Patent ID: 7482403

Claim:
A fuel-cell, including a plurality of polymer electrolyte fuel-cell separators used in a stack, at least one side edge of each separator being sealed with a cured product of a sealing material comprising in parts by weight as essential components: (A) 100 parts of an organopolysiloxane containing at least two alkenyl groups each attached to a silicon atom in a molecule, (B) 5 to 50 parts of a resinous copolymer consisting of (R) 3 SiO 1/2 units and SiO 2 units, or of (R) 3 SiO 1/2 units and SiO 2 units and (R) 2 SiO 2/2 units, or of (R) 3 SiO 1/2 units and SiO 2 units and RSiO 3/2 units, or of (R) 3 SiO 1/2 units and SiO 2 units and (R) 2 SiO 2/2 units and RSiO 3/2 units, in a molar ratio of (R) 3 SiO 1/2 units to SiO 2 units [(R) 3 SiO 1/2 /SiO 2 ] of 0.5:1 to 1.5:1, (R) 2 SiO 2/2 units and RSiO 3/2 units being contained in a total amount of up to 50 mol % based on the entire molecule, wherein R is a substituted or unsubstituted monovalent hydrocarbon group, and containing 5×10 −3 to 1×10 −4 mol/g of vinyl groups, (C) 0.5 to 20 parts, per 100 parts of components (A) and (B) combined, of an organohydrogenpolysiloxane containing at least two hydrogen atoms each attached to a silicon atom in a molecule, (D) 10 to 30 parts, per 100 parts of components (A) and (B) combined, of fumed silica having a specific surface area of 150 to 400 m 2 /g, and (E) a catalytic amount of an addition reaction catalyst, wherein said cured product has a compression set of 32.2% or less measured under the conditions of 120° C.×500 hours in 0.01 N sulfuric acid solution and has improved acid resistance as indicated by a weight loss of 2.8% or less measured by immersing a specimen having the dimensions 3 mm×3 mm×1 mm in a 10% sulfuric acid solution at 100° C. for 500 hours.