An apparatus and method for reducing an exhaust hydrogen concentration in a fuel cell system includes a first air cut-off valve (ACV) blocking ambient air supplied to a cathode, a second ACV blocking exhaust hydrogen discharged from the cathode, and an air suction valve (ASV) operating in a first mode connecting the cathode and an intake port of an air compressor and in a second mode blocking connection between the cathode and the intake port of the air compressor. The apparatus also includes a controller for operating the ASV in the first mode to store air of the cathode while the first ACV is opened and the second ACV is closed when hydrogen is supplied to an anode, and for operating the ASV in the second mode to discharge ambient air through an exhaust line while the first ACV is opened and the second ACV is opened when ambient air is supplied to the cathode.

A method for shutting down a fuel cell system (2) having at least one fuel cell (3), which fuel cell comprises an anode chamber (10) and a cathode chamber (6), wherein after the shut-down hydrogen remains in the anode chamber (10) of the fuel cell (3) in order to prevent carbon corrosion and to ensure a hydrogen protection time. The invention is characterized in that when the hydrogen in the anode chamber (10) is largely used up directly or after a specified number of subsequent meterings of hydrogen at least into the anode chamber (10), the hydrogen protection time is actively terminated by air being actively admitted into the cathode chamber (6), the fuel cell (3) being actively cooled before air is actively admitted into the cathode chamber (6).

A method for determining the starting state of a fuel-cell system is provided having cathode and anode chambers separated by a membrane-electrode assembly, comprising the steps of initially introducing hydrogen into the anode chamber, measuring the voltage and evaluating whether at least a threshold value has been reached immediately after the start of the introduction of hydrogen into the anode chamber, and determining the starting state as a function of whether the threshold value has been reached.

The invention relates to a method to determine a content of a gas component in a gas mixture delivered recirculating through an anode chamber (12) or a cathode chamber (13) of a fuel cell (10), wherein the delivery takes place via a delivery device (26) functioning according to the positive displacement principle. The invention also relates to a fuel cell system (100) configured to execute the method. According to the invention, the content of the gas component is determined depending on geometric parameters (V, ) and operating parameters (n, U, I) of the delivery device (26), as well as on thermodynamic state variables (p, T) of the gas mixture. The sought target quantity, for example a hydrogen component of an anode gas, can thus be determined in a simple and robust manner from quantities that are already known or measured.

Molten carbonate fuel cell configurations are provided that include one or more baffle structures within the cathode gas collection volume. The baffle structures can reduce the unblocked flow cross-section of the cathode gas collection volume by 10% to 80%. It has been discovered that when operating a molten carbonate fuel cell under conditions for elevated CO.sub.2 utilization, the presence of baffles can provide an unexpected benefit in the form of providing increased transference and/or increased operating voltage.

Cathode collector structures and/or corresponding cathode structures are provided that can allow for improved operation for a molten carbonate fuel cell when operated under conditions for elevated CO.sub.2 utilization. A cathode collector structure that provides an increased open area at the cathode surface can reduce or minimize the amount of alternative ion transport that occurs within the fuel cell. Additionally or alternately, grooves in the cathode surface can be used to increase the open area.

A reforming element for a molten carbonate fuel cell stack and corresponding methods are provided that can reduce or minimize temperature differences within the fuel cell stack when operating the fuel cell stack with enhanced CO.sub.2 utilization. The reforming element can include at least one surface with a reforming catalyst deposited on the surface. A difference between the minimum and maximum reforming catalyst density and/or activity on a first portion of the at least one surface can be 20% to 75%, with the highest catalyst densities and/or activities being in proximity to the side of the fuel cell stack corresponding to at least one of the anode inlet and the cathode inlet.

A fuel cell system includes: a fuel cell which performs electric power generation using a fuel gas containing hydrogen and an oxidant gas; a first supply pipe which supplies the fuel gas to the fuel cell; a first discharge pipe which discharges a fuel off gas and water led out from the fuel cell, by electric power generation of the fuel cell, to the outside; a second supply pipe which supplies the oxidant gas to the fuel cell; and an exhaust and drain valve which is disposed in the first discharge pipe, and regulates or allows the fuel off gas and the water to be discharged to the outside. The exhaust and drain valve includes a housing, a valve body, a diaphragm, a first port, a second port, a third port, and a valve seat.

An electrochemical battery including: a battery module comprising at least one electrochemical cell; an air supplier configured to supply air to the battery module and constantly maintain an oxygen concentration in the air that is supplied to the battery module; and an air recirculator configured to recirculate air exhausted from the battery module, wherein the battery module comprises an air inlet port though which air is introduced from the air supplier, and an air outlet port through which air remaining after a reaction in the at least one electrochemical cell is exhausted, and wherein the air recirculator is configured to recirculate the air exhausted through the air outlet port of the battery module to the air inlet port of the battery module.

A method of controlling the operation of a fuel cell system is provided. The method includes diagnosing a water shortage state in a fuel cell stack based on degradation of cooling performance and deterioration of the fuel cell stack and determining a diagnosis level of the fuel cell system based on the diagnosed water shortage state of the fuel cell stack. In addition, a regenerative operation is performed by selecting a regenerative operation mode which corresponds to the determined diagnosis level.