The fundamentals of the operation of polymer electrolyte membrane fuel cells under dry and flooded conditions with an efficient approach to the management of liquid water.

摘要

Polymer electrolyte membrane (PEM) fuel cells are power conversion devices that have the potential to become an important part of a distributed energy portfolio independent of fossil fuels. In order to improve their performance and make their mainstream use possible, the fundamental physics of PEM fuel cell operation must be thoroughly understood. Included in this is the effect of the water balance inside the fuel cell. Either too little water or an excess leading to liquid water accumulation can cause fuel cell failure. Several factors affect the water balance, some inherent in fuel cells and others determined by the system design.;The tool used to study fuel cell operation was the Segmented Anode Parallel Channel (SAPC) fuel cell. Transparent flow channels and a segmented anode allowed for direct visualization of liquid water and measurement of the current distribution along the flow channel. Under dry conditions, hydration fronts were observed to propagate along the flow channel as the fuel cell ignited or extinguished. Under wet conditions, liquid water accumulation observed in the flow channel created areas of local reactant starvation. Each segment of the SAPC fuel cell was modeled as a differential element, coupled together electrically and through the flux of the reaction components.;The design of the SAPC fuel cell was very simple. The fuel cell was allowed to operate autonomously without potentiostatic or galvanostatic controllers that hide much of the physics of fuel cell operation. The setup and experimental results elucidated the importance of flow pattern, temperature, load resistance, flow channel orientation with respect to gravity, gas diffusion layer material, flow rates, and flow field construction. Each of these factors changed how much water was removed as a vapor or how severely liquid water hindered the fuel cell operation. It was shown that the design of the fuel cell can be tailored to maintain the fuel cell hydration while also effectively removing excess liquid water. The flow rates could be kept low, allowing for high fuel utilization and dry feeds. The need for extra peripheral equipment, such as humidifiers or feed recycling, was alleviated.