NOVELTY - A device comprises at least one electrochemical conversion cell including a membrane electrode assembly having a polymer electrolyte membrane (24). A gas crossover barrier material (26) is bonded to the polymer electrolyte membrane along a majority of its peripheral edge portion. Interior region (28) of the electrolyte membrane has a relatively low amount of the gas crossover barrier material.    USE - As an electrochemical conversion cell containing the device useful in e.g. automobiles.    ADVANTAGE - The gas crossover barrier material has a material having sufficient viscosity when uncured to enhance penetration prior to curing. The gas crossover barrier material is bonded to the polymer electrolyte membrane in a manner that introduces a negligible increase (0.33 mm) in a thickness dimension (less than 0.35 mm) of the peripheral edge portion of the membrane. The increase in the thickness is not greater than 5%, of the thickness dimension of peripheral edge portion of the membrane. The gas crossover barrier material is selected and configured such that it introduces negligible changes in the compressibility of the membrane; and has sufficient viscosity when uncured to penetrate a thickness dimension of the polymer electrolyte membrane. The gas crossover barrier material exhibits cross-linking upon curing; and cures at a temperature below the operating temperature of the electrochemical conversion cell. The gas crossover barrier materials may be a one-part, flowable material of sufficient viscosity to penetrate the membrane material; may be presented as a solvent-free material that cures at or near room temperature. The barrier material exhibits good adhesion to the particular membrane materials in use; and stability and structural flexibility over a wide temperature range, or operating temperature range of the device in which it is to be incorporated. The barrier material exhibits good dielectric properties.    DETAILED DESCRIPTION - A device comprises at least one electrochemical conversion cell (10) configured to convert first and second reactants to electrical energy. The electrochemical conversion cell includes a membrane electrode assembly (20) defining a partition between first (30) and second (40) reactant supplies and comprising a polymer electrolyte membrane (24) configured to conduct protons. The polymer electrolyte membrane defines a peripheral edge portion along the perimeter of the membrane and an interior region (28) bounded by the peripheral edge portion. A gas crossover barrier material (26) is bonded to the polymer electrolyte membrane along a majority of the peripheral edge portion. The interior region of the membrane has a relatively low amount of the gas crossover barrier material. The device further comprises a first catalytic electrode formed on a first surface of the polymer electrolyte membrane in communication with first reactant supply; and a second catalytic electrode formed on a second surface of the polymer electrolyte membrane in communication with second reactant supply.    An INDEPENDENT CLAIM is included for the production of the above device involving providing the polymer electrolyte membrane; bonding a gas crossover barrier material to the polymer electrolyte membrane through a silk screening process, where interior region of the membrane has a relatively low amount of gas crossover barrier material; and assembling electrochemical conversion cell including the polymer electrolyte membrane.    DESCRIPTION OF DRAWING(S) - The figure shows an exploded view of the electrochemical conversion cell.    electrochemical conversion cell (10)    membrane electrode assembly (20)    polymer electrolyte membrane (24)    gas crossover barrier material (26)    interior region (28)    first reactant supply (30)    second reactant supply. (40)