Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Patent
1998-11-05
2000-12-19
Nuzzolillo, Maria
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
429 13, 429 24, 429 12, H01M 804
Patent
active
061625574
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for determining the utilisation of a reactant at the anode side or cathode side of an electrochemical cell.
BACKGROUND OF THE INVENTION
Because the utilisation of the reactant concerned is known, the flow rate of said reactant can be determined. This is important for diverse applications.
In particular, a method of this type can be used to determine the relationship between the flow rates in the various cells of a stack of fuel cells.
After all, in the case of a cell stack it is important that all cells make approximately the same contribution to the total voltage. If one of the cells functions less well, this immediately has an effect on the entire stack, in particular if, as is customary, it is a matter of electric current in a serial circuit.
In the case of the production of electrochemical cells, and more particularly fuel cells, on an industrial scale, the flow resistance of the separator plates and/or other constructions for feeding in and removing the reactants will be different, inter alia because of manufacturing tolerances, creep and corrosion. If reactants are introduced in parallel into a cell stack, then, with the manifolding used, all the gas introduced will be fed over the first cell and that portion for said first cell will be removed at the latter, all the gas minus the gas removed for the first cell will be fed over the second cell, etc. The same applies for the outlet side. This means that there are always different flow conditions. Because in the case of a serial circuit the electric current which passes through each cell is the same, there will be more polarisation in a cell where an inadmissible restriction in the flow occurs, as a result of which the cell voltage falls.
Methods are proposed in the prior art for determining the hydraulic resistance per cell using conventional flow meters at the output for reactants at the anode and the cathode and measuring the pressure drop and in this way investigating whether inadmissible deviations between cells occur during production or operation.
A method of this type is suitable only for a single cell and is unsuitable for measuring during operation of a fuel cell stack. The effect of, for example, manifolding on cells cannot be measured by this method. This applies in particular if a fuel cell stack is operated at higher temperatures or under other conditions which deviate from ambient conditions. This means that a measurement under operating conditions is not possible and, therefore, does not yield results which are adequately in accord with the operating conditions.
Furthermore, the measurement described above is complex. As a result, during mass production of electrochemical cells one will not be readily inclined to conduct such measurement as standard for every cell.
SUMMARY OF THE INVENTION
The aim of the present invention is to avoid the disadvantages described above and to provide a method with which the flow rate of a reactant can be determined per cell in a simple manner.
This aim is achieved by feeding through a high flow reactant of known composition at the cathode or anode side, feeding through a low flow reactant of known composition at the anode or cathode side, setting a low average current density in the cell, determining the cell voltage, providing a table in which the relationship between the Nernst voltage under the outlet conditions of said cell, such as the temperature, and the utilisation of the gas with low flow is incorporated, equating the Nernst voltage and the cell voltage and determining the utilisation from the table.
The ingoing flow rate of the low flow reactant is determined by determining the inverse of the utilisation and multiplying by the set electric current and dividing by the Faraday constant (F=96485 C/mol), the number of electrons involved in the overall reaction and the fraction of the molecule in the reactant for which the utilisation has been determined. The outgoing flow rate of reaction products and unreacted reactant can be c
REFERENCES:
patent: 3980496 (1976-09-01), Ludwig et al.
patent: 4378385 (1983-03-01), Hughes
patent: 5479700 (1996-01-01), Nachlas et al.
patent: 5547494 (1996-08-01), Prasad et al.
Alejandro Raymond
Nuzzolillo Maria
Stichting Energieonderzoek Centrum Nederland
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