A fuel cell system including a fuel cell that receives a supply of an anode gas and a cathode gas and generates power is provided. The fuel cell system includes a water content calculation unit configured to calculate a water content of the fuel cell, an internal impedance calculation unit configured to calculate an internal impedance of the fuel cell, and a starting temperature calculation unit configured to calculate a fuel cell temperature at a start of the system, based on the water content of the fuel cell as of a last time the system was stopped, and the internal impedance of the fuel cell at the start of the system.

A method for determining a spatial distribution (Rc.sub.x,y.sup.f) of a parameter of interest (Rc) representative of a contact resistance between a bipolar plate and an adjacent electrode of an electrochemical cell, in which a spatial distribution (Rc.sub.x,y.sup.f) of the parameter of interest (Rc) is determined depending on the spatial distribution (Q.sub.x,y.sup.e) of a second thermal quantity (Q.sup.c) estimated beforehand from the spatial distribution (T.sub.x,y.sup.c) of a set-point temperature (Tc) and from the spatial distribution (D.sub.x,y.sup.r) of a first thermal quantity (D.sup.r).

The invention relates to a method for determining critical operating states in a fuel cell stack, consisting of single cells connected in series, wherein a low-frequency current or voltage signal is applied to the fuel cell stack, the resulting voltage or current signal is measured and the distortion factor thd is determined. According to the invention, the weighted sum of a term dependent on the membrane resistance Rm and a term dependent on the distortion factor thd is used to determine an indicator THDA.sub.dryout correlating with the drying out of the fuel cell membranes of the fuel cell stack, the membrane resistance Rm being detected by impedance measurement.

A fuel cell system includes a fuel cell including an electrolyte membrane, a sensor configured to measure a temperature of the fuel cell, and a controller. The controller is configured to cause the fuel cell to perform a wet operation to increase a water balance at a cathode of the fuel cell to a value higher than a water balance at the cathode during a normal operation of the fuel cell, when the temperature of the fuel cell measured by the sensor is maintained at a first threshold temperature or higher for a prescribed period of time or longer and then the temperature of the fuel cell decreases to below a second threshold temperature that is equal to or lower than the first threshold temperature.

A method of operating a redox flow battery, may include maintaining a positive electrode compartment pressure greater than a negative electrode compartment pressure, and maintaining a cross-over pressure less than a membrane break-through pressure, wherein the cross-over pressure equals the negative electrode compartment pressure subtracted from the positive electrode compartment pressure. In this way, ionic resistance across the separator can be maintained at a lower level by reducing gas bubbles trapped therein while reducing separator break-through, thereby increasing performance of the redox flow battery system.

A state detection device for fuel cell includes a supposed high-frequency impedance value setting unit configured to set a supposed high-frequency impedance value on the basis of an impedance measurement value belonging to an arc region of an impedance curve of the fuel cell, an actually measured high-frequency impedance value calculation unit configured to obtain an actually measured high-frequency impedance value on the basis of an impedance measurement value belonging to a non-arc region of the impedance curve of the fuel cell, and an ionomer resistance estimation unit configured to estimate a value obtained by subtracting the actually measured high-frequency impedance value from the supposed high-frequency impedance value as an ionomer resistance value. The supposed high-frequency impedance value setting unit sets a value of an intersection of an equivalent circuit impedance curve set on the basis of the impedance measurement value belonging to the arc region and a real ads as the supposed high-frequency impedance value.

The invention relates to a method for controlling operation of a microbial fuel cell arrangement having at least one microbial fuel cell unit. The unit comprises an anode and a cathode, which are connected with each other via an external electrical circuit. In the method an influent flow of liquid medium, which comprises organic substance(s), is fed to the microbial fuel cell unit, and at least a part of the organic substance(s) are converted into electrical energy in the microbial fuel cell unit by using microorganisms. Potential of the anode is measured against a reference electrode and obtaining measurement value(s), and the measured value(s) are used for controlling the feed of the influent flow to the microbial fuel cell unit. An effluent flow of treated liquid medium is removed from the microbial fuel cell unit. The invention relates also to microbial fuel cell, which comprises a controller, which is arranged in functional contact with the means for measuring the potential of the anode and with the means for adjusting the influent flow to the inlet.

An electrochemical cell system and a method of controlling water imbalance is provided. The electrochemical cell system and the method both include 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; 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 adjusting a flow rate of the oxidant feed gas entering the electrochemical cell based on the cumulative water imbalance.

A fuel cell system comprises a fuel cell; a reactive gas supply mechanism configured to supply a reactive gas to the fuel cell; a discharge flow path configured to discharge an off-gas and water discharged from the fuel cell; a valve provided in the discharge flow path; a remaining water purging controller configured to control a remaining water purging process of the fuel cell by using the reactive gas supply mechanism and the valve; a heating portion configured to heat the valve; and a failure detector configured to detect a failure of the heating portion. When a failure of the heating portion is detected, the remaining water purging controller performs the remaining water purging process and increases a water discharge power in the remaining water purging process than a water discharge power in the remaining water purging process performed when no failure of the heating portion is detected.

An electrochemical cell degradation monitoring method. The method includes applying first and second bias potentials to an electrode of an electrochemical cell during an operating state thereof. The method further includes measuring impedance spectra of the electrode of the electrochemical cell during the operating state biased to the first and second bias potentials. The method also includes determining a deviation in the impedance spectra at the first and second bias potentials. The method determines a degradation state of the electrode of the electrochemical cell in response to the deviation in the impedance spectra at the first and second bias potentials of the electrode of the electrochemical cell.