NOVELTY - A fuel cell stack (50) comprises microfuel cell units having a microelectric conductive tube defining an inner axial flow path, and a fuel cell module (20) including an electric conductive planar sheet (21).    USE - Used for e.g. portable or wireless electronics devices such as consumer electronics, micro sensors, and microelectromechanical or microfluidic systems; and micro aero vehicles.    ADVANTAGE - The fuel cell stack operates at a lower current density with much improved energy efficiency without materially increasing the size/weight of the stack.    DETAILED DESCRIPTION - A fuel cell stack comprises micro fuel cell units having a micro electric conductive tube defining an inner axial flow path, the tube including a porous section, an inner electrode coaxially around and in intimidate contact with the peripheral surface of the porous section, a solid electrolyte member coaxially around and in intimate contact with the inner electrode, and an outer electrode coaxially around and in intimate contact with the electrolyte, the inner electrode, electrolyte and outer electrode defining a reactive zone and covering the peripheral surface of the porous section of the micro tube. The fuel cell stack comprises a fuel cell module including an electric conductive planar sheet, and the micro fuel cell units are laid side by side on the electric conductive planar sheet in a parallel arrangement, with the inner electrodes of the fuel cell units electrically interconnected and isolated from the conductive sheet. The fuel cell modules are stacked one over another with an electrical insulating material being sandwiched between the outer electrodes of the fuel cell units of a first module and a second module's conductive planar sheet overlying the outer electrodes of the first module, and where the stacked fuel cell modules being electrically connected in series.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic perspective illustration of the fuel cell stack.    Fuel cell module (20)    Electric conductive planar sheet (21)    Fuel cell stack (50)    Fuel stream (53)    Spaces (55)