A system and method controls operation of a fuel cell system comprising a fuel cell unit that comprises a fuel cell stack comprising a cathode and an anode, and a cathode recirculation passage configured to divert a cathode exhaust flow to a cathode inlet line. A control system is configured to, responsive to a value of a power output that is requested from the fuel cell system being below a first threshold power level, control a target coolant inlet temperature of a coolant at a coolant inlet of the fuel cell stack and control an air pressure at the cathode. Responsive to the value of a power output being below at least one second threshold power level, additionally, an oxygen partial pressure in the air flow may be reduced by controlling a volume flow rate of a cathode exhaust flow that is directed to the cathode inlet line.

The invention relates to a method for operating a fuel cell system (1) comprising at least one fuel cell stack (100) having a cathode (110) and an anode (120), wherein, during normal operation of the fuel cell system (1), the cathode (110) is supplied with air via a supply air path (111), and exhaust air exiting the fuel cell stack (100) is discharged via an exhaust air path (112), and wherein the anode (120) is supplied with hydrogen via an anode circuit (121). If poisoning of an anode catalyst of the fuel cell stack (100) is identified, regeneration of the anode catalyst is initiated, wherein exhaust air is diverted out of the exhaust path (112) or an exhaust path (212) of a further fuel cell stack (200) and is introduced into the anode circuit (121) of the anode (120).

The invention relates to a method for preventing an automatically continued ignition of hydrogen in an exhaust (150) of a fuel cell unit, in particular of a fuel cell vehicle, when the fuel cell unit is started, characterized in that, when at least one start condition of the fuel cell unit is met, reactive hydrogen is removed from a cathode- side and/or exhaust-side gas of the fuel cell unit until, when the fuel cell unit is started, an actual level of a hydrogen concentration in the exhaust (150) is below the lower hydrogen explosion limit, and the method is preferably carried out only when an initial level of the hydrogen concentration of the cathode-side and/or exhaust-side gas in the fuel cell unit is above the lower hydrogen explosion limit for the exhaust (150).

A fuel cell system includes a fuel cell stack having a plurality of fuel cells that each contain a plurality of fuel electrodes and air electrodes. The system includes a fuel receiving unit connected to the fuel cell stack, which receives a hydrocarbon fuel from a fuel supply. The system includes a fuel exhaust processing unit fluidly coupled to the fuel cell stack by a slip stream, where the fuel exhaust processing unit processes fuel exhaust from the fuel cell stack, and the slip stream is fluidly connected to an exhaust stream flowing from the fuel cell stack. The fuel processing unit removes a first portion of carbon dioxide (CO.sub.2) from fuel exhaust within the slip stream, outputs the first portion of CO.sub.2 in a first stream, and outputs a second portion of CO.sub.2 remaining from the fuel exhaust in the slip stream into a second stream, which includes hydrogen.

During some operations, a fuel cell system of a FCEV is operated in a voltage suppression mode when the FCEV is in park and power demand is low to reduce wear of the fuel cell system. However, in the voltage suppression mode, liquid water may accumulate in the fuel cell system, because of low flow of reactant gases which typically remove the water. If the FCEV exits the park state and undergoes a high acceleration, the water can inhibit reactant flow.

A method of controlling selective purging of reacted fuel gas at the anode of a hydrogen fuel cell includes initiating a selective purging of reacted fuel gas, initiating air flow through the fuel cell necessary to dilute a concentration of hydrogen present within the reacted fuel gas exhausted from the fuel cell, and opening an anode valve adapted to allow reacted fuel gas within the anode to vent from the fuel cell after the air flow through the fuel cell reaches an estimated required air flow rate necessary to dilute the level of hydrogen present within the reacted fuel gas exhausted from the fuel cell.

A fuel cell system includes an FC stack, a hydrogen gas supply passage, a hydrogen off-gas circulation passage, an ejector, an exhaust-drain valve, a pressure sensor for hydrogen gas, and a controller. The controller variably controls a time ratio between an opening time and a closing time of the exhaust-drain valve per one control cycle, and controls the number of opening-closing operations of the exhaust-drain valve per unit time by keeping the opening time constant and controlling the closing time variably. The controller controls the number of opening-closing operations of the exhaust-drain valve according to a pressure measured value of the pressure sensor in order to adjust the concentration of hydrogen gas in hydrogen off-gas caused to circulate to the hydrogen gas supply passage via the hydrogen off-gas circulation passage.

A fuel cell system includes a stack of fuel cells, a fuel supply line configured to provide a fuel to the stack, an anode exhaust line configured to receive an anode exhaust from the stack, and a trapping component configured to sequester silicon species included in the anode exhaust.