A method of measuring impedance of a fuel cell stack in a vehicle during driving of the vehicle includes: determining whether an impedance measurement of the fuel cell stack is requested during driving of the vehicle driven by power of the fuel cell stack; turning off a first relay connected between the fuel cell stack and a battery charged by the fuel cell stack when the impedance measurement of the fuel cell stack is requested; connecting a stack load to the fuel cell stack via a second relay and supplying air to the fuel cell stack; and measuring the impedance of the fuel cell stack.

In a fuel cell state determination method for determining an internal state of a fuel cell supplied with an anode gas and a cathode gas to generate electricity, a decrease of a reaction resistance value of the cathode caused by hydrogen evolution reaction generated in the cathode as the fuel cell has an oxygen deficiency state is detected, and the oxygen deficiency state is determined on the basis of detection of the decrease of the reaction resistance value.

A fuel cell device is provided, including a media system for supplying fluid media to electrochemical units of the fuel cell device and/or for discharging fluid media from the electrochemical units of the fuel cell device, wherein the media system includes at least one valve to which, in a standard operating state of the fuel cell device, an electrical standard input power is suppliable in order to maintain the valve in a desired valve state. The fuel cell device is able to be reliably started with as little effort as possible, even under frost conditions. The fuel cell device is switchable into a heating operating state in which an electrical heating input power that is greater than the electrical standard input power is suppliable to the at least one valve.

A fuel cell system includes: a fuel cell unit; first and second supply systems; a switching device; a switching control unit; an open circuit voltage obtaining unit; and a supply system control unit.

A system and method of controlling water imbalance in an electrochemical cell is provided. The method includes determining a present water imbalance in the electrochemical cell by summing a water.sub.in and a water.sub.created less a water.sub.out. Water.sub.in represents an amount of water introduced into the electrochemical cell by an oxidant feed gas; water.sub.created represents an amount of water created by the electrochemical cell from the electrochemical reaction; and water.sub.out represents an amount of water discharged from the electrochemical cell by an oxidant exhaust gas. The method includes tracking a cumulative water imbalance during operation of the electrochemical cell by repeatedly determining the present water imbalance and continuing to sum the results during operation. And, the method also includes adjusting a flow rate of the oxidant feed gas entering the electrochemical cell based on the cumulative water imbalance.

A fuel cell including a plurality of elementary modules stacked on each other, at least one of the elementary modules including an oxidation unit generating electrons by oxidation of a fuel with an oxidant, an anode block including a fuel transporter support, for transporting an anode feed flow containing the fuel to an anode chamber, onto which is attached an anode electron collector, a cathode block including an oxidant transporter support, for transporting a cathode feed flow containing the oxidant to a cathode chamber, onto which is attached a cathode electron collector, the elementary module defining the anode chamber, respectively, the cathode chamber between the oxidation unit and the fuel transporter support, respectively, the oxidant transporter support, and being such that, prior to the assembly of the elementary module in said plurality, the anode block, respectively, the cathode block and the oxidation unit are attached to each other.

A method for maintaining a target electrochemical impedance (ECI) for a fuel cell, which corresponds to a target hydration state for the fuel cell. The method includes determining a target electrochemical impedance (ECI) for the fuel cell based on current operating conditions. The method further includes determining actual ECI for the fuel cell and comparing actual ECI to the target ECI. The method further includes adjusting a cathode flow to the fuel cell based on a deviation of the actual ECI from the target ECI.

Provided is a method for simultaneous detection of parameters of membrane electrode assemblies of a fuel cell stack, which includes: supplying hydrogen to an anode of the fuel cell stack and inert gas to a cathode of the fuel cell stack, controlling operating conditions of the fuel cell stack at respective preset values; applying different voltage excitations or micro-current excitations to the fuel cell stack, collecting a current signal of an entire stack and a voltage signal of each fuel cell; and analyzing a hydrogen crossover current, a catalyst electrochemical surface area, a double-layer capacitance, and a short-circuit resistance of a membrane electrode assembly of each fuel cell based on an excitation-response formula of a fuel cell. The present disclosure does not limit a form of a current or voltage excitation, thereby improving accuracy of a parameter test of a membrane electrode assembly while reducing the test cost.

A method of controlling a fuel cell device includes: a step of determining whether impedance between a fuel electrode and an oxidant electrode is greater than a predetermined threshold during a steady operation of the fuel cell device; a step of decreasing a flow rate of a gas circulating via a circulation passage connecting a gas introduction passage of the gas supply unit to a gas discharge passage when the impedance is greater than the predetermined threshold; a step of measuring the voltage between the fuel electrode and the oxidant electrode when the impedance is equal to or less than the predetermined threshold, and determining whether the voltage is equal to or less than a first predetermined threshold; and a step of increasing the flow rate of the gas circulating via the circulation passage when the voltage is equal to or less than the first predetermined threshold.

A fuel cell system includes: a fuel cell including an MEA including an electrolyte membrane and anode and cathode catalyst layers sandwiching the electrolyte membrane; an impedance measuring device measuring AC impedance of the fuel cell when AC voltage is applied to the fuel cell; an impedance acquisition unit configured to obtain a first imaginary part value of the AC impedance measured when AC voltage with a fixed frequency satisfying Fixed frequency [Hz](Thickness of the electrolyte membrane [m]).sup.2500 [Hzm.sup.2] is applied in a state where a relative humidity of the MEA is 20% or greater, and a fuel gas is present and an oxidant gas is absent in the anode and cathode catalyst layers; and a metal ion estimation unit configured to estimate a content of metal ions in the electrolyte membrane based on the first imaginary part value of the AC impedance.