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. A method for coating a spacer to produce a unipolar or bipolar ionically-conductive spacer comprising the steps of:
cutting a spacer to a desired shape for fluid movement through and around the spacer and inserting appropriately shaped fluid channels for fluid movement through to ion exchange membranes, wherein the spacer has an exterior surface having a first side and a second side opposite the first side;
modifying the spacer to enable greater adhesion between an inert plastic substrate and an ionic coating and promotion of turbulence;
cleaning the spacer via alternating light alcohols and deionized water;
applying a cationic exchange ionomeric coating comprising spray-coating a first solubilized ionomer solution to the first side of the spacer exterior surface;
applying an anionic exchange ionomeric coating comprising spray-coating a second solubilized ionomer solution to the second side of the spacer exterior surface, wherein the cationic exchange ionomeric coating is different from the anionic exchange ionomeric coating;
drying the spacer to remove excess solvent and to cure and set the cationic and anionic ionomeric coatings as a resin which is accomplished concurrently or subsequently to the coating process via air-drying or fan drying, with or without a heat source;
immersing the spacer into a salt-containing solution for the first and second solubilized ionomers to exchange their counterions for a salt ion; and
fitting the spacer into an electrochemical device such that a conductive coating fits within an active area of the device.
2. The method of claim 1 , wherein the ionomeric coating application on the spacer surface is partial, intermittent, directed, degreed, uniform, and/or non-uniform as dictated by the desired directed ion-exchange rate, direction, flow, and/or pathway.
3. The method of claim 1 , wherein the ionomeric coating application process is accomplished through a technique where the ionomer solution is entrained in an air stream and applied via an atomizing spray nozzle and applied to the spacer surface in such a manner as to provide optimum solution placement and adherence upon spacer surface and application process is continued until the desired coating thickness is achieved.
4. The method of claim 1 , wherein the ionomeric coating application process is accomplished through dip-coating, spray-coating, or roll-coating.
5. The method of claim 1 , wherein a spray coating is applied by an atomizing spray nozzle moved with relation to said spacer, said spacer is moved with relation to said nozzle, or both nozzle and spacer are both moved in such a way to ensure complete or incomplete spacer surface exposure and desired solution concentration and thickness where number of passes, flow rate and droplet size are optimized to ensure proper uniform or non-uniform spacer coverage with solubilized ionomeric solution.
6. The method of claim 1 , wherein the surface of said spacer is first prepared and then modified to enable greater adhesion between the inert plastic substrate and the ionic coating.
7. The method of claim 1 , wherein the spacer may be cut to shape prior to coating, after coating or in an intermediate step in a spacer production process.
8. The method of claim 1 , wherein the spacer, is oriented in such a way that the anionic exchange ionomeric coated surface faces a like-charged anion exchange membrane and the cationic exchange ionomeric coated surface faces a like charged cation exchange membrane.
9. A method of claim 1 , wherein the ionomeric solution spray-coating application process for coating the spacer to produce an ionically-conductive spacer is achieved through the implementation of a container (spray gun) and spray nozzle, or a plurality of containers and spray nozzles, for the pressurization and atomization of solution microdroplets for depositing onto the exterior surface of the spacer.
10. The method of claim 9 , wherein the container is a spray gun.
11. The method of claim 1 , wherein the salt-containing solution comprises sodium chloride and water, the pendant charge group comprises hydroxide, and the salt ion comprises chloride.
12. The method of claim 1 , wherein the solubilized ionomer solution is a 1 wt. % solubilized ionomer solution.
13. The method of claim 1 , wherein the solubilized ionomer solution is applied at a 1.25 mg/in 2 loading.
14. The method of claim 1 , wherein bulk spacer material is coated with the solubilized ionomer solution using a roll-to-roll process wherein a first side of the spacer and a second side of the spacer opposite the first side of the spacer are simultaneously coated, and the bulk spacer material is subsequently cut to the desired shape.