Source: http://www.google.com/patents/US5045163?dq=7,321,221
Timestamp: 2014-09-23 13:23:06
Document Index: 69555922

Matched Legal Cases: ['Application No. 38', 'Application No. 38', 'Application No. 38', 'Application No. 38', 'Application No. 2', 'Application No. 63', 'Application No. 67', 'Application No. 74', 'Application No. 128', 'Application No. 119', 'Application No. 84', 'Application No. 84', 'Application No. 84', 'Application No. 84', 'art 663', 'art 735', 'arth 142', 'arth 142']

Patent US5045163 - Electrochemical method for measuring chemical species employing ion exchange ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsAn electrode, preferably of a conductive polymer, has on its surface, preferably over all of its surface, an ion exchange material, preferably of significant thickness. Such a coated electrode may be used for sensing the presence or measuring the concentration of an ionic species, or for removal from...http://www.google.com/patents/US5045163?utm_source=gb-gplus-sharePatent US5045163 - Electrochemical method for measuring chemical species employing ion exchange materialAdvanced Patent SearchPublication numberUS5045163 APublication typeGrantApplication numberUS 07/534,316Publication dateSep 3, 1991Filing dateJun 5, 1990Priority dateFeb 20, 1986Fee statusPaidPublication number07534316, 534316, US 5045163 A, US 5045163A, US-A-5045163, US5045163 A, US5045163AInventorsEric D. Nyberg, Ken A. Klingman, Jeff Curtis, Ray F. StewartOriginal AssigneeRaychem CorporationExport CitationBiBTeX, EndNote, RefManPatent Citations (23), Non-Patent Citations (4), Referenced by (8), Classifications (22), Legal Events (6) External Links: USPTO, USPTO Assignment, EspacenetElectrochemical method for measuring chemical species employing ion exchange materialUS 5045163 AAbstract An electrode, preferably of a conductive polymer, has on its surface, preferably over all of its surface, an ion exchange material, preferably of significant thickness. Such a coated electrode may be used for sensing the presence or measuring the concentration of an ionic species, or for removal from or release of an ionic species into an electrode.
We claim: 1. A method of monitoring an electrolyte to determine a change in the concentration of a chemical species in that electrolyte, or of monitoring the presence of an electrolyte comprising a chemical species, which method comprises:(I) providing a source of electrical power, (II) providing an apparatus comprising:(a) a first electrode which is connectable to the source of electrical power; (b) a second electrode which is connectable to the source of electrical power, and which is spaced apart from the first electrode, the first and second electrodes being so positioned and arranged that when an electrolyte containing a chemical species is between the electrodes and the source is connected to the electrodes, current passes between the electrodes through the electrolyte; and (c) an ion exchange material which(i) is in electrical and physical contact with and substantially entirely surrounds the surface of one of the electrodes, and (ii) has an ionic resistance to the passage of the current, which ionic resistance depends upon the concentration of the chemical species in the electrolyte; (III) connecting the source of electrical power to the first and second electrodes whereby when the electrolyte is between the electrodes, an electrochemical reaction takes place at the interface of the ion exchange material and the electrode contacted thereby, generating an ionic species, and substantially all the ionic species so generated passes through the ion exchange material; and (IV) monitoring a voltage change between the electrodes or along at least one of the electrodes, associated with a change in the ionic resistance of the ion exchange material. 2. A method of monitoring an electrolyte to determine a change in the concentration of a chemical species in that electrolyte, or of monitoring the presence of an electrolyte comprising a chemical species, which method comprises:(I) providing a source of electrical power, (II) providing an apparatus comprising:(a) a first electrode which is connectable to the source of electrical power; (b) a second electrode which is connectable to the source of electrical power, and which is spaced apart from the first electrode, the first and second electrodes being so positioned and arranged that when an electrolyte containing a chemical species is between the electrodes and the source is connected to the electrodes, current passes between the electrodes through the electrolyte; and (c) an ion exchange material which(i) is in electrical and physical contact with and lies on a surface of one of the electrodes, with the remaining surfaces of said one of the electrodes being electrically insulated from the electrolyte by an electrically insulating layer, and (ii) has an ionic resistance to the passage of that current, which resistance depends upon the concentration of the chemical species in the electrolyte; (III) connecting the source of electrical power to the first and second electrodes whereby when an electrolyte is between the electrodes, an electrochemical reaction takes place at the interface of the ion exchange material and the electrode contacted thereby, generating an ionic species, and substantially all the ionic species so generated passes through the ion exchange material; and (IV) monitoring a voltage change between the electrodes or along at least one of the electrodes, associated with a change in the ionic resistance of the ion exchange material. 3. A method according to claim 1 or 2, wherein in the presence of the chemical species, a component of the electrolyte is absorbed by the ion exchange material reducing the ionic resistance of the ion exchange material, said component contacting the first electrode and undergoing an electrochemical reaction at the electrode surface producing a product that reacts with the ion exchange material and thereby converting the ion exchange material back to a state of higher ionic resistance upon a decrease in the concentration of the chemical species.
(3) a second electrode; and
(4) an electrolyte which electrically connects the first and second electrodes;
(4) an electrolyte which electrically connects the first and further electrodes, and which, at the interface between the first electrode and the ion exchange material A, undergoes an electrochemical reaction which generates an ionic species I6A which replaces the ionic species I3A .
Such methods can be used to extract species from or release species into a liquid or other electrolyte by means of various electrochemical processes, for example water electrolysis, where a resulting ionic species directly or indirectly effects a modification of the ion exchange material. One purpose of such methods is the purification of the liquid, and another is the recovery of the species For example industrial wastes, sewage, or mining liquors etc. may be cleaned or salt water may be desalinated. Examples of species that may desirably be recovered include heavy metals, cyanide, phosphates and sodium Selective ion removal for recovery may be desirable in hydrometallurgical mining operations, metal plating operations and mining of natural waters such as the ocean.
For these methods, the capacity of the ion exchange material may be important, and we prefer that the material have an ion exchange capacity of at least 0.1, particularly at least 0.4 milliequivalents per gram. Preferably the material is in the form of a layer which has a thickness of at least 0.04 mils (1�10-6 m), more preferably at least 0.4 mils (1�10-5 m), especially at least 4 mils (1�10-4 m). However, ion exchange materials may increase substantially in volume between a dry state (in which they are generally manufactured) and a solvated state in which we prefer to use them. It is impossible using prior art techniques to prepare a device comprising an electrode and a layer of an ion exchange material which (a) is less (especially if substantially less) than 100% solvated, (b) is at least 0.04 mils (1�10-6 m) thick in the fully solvated state, and (c) is secured to an electrode sufficiently well to make it possible to use it in the methods defined above. As will be explained below, we have solved these problems by using an electrode than can change its dimensions sufficiently to accommodate changes in the dimensions of the ion exchange material, for example as the solvation of the ion exchange material increases. Preferably the electrode comprises a material which electrically and physically contacts the ion exchange material and which has an elastic modulus less than 1013 dynes/cm2, particularly less than 1011 dynes/cm2, especially less than 109 dynes/cm2. Particularly useful such materials are conductive polymers, i.e. mixtures of a conductive filler and an organic polymer (this term being used to include polysiloxanes), the filler being dispersed in, or otherwise held together by, the organic polymer.
The invention in its second set of embodiments is of particular value as an acid sensor (i.e. for detecting the presence of, or a change in concentration of, hydrogen ions), especially as part of a system disclosed in the following patent specifications, the disclosure of each of which is incorporated herein by reference: EP 0,133,748, U.S. Ser. No. 509,897, Masia et al.; U.S. Ser. No. 599,047, Masia et al.; U.S. Ser. No. 599,048, Masia et al.; EP 0,144,211, U.S. Ser. No. 566,740, Walsey; U.S. Ser. No. 566,829, Walsey; EP 0,164,838, U.S. Ser. No. 618,106, Hauptly; U.S. Ser. No. 618,109, Reeder; U.S. Ser. No. 618,108, Brooks et al.; U.S. Ser. No. 608,485, Brooks et al.; EP 0,160,441; U.S. Ser. No. 603,484, Frank et al; EP 0,191,547; U.S. Ser. No. 691,291, McCoy et al.; U.S. Ser. No. 809,321, McCoy et al.; U.S. Ser. No. 744,170, Stewart et al.; U.S. Ser. No. 787,278, Stewart et al.. These specifications together with the present specification will allow the skilled man to design various systems for location of acid or other electrolytes.
(b) an ion exchange material affixed to a surface of the electrode, the ion exchange material being less than 10% swollen with a liquid; the material being affixed to said surface and the electrode being such that when the ion exchange material is 100% swollen the ion exchange material remains in electrical and physical contact with the electrode.
The precursor may have ion exchange functionality, or such functionality may be introduced during or after polymerization.
BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 show a series of electrodes for use in ion exchange;
FIG. 5 shows a composite electrode before affixing to an ion exchange material;
FIG. 15 shows further arrangements of a sensor within a battery.
DETAILED DESCRIPTION OF FIRST EMBODIMENTS OF THE INVENTION The following description relates to the use of the invention for extraction of a species from an electrolyte, or release of a species into an electrolyte. (Description of the invention relating to sensing will follow afterwards.)
A. In the Anode region at the interface
2H2 O&#8594;O2 +4e- +4H+ (species I2A )
B. In the Cathode region at the interface
2H2 O+2e- &#8594;H2 +2OH- (species I2B ).
We have discovered that prior art techniques disclosed in connection with ion-exchange resins are often not suitable for use in the production of articles for use in carrying out the method of the present invention In particular, we have found problems in delamination of resins from electrodes and have found that such problems can be overcome by in situ polymerization of ion-exchange monomers or other precursors.
P--R                                                       I
The ion exchange material is preferably coated as a layer of substantially uniform thickness on the electrode. Preferably the layer has a thickness of at least 1�10-6 m. More preferably it has a thickness in the range 2�10-5 to 1�10-3 m, particularly in the range 5�10-5 to 1�10-3 m, especially in the range 1�10-4 to 1�10-3 m. Preferably the ion exchange material covers substantially the entire surface of the electrode.
A conductive polymer is a mixture of a conductive filler and an organic polymer (this term being used to include polysiloxanes) the filler being dispersed in, or otherwise held together by, the organic polymer. Any suitable conductive filler may be used, for example, carbon black, graphite, metal or metal oxide particles or a mixture thereof. Documents describing conductive polymer compositions and devices comprising them include U.S. Pat. Nos. 2,952,761, 2,978,665, 3,243,753, 3,351,882, 3,571,777, 3,757,086, 3,793,716, 3,823,217, 3,858,144, 3,861,029, 3,950,604, 4,017,715, 4,072,848, 4,085,286, 4,117,312, 4,177,376, 4,177,446, 4,188,276, 4,237,441, 4,242,573, 4,246,468, 4,250,400, 4,252,692, 4,255,698, 4,271,350, 4,272,471, 4,304,987, 4,309,596, 4,309,597, 4,314,230, 4,314,231, 4,315,237, 4,317,027, 4,318,881, 4,327,351, 4,330,704, 4,334,351, 4,352,083, 4,388,607, 4,398,084, 4,413,301, 4,425,397, 4,426,339, 4,426,633, 4,427,877, 4,435,639, 4,429,216, 4,442,139, 4,459,473, 4,481,498, 4,476,450, and 4,502,929; J. Applied Polymer Science 19, 813-815 (1975), Klason and Kubat; Polymer Engineering and Science 18, 649-653 (1978), Narkis et al; and commonly assigned U.S. Ser. No. 601,424 now abandoned, published as German OLS No. 1,634,999; 732,792 (Van Konynenburg et al), now abandoned, published as German OLS No. 2,746,602; 798,154 (Horsma et al), now abandoned, published as German OLS No. 2,821,799; 134,354 (Lutz); 141,984 (Gotcher et al), published as European Application No. 38,718; 141,988 (Fouts et al), published as European Application No. 38,718, 141,989 (Evans), published as European Application No. 38,713, 141,991 (Fouts et al), published as European Application No. 38,714, 150,909 (Sopory), published as UK Application No. 2,076,106A, 184,647 (Lutz), 250,491 (Jacobs et al) published as European Application No. 63,440, 272,854 and 403,203 (Stewart et al), published as European Patent Application No. 67,679, 274,010 (Walty et al), 300,709 and 423,589 (Van Konynenburg et al), published as European Application No. 74,281, 369,309 (Midgley et al), 483,633 (Wasley), 493,445 (Chazan et al), published as European Patent Application No. 128,664, 606,033, (Leary et al), published as European Application No. 119,807, 509,897 and 598,048 (Masia et al) published as European Application No. 84,304,502.2, 524,482 (Tomlinson et al) published as European Application No. 84,305,584.7, 534,913 (McKinley), 535,449 (Cheng et al) published as European Application No. 84,306,456.9, 552,649 (Jensen et al) published as European Application No. 84,307,984.9, 573,099 (Batliwalla et al) and 904,736, published as UK Patent Nos. 1,470,502 and 1,470,503, and commonly assigned application Ser. Nos. 650,918 (Batliwalla et al, MP0959), 650,920 (Batliwalla et al, MP0961-USl), continuation-in-part 663,014 (Batliwalla et al, MP0961-US2), continuation-in-part 735,408 (Batliwall et al, MP0961-US3), 650,919 (Batliwalla et al, MP0962),650,921 (Kheder, MP0973), 711,790 (Carlomagno, MP0991), 667,799 (Frank, MP0998), 711,908 (Ratell, MP1016), 711,907 (Ratell, MP1021), 711,909 (Deep et al, MP1022), 720,118 (Soni et al, MP1039), and 711,910 (Au et al, MP1044). The disclosure of each of the patents, publications and applications referred to above is incorporated herein by reference.
In one embodiment the electrode comprises a conductive polymer, and the ion exchange material comprises a polymeric material which has been bonded to the electrode surface in such a manner that there is produced a layer of a polymer blend between electrode and material which is at least 1 optionally at least 5 microns thick. The polymer blend layer is a blend of the polymer of the ion exchange material or the ion exchange material precursor, and the conductive polymer of the electrode.
Preferably the electrode has an elastic modulus less than 1013 dynes./cm2, and it is preferably solid in cross-section.
A particularly preferred embodiment of the invention when used for ion removal comprises a plurality of electrodes, preferably planar, which are arranged in a stack, that is with each face of an electrode facing a face of its adjacent electrode. In the stack each electrode is preferably a bipolar electrode, that is one of its faces behaves as an anode and the other of its faces behaves as a cathode. With this arrangement each adjacent pair of electrodes functions as a cell which can effect ion extraction and expulsion. Thus for a stack of bipolar plates the capacity for ion exchange and expulsion is approximately n�capacity of a single anode/cathode cell.
Referring now to the drawings, FIGS. 1 and 2 show a stack of electrodes 2 supported in a casing 4 by insulating supports 6. Each electrode is planar and is arranged substantially parallel to its neighbor. The outermost electrodes (that is those nearest to the casing sides) are connected to a DC power source 8. As illustrated in FIG. 1 the electrode on the right of the drawing is connected to the negative terminal of the power source, and the electrode on the left of the drawing is connected to the positive terminal of the power source. A liquid 10 containing an ionic component (MA) is recycled through the casing as shown by the arrows The inlet and outlet for the liquid 10 are at opposite ends of the casing 4. Thus the liquid 10 passes over each electrode 2. The liquid 10 contains a number of ionic species. From the liquid, cation M+ and anion A- are to be extracted.
Each electrode 2 is a bipolar electrode, that is one of its surfaces behaves as an anode (oxidation occurs at its surface), and the other of its surfaces behaves as a cathode (reduction occurs at its surface). Each electrode comprises a conductive polymer core, which may include a metallic current collector. The outermost electrodes are coated on their inward facing surfaces with an ion exchange material. The central electrodes are coated on both their surfaces with an ion exchange material. All those surfaces facing one direction (to the left as illustrated) are coated with a weak acid cation exchange material PCOOH 12, (in which the exchangeable ion is H+). All those surfaces facing in the opposite direction (to the right as illustrated) are coated with a weak base anion exchange material PNR2 14. The cation exchange material PCOOH has a greater affinity for M+ than for any of the other cations in solution 10. It also has a greater affinity for H+ ions than for M+ ions. The weak base anion exchange material has a greater affinity for OH- ions than for A- ions With the power source connected as shown, the left facing surface of each electrode behaves as a cathode, and the right facing surface of each electrode behaves as an anode. Thus a series current passes between the outermost electrodes. As current is passed the following reactions occur at each anode and cathode surface, and in the ion exchange materials.
The extracted ions M+ and A- may then be expelled into a liquid. To do this the liquid 10 may be replaced by pure water, and the electrical connections to the power source reversed With the reversed connections each surface coated with a cation exchange material now behaves as an anode, and each surface coated with an anion exchange resin now behaves as a cathode. As current is passed the following reactions occur at each cathode and anode surface.
Ion exchange is more efficient than previous methods employing chemical or electrical regeneration because all H+ and OH- "eluant" must pass through the ion exchange layer bonded to the electrode. In contrast, the passage of eluant through any system using ion exchange resin beads, as in the prior art, leaves open the possibility that eluant ions will bypass many beads. This is a particular possibility when the ion exchange material exhibits a large ionic resistance, for example when the beads do not swell considerably. The present invention (unlike some of the prior art systems employing electrochemical regeneration, e.g. U.S. Pat. No. 4,032,452, Davies) can allow the use of ion exchange layers and solutions of a broader range of resistivities The present invention in particular can allow the use of low or high resistivity solutions regardless of the resistivity of the ion exchange layer When compared to chemical regeneration, the methods of regeneration disclosed herein benefit from the economy, safety, cleanliness and convenience achievable with electrical regeneration.
FIG. 3 shows an alternative arrangement illustrating a parallel circuit design. Each bifunctional electrode 30 is substantially planar and comprises five layers The five layers are from left to right, cation exchange layer 32, conductive polymer 34, insulating core 36, conductive polymer 34, and anion exchange layer 38. Each conductive polymer layer is connected to a power supply 8. The conductive polymer layer may include a metallic current collector. As in the series circuit, each electrode is arranged such that all the surfaces facing in one direction behave as anodes and all the surfaces facing in the other direction behave as cathodes. Liquid 10 is fed into the casing 4 as in the embodiment illustrated in FIGS. 1 and 2. Thus a series of parallel electrochemical cells are produced. Equivalent extraction and expulsion processes to those described with reference to FIGS. 1 and 2 can be carried out.
A preferred method will now be described of making an ion-binding article, suitable for use in the method of replacing an ionic species described above. This preferred method allows an ion-exchange material to be attached to an electrode sufficiently securely that swelling forces, resulting for example from the immersion of a dry or less than 100% solvated article in a solution, for example an aqueous solution, may be resisted. In general, one or more monomers or other ion-binding resin precursors are polymerized in situ, i.e. in contact with an electrode. The precursor may have ion-exchange functionality before is brought in contact with the electrode, functionality may be introduced during polymerization, or functionality may be introduced after polymerization is complete.
It is preferred that the electrode in contact with monomers or other precursors be capable of absorbing one or more of the precursors. It is also preferred that the electrode comprise a thermoplastic material, for example a conductive polymer, especially a polymer having carbon black therein Absorption of the precursor, we have found, can result in a bond between the electrode and the resulting ion-exchange resin that is surprisingly strong. It is believed that this bond has the nature of an interpenetrating network. The bond region may penetrate the surface of the electrode to a distance from, say, 10-7 to 10-3 m, preferably 10-7 to 1�10-4 m. The depth achieved in practice will depend on the solubility of the precursor in the electrode material, and on the temperature at which polymerization is carried out. Thus, the temperature, the precursor and electrode materials (and thus the solubility of one in the other) may be varied to achieve the desired depth of interpenetration, and thus the desired bond strength.
Two examples may be given. Firstly, an electrode comprising a composite of metal wire and SCLAIR 11W plus carbon was penetrated to a depth of about 5�10-5 m by a polymerizing liquid monomer polymerized at a temperature 20� C. above the Tm (melt temperature) of the electrode composite. Secondly, a depth of penetration of about 1�10-4 m was achieved in the case of an Elvax 360/carbon electrode composite and a liquid monomer polymerized at 40� C. above Tm.
Which route is chosen for the introduction of functionality will, of course, depend on the functional group desired and on the chemical nature of the electrode and polymer backbone of the ion-exchange resin, and on any solvent employed It may, also, however, depend on other behavior of the various chemical species, for example on the solubilities of the species in a common solvent such as a coating solution, and upon the solubility of the various possible precursors in the electrode material.
EXAMPLE 1 An electrode 56 before bonding to an ion exchange membrane, is 3.3 cm wide, 6.0 cm long and 0.3 cm thick. It is illustrated in FIG. 5 and it consists of three materials, a conductive polymer blend of 41.8% graphite (GP-39, trade mark), 12.6% carbon (Conductex 975, trade mark), and 43.5% base polymer 51 and 52, an aluminum mesh current collector 53, and unfilled base polymer for insulation 54 and 55. The insulating material is positioned such that only one face of conductive polymer 51, the active electrode surface, is exposed upon immersion in a liquid, and the current collector is placed between the conductive polymer face opposite the exposed face and the insulating layer. The aluminum mesh and insulating layer extend above the active electrode surface 51 to conductive polymer 52 to provide a place for the electrical connection.
The ion exchange material may be deposited in one step by employing a monomer possessing the desired ion exchange functionality. Electrode 56 was heated on a hot plate to 135� C. for 3 min. and 0.25 g of a solution of 47.43 weight percent 2-ethylhexyl acrylate, 45.90% 4-vinylpyridine, 3.49% technical divinylbenzene (55% grade), and 3.18% t-butylperoctoate added dropwise to cover the surface of the exposed face of the conductive polymer. The electrode was then covered with a shallow dish to contain vapors and left at 135� C. for 10 min., when it was removed and allowed to cool. This was swollen in 1 M HCl to form the pyridinium chloride form of the ion exchange material.
EXAMPLE 2 Rather than using a functional monomer as in Example 1, the ion exchange functionality may be incorporated during the polymerization. Electrode 56 was heated to 120� C. on a hot plate for 3 min , and 0.56 g of a solution of 37.75 weight % vinylbenzylchloride, 7.5% 4-vinylpyridine, 4.2% technical divinylbenzene, 1.3% t-butylperoctoate, and 50% 1-methylnapthalene (an inert diluent) added dropwise to cover the surface of the exposed face of the conductive polymer. The electrode was then covered with a shallow dish to contain vapors and left at 120� C. for 6 min., when it was removed and allowed to cool. After soaking the article for 24 hours first in 50/50 methylethyl ketone/methanol then in water, the article could be placed in 1 M HCl to form the pyridinium chloride form of the ion exchange material.
EXAMPLE 3 This article was prepared as in Example 2 but a monomer solution of 30.66 weight percent 4-vinylpyridine, 12.86% vinylbenzyl chloride, 5.0% technical divinylbenzene, 1.48 % t-butylperoctoate, and 50% 1-methylnapthalene was added dropwise to the electrode 56 heated to 120� C.
EXAMPLE 4 A hydrophobic layer containing an ion exchange precursor may be attached to electrode 56 as described in Example 1, and subsequently reacted in one or more steps to introduce the ion exchange group. In this example a two step functionalization process is required to produce a water swellable ion exchange layer with high capacity for copper ion. Electrode 56 was heated to 135� C. on a hot plate for 3 min. and 0.25 g of a solution of 91.4 weight percent vinylbenzyl chloride, 6.2% technical divinylbenzene, and 2.4% t-butylperoctoate added dropwise to cover the exposed face of the conductive polymer. This was covered with a shallow dish to contain vapors, left at 135� C. for 10 min., and allowed to cool. The weight of the ion exchange precursor layer was determined gravimetrically, and found to be 0.20 g.
Twenty percent quaternization, based on vinylbenzyl chloride, was introduced by using enough dimethylethylamine to react with 30% of the vinylbenzyl chloride groups (one-third of this reagent does not react). This functionality is required to provide adequate water swellability and to allow the introduction of sufficient sarcosine functionality in the following step. The article with a 0.20 g layer (possessing 0.18 g vinylbenzyl chloride) was therefore swollen in a mixture of 200 ml methylethyl ketone and 0.026 g dimethlethylamine for 2 hours then heated at 40� C. for 16 hours. After stirring in water several hours the article could be treated with 1 M KBr to exchange bromide for chloride. The relative intensities of the bromide and chloride peaks in an X-ray fluorescence spectrogram confirmed that 20% of the vinylbenzyl chloride groups had been quaternized.
The 20% quaternized article, with or without the KBr exchange step, was functionalized with sarcosine by placing it in a solution of 18.3 g sodium sarcosinate, 180 ml methanol and 120 ml water, stirring 20 hours, and then heating at reflux for 16 hours. After cooling to room temperature, 165 ml. of 1 M HCl was added slowly, and the article rinsed in water. The copper capacity of this ion exchange layer was measured by stirring in 1 M CuCl2 for 2 hours, rinsing for 2 hours, and finally extracting the copper in 1 M HCl. The absorbence of the HCl solution at 788 nm was used to calculate the copper ion concentration with Beer's law (using an extinction coefficient of 11.4), and this article was found to have a copper capacity of 0.76 mmoles Cu/g ion exchange layer (based on an ion exchange precursor layer weight of 0.20 g.).
EXAMPLE 5 This is a further example of introduction of the sarcosine ion exchange functionality following the polymerization of the monomers. The article from Example 2 (without the HCl treatment) was placed in a solution of 18.3g sodium sarcosinate, 180 ml. methanol and 120 ml. water, stirred for 2 hours at room temperature, then heated at reflux for 16 hours. The mixture was cooled to room temperature, 165 ml. of 1 M HCl added slowly, and the article rinsed in water for 16 hrs. After stirring in 1 M KOH for 2 hours, water for 2 hours, 1 M CuCl2 for 2 hours, and finally water for 2 hours, the copper ion capacity was measured by extraction of the article with 1 M HCl and measurement of the solution absorbance using visible spectroscopy. The copper capacity was found to be 0.90 mmoles Cu/g ion exchange material.
EXAMPLE 6 FIG. 6 shows a first electrode 62 as described in Example 4 with the sarcosine ion exchange layer 63 in the copper form placed in a 3.5 cm wide by 5.5 cm high by 1.3 cm wide plexiglass cell 64 facing a second electrode 66 without an ion exchange layer, and 11.0 ml 0.1 F NaClO4 liquid electrolyte added immediately to level 67 just above the top of layer 63. Powered expulsion of copper(II) was effected by connecting the two electrodes through silver painted conductive polymer tabs 68 to a constant current power supply 69 with the first electrode 62 as the anode. A current of 1 mA/cm2 (6mA total) was applied for 80 minutes, passing a total of 1.4 mmole electrons/g ion exchange layer and providing 1.5 mmole H+ /g via the electrochemical oxidation of water. (Two H+ are required for each copper(II) originally in the ion exchange layer.) The direct electrochemical expulsion of Cu(II) is represented by the following reactions:
(PsarcH)2 Cu+2H+ &#8594;Cu+2 +2Psarc       b.
Psarc in reaction b represents the sarcosine functionalized in the ion exchange layer. A light blue Cu(OH)2 precipitate forms during the expulsion. The power supply was disconnected and the cell left to rest for one hour. The electrodes 62,66 were removed and the quantity of copper expelled calculated directly from the copper found as Cu(OH)2 precipitate, and by difference after measuring the copper remaining in the ion exchange material on electrode 62. The Cu(OH)2 solid was dissolved by adding 1.0 ml 1.0 M aqueous HCl, and the copper concentration measured by visible spectroscopy. The copper remaining in the ion exchange layer after expulsion was measured as before for the capacity measurement by extraction with 1.e M HCl.
For this example both measurements found the efficiency of copper(II) expulsion to be 20%, defining this quantity as 100�(2�moles copper expelled/moles electrons passed).
EXAMPLE 7 The electrode article prepared in Example 5, with the copper sarcosinate ion exchange material (the first electrode 62) and the article prepared in Example 3, with the pyridinium chloride material (the second electrode 66) were placed in the plexiglass cell 64 of FIG. 6, again with the active electrode surfaces 51 facing each other, and 11.0 ml 0.1 F NaClO4 liquid electrolyte added immediately. Powered expulsion was effected by connecting the first electrode 62 in the copper form to the positive terminal of a constant current power supply 69, and the second electrode 66 in the proton form to the negative terminal. A current of 1 mA/cm2 (6mA total) was applied for 96 minutes, passing a total of 1.8 mmole electrons/g ion exchange material and providing 1.8 mmole H+ /g to the first electrode 62 (2H+ are required for each Cu(II)). The direct Cu(II) expulsion at the first electrode is as described in example 6. The indirect chloride expulsion at the second electrode is represented as follows:
Ppy in reaction d represents the pyridine (py) functionalized in the ion exchange layer. The copper(II) was expelled into the liquid as soluble CuCl2 rather than the solid Cu(OH)2 in example 1 because the OH- produced via water reduction at the second electrode 66 in reaction C. reacts with the pyridinium chloride group of the second ion exchange layer. The cell was disconnected and left to rest for one hour, and the quantity of expelled copper(II) measured as in Example 6. The efficiency of copper(II) expulsion in this experiment was 98%.
DETAILED DESCRIPTION OF SECOND EMBODIMENTS OF THE INVENTION The following description relates to sensing a chosen chemical species and to control of operation of a battery or single cell. A sensor may comprise first and second electrodes to which a power source is connected, and an ion exchange material attached to at least one of the electrodes, or otherwise separating them. The sensor will in general, therefore, function as an electrolytic cell.
When a power source is connected to the electrodes of the sensor cell, a current flows between the electrodes, the magnitude of the current depending on (as hereinbefore defined) the concentration of the chemical species in the liquid. In one embodiment, using a particular ion exchange material, in the substantial absence of the chemical species a nominal or trickle current flows, of the order of 10-8 A/cm2, and in the presence of chemical species in concentrations of 10-3 M (the threshold value) or greater a significant current flows, of the order of 10-4 A/cm2. These current and threshold concentration quantities depend at least in part on the ion exchange material employed, and may vary by many orders of magnitude when using alternative ion exchange materials. The change in the current flow is explained as follows. When the ion exchange material is in the presence of the chemical species it exhibits a lower ionic resistance. At each electrode surface an electrochemical reaction takes place, electrons being provided for chemical reduction at the cathode and consumed in chemical oxidations at the anode. Thus, in the presence of a sufficient concentration of chemical species, that is a concentration exceeding the threshold value, a more active electrochemical cell is formed, and a larger electrical current flows between the electrodes. The speed with which the cell current increases depends upon the concentration of the chemical species, that is upon the degree to which the concentration exceeds the threshold level, 10-3 M in this example. Thus the cell current increases faster for greater chemical species' concentrations. In this example, for a concentration of 10-1 M, the cell requires an hour before passing 10-4 A/cm2, and for concentration of 3M, requires 2 minutes to reach this same current density. In contrast, in the absence of the chemical species the ion exchange material exhibits a greater ionic resistance. Thus a less active electrochemical cell is formed and a smaller, or only a trickle, electrical current flows between the electrodes.
For some applications, the ion exchange material is preferably crosslinked. Crosslinking may be effected by chemical means, or by irradiation, for example with a beam of fast electrons or gamma rays. Crosslinking 0.2-20 mol%, especially 0.5-6 mol%, is preferred.
The electrode is preferably flexible by which is meant that at 23� C. it can be wrapped around a 4 inch (10 cm) mandrel, preferably 1 inch (2.5 cm) mandrel, without damage.
P--R                                                       (1)
Cathode: 2H2 O+2e- &#8594;2OH- +H2 (g)(1)
Anode: 2H2 O&#8594;4e- +4H+ +O2 (g)   (2)
When the relevant chemical species from the liquid contacts the first electrode, generally after being absorbed by and after passing through the ion exchange material, it may undergo an electrochemical reaction at the electrode surface. Another chemical species will undergo another chemical reaction at the second electrode surface, thus allowing the passage of current. In preferred embodiments for detecting hydrogen ions in an aqueous liquid, when water contacts the first electrode as a cathode it reacts to produce hydroxide ions (Reaction (1)). Similarly in a preferred embodiment for detecting basic solutions in aqueous solution, when water contacts the first electrode as an anode it reacts to produce hydrogen ions (Reaction (2)). Preferably the ion exchange material is positioned at that electrode where the products of the electrochemical reaction are those which will drive the ion exchange material back to its less conductive state. For example, for the detection of hydrogen ions when the ion exchange material comprises a polymer comprising units having the general formula P--C5 H4 N, the ion exchange material should be positioned at the cathode. The reactions that take place are as follows:
P--C5 H4 N+H+ &#8594;P--C5 H4 NH+(3)
At cathode: 2H2 O+2e- &#8594;2OH- +H2 (g)(4)
P--C5 H4 NH+ +OH- &#8594;P--C5 H4 N+H2 O(5)
P--COOH+OH- &#8594;P--COO- +H2 O           (6)
At anode: 2H2 O&#8594;4e- +4H+ +O2 (g)(7)
P--COO-+H+ &#8594;P--COOH                            (8)
In one embodiment, the electrodes are preferably elongate and form part of an electrical circuit which can measure the position, along at least one of the electrodes, at which the chemical species is present. For example, the electrodes may have a length which is substantially greater, such as at least 100 times greater, often at least 1000 times greater, sometimes at least 10000 times greater than either of its other dimensions. Such an arrangement not only detects the presence of the chemical species but also its location.
EXAMPLE 8 Ion exchange material may also be applied to a wire. As an example, a solution was prepared from 51.3 mole percent 4-vinylpyridine, 31.0% 2-ethylhexyl acrylate, 37 % technical divinylbenzene, 4.0% benzoyl peroxide, and 10% of a linear polymer for thickening. This polymer consisted of 65 mole percent 4-vinylpyridine and 35% 2-ethylhexyl acrylate, was produced in a free radical polymerization in a preceding step, and had a weight average molecular weight of approximately 200,00. Ten percent of this thickening polymer produced a solution of 800 cps. A 1.10 mm diameter conductive polymer wire (with a 24 gauge metallic core) was dipped in this thickened solution and drawn upward into and through a ten foot (3.3 m) heating tower held at 135� C. The wire with a 1.2�10-4 m coating of ion exchange material was spooled at room temperature and samples could be placed in 1 M HCl to produce the pyridinium chloride form of the ion exchange layer.
EXAMPLE 9 Source and locating wires as in FIG. 8 for an acid sensor were prepared using a Copel wire (3 ohm per ft., 0.1 ohm per cm) covered with a conductive polymer jacket comprising a linear low density polyethylene carbon black blend. The ion exchange material bonded to this wire was 100 microns thick and comprised a terpolymer of 35 mole percent 4-vinylpyridine, 67 mole percent ethylhexyl acrylate, and 3 mole percent technical divinylbenzene. These wires were incorporated in a sensor as described in FIG. 10. After submersion of a 4 inch (10 cm) length of sensor (or 3 cm2 area on each electrode) in tap water (pH=6), for several days the current was found to be 2�10-8 A. This sample was then exposed to a 3M HCL liquid, and the current measured as a function of time. The current reached 3�10-4 A, within 2 minutes, and was rinsed and replaced in tap water to regenerate. After 20 minutes the current was reduced to 1.5�10-5 A, and continued to drop over the next hours and days to 4�10-7 A. A representative response/regeneration curve is shown in FIG. 12.
EXAMPLE 10 A second specific example is illustrated in FIGS. 13 and 14. Here, some operation connected with a battery 130 is controlled. The battery may be of any type, and the one illustrated is a lead-acid accumulator comprising six cells 131, three only of which are shown. The battery has two terminals 132 connected to electrode plates 133, of which there may be many, but two are shown. A sensor cell 134 is shown immersed in the electrolyte 135 of the battery. The sensor cell, which may be of the type described above, preferably comprises a casing 136, permeable to the electrolyte 135, containing first and second electrodes 137,138, at least one of which is surrounded by an ion exchange resin 139. If desired one of the battery electrodes 133 may function also as one of the sensor cell electrodes.
A known voltage is applied to the first and second electrodes 137,138 and the resistance or impedance between them is measured. The resistance will depend on the resistance of the ion-exchange resin 139, as explained above Thus, an indication of the pH (or other concentration) will be provided. The sensor cell 134 may be positioned such that the pH measured gives an accurate indication of the overall state of charge of the battery.
Battery 140 has terminals 141, one of which is connected to earth 142, and the other to various electrical devices, represented generally as load 143. A generator 144 is connected between earth 142 and the live side of the battery A computer, or other control system, 145 controls the generator 144 in response to a signal from the sensor cell 134. A power supply 146 supplies a fixed voltage to the sensor cell electrodes 137,138. The fixed voltage, which is preferable from 2-9 volts, especially from 3-7 volts (in the case of a normally 12 volt lead-acid accumulator) may be tapped from the battery 140 itself since that voltage will be available in all but the lowest state of discharge. The computer 145 measures current in the sensor cell circuit, for example by measuring the voltage drop across a resistor 66. The resistance of the sensor cell 134 will depend on the pH (or other concentration) within the battery 140, and is represented by a variable resistance 147. The value of variable resistance 147 will affect the voltage drop across resistor 148. The signal that the computer 145 receives from the sensor cell is used to control the output of generator 144. In this way, charging of the battery can be limited or stopped when its pH reaches a sufficiently low value. This may be desirable for extending the cycle life of batteries.
It can be seen that the power supply 146 is isolated from the anode and cathode of the battery 140. In spite of this isolation, some undesirable current loops can form which may affect the current flowing through the sensor cell. In general, the situation can be improved by employing a sensor cell powered by a periodic waveform, for example alternating voltage and having some means of DC isolation, for example a capacitor. Since any undesirable voltages due to the battery that may be impressed on the sensor cell circuit will be DC they will have no effect on current flowing in the sensor cell. An alternating voltage may be generated simply by standard techniques, and components may be present to protect the circuit against surge or transients etc , for example on starting of a car engine.
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