Electrochemical actuator

Details Electrochemical actuator Electrochemical actuator

1995-04-07

1996-10-22

Skapars, Anthony

Chemistry: electrical and wave energy

Apparatus

Electrolytic

429 27, 429210, C25B 900, H01M 818

Patent

active

055672841

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to an electrochemical actuator with a sealed gas space and multiple cells each of which includes a solid electrode made from an electrochemically reversibly oxidizable material and a counter electrode. A reversible electrochemical reaction initiated by a direct current generates in the gas space an increase or a decrease in the prevailing pressure.
German patent document DE 41 16 739 C1 discloses an electrochemical actuator with a housing in which electrochemical cells are stacked. When a direct current is applied, gas is generated or absorbed, depending on the direction of the current, so that a bellows operatively coupled with the cells expands or contracts. Each cell in the stack has a solid electrode, a separator and a counter electrode. The counter electrode is made of carbon layers and has a water repelling carbon layer to prevent that the electrolyte contacts a back layer made of graphite paper. The stack of cells is assembled from individual electrodes and separators and is disposed inside an isolating envelope. The layered construction of the counter electrode as well as the manner in which the stacks must be built up is complicated and relatively expensive. Additionally, the disclosed actuator has the disadvantage that generated heat is insufficiently conducted away from the cells, which adversely affects both the service life and functioning of the actuator.


SUMMARY OF THE INVENTION

The problem underlying the present invention is to provide an electrochemical actuator constructed as set forth above but which is simpler and less costly to produce, which has a longer service life, and which functions better.
This is achieved by providing for each cell a stackable spacer frame constructed of a material which is an electric isolator and has good heat conducting characteristics. A metallic cell cup filled with a matrix soaked in the electrolyte is attached to the frame. Each cell further includes a solid body electrode, a separator and a counter electrode. When stacked, the counter electrodes of the cells engage the cell cup of the adjoining cells.
The provision of spacers which can be stacked has the advantage that the assembly and stacking of the cells is quick and efficient. A cell cup incorporated in the spacer receives a matrix for the electrolyte. The other components of the cell; namely, a solid electrode, a separator and a counter electrode, are placed on top thereof. The assembled cells are placed one on top of the other for stacking them so that the counter electrode protrudes slightly from the spacer, extends into the spacer of an adjacent cell, and engages the cell cup of the latter. This construction prevents a lateral displacement of the cells in the stack.
The spacer with the cell cup is made of an electrically isolating material and substantially prevents stray currents between the cells. In addition, the spacers are constructed of a material which is a good heat conductor so that generated heat is carried away from the cells. Several materials or composites have such properties. The spacer can be injection molded from a plastic material including a powdered additive which is a good heat conductor and an electric isolator. Suitable additives are, for example, aluminum oxide, titanium oxide or quartz. However, the spacers can also be made of ceramic oxide materials.
The spacer preferably has cutouts for coupling the gas generating or absorbing counter electrode of the cell with the sealed gas space of the actuator. The cutouts form channels to the gas space along the circumference of the stack of cells. This assures an efficient pressure increase or decrease in the bellows surrounding the gas space.
The removal of heat from the cells is enhanced by positioning the spacers of the cells closely against the housing in which they are received.
The matrix is advantageously soaked with the electrolyte to provide the relatively large amount of electrolyte that is needed for the long-term use of the actuator. A variety of electrode pairs c

REFERENCES:
patent: 3563878 (1971-02-01), Grotheer
patent: 3875040 (1975-04-01), Weltin et al.
patent: 4159367 (1979-06-01), Berchielli et al.
patent: 4565749 (1986-01-01), Ommering et al.
patent: 5425864 (1995-06-01), Botte

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