IE46082B1 - Electrode assembly for an electrolytic cell - Google Patents

Abstract

1534942 Coated electrodes PORTALS WATER TREATMENT Ltd 3 Nov 1977 [11 Nov 1976] 46958/76 Heading C7B At least one catalytically coated electrode in a mono- or bi-polar set (e.g. in a seawater hypochlorite cell) is peripherally uncoated whereby to centralize current flow and minimize edge fouling. Sinuous liquid flow may be provided.

Description

The present invention relates to an electrode assembly for an electrolytic cell.

In electrolytic cells such as those used for the preparation of hypochlorite from sea water, chlorine is liberated at an anode with the result that the electrolyte immediately adjacent to the anode is acidic. Adjacent to the cathode however, caustic soda is liberated making the electrolyte strongly alkaline and if hardness in the form of calcium or magnesium are present, this may precipitate in the form of a scale or deposit. · In a correctly designed cell the velocity combined with the scouring action of hydrogen bubbles liberated, is usually sufficient to prevent the deposit building up into a hard scale. On the other hand, at the edges of the electrode, adjacent to the support, flow is Inevitably restricted and a laminar flow boundary layer is inevitably established.

Once scale starts to form, progressive further deposition may well continue because the resultant deposit is inevitably porous -246082 and further magnesium ions may penetrate the porous mass and be precipitated adding to the growth.

Ultimately this may cause complete starvation of the electrolyte flow.

In applications such as the above, it is common practice to apply a coating material over the base substance of the electrode, in order to reduce the electrode voltage and improve the electrochemical efficiency. In many cases also this coating prevents erosion or dissolution of the base electrode material. Such coating materials commonly comprise metals such as platinum or other noble metals or oxides of such metals or indeed lead dioxide. In a hypochlorite cell for example the base electrode material may comprise titanium. However, fouling still occurs at the edges of the electrode.

An object of the invention is to provide an electrode assembly in which during electrolyses fouling at the edges of the electrode is minimised.

'The invention provides an electrode assembly for an electrolytic cell comprising, a first electrode plate having on a major surface thereof a central portion coated with a voltage-reducing material and an uncoated peripheral portion bordering the central portion, together with a second electrode plate which is spaced from and faces said one major surface of the first electrode plate, the arrangement being such that, in use, current is channelled through the central portion of the first electrode plate and this is reflected in a like channelling of current through the second electrode plate thereby minimising fouling of the opposed peripheral portions of both the first and second electrode plates. 346082 The Invention further provides an electrolytic cell having the above-described electrode assembly.

The said first electrode plate may, for example, be the anode of a pair of electrodes or of a set of bipolar electrodes.

The invention will now be described with reference to an embodiment shown by way of example only in the accompanying drawing, wherein: Figure 1 is a vertical section normal to the flow direction through an electrode assembly according to the invention, and Figure 2 is an exploded perspective view of the electrode plates of Figure 1.

In the drawing, an electrode assembly comprises three electrode plates 1, 2, 3 separated by spacer gaskets 4. As can be seen from Figure 1, the cathode plate 1 is uncoated and the other plates 2 and 3 are provided with an active coating 5, e.g. of titanium, graphite, a noble metal or alloys thereof or oxides thereof, or lead dioxide. The active coating 5 terminates before the edge of each plate 2, 3, so as to leave a peripheral nonactive margin 6. The limit of contact of the gaskets 4 with the plates is shown by broken lines 7 in Figure 2.

The plates are each provided with a transverse slot 8 near one end of the plate, the slots being staggered with respect to each other so as to provide a sinuous path as shown by the arrows in Figure 2.

In use, current through the electrode plates 2, 3 flows mainly or only through the coatings 5, leaving the uncoated -44 6082 margins 6 substantially inactive. This channelling of current through the coatings 5 is reflected in a like channelling of current on the cathode plate 1.

Any intermediate supports on the electrode assembly such 5 as studs placed in the centre to maintain inter-electrode separation, may be similarly treated so as to be non-active.

Having regard to the provisions of Section 14 of the Patents Act,1964 attention is directed to the claims of Patent No. 44,616..

Claims (4)

1. An electrode assembly for an electrolytic cell comprising, a first electrode plate having on a major surface thereof a central portion coated with a voltage-reducing material and an uncoated peripheral portion bordering the central portion together with a second electrode plate which is spaced from and faces said one major surface of the first electrode plate, the arrangement being such that, in use, current is channelled through the central portion of the first electrode plate and this is 15 reflected In a like channelling of current through the second electrode plate thereby minimising fouling of the opposed peripheral portions of both the first and second electrode plates.

2. An electrode, assembly as claimed in Claim 1, wherein said first electrode plate is the anode of a pair of electrodes or of 20 a set of bipolar electrodes.

3. An electrode assembly substantially as herein described with reference to the accompanying drawing. -5

4. An electrolytic cell having an electrode assembly as claimed in any one of the preceding claims.