Observations of Transient Flooding in a Proton Exchange Membrane Fuel Cell Using Time-Resolved Neutron Radiography

The generation and transport of water in both liquid and gas phases during device operation are important areas to understand both steady state and transient performance of proton exchange membrane fuel cells. Localized concentrations of liquid water within the cell can cause flooding, which leads to decreases in cell performance, fuel starvation, degradation, or, in extreme cases, collapse of cell output. A variety of experimental and simulation techniques have been used to elucidate flooding events; yet, a comprehensive understanding of what leads to flooding and the specific details of how flooding affects fuel cell performance, especially during transient operation, have not been completely developed. The work reported here couples direct observations of liquid water flooding, primarily in the gas flow channel, with measurements of cell performance, outlet temperature, and outlet dew point during a step change in current density. Liquid water buildup and water slug dynamics were monitored with the temperature and electrical performance of the cell in real time. The size of the water slugs was connected to the cell performance to illustrate how the liquid water influences cell operation and how the conditions of the cathode gas flow control the liquid water content of the cell. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3250864] All rights reserved.