Abstract
The water balance in operating hydroxide-exchange-membrane fuel cells (HEMFCs) is a key challenge for improved performance and durability. For every 4 electrons produced in an HEMFC, 4 water molecules are generated in the anode, 2 water molecules are consumed in the cathode. Water is also transported from cathode to anode along with the hydroxide due to electroosmosis. Consequently, there is a concentration gradient of water that transport water from anode to cathode. Ineffective water management could lead to cathode dry-out, where insufficient water in the cathode limits the rate of reaction or causes ionomer degradation through alkaline instability, or to anode flooding, where excess liquid water in the anode limits gas diffusion. To address these issues, it is critical to measure the transport of water across the hydroxide-exchange membrane during cell operation. We built a water-flux station to measure the water in and out of the anode and cathode during cell operation with different inlet relative humidities and back pressures. Here, the effect of the membrane thickness and the effect of stacking hydroxide-exchange membranes on the water transport across the hydroxide exchange membrane is studied. The stacking of hydroxide-exchange membranes creates an interfacial ohmic resistance between membranes, measured from the high frequency resistance, but not an interfacial water transport resistance. This study shows that the water transport across the hydroxide-exchange membrane is sufficient for water consumption in the cathode and is not significantly affected by the membrane thickness or stacking. However, the added ohmic resistance from the increased membrane thickness or stacking membranes significantly affects the performance.
Published Version
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