient voltage curve and transient ohmic resistance (due to on/off of the outlet solenoid valve) are measured under anodic dead-end and flow-through modes. The study shows that excessive water vapour in the anode can significantly deteriorate the performance of a cell operated in an anodic dead-end mode, but negligible in an anodic flow-through mode. The performance can rapidly recover after switching the cell from a dead-end mode to a flow-through mode. The study allows fundamental understanding of the operation in anodic dead-end and flow-through modes, which offers guidelines for operating a HT-PEMFC with improved fuel utilization.