A fuel cell stack includes a stack body including a plurality of power generation cells stacked together, a stack case storing the stack body, and an auxiliary device case storing a fuel cell auxiliary device. Two exhaust gas openings are provided in an upper part of the stack case. One exhaust gas opening is provided in an upper part of the auxiliary device case. An exhaust duct is connected to the only three exhaust gas openings in total.

The present disclosure relates to an apparatus and a method for controlling a concentration of exhaust hydrogen in a fuel cell system. The apparatus may include an air exhaust valve for discharging hydrogen from a cathode in a fuel cell stack to an outside environment through an air exhaust line, an air compressor for supplying ambient air to the air exhaust line, an air cut-off valve for blocking air supplied to the cathode, and a controller that opens the air exhaust valve and drives the air compressor when starting to supply hydrogen to the fuel cell stack, and opens the air cut-off valve such that a concentration of the hydrogen discharged from the cathode is reduced by air in the air exhaust line when the hydrogen supply is completed.

A redox flow battery includes first and second cells. Each cell has electrodes and a separator layer arranged between the electrodes. A first circulation loop is fluidly connected with the first electrode of the first cell. A polysulfide electrolyte solution has a pH 11.5 or greater and is contained in the first recirculation loop. A second circulation loop is fluidly connected with the second electrode of the second cell. An iron electrolyte solution has a pH 3 or less and is contained in the second circulation loop. A third circulation loop is fluidly connected with the second electrode of the first cell and the first electrode of the second cell. An intermediator electrolyte solution is contained in the third circulation loop. The cells are operable to undergo reversible reactions to store input electrical energy upon charging and discharge the stored electrical energy upon discharging.

A fuel cell system includes: a fuel cell; a supply device; and a control unit configured to lower output voltage of the fuel cell to a target value so as to execute recovery processing to recover power generation performance of the fuel cell. In a case of having an execution request of the recovery processing, the control unit restarts power generation of the fuel cell when open circuit voltage of the fuel cell is lowered to or smaller than a threshold value higher than the target value by controlling a flow rate of a cathode gas while the power generation of the fuel cell is paused, and the control unit executes the recovery processing while controlling an output current value of the fuel cell to be smaller than an idle current value that is an output current value of the fuel cell in an idle operation state.

The present disclosure provides a method of shortening an aging period of a polymer electrolyte fuel cell immediately after production to increase shipping inspection speed and production speed of the polymer electrolyte fuel cell. The present disclosure relates to an aging method of a fuel cell which comprises a membrane electrode assembly comprising a fuel electrode, an electrolyte membrane, and an oxidant electrode, wherein the method comprises applying a potential cycle, wherein the lowest cell potential when a load is applied and OCV are alternately repeated between the fuel electrode and the oxidant electrode, and in the potential cycle, fuel gas is supplied to the fuel electrode, and oxidant gas and carbon monoxide gas are supplied to the oxidant electrode.

A fuel cell system includes a fuel cell in which cells are stacked, a voltage sensor that detects a voltage in unit of one or more of the cells, a control unit that determines an operating point of the fuel cell and causes the fuel cell to operate. The control unit causes the fuel cell to operate at a low efficiency operating point having a lower efficiency than an efficiency of a reference operating point in a warm-up operation. In the warm-up operation, the control unit calculates a total number of the cells in which the voltage detected by the voltage sensor is equal to or less than a predetermined first reference voltage and calculates an exhaust hydrogen concentration based on the total number or the cells.

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.

Systems and methods are provided for using fuel cell staging to reduce or minimize variations in current density when operating molten carbonate fuel cells with elevated CO.sub.2 utilization. The fuel cell staging can mitigate the amount of alternative ion transport that occurs when operating molten carbonate fuel cells under conditions for elevated CO.sub.2 utilization.

A system for maintaining insulation resistance of a fuel cell includes a fuel cell stack, a coolant line that allows coolant to pass through the fuel cell stack, a circulation pump that circulates the coolant in the coolant line, a deionizer that removes impurities or ions from the coolant in the coolant line, and a controller configured to measure the insulation resistance of a high-voltage terminal connected to the fuel cell stack, to determine whether recovery control is necessary based on the measured insulation resistance, and upon determining that recovery control is necessary, to control the circulation pump so as to change the flow of the coolant passing through the deionizer.

A method for determining if there is a gas leak in an anode volume of a fuel cell stack in a fuel cell system. The method includes determining a total amount of gas loss in the anode volume of the fuel cell stack during a predetermined period of time, and monitoring losses of the gas from the anode volume during the predetermined period of time, such as reaction losses, crossover losses and overboard losses. The method also includes subtracting the losses of the gas from the total amount of gas loss to get an anode leak loss and comparing the anode leak loss to a predetermined threshold to identify a hydrogen gas leak.