GB2545185A - Electrochemical cell - Google Patents

Abstract

Two electrodes 12 are mounted in an electrochemical cell. The cell is formed from two clamped 27 halves 16 and the distance between the electrodes is variable. The variation can be achieved by a bolt 27 engaging screw threads 30 in a knob 34 retained within an orifice of the cells end plate 40. The end of the bolt within the cell can contact the electrode via a pressure plate and the other end can link to an electrical contact. There may be an end plate 40 at either end of the cell and a bolt engaged in each so that the position of each electrode can be adjusted independently. Reference electrodes can project through apertures in the cell and contact the main electrodes and/or the electrolyte around them to measure the cells efficiency. The electrodes and the recesses housing them can be rectangular.

Description

ELECTROCHEMICAL CELL

This invention relates to an electrochemical cell - a device for carrying out electrochemical reactions with products either in solution or adhering to the surfaces of electrodes.

Electrochemical cells are in common use in industry for a wide range of reactions, for energy storage, and are also used in research laboratories for developing new industrial processes and for scientific investigations. Electrochemical cells must contain amongst other components electrodes to make the electrical circuit, means to introduce liquids and in some designs gases, semipermeable membranes to separate different liquid streams but allow electrical current (ions) to pass, spacers to ensure correct spacing of membrane and electrodes. Conductive felts such as graphite felt or other porous materials may be included in order to increase the effective area of the electrodes. All of these components must be assembled in a device that does not leak. This necessitates the use of gaskets and or O-rings and in some cases sealing compounds. This means that electrochemical cells are by their nature time consuming to disassemble and reassemble and prone to leaking if incorrectly assembled. A particular requirement for some research and development applications is the ability to change the geometry of the cell for example the ability to vary the thickness of components including felts or porous materials. This capability is used by researchers and developers of fuel cells and redox flow batteries for example. The ability to vary the cell geometry in this way is also of interest in other research and development activities covering other electrochemical processes such as electrochemical synthesis or reaction.

Electrochemical cells for research and development are available that allow for variable compression of the stacked components by means of applying hydraulic or pneumatic pressure to the stack of materials constituting the cell. This approach allows controlled pressures to be exerted on the assembled components, thereby varying the thickness of the more compressible components such as porous felts. This approach does not allow for relatively large variation of the geometry and it does not allow for accurate determination of distances when using highly porous or compressible materials. It has the additional drawback of needing a controlled pressure supply with control valves. With standard designs of electrochemical cells changing the geometry involves dismantling the cell and replacing or modifying components, which is a time-consuming process.

This invention is a design of electrochemical cell that overcomes these shortcomings. It provides for precise variation of the cell geometry without the need for any additional apparatus or tools. This is achieved by means of a screw thread and control knob on each face of the cell. This feature can be used to vary the electrode spacing with or without a membrane, and with or without other components in the cell such as porous felts. The invention includes sealing arrangements for the variable geometry component so that electrolyte is not released, and a design of electrolyte path that allows the electrode to operate very close to the cell membrane as well as further away from it.

The invention will now be described with reference to the accompanying drawings.

Figure 1 is a front view of the assembled cell

Figure 2 is a cross section through the cell on a plane passing from top to bottom and from front to back face.

Figure 3 is a cross section in plain view through the cell on a plane passing through the cell at mid-height Figure 4 is a perspective view of the assembled cell An electrochemical cell 10 according to the invention has a pair of opposed parallel electrodes 12 each side of the centre 11 of the cell. The electrodes 12 are machined from solid pieces and can be of different materials, but impregnated graphite is commonly used. The electrodes are each mounted in recesses 14 in a pair of cell body halves16. The recesses 14 are deeper than the thickness of the electrodes 12, allowing the electrodes 12 to assume different positions in the recesses 14. The recesses 14 and the active electrode faces 18 in contact with the solution in the cells are rectangular in cross-section prevents the electrodes 12 from rotating. Cylindrical extensions 22 extend from the back 20 of each the electrodes 12 into circular cross sectioned holes 24 in the cell body parts 16. O-ring seals 26 seal between the shafts 22 and the cell body parts 16. Fixed to each of the extensions 22 are conducting cylinders 27 having external screw threads 30.The conducting cylinders have bolts 28 passing through and engaging treaded holes 29 in the extensions 22 to secure the cylinders 27 to the extensions 22. The screw threads 30 engage pins 32 (see figure 3) mounted in an insulating knob 34. Each of the insulating knobs 34 have peripheral lips 36 at one end engaging corresponding recesses 38 in a pair of parallel end plates 40 mounted each side of the cell bodies, the recesses 38 enabling the lips 38 to be retained between the end plates 40 and the cell body parts 16, with the insulating knobs 34 passing through a central holes 42, one in each of the end plates 40. Thus the insulating knob can rotate but not move in or out. The pins 32 mounted on the insulating knob 34 interacting with the screw threads 30 on conducting cylinders 27 move the electrodes 12 inwards and outwards with respect to recesses 14 as the insulating knob 34 is rotated. Graduations are marked on the outside of the end plates 40 to correspond with the position of the insulating knobs 34 to show the distance of the electrode faces 18 from the centre of the cell 10. A narrow port 46 (seen in figure 3) passes through the conducing cylinders 27, the extensions 22 to close to the faces 18 of the electrodes 12, allowing a reference electrode (not shown) to be placed in to the rear of the electrode faces 18, close to the interface with any electrolyte between the faces 18. This allows for accurate determination of the potential at the electrodes 12.

Electrode terminals 48 having externally threaded shanks 50 are screwed into internally threaded holes 52. This enables electrical connection to be made to the electrodes 12. A cover 54 is attached to the outside of each pf the insulating knobs to cover the ends of conducting cylinders 27.

Extending through each of the pairs of cell body halves'! 6 into the recesses 14 at their innermost extremities are a pair of reference electrode ports 56 containing reference electrodes 57. The reference electrodes extend to contact any electrolyte close to the electrode faces 18 and the electrode faces 18 themselves.

Between the pairs of cell body halves16 is a semipermeable membrane 58 in membrane supports 60 clamped in recesses 62 in the pairs of cell body halves16. To one side of the semipermeable membrane 58 is a felt 64, both of the semipermeable membrane 58 and felt 64 are of conventional form and do not form part of the invention as such.

Inlets 66 and outlets 68, again of conventional form take fluid streams to and from chambers 70 each side of the semipermeable membrane 58 from where the fluids can flow either side of the semipermeable membrane.

Assembly of the cell 10 can be carried out without the use of tools, simply using the knurled nuts 72, which pass through one of the pairs of end plates 40 into threaded holes in the other of the pairs of end plates. Tightening of the knurled nuts simply clamps the cell, and in particular the pairs of cell body halves16 together. O-rings 74 set in recesses 76 which going around the recesses 14 and 62 seal the cell. A skilled worker will be able to amend the specific elements of the cell design without departing from the basic principle of the invention which is to provide a system in which the separation of the electrodes and their position in respect to other elements which might be contained in the cell, such as membranes and felts can be adjusted easily without the need to disassemble the cell. Furthermore felts, in particular, can easily be put under a degree of compression.

Claims (8)

Claims

1. An electrochemical cell comprising a pair of cell body halves clamped together, at least two spaced apart electrodes mounted in recesses in the cell body halves, each electrode with electrode faces towards the centre of the cell, and means to change the separation of the electrodes and/or their position relative to the centre of the cell without disassembling the cell.

2. An electrochemical cell according to claim one in which the means comprises a knob interacting with a screw thread, said screw thread being associated with an electrode wherein rotation of the knob moves the electrode with respect to the centre of the cell.

3. An electro-chemical cell according to claim 2 having two knobs and two screw threads, a knob and screw thread moving on electrode, the other knob and screw thread moving the other electrode.

4. An electrochemical cell according to claim 2 or 3 having a pair of end plates, each end plate being outside a cell body half, the end plates having a central hole and recess around the central hole, each knob having an external flange engaging in the recesses around the central holes, the knob having a pin engaging with the screw thread, in which rotation of the knob moves the associated electrode towards or away from the centre of the cell.

5. An electrochemical cell according to any preceding claim additionally comprising an electrode potential probe aperture extending into the sell to behind the electrode faces.

6. An electrochemical cell according to any preceding claim additionally comprising reference electrodes in contact with any electrolyte close to the electrode faces and the electrode faces themselves.

7. An electrochemical cell according to any preceding claim in which the electrodes are rectangular and the recesses in the cell body halves are rectangular.

8. An electrochemical cell substantially as hereinbefore described with reference to the accompanying drawings.