Observations of Transient Flooding in a Proton Exchange Membrane Fuel Cell Using Time-Resolved Neutron Radiography
Michael A. Hickner, Nathan P. Siegel, Ken S. Chen, Daniel S. Hussey, David L. Jacobson
The generation and transport of water in both the liquid and gas phases during device operation is an important area of study to understand both steady-state and transient performance of proton exchange membrane fuel cells. Specifically, localized high concentrations of liquid water within the cell can cause flooding, which leads to decreases in cell performance, localized fuel starvation and degradation, or in extreme cases, collapse of the 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 operational modes, have not been completely developed. The work reported here couples both direct observation 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. The evolution of the water buildup and water slug dynamics was monitored as well as the transient temperature and electrical performance of the cell in real time. This investigation is useful in that both the size and location of the water slugs and the cell performance can be connected to describe how the liquid water influences cell operation.