During operation of the solid polymer fuel cell (SPFC). its performance is limited by
the concentrations of hydrogen and oxygen at the reaction interfaces and in most
SPFC designs, the hydration state of the membrane. Since in general, the
concentrations of water and the gaseous species vary along the flow channel, the
performance is also likely to change along the flow channel. In order to study this
phenomenon, a measurement system was developed to map the current distribution
across the electrode surface.
The current distribution has been measured by dividing one of the current collectors
into a number of electrically isolated segments. The current flowing through each of
the segments was measured while maintaining a constant potential across the surface
of the gas diffusion layer. Two separate segmented current collectors were developed.
The first was used to measure the current distribution for an 80 cm2 single cell, and
the second was used to investigate the local current densities around a single flow
The effects of the feed gas humidities on the spatial current density in the 80 cm2 fuel
cell were investigated for two different membrane-electrode configurations. With
Nafion 117 as electrolyte and at a cell temperature of 80·C. the membrane was found
to dehydrate in the initial portion of the gas flow channel when the relative humidity
of both the hydrogen and oxygen feed gases was less than 50%. With a Gore-Select
membrane electrode assembly (hydrogen and air. temperature- 60·C). the membrane
was sufficiently hydrated at all feed gas humidification conditions. The performance
of the cell was found to deteriorate at higher feed gas humidities as a result of the
lower partial pressures of the reactant gases.
Measurements of the effects of gas pressures, stoichiometries and humidities on the
length-wise and width-wise perfonnance around a single flow channel (Gore-Select
membrane electrode assembly) are discussed in relation to a gas flow model.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.