Abstract: A high-temperature polymer electrolyte membrane fuel cell stack has at least two high-temperature polymer electrolyte membrane fuel cells (HT-PEFC), which comprise at least one means for determining the CO2 concentration of the cathode waste gas. A method for checking this fuel cell stack is thus possible, wherein at least the CO2 concentration of the cathode waste gas is determined. Optionally, the CO2 concentration of the oxidizing agent that is supplied can also be determined. The CO2 concentration is advantageously conducted in the region of individual cells or cell sections. This can be done, for example, by way of a displaceable lance in the cathode waste gas channel or a plurality of outlets (valves) in the cathode waste gas channel. If a threshold value defining the normal state of functional individual cells is exceeded, appropriate measures can be initiated, such as switching off the entire stack and optionally replacing cells or cell blocks.

Abstract: In low-temperature fuel cells according to prior art, the problem often arises that the diffusion layer of the cathode is filled by water which is permeated or produced on the cathode, such that oxygen can no longer be transported to the catalyst layer of the cathode in a frictionless manner. As a result, said fuel cells are regularly used with a high excess of oxygen in order to reduce the cited transport problems for the oxygen. The inventive fuel cell enables said problem to be solved in that the arrangement of the diffusion layer and the catalyst layer of the cathode is inverted. The diffusion layer, which is embodied in such a way as to also conduct ions, is directly adjacent to the electrolyte membrane. The catalyst layer oriented towards the free cathode space can advantageously directly react with the supplied oxygen without further transport problems.

Abstract: The invention relates to a low-temperature fuel cell stack comprising a specific device for the supply of fuel. Said low-temperature fuel cell stack is characterised in that, in addition to the central fuel supply device, it comprises a supply or storage device for a liquid fuel, and a plurality of separately controllable dosing devices that lead into the central fuel supply device, especially respectively upstream of a distribution channel to the individual cells. Controllable valves, controllable piezoelectric pumps or thermally controllable supply elements are suitable as dosing devices. The invention also relates to a method for operating one such low-temperature fuel cell stack, which advantageously enables a defined concentration of fuel, or a defined humidity of the oxidation medium, to be adjusted at certain points in the fuel cell stack, especially on the inlet for the individual cells.

Abstract: The invention relates to a fuel cell stack in which, according to the invention, several elements of the fuel cell stack are advantageously sealed by a seal in order to form a continuous operating material channel. The inventive fuel cell stack can be provided with a very compact design, whereby the layer thickness of an individual fuel cell is, on a regular basis, distinctly less than 1.5 mm and, advantageously, even less than 1.2 mm.

Abstract: In low-temperature fuel cells according to prior art, the problem often arises that the diffusion layer of the cathode is filled by water which is permeated or produced on the cathode, such that oxygen can no longer be transported to the catalyst layer of the cathode in a frictionless manner. As a result, said fuel cells are regularly used with a high excess of oxygen in order to reduce the cited transport problems for the oxygen. The inventive fuel cell enables said problem to be solved in that the arrangement of the diffusion layer and the catalyst layer of the cathode is inverted. The diffusion layer, which is embodied in such a way as to also conduct ions, is directly adjacent to the electrolyte membrane. The catalyst layer oriented towards the free cathode space can advantageously directly react with the supplied oxygen without further transport problems.

Abstract: In a direct-methanol fuel cell stack with an at least partial circulation (7, 9) of the fuel, according to the invention a means is arranged in this circulation for reducing the concentration of an undesired byproduct. This means is comprised especially of a further electrochemical cell (8) to which electric current is applied and which at least partly transforms the byproducts by an electrochemical reduction reaction again to methanol and water. Since the concentration of byproducts is small, the loss in electric current required for the additional reduction reaction has no noticeable effect on the efficiency of the fuel cell stack.

Abstract: The invention relates to a device for cleaning waste gases for a direct alcohol fuel cell or for a direct alcohol fuel cell stack, comprising at least one supply line for supplying an oxidizing agent into a cathode space of a fuel cell and at least one evacuation line for evacuating waste gas out of a fuel cell. The supply line and evacuation line are arranged next to one another at least in one area and are separated by a porous layer. A catalytic converter is placed on the surface of the porous layer oriented toward the evacuation line. In the inventive waste gas cleaning device, the advantages of an internal utilization of heat and of an at least partial water circuit with an effective catalytic conversion and reduction of removed non-converted alcohol, particularly methanol, locally unite at one location of the fuel cell system. The waste gas cleaning device simultaneously serves to preheat and wet the supplied oxidizing agent and can be advantageously provided with a very compact design.

Abstract: In a direct-methanol fuel cell stack with an at least partial circulation (7, 9) of the fuel, according to the invention a means is arranged in this circulation for reducing the concentration of an undesired byproduct. This means is comprised especially of a further electrochemical cell (8) to which electric current is applied and which at least partly transforms the byproducts by an electrochemical reduction reaction again to methanol and water. Since the concentration of byproducts is small, the loss in electric current required for the additional reduction reaction has no noticeable effect on the efficiency of the fuel cell stack.

Abstract: The invention relates to a fuel cell stack in which, according to the invention, several elements of the fuel cell stack are advantageously sealed by a seal in order to form a continuous operating material channel. The inventive fuel cell stack can be provided with a very compact design, whereby the layer thickness of an individual fuel cell is, on a regular basis, distinctly less than 1.5 mm and, advantageously, even less than 1.2 mm.

Abstract: The invention relates to a device for producing and simulating two-phase flows. The device is at least partially transparent, thereby allowing observation of the interior of the device. Two-phase flows, such as occur for example in fuel cells, heat exchangers or other chemical or electrochemical reactors can be easily simulated if such a device forms part of a fuel cell, a heat exchanger or another reactor. The invention further relates to a method for producing and simulating two-phase flows in an electrochemical or chemical reactor, such as fuel cells, comprising the following steps: introducing a gas-emitting solution into an at least partially transparent device that comprises means for producing two-phase flows, and producing and recording the two-phase flow.

Abstract: The invention relates to a bipolar plate for application in a fuel cell, comprising a channel forming structure. The bipolar plate further comprises, at least partly, a porous region, which borders a formed channel. According to the invention, in a fuel cell with the above bipolar plate, an improved distribution of the operating material under differing load conditions (high and low throughflow) with reduced pressure loss is made possible by means of the combination of channels and open pores within the porous region. The above regularly leads to an improved efficiency for the fuel cell.

Abstract: An electrode-electrolyte unit for a fuel cell which prevents the permeation of the fuel used or the permeation of water through the electrolyte layer. An electrolyte is subdivided into two electrolyte layers with a barrier layer disposed between them. The barrier layer is permeable only to protons and may be coated with a catalytically active porous layer having a high effective surface area. A porous layer on the side of the unit facing the cathode increases the electrochemically active surface area and a porous layer on the side of the unit facing the anode ensures that a sufficient amount of hydrogen is dissolved. The fuel used can be hydrogen or methanol and suitable electrolytes include membranes or other solid or liquid electrolytes.

Abstract: In a fuel cell arrangement with at least one fuel cell operated by a fuel and an oxidizing agent, means are provided for effecting gravity driven circulation of the fuel and the oxidizing agent through the fuel cell so that no pumping means, which consume power and need servicing, are required.