Neutron imaging technique for in situ measurement of water transport gradients within Nafion in polymer electrolyte fuel cells

Water transport is an important consideration in the optimization of polyme r electrolyte fuel cell (PEFC) performance, affecting both internal resista nce and cathode polarization losses. Novel experiments are described using neutron radiography to measure water gradient profiles within Nafion(R) in an operating PEFC. Preliminary neutron intensity gradients show qualitative agreement with the expected response of membrane water content to changes in feed gas humidification and fuel cell current. Previous experimental mea surements of similar water gradients have generally relied on "integral" me asurements such as ac impedance spectroscopy which cannot probe details of the gradient within the membrane. This is one of the first "differential" m easurements of water gradients within Nafion. (C) 1999 The Electrochemical Society. S0013-4651(98)10-004-6. All rights reserved.