A fuel cell system and method, the system including power generating fuel cells disposed in a stack, each power generating fuel cell including an anode, a cathode, and an electrolyte, a sensing fuel cell including an anode, a cathode, and an electrolyte, and a fuel processor configured to purify a fuel provided to the power generating fuel cells and the sensing fuel cell. The anode of the sensing fuel cell is thinner than the anodes of the power generating fuel cells.

A fuel cell monitoring device includes: an impedance measuring part measuring an impedance at each fuel cell and an impedance at a fuel cell stack as a whole; a water content estimating part calculating a water content estimated value at each fuel cell using a gas diffusion resistance obtained from a measurement result about the impedance at each fuel cell, and calculating a water content reference estimated value indicating a water content in each fuel cell using a gas diffusion resistance obtained from a measurement result about the impedance at the fuel cell stack as a whole; and a determining part detecting at least either the occurrence of deterioration of catalyst in the fuel cell or the occurrence of a distribution failure of reactive gas at the fuel cell by determining based on the magnitude of the water content estimated value relative to the water content reference estimated value.

A method for operating a fuel cell system comprising a control unit and at least one fuel cell comprises a cycle of the following steps: recording of an actual U/I characteristic curve of the fuel cell, comparison of the recorded actual U/I characteristic curve of the fuel cell with a target U/I characteristic curve stored in a memory, at least within a predetermined or pre-determinable current range, and determination of the difference between the target U/I characteristic curve and the actual U/I characteristic curve within the current range, comprising the following steps: continuous or clocked repetition of the cycle until the difference reaches or exceeds a predetermined or pre-determinable difference limit value, and adjustment of at least one parameter of the control unit to reduce or minimize the difference.

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.

In a method for regulating a fuel cell stack (1), a current-voltage characteristic of the fuel cell stack is detected and evaluated to determine an operating point of the fuel cell stack, wherein a current-voltage characteristic of the fuel cell stack (1) is detected at time intervals in operation whose gradient has a minimum, a characteristic value (R.sub.min) for the minimum of the gradient is respectively determined from the detected current-voltage characteristic and a desired value for the operating point is determined by addition of a predefined offset value (R.sub.offset) to the characteristic value, and wherein the fuel cell stack (1) is regulated by the desired value determined in this manner.

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.

Methods for detecting a hydrogen leak and quantifying a rate of the same in a polymer electrolyte membrane fuel cell stack are provided, as well as a fuel cell diagnostic apparatus that diagnoses a hydrogen leak in a fuel cell stack.

Systems, methods, and devices of the various embodiments provide a hardware and software architecture enabling electrochemical impedance spectroscopy (EIS) to be performed on multiple electrochemical devices, such as fuel cells, at the same time without human interaction with the electrochemical devices and to use EIS to dynamically monitor the performance of a fuel cell system. Embodiment methods may include determining an impedance of a set of fuel cells using electrochemical impedance spectroscopy, determining an ohmic polarization of the set of fuel cells from the impedance, determining a concentration polarization of the set of fuel cells from the impedance, comparing the ohmic polarization of the set of fuel cells to a first threshold, comparing the concentration polarization of the set of fuel cells to a second threshold, and initiating a corrective action when the ohmic polarization is above the first threshold or when the concentration polarization is below the second threshold.

Provided is a fuel cell system including: a fuel cell; a reactant gas supply section; a converter; an alternating-current superimposing unit; a phase difference deriving unit configured to derive a phase difference that is a phase lag of an alternating-current voltage relative to an alternating current in an alternating-current component output from the fuel cell; and a first inference unit. The first inference unit infers that the fuel cell is in an inappropriate wet state, when the absolute value of an amount of change in the phase difference has become equal to or larger than a predetermined criterion value immediately after the magnitude of a change in the value of at least one of parameters that are a flow rate of a reactant gas, a stoichiometric ratio, and an output current has exceeded a predetermined criterion.

A method of controlling the operation of a fuel cell system is provided. The method includes diagnosing a water shortage state in a fuel cell stack based on degradation of cooling performance and deterioration of the fuel cell stack and determining a diagnosis level of the fuel cell system based on the diagnosed water shortage state of the fuel cell stack. In addition, a regenerative operation is performed by selecting a regenerative operation mode which corresponds to the determined diagnosis level.