Study of water accumulation dynamics in the channels of an open-cathode fuel cell through electro-thermal characterisation and droplet visualisation

Open-cathode polymer electrolyte fuel cells have the advantage of simplified construction and the potential for cost reduction. However, effective water and temperature management calls for a different approach to conventional fuel cells. Improved understanding of the link between current density, temperature, water formation and hydration of the membrane is required to optimise cell design. This work uses thermal imaging, optical visualisation, gravimetric analysis and electrochemical impedance spectroscopy to study the links between these factors and also examines the effect of cell orientation on performance. The results reinforce the importance of cell temperature for water management, which is a function of current density. Regions of the cell with higher temperature avoid flooding by promoting vapour phase water; however, this can lead to higher membrane resistance due to dehydration. The results reveal that transition in the water balance regime from continuous hydration and flooding to drying with increasing current density occurs between 34 degrees C-40 degrees C (at 250 mA cm(-2)) and water generation is balanced with evaporation at similar to 50 degrees C (550 mA cm(-2)). Finally, fuel cell orientation affects performance after extended operation due to the effect of water accumulation and evaporation, with the cathode in a 'flat upwards' orientation found to be most resistant to flooding and cathode in a flat downwards orientation the most likely to flood. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.