A fuel cell is formed by stacking first cell units and second cell units alternately. The panel includes a sandwich blank having outer layers of solid consistency, and at least one supple inner layer with a lightweight, possibly \u201choneycomb\u201d or supple foam material, structure. The I-O panel comprises an array of I-O panel connectors and defines an xy-plane. In one embodiment, the adhesive is a layer of material that is adhesive on both surfaces thereof, one of which has the releasable liner thereon.