NOVELTY - The polymer layer (1) or second layers (3) are corrugated, folded or embossed to form the gas channels (4). Note: both the electrode (2, e.g. carbon fiber) and the second sheet (3, metal sheet) are conductive and connected.    USE - A fuel cell, e.g. for mobile applications, with high power to weight and volume ratio.    ADVANTAGE - The design achieves greater technical simplicity and more economical construction than prior art. Structuring of layers increases active area available. Per unit of volume, power density is increased. Power to weight ratio is also increased. These are key advantages for mobile use. The structure also improves functional reliability over earlier types. Excellent exchange of mass and heat is achieved by the channels formed. Downward gas flow assists clearance of water produced in appropriate channels. Adjacent channels are well sealed from each other, due to the compressible layers. Further physical and electrical specifications appear in the disclosure text. Commercially-available materials and practical examples are discussed. Voltage/current graphs are provided in terms of fleece material selections.    DETAILED DESCRIPTION - Preferred features: The first layer is a porous weave, knit or fleece of short or continuous fibers. Its pores are impregnated to the point of saturation with electrolyte, to which it is inert both chemically and physically, up to 200 degrees C. As fleece, it comprises microfibers, film fibrils or microfilaments. The first layer has mean pore radius of 20 nm -10 micrometers. It has a weight of 20-200 grams per square meter and a thickness when saturated with electrolyte, of up to 1 mm. The mean pore radius is 0.1 - 10 micrometers and pore volume is 65%-92%. The first sheet (1) is lined between the electrodes (2). Electrodes and first layer are adhered together in plane regions with spacing. Electrode weight is 20-100 grams per square meter, at a thickness less than 0.5 mm. The second layer (3) is metal sheet. Channels are operated in counterflow. Channel (4) ends open into the casing with comb-like interpenetrating projections, the corrugated, folded or embossed layer resting in sealing contact.    DESCRIPTION OF DRAWING(S) - The internal corrugated structure is illustrated in cross section, in a perspective view of the assembly.    first polymer layer (1)    electrode layer (2)    second plane metal sheet layers (3)    gas channels (4)