The invention provides for reducing the number of parts and the number of interfaces found in certain types of chemical reactors, particularly in electrochemical reactors, and especially in the type or reactor known as a fuel cell or fuel cell stack This reduction comes from the use of a unified structure that combines the functions normally carried out by several components in the unit, particularly by combining the functions of the gas distribution structure and the gas diffusion structure, the gas distribution structure and the gas barrier structure, or all three structures into a single, unitary, metallic part. This offers the advantages of simplified design, better performance, and lighter weight.