NOVELTY - A curable composition for sealing fuel cell components, comprises polymerizable oligomer selected from e.g. branched polyisobutylene and alkenyl terminated hydrocarbon oligomer; polyfunctional alkenyl monomer; silyl hardener having at least two silicon hydride functional groups; hydrosilylation catalyst; and a peroxide initiating or crosslinking agent.    USE - For sealing fuel cell components e.g. membrane electrode assembly of electrochemical cell such as fuel cell (claimed) e.g. proton exchange membrane (PEM) fuel cell useful for producing electricity from chemical sources.    ADVANTAGE - The nonconductive sealant penetrates the gas diffusion layers to prevent electrical shorting within the fuel cell. The molding process provides membrane electrode assembly with an edge seal, which can be easily handled. The composition improves adhesion to seal the membrane electrode assembly, and prevents gas diffusion layers from touching, which results in a short circuit. The curable composition provides one-step sealing process that reduces the assembly time and number of seals in the fuel cell stack. The compostion reduces the viscosity of alkenyl functional polyisobutylene resins; increases peak exotherm of the reaction from 96-137degreesC; allows use of higher concentration of platinum catalyst; and has ability to manufacture compositions without gelling. The composition improves stability using moieties that cross-link into polymer network thus reducing diffusion or extraction of species in fuel cell.    DETAILED DESCRIPTION - A curable composition (140) for sealing fuel cell components, comprises a polymerizable oligomer; polyfunctional alkenyl monomer; silyl hardener having at least two silicon hydride functional groups; hydrosilylation catalyst; and a peroxide initiating or crosslinking agent. The polymerizable oligomer is selected from branched polyisobutylene oligomer backbone, linear or branched polyisobutylene having pendent alkenyl or other functional groups with the terminal ends being free of alkenyl or allyl groups, alkenyl terminated hydrocarbon oligomer having a branched oligomer backbone, co-polymer of polyisobutylene and another monomer or polymer, linear or branched polyisobutylene polymer or co-polymer composition having terminal or pendent silicon-methyl (Si-CH3) groups, a linear or branched polyisobutylene polymer or copolymer composition having terminal cycloaliphatic epoxide end groups, a linear or branched polyisobutylene polymer and/or co-polymer composition having terminal vinyl ether end groups. The curable sealant composition comprises actinic a radiation curable material selected from (meth) acrylate, urethane, polyether, polyolefin, polyester and/or their copolymers. The curable sealant composition comprises a telechelic-functional polyisobutylene, a silyl crosslinker having at least about two silicon hydride functional groups, a platinum catalyst and a photoinitiator. INDEPENDENT CLAIMS are included for the following:    (1) formation of a fuel cell involving providing a fuel cell component; positioning a mold so that cavity is in fluid communication with the fuel cell component; applying the curable liquid sealant composition into the cavity; and thermally curing the sealant at less than or equal to 130degreesC;    (2) a system for forming a fuel cell comprising two mold members having opposed mating surfaces, and a source of actinic radiation;    (3) a membrane electrode assembly having the cured sealant composition disposed over peripheral portions of the assembly;    (4) formation of fuel cell component involving providing a two-part sealant comprising polymerizable material; applying the first part of the sealant to a substrate of a first fuel cell component; applying the second part of the sealant to a substrate of a second fuel cell component; aligning the substrates of the fuel cell components; and curing the sealant;    (5) a system for forming a fuel cell component comprising first and second dispensers for providing first and second parts of a two-part sealant; first and second stations for applying first and second parts of the sealant to a substrate; a third station for aligning the substrates of the first and second fuel cell components; and a curing station for curing the sealant;    (6) an electrochemical cell comprising a first electrochemical cell component having a mating surface; the cured sealant composition disposed over the mating surface of the first electrochemical cell component; and a second electrochemical cell component.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of the fuel cell having the sealant composition disposed between membrane electrode assembly and flow field plates of the fuel cell.    fuel assembly (110')    anode flow field plate (112)    gas diffusion layer (118)    anode catalyst (120)    cathode field plate (128)    curable composition. (140)