Abstract: An electrode for fuel cells includes several consecutive layers of electrically conductive porous material. The consecutive layers include recesses which form sections of flow channels. Within the individual layers, however, the channels are not continuous. When the consecutive layers are combined, the channel sections of the various layers, which are disposed in such a way that there are overlaps between them, complement one another to form a complete fluid-distributor structure. A distribution of fluid also takes place in the thickness direction of the electrode by virtue of the fact that the flow channels pass over repeatedly from one layer into the other, besides the distribution of fluid in a plane. A composite structural unit for fuel cells and a polymer-electrolyte-membrane fuel cell, are also provided.

Abstract: The invention relates to a fuel cell system (11, 111) comprising an anode chamber (13, 113) and a cathode chamber (14, 114) which are separated from each other by a proton conducting membrane (15, 115). When the fuel cell system is operated, fuel, in particular H2 or a water/methanol mixture, can be fed to the anode chamber and an oxidant, in particular oxygen, can be fed to the cathode chamber. In standby mode, the cathode chamber (14, 114) does not allow flow through and the oxidant and fuel are present in both the cathode chamber (14, 114) and the anode chamber (13, 113), respectively. The fuel cell system remains at operating temperature in the standby mode. This enables the fuel cell system (11) to be used as a combined interruption-free power supply unit and backup unit.

Abstract: An arrangement is disclosed for ensuring an uninterrupted current supply to at least one electrical consumer which draws energy from an alternating voltage network and is supplied with energy in the event of a network failure by a fuel cell. The fuel cell (8) is connected at its electrical outputs to at least one current inverter (7) whose output is connected to the minimum of one alternating voltage consumer (1, 2) and to a branch containing a switch (4) on the consumer side of the switch; the switch is connected to an alternating voltage network (6) and is opened in the event of the voltage in the alternating voltage network falling below a predetermined level and closed if the alternating voltage is above that threshold; and the fuel cell operates in stand-by mode if the network voltage is above the threshold, and, if voltage is below the threshold, in a mode in which the energy required by the consumer is supplied via the current inverter (7).

Abstract: For determining the half-cycle durations of the input signal which is presented as a sequence of sampled values, its zero crossings are approximated by lines which interconnect the two sampled values of different signs on both sides of the zero crossing. The half-cycle duration is derived from the number of sampled values within a period, i.e. between two consecutive zero crossings, and from the time intervals at the beginning and end of each half-cycle determined by the intersection of the approximation line with the axis. The time intervals at the beginning and end of each period are corrected for a more accurate determination of the duration and the time intervals during which the values of the individual half-cycle durations are stored, are made to approximate to these half-cycle durations. The instantaneous frequency of the input signal is determined from the values of the half-cycle durations which have thus been shifted in time by forming the reciprocal.