NOVELTY - Fabricating a fuel cell comprises positioning a mold cavity to be in fluid communication with a membrane electrode assembly (36) comprising a gas diffusion layer. A curable liquid sealant composition is applied into cavity and cured at less than or equal to130degreesC or at room temperature by providing actinic radiation. The composition comprises an alkenyl terminated polyisobutylene oligomer, a polyfunctional alkenyl monomer, a silyl hardener having greater than or equal to2 silicon hydride functional groups, and a hydrosilylation catalyst; or a radiation-curable acrylate, urethane, polyether, polyolefin, polyester, or their copolymers.    USE - For fabricating a fuel cell.    ADVANTAGE - The hydrocarbon sealant material is stable for long times in the aggressive acidic and thermal conditions of a fuel cell. It provides the necessary sensitivity to organic contaminants and the necessary impregnation to the gas diffusion layers to prevent electrical shorting once assembled in the fuel cell. The hydrocarbon sealant material is not costly and does not need to be cured above the degradation temperature of the proton exchange membrane.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a fuel cell fabrication system comprising two mold halves and an actinic radiation source; and    (2) a membrane electrode assembly having a cured sealant composition over peripheral portions of the assembly.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of a fuel cell having an anode flow field plate, a gas diffusion layer, an anode catalyst, a proton exchange membrane, a cathode catalyst, a second gas diffusion layer, and a cathode flow field plate.    Anode flow field plate (12)    Resin plate (13)    Open face coolant channels (14, 30)    Anode flow channel (16)    Gas diffusion layer (18, 26)    Anode catalyst (20)    Proton exchange membrane (22)    Cathode catalyst (24)    Cathode flow field plate (28)    Cathode flow channel (32)    Anode (34)    Membrane electrode assembly (36)    Cathode (38)