Abstract: Mechanical stresses of the membrane of a fuel cell can be reduced by virtue of the fact that the supply of feed gas to a gas chamber of the fuel cell takes places, initially, by means of a first pressure increasing speed and then by means of a second pressure increasing speed. The first pressure increasing speed is slower than the second pressure increasing speed. Pressure surges are prevented in the membrane due to the lower pressure increasing speed in the first phase of the gas supply, and as a result, the life span of the membrane is increased.

Abstract: During the operation of a fuel-cell assembly, the latter is supplied with ambient air with the aid of a liquid ring pump. Any foreign matter that is contained in the air is taken up by the service fluid of the liquid ring pump. The charging of the service fluid with foreign matter is controlled. In particular, the service fluid is continuously conducted in an circuit via a purification device.

Abstract: Disclosed is a fuel cell system comprising a fuel cell stack, supplied with a reaction gas on the gas inlet side and comprises at least one flush valve on the gas outlet side on a flush cell. A control device, which controls the actuation of the flush valve as a function of the voltage of the flush cell, is provided, wherein the voltage tap is provided in a region of the flush cell at which the concentration of the reaction gas drops the fastest to a predefined threshold value. Due to the voltage tap in the region where the concentration of the reaction gases drop the fastest to a predefined threshold value, a significantly more sensitive and precise regulation of the flush is possible and voltage dips are effectively prevented in the flush cell, as a result of which the overall risk of corrosion are minimized for the flush cell.

Abstract: Mechanical stresses of the membrane of a fuel cell can be reduced by virtue of the fact that the supply of feed gas to a gas chamber of the fuel cell takes places, initially, by means of a first pressure increasing speed and then by means of a second pressure increasing speed. The first pressure increasing speed is slower than the second pressure increasing speed. Pressure surges are prevented in the membrane due to the lower pressure increasing speed in the first phase of the gas supply, and as a result, the life span of the membrane is increased.

Abstract: The invention relates to a fuel cell system comprising a fuel cell stack whereon the reaction gas can be guided to the gas inlet slide and which comprises at least one flush valve, which is arranged on the gas outlet side, on a flush cell. A control device, which controls the actuation of the flush valve according to the voltage of the flush cell, is provided. The voltage tap is carried out in the region of the gas outlet towards the flush valve, in particular on a bipolar plate. Significantly sensitive and precise control is obtained by means of the lower voltage tap compared to a higher voltage tap and voltage dips are actively prevented in the flush cell, which enables the total risk of corrosion the maintained at a minimum for the bipolar metal plate.

Abstract: During the operation of a fuel-cell assembly, the latter is supplied with ambient air with the aid of a liquid ring pump. Any foreign matter that is contained in the air is taken up by the service fluid of the liquid ring pump. The charging of the service fluid with foreign matter is controlled. In particular, the service fluid is continuously conducted in an circuit via a purification device.

Abstract: A method is for detecting a gas leak between the anode gas region and the cathode gas region of a PEM fuel cell. According to the method, a) the fuel cell is charged with a direct current, and b) the temporal course of the electrical voltage on the fuel cell is measured. Using only a small amount of equipment, a leak test can be carried out on a fuel cell stack. The test is highly sensitive even to extremely small leaks, but can also be used for large leaks, and indicates the exact position of defective fuel cells within the fuel cell.

Abstract: The air supplied to a fuel cell module is pumped with a compressor that has a moisturizing function in order to provide sufficiently moisturized oxidant. The compressor operates at very low pressure and the moisturization corresponds approximately to the dew point at the cooling water outlet temperature. If adequate moisturizing of the oxidant is no longer occurring at the defined low pressure, the input pressure is increased and the oxidant output is choked in a regulated manner. A corresponding fuel cell assembly with a polymer electrolyte membrane, i.e., a PEM fuel cell system includes the corresponding pump compressor and a controlled throttle valve at the exit side.

Abstract: Undetected gas leaks in a fuel cell can lead to a fire inside the fuel cell and thus to the destruction of the fuel cell. A method is for localizing a gas leak inside a fuel cell system including a number of fuel cells. After supplying the fuel cells with the fuel gases, the fuel gas supply to at least one of the two gas chambers of the fuel cells is interrupted. The gas chamber which is separated from the fuel gas supply is rinsed with an inert gas. The fuel cells are brought into electrical contact with a discharging resistor or are already in contact therewith, and the cell voltage of the fuel cells is monitored.

Abstract: A method for operating a fuel cell system which uses a combustion gas and an oxidant, must take care to ensure sufficient humidification of the combustion gas by evaporating humidifying water. The energy source for the evaporation of the combustion gas and/or oxidant is the heat generated by the coil temperature of an electric motor used to transport the gas.

Abstract: The invention relates to a method for operating a fuel cell arrangement and to a fuel cell arrangement for carrying out the method. A fuel cell arrangement (1) comprising a number of fuel cells that are located in a protective housing (4) is to be operated with a high degree of operating reliability and a particularly long service life. To this end, at least a proportion of the gas that is located in the inner area (6) enclosed by the protective housing (4) is guided out of the inner area (6) and replaced with fresh gas.

Abstract: A method for starting a mobile fuel cell system, in particular for a vehicle, includes conveying air to be supplied to the system during starting and operation of the system by a motor-powered compressor, in order to ensure a necessary operating pressure and, if required, additional humidifying of the air. A motor drive for the compressor has an electric motor which is supplied from a mobile starter battery during a starting phase. An output voltage of the starter battery is different from an operating voltage at an output of a fuel cell stack of the fuel cell system. A control device is provided between an output of the starter battery or of the fuel cell stack and a motor input. The control device interrupts the starting voltage supplied from the output of the starter battery and switches over to the output voltage of the fuel cell stack when the output operating voltage of the fuel cell stack reaches an adequate level. A fuel cell system is also provided.

Abstract: In a method and an apparatus for monitoring a selected group of fuel cells of a high-temperature fuel cell stack, a change over time in an averaged electrical voltage of the fuel cells of the selected group is ascertained and compared with a reference value that detects at least a change over time in a voltage of other fuel cells. The method permits a reliable detection of the failure of one fuel cell of a stack with simple measures.

Abstract: A fuel cell system having a fuel cell block is operated by compressing an operating agent for the fuel cell block with a liquid ring compressor. After compressing the operating agent, water is separated from the operating agent in an apparatus for water separation. The fuel cell block is cooled with the water and, after the cooling, at least a portion of the water is fed back into the apparatus for water separation. This measure reduces the number of components which form the fuel cell system.

Abstract: A process for operating a PEM fuel cell unit containing at least one PEM fuel cell block and a speed-controlled compressor connected upstream. To control changing an electrical current I of the PEM fuel cell block to a new reference value I.sub.SN, a speed n of the compressor is set in a first step to a maximum value n.sub.M and in a second step is reduced to a speed n.sub.SN corresponding to the new reference value I.sub.SN. By this expedient improved dynamics for brief and rapid load changes are achieved.

Abstract: A process for operating a fuel cell installation and a fuel cell installation for carrying out the process include at least one fuel cell block. A process gas for the fuel cell block is fed into the fuel cell block with a liquid ring compressor. In this way, the process gas is humidified at the same time as it is compressed, thus using the compression heat simultaneously as evaporation enthalpy, as well as the heat from the cooling circuit of the fuel cell stack.