NOVELTY - A fuel cell device comprises at least one electrochemical conversion cell (10) to convert first reactant (e.g. hydrogenous gas) and second reactant (e.g. oxygen) to electrical energy, comprising a membrane electrode assembly (20) and at least one membrane reinforcement layer (50). The membrane reinforcement layer defines an elastic modulus (Er) and a thickness (hr) and is bonded to at least one side of the membrane electrode assembly along a dimension parallel to the longitudinal component of the operational stress.    USE - For generating electric power for vehicle.    ADVANTAGE - The combination of elastic modulus and thickness of the reinforcement layer and the bond between the reinforcement layer and the membrane electrode assembly are sufficient to enhance the structural integrity of the membrane electrode assembly beyond the operational degradation threshold of the assembly. The reactant gas crossover leak can be reduced by reducing crack driving force and crack open area associated with mechanical stresses induced during thermal and hydro cycling in the cell.    DETAILED DESCRIPTION - A fuel cell device comprises at least one electrochemical conversion cell to convert first reactant (e.g. hydrogenous gas) and second reactant (e.g. oxygen) to electrical energy, comprising a membrane electrode assembly and at least one membrane reinforcement layer. The membrane electrode assembly is subject to a degree of operational stress during operation of the electrochemical conversion cell. The operational stress has a longitudinal component oriented along a major planar dimension of the membrane electrode assembly. The membrane electrode assembly defines a fracture toughness that is insufficient to preserve the structural integrity of the membrane electrode assembly beyond a given operational degradation threshold under the longitudinal component of the operational stress. The membrane reinforcement layer defines an elastic modulus (Er) and a thickness (hr) and is bonded to at least one side of the membrane electrode assembly along a dimension parallel to the longitudinal component of the operational stress. The elastic modulus Er and the thickness hr of the reinforcement layer and the bond between the reinforcement layer and the membrane electrode assembly are sufficient to enhance the structural integrity of the membrane electrode assembly beyond the operational degradation threshold. The membrane reinforcement layer comprises an electrically conductive material. The electrochemical conversion cell comprises gaseous diffusion media layers (32, 42) interposed between sources of the reactants and the membrane electrode assembly.    DESCRIPTION OF DRAWING(S) - The figure is an exploded illustration of an electrochemical conversion cell.    Electrochemical conversion cell (10)    Membrane electrode assembly (20)    Gaseous diffusion media layers (32, 42)    Flow field plates (34, 44)    Membrane reinforcement layer (50)