NOVELTY - A proton exchange membrane fuel cell power system comprises many discrete self-humidifying proton exchange membrane (150) fuel cell modules (100), each having a cathode air flow which removes the bulk of the heat energy produced.    USE - As a proton exchange membrane fuel cell power system (claimed)    ADVANTAGE - The system is modularized, simple, efficient and easy to maintain in that inoperable modules can readily be removed. The modules are self-humidifying and heat removal and capture are effective.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (a) a system as above comprising at least two membrane electrode diffusion assemblies each having opposite anode and cathode sides with current collectors in ohmic contact and individual force application assemblies for applying a given force to each pair of collectors and assemblies;    (b) a system as above comprising many modules as above, each having a hydrogen distribution frame defining discrete, opposed cavities in which the assembly with opposite anode and cathode sides is sealably mounted, current collectors, a pressure transfer assembly in each cavity and a cathode cover mating with the frame and partly occluded in relation to each cavity;    (c) a system as above with a passageway delivering hydrogen to each cavity and one removing impurities, water and unreacted hydrogen, a third passageway for air delivery to each cavity and the cathode side and a biasing assembly between the cathode covers and pressure assembly to realize a force of at least 175 psi between the diffusion assembly and current collectors;    (d) a power system housing comprising an enclosure defining a cavity in which is mounted a subrack supporting many oriented fuel cell modules;    (e) a cavity as above having a hydrogen distribution assembly and an air distribution assembly;    (f) a housing as above in which the modules produce dc voltage and the air distribution assembly includes a plenum and intake and exhaust ends, an air mixing valve for flow control and an a dc -to-ac inverter;    (g) a module as above which is self-humidifying and the cathode air flow removes most of the heat energy;    (h) a module as above comprising a solid proton-conducting electrolytic membrane and individual catalytic anode and cathode electrodes in ionic contact with the electrolyte and carrying a conductive diffusion layer;    (i) a module as above in which the electrolyte membrane has a concentration of at least 20 mol % of sulfonic acid;    (j) a module as above in which the conductive diffusion layer above is non-catalytic and comprises two diffusion layers of variable porosity;    (k) an assembly as above in which the first diffusion layer has a hydrophobic gradient and the second has a variable porosity and a thermoplastic binder binds the diffusion layer to the electrodes;    (l) an electrolytic membrane comprising crosslinked polymeric chains incorporating sulfonic acid groups or crosslinked copolymeric chains comprising methacrylate and a crosslinking agent;    (m) an electrolytic membrane comprising 35-50 molar % of methacrylate, 30-50% acrylate 25-45 % sulfonic acid and 5-20 % of a compatible crosslinking agent and additionally plasticizer;    (n) an electrolyte membrane comprising 10-50 mol % of copolymer having monomer units selected from poly(ethylene/propylene glycol) methacrylate or methyl/ethyl ether methacrylate, hydroxypropyl/2-hydroxyethyl methacrylate and 4-hydroxybutyl acrylate; 25-45% of 3-alkyloxy-2-hydroxy-1-propanesulfonic acid, 4-styrenesulfonic acid, vinylsulfonic acid or sulfacrylates or fluorinated derivatives, 5-20 % of (di)ethlyene or trimethylene glycol divinyl ether or dimethacrylates, diallyloxy-acetic acid or allyl methacrylate, a plasticizer and an insulating support matrix of minimum porosity;    (o) a current collector comprising a base conductive substrate and a contact layer which is galvanically cathodic, conductive and oxygen stable;    (p) a method of forming a diffusion layer for the above comprising providing a carbon backing layer of cloth, paper or sponge, applying a hydrophobic polymer and sintering above the melting point of the polymer;    (q) a method for the above comprising applying a slurry of carbon, binding resin and delivery fluid to the backing layer; and    (r) a method of forming a diffusion layer as above in which the coating has a hydrophobic gradient and comprises 20-90 weight % of carbon particles, removing the delivery fluid, sintering, applying pressure to vary the porosity and applying a thermoplastic binding emulsion.    DESCRIPTION OF DRAWING(S) - An exploded view of a fuel cell module is shown.    Discrete module (100)    Membrane electrode assembly (150)    Electrodes (153,154)    Current collectors (190)