A hydrogen supply control system for a fuel cell is provided. The system includes a fuel cell stack that generates electricity using supplied hydrogen and air and a recirculation line that supplies hydrogen discharged from an outlet of the fuel cell stack back to an inlet of the fuel cell stack. A purge valve is disposed at an outlet side of the fuel cell stack of the recirculation line and discharges hydrogen in the recirculation line to the outside as the outlet is opened. A recirculation determining processor determines a recirculation state of the recirculation line and a concentration estimator estimates a purge amount for each gas, which is purged by the purge valve, based on the determined recirculation state and estimates a concentration of hydrogen in the recirculation line based on the estimated purge amount for each gas.

A redox flow battery system includes an anolyte having chromium ions in solution; a catholyte having iron ions in solution, where a molar ratio of chromium in the anolyte to iron in the catholyte is at least 1.25; a first electrode in contact with the anolyte; a second electrode in contact with the catholyte; and a separator separating the anolyte from the catholyte.

Proposed are a fuel cell system and a method of controlling the fuel cell system. The fuel cell system includes: a hydrogen supply unit connected to a hydrogen inlet side of a fuel cell stack, with a supply valve and a sensor being provided in the hydrogen supply unit; a hydrogen discharge unit connected to a hydrogen outlet side of the fuel cell stack, with a water trap and a purge valve being provided in the hydrogen discharge unit; and a controller configured to calculate an amount of hydrogen discharged through the purge valve from an amount of hydrogen supplied to the fuel cell stack and an amount of hydrogen consumed therein, and to perform compensation control of the supply valve when the amount of the discharged hydrogen is at or above a reference value.

An apparatus (10) configured to determine reactant purity comprising: a first fuel cell (11) configured to generate electrical current from the electrochemical reaction between two reactants, having a first reactant inlet (13) configured to receive a test reactant comprising one of the two reactants from a first reactant source (7, 5, 16); a second fuel cell (12) configured to generate electrical current from the electrochemical reaction between the two reactants, having a second reactant inlet (14) configured to receive the test reactant from a second reactant source (5); a controller (20) configured to apply an electrical load to each fuel cell and determine an electrical output difference, OD.sub.t, between an electrical output of the first fuel cell (11) and an electrical output of the second fuel cell (12), and determine a difference between a predicted output difference and the determined electrical output difference, OD.sub.t, the predicted output difference determined based on a historical output of difference and a historical rate of change in said output difference determined at an earlier time, said controller (20) configured to provide a purity output indicative of the test reactant purity at least based on the difference between the predicted and determined output difference.

An illustrative example hydrogen concentration sensor includes a plurality of electrically conductive plates. A hydrogen evolving electrode assembly in a first location between two of the plates is configured to generate hydrogen. A detection electrode assembly in a second location between two of the plates is configured to provide an indication of a concentration of hydrogen in a fluid of interest. A plurality of isolating layers includes a first isolating layer at the first location between two of the plates and a second isolating layer at the second location between two of the plates. The first and second isolating layers each include a sealant that secures the two plates together and seals a perimeter around the electrode assembly at the corresponding location.

An illustrative example hydrogen concentration sensor includes a first end plate. A hydrogen evolving electrode assembly that generates hydrogen is situated adjacent the first end plate and at least partially exposed through an opening through the end plate. A separator plate is between the hydrogen evolving electrode assembly and a detection electrode assembly. The separator plate includes a passage to allow a flow of hydrogen generated by the hydrogen evolving electrode assembly to the detection electrode assembly. A second end plate is situated adjacent the detection electrode assembly and includes a second opening where a portion of the detection electrode assembly is exposed to a fluid of interest to provide an indication of a concentration of hydrogen in the fluid of interest.

The invention relates to a detection system (10a; 10b; 10c) for detecting hydrogen (11) in a cavity (12) of a fuel cell vehicle (13), comprising a fuel cell system (15) with a fuel cell housing (16) and a purging air line (17) for purging the fuel cell housing (16) and a hydrogen sensor (14) outside the fuel cell housing (16), wherein the purging air line (17) has a purging air outlet (18) for discharging purging air (19) out of the fuel cell housing (16), wherein the purging air outlet (18) is designed for applying the hydrogen sensor (14) with the purging air from the purging air line (17). The invention also relates to a fuel cell vehicle (13) comprising a detection system (10a; 10b; 10c) according to the invention.

A method of operating a redox flow battery string including at least first and second redox flow batteries and an outside power source includes: providing a least first and second redox flow batteries in a string electrically connected in a string, and each redox flow battery having a state-or-charge (SOC); obtaining an SOC value for each redox flow battery in the string; identifying a target SOC value in the string; and adjusting the SOC value for at least one of the first and second redox flow batteries to correspond to the target SOC value.

A device for diagnosing a valve failure of a fuel cell system is capable of accurately and quickly determining whether an integrated valve in a fuel cell system is operated abnormally, and preventing problems caused by the operation abnormality of the integrated valve.

An aircraft electrical power supply system includes a fuel cell auxiliary power unit (APU) that supplies auxiliary electrical power to an aircraft, a fuel cell power plant that supplies primary electrical power to the aircraft, and a hydrogen storage unit that supplies hydrogen to the fuel cell APU and the fuel cell power plant.