Water and Thermal Management of PEM Fuel Cells

Proton Exchange Membrane (PEM) fuel cells have a great potential to replace conventional fossil fuel dependent power conversion technologies in a wide range of portable, automotive and stationary applications and this is due to their high efficiency, quick start-up and sizing flexibility. However, there are still some technical challenges that hinder the widespread deployment of this clean technology into the marketplace. Two of the key challenges are the water management and thermal management of the fuel cell; any mismanagement of water and/or heat could lead to water flooding or membrane dry-out which are both detrimental to the fuel cell performance and durability. In order to have insights on how to manage water and heat within the fuel cells, a transparent and commercially available PEM fuel cell has been directly visualised using high-resolution digital and thermal cameras at both sides of the fuel cell. With this technique, real-time videos that show how liquid water and heat evolve have been recorded. There has been a particular emphasis on how liquid water forms, accumulates and moves along the flow channels. Further, the sensitivity of the distribution of liquid water and temperature within the fuel cell to the operating conditions has been investigated. For this investigation, a new parameter, termed as the wetted bend area ratio, has been introduced to give an indication on how flooded the flow channels are and subsequently explain the variations in the performance of the PEM fuel cell as the operating conditions change. The main findings are the temperature distribution across the MEA becomes less uniform as the wetted ratio number decreases. Further, the temperature distribution along the MEA at the cathode side becomes less uniform as the air flow rate increases. In addition, there exist optimum values for the operating conditions to increase the fuel cell performance. Since the operation of the PEM fuel cell at high temperatures (i.e.>100°C) is an increasingly adopted way to resolve water flooding problems, the reliability of the currently used components remain questionable. To partly answer this question, the gas permeability of the diffusion media used in PEM fuel cells has been investigated under higher temperatures for the first time. The results show that the gas permeability increases as the operating temperature increases and this may enhance the reactant transport within the PEM fuel cell.