Bipolar electrochemical spacer
The present invention provides a device capable of reducing the resistance and increasing the ion exchange rate in an electrodialysis, electro-deionization, or capacitive deionization apparatus and a method for producing said device. More specifically, the device is an electrodialysis spacer designed to have an ionically conductive surface of either cationic nature, anionic nature or a combination of both, which act as conductive pathways for ions as they move towards their respective electrode. The method of producing said spacer involves coating a substrate, such as a woven mesh, expanded netting, extruded netting or non-woven material, with perm-selective ionomer solutions and applying that substrate to an inert spacer material that has undergone chemical or mechanical etching.
1. An electro-chemical apparatus for reducing the resistance in an electrodialysis, electro deionization, or capacitive device, comprising:
a. a pair of electrodes;
b. an applied voltage;
c. alternating anionic and cationic exchange membranes placed between the pair of electrodes for separation of ions from a depleted stream to a concentrate stream;
d. an ionically neutral, non-conducting spacer which may be woven, porous or non-woven;
e. said spacer with an exterior surface having a first side and a second side opposite the first side, the first side comprises a first coating comprising a cationic exchange ionomer and the second side comprises a second coating comprising an anionic exchange ionomer, wherein the first coating is different from the second coating.
2. The electrochemical apparatus of claim 1 , wherein the first and second coatings are a topical application onto the exterior surface of said ionically neutral, non-conductive spacer that is a woven mesh, expanded netting, extruded netting or a non-woven material.
3. The electrochemical apparatus of claim 1 , wherein the first and second coatings are applied to said spacer via a coating process comprising spray-coating, inkjet printing, curtain coating or dip-coating.
4. The electrochemical apparatus of claim 3 , wherein the coated spacer is cured to assure adherence of ion-conducting, ionically charged material to said spacer.
5. The electrochemical apparatus of claim 1 , wherein the first and second coatings form a network of anionic or cationic exchange channels, which act as an array of conductive pathways for ions and ion exchange.
6. The electrochemical apparatus of claim 1 , wherein said spacer's surface is chemically altered via acid etching treatment with strong, peroxide attack, and etching with strong bases to create deformities in said spacer's surface for the creation of turbulent rheologic disturbances for an enhanced ion-exchange rate.
7. The electrochemical apparatus of claim 1 , wherein said spacer's surface is mechanically altered via flame oxidation, corona discharge plasma, laser etching, hollow cathode glow discharge, or sand-blasting for the creation of turbulent rheologic disturbances for an enhanced ion exchange rate.
8. The electrochemical apparatus comprising:
a. a spacer for reducing the resistance in an electrodialysis, electro-deionization, or capacitive device where the spacer has a first side and a second side opposite the first side, the first side comprises a first coating comprising a cationic exchange ionomer and the second side comprises a second coating comprising an anionic exchange ionomer, wherein the first coating is different from the second coating, residing between anionic and cationic ion exchange membranes, which facilitates transport of n ionic solution through oppositely charged ionic pathways to surfaces of the ion exchange membranes;
b. at least one anode or a plurality of anodes;
c. at least one cathode or a plurality of cathodes;
d. one or a plurality of fluid channels separated by anionic and cationic ion exchange membranes, where the anionic exchange membranes preferentially allow the passage of negatively charged ions and substantially block the passage of positively charged ions and cationic exchange membranes preferentially allow the passage of positively charged ions and substantially block the passage of negatively charged ions and exhibit alternating pathways of ever decreasing ionic concentration streams and increasing ionic concentration streams;
e. electrolyte containing fluid channels in direct contact with the anode and cathode which may be the same or different fluid as the fluid entering the electrodialysis device; and
f. an electric charge applied to the anode and cathode thereby causing the ions in the fluid stream to flow through the fluid channels and migrate toward the electrodes displaying the opposite electric charge.
9. The electrochemical apparatus of claim 8 , wherein the first and second coatings extend the ion exchange material into the flow paths away from the surface of the ion exchange membranes thereby lowering the resistance within the flow channels.
10. The electrochemical apparatus of claim 8 , wherein the spacer residing between ionically charged membranes comprises: (1) a spacer frame that acts as a seal between fluid chambers and as a seal between internal fluids and the exterior; and (2) a spacer mesh, which is either woven or extruded netting, that spans the internal opening in the sealing frame and provides fluid channels between ionically charge membranes through alternating fluid pathways through said spacer and into contact with said ionically charged membranes.
11. The electrochemical apparatus of claim 9 , wherein the spacer is made of a non-reactive, non-ionic plastic or elastomeric material that is made to display ionomers resulting in a spacer that is bipolar in nature.