A process for manufacturing a gas diffusion device includes providing a superposition of a composite layer and of an electrically conductive element, the composite layer including electrically conductive fibers and a polymerizable resin impregnating the conductive fibers, and the electrically conductive element having an open porosity between a first face and a second face. The process also includes compressing the superposition of the composite layer and of the conductive element so as to bring said conductive fibers into contact with the first face of the element, so as to make said resin flow into said element without the resin impregnating all the volume of said conductive element; and polymerizing the resin.