Patent ID: 7931996

Claim:
A method of operating a fuel cell ( 40 ) for producing electricity from reducing fluid and oxygen containing oxidant reactant streams flowing through the fuel cell ( 40 ), comprising the steps of: a. providing a first catalyst ( 12 ′) and a second catalyst ( 14 ′) secured to opposed surfaces of an electrolyte ( 16 ′); b. defining a first flow field ( 26 ′) secured in fluid communication with the first catalyst ( 12 ′), the first flow field ( 26 ′) defining a plurality of flow channels ( 30 A′, 30 B′, 30 C′, 30 D′) between a plurality of ribs ( 32 A′, 32 B′, 32 C′, 32 D′, 32 E′) of the first flow field ( 26 ′); c. providing a backing layer ( 42 ) secured between and in fluid communication with the first flow field ( 26 ′) and the first catalyst ( 12 ′); d. preventing the backing layer ( 42 ) from deforming into the flow channels ( 30 A′, 30 B′, 30 C′, 30 D′) during operation of the fuel cell ( 40 ) by the backing layer ( 42 ) including; i. between 5 wt % and 25 wt % carbon black; ii. between 50 wt % and 90 wt % carbon fibers ( 44 ), where the carbon fibers ( 44 ) have a length that is at least twice as long as a width ( 46 ) of a widest flow channel ( 30 ′D), wherein the width ( 46 ) of the widest flow channel ( 30 ′D) is a shortest distance between flow field ribs ( 32 D′, 32 E′) defining the widest flow channel ( 30 D′) of the first flow field ( 26 ′); iii. between 5 wt % and 25 wt % of a hydrophobic polymer; and, iv. the carbon fibers ( 44 ) being randomly dispersed with the carbon black and hydrophobic polymer so that the resulting backing layer ( 42 ) has a thickness between the first catalyst ( 12 ′) and the first flow field ( 26 ′) of between about 25 and 250 microns, and a compressive strength greater than 5 kgf/cm 2 .