Fuel cells

Details Fuel cells Fuel cells

1996-01-16

1998-04-14

Kalafut, Stephen

Chemistry: electrical and wave energy

Apparatus

Electrolytic

204431, G01N 2726

Patent

active

057387737

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to fuel cells and in particular, but not exclusively, such cells which act as sensors for oxidisable components in gases.


BACKGROUND OF THE INVENTION

Fuel cells were first invented by Sir William Grove in 1839 and in recent years have been used in many arrangements for the detecting of oxidisable components of gases or vapours, for example in breath testing equipment. Essentially the fuel cell comprises a working electrode or anode and a counter electrode or cathode which are separated by an electrolyte, usually by a porous disc impregnated with an acidic electrolyte. The electrochemical oxidation of the fuel component in the gas results in the development of an electrical potential difference resulting in a flow of electrons from the anode to the cathode and this current and/or potential difference can be detected. One such fuel cell is made by Lion Laboratories Plc.
Although these fuel cells have been successful in a limited field, considerable problems have been experienced both in the time taken for the fuel cell to consume the oxidisable component in the sample and in the time taken for the cell to clear so that it is ready to sense a further sample.


SUMMARY OF THE INVENTION

From one aspect of the invention there is provided a sensor for detecting oxidisable fuel components in a gas or vapour including a pair of working electrodes facing other to define a sample receiving space between them.
This arrangement of facing working electrodes substantially increases the surface area of the working electrode for a given cross-sectional dimension and hence significantly reduces the time taken for a fuel component to contact and hence react with the working electrode. It further enables the working electrodes to be placed very close to one another hence reducing the length of the mean free path available to any fuel component molecule injected into the sample space before it strikes a working electrode. In traditional designs there can be a significant dead space above the single working electrode.
In a preferred embodiment the working electrodes are electrically connected. Further it is preferred that there is a counter electrode for each working electrode and they will be separated from each other by a suitable electrolytically impregnated body. The counter electrodes should also be electrically connected, when this is true of the working electrodes. The respective sets of electrodes can be connected in parallel or in series. In the former arrangement the electrodes could be viewed as being a single cell in a bent configuration, and such an arrangement is included in the invention and indeed other wrapped around arrangemennts may be possible although these may introduce constructional complexities which limit the closest approach of the two working electrode sections.
Preferably the spacing between the working electrodes is between 0.5 mm and 5 mm and a spacing of 1 mm to 2 mm has been found to be a good compromise between cell efficiency and constructional simplicity.
The rate of clearing of the cell may be a function of the net load and it has been found convenient to have a net load of approximately 10 ohms. The sensor may thus have a load resistor across its output which is approximately equal to its impedance.
From another aspect the invention consists in a fuel cell having a closed loop electrical contact for at least one of its electrodes, the loop being substantially circumjacent the operative surface of the electrode.
Traditionally single wire contacts have been used and these can cause local resistance problems and manufacturing difficulties. The use of a closed loop, and preferably annular, contact ensures that there is electrical contact between the electrode and the contact at at least some parts of the contact and removes many localised affects.
The invention also consists in a sensor as described above with the closed loop contact set out above.
Although the invention has been defined above it is to be understood that it includes any inventi

REFERENCES:
patent: 3246235 (1966-04-01), Allsopp
patent: 4647362 (1987-03-01), Watanabe
patent: 4758325 (1988-07-01), Kanno et al.
patent: 5338429 (1994-08-01), Jolson et al.

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