WO2001079706A2 - Electrolytic cell - Google Patents
Electrolytic cell Download PDFInfo
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- WO2001079706A2 WO2001079706A2 PCT/EP2001/004265 EP0104265W WO0179706A2 WO 2001079706 A2 WO2001079706 A2 WO 2001079706A2 EP 0104265 W EP0104265 W EP 0104265W WO 0179706 A2 WO0179706 A2 WO 0179706A2
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- Prior art keywords
- electrodes
- rate
- gas
- cell
- electrolyte
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Classifications
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/142—Pressure infusion, e.g. using pumps
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/142—Pressure infusion, e.g. using pumps
- A61M2005/14204—Pressure infusion, e.g. using pumps with gas-producing electrochemical cell
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B15/00—Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith
- F15B15/20—Other details, e.g. assembly with regulating devices
- F15B2015/208—Special fluid pressurisation means, e.g. thermal or electrolytic
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Definitions
- the present invention is directed to an improved electrolytic ceil having novel electrolytes and/or novel electrode materials.
- the electrolytic cell can be used as a gas generator for a drug delivery device.
- 5.062,834 (“the '834 patent"), for "Device for Dispensing a Liquid Particularly Useful for Delivering Medicaments at a Predetermined Rate,” describes a device for dispensing a liquid at a predetermined rate.
- the device comprises a container for the liquid to be dispensed and a piston assembly movable within the container and dividing the container into two expandable-contractible chambers.
- the first chamber contains the liquid to be dispensed and the second chamber contains pressurized gas which functions to dispense the liquid from the first chamber of the container.
- the second expandable-contractible chamber includes an electrolytic cell having electrodes and an electrolyte. Upon energization of the cell, the electrolyte conducts current between the electrodes, triggering the generation of gas.
- the electrolytic cell of the * 834 patent comprises a pair of electrodes and an electrolyte capable of generating a gas upon energization of the electrodes.
- the gas expands the second chamber which results in displacing a piston, thereby forcing the liquid out from the first chamber.
- useful electrolytes include saline solution and other polar solutions or gels which generate hydrogen, oxygen, nitrogen or carbon dioxide.
- a similar device containing an electrolytic cell is described in U.S. Patent No. 5,242,406 for "Liquid Delivery Device Particularly Useful for Delivering Drugs.”
- U.S. Patent No. 5,090,963 for "Electrocherrucally Driven Metering Medicament Dispenser.”
- This patent describes a Uquid material dispenser comprising an electrolytic cell capable of generating a gas when energized by a source of electric current.
- the liquid material dispenser comprises a rigid housing having a flexible partition fanning two compartments. Upon energization by a source of electric current, the electrolytic cell in the first compartment generates a gas, thereby expanding the first compartment of the dispenser. This results in contracting the second compartment containing the liquid material, thereby dispensing the liquid material.
- the electrolyte can be an 8% solution of sodium bicarbonate (NaHCO 3 ) in water or a 4% solution of copper sulphate (CuSO ⁇ in water.
- NaHCO 3 sodium bicarbonate
- CuSO ⁇ copper sulphate
- the electrolyte can be a water solution of various salts or acids, such as baking soda (sodium bicarbonate), caustic soda, magnesium sulphate, potassium sulphate, sodium sulphate, potassium nitrate, potassium bicarbonate, boric acid, acetic acid, formic acid, or carbonic acid.
- baking soda sodium bicarbonate
- the '8Q5 patent teaches (hat particularly good results were obtained using an 8% solution of baking soda (sodium bicarbonate) as an electrolyte.
- a liquid material dispenser in which the liquid is forced from the dispenser by a gas generated by an electrolytic ceil, is described in U.S. Patent No. 5,704,520.
- the electrolytic cell contains electrodes and electrolyte. Suitable electrolytes are disclosed to be sodium bicarbonate and potassium acetate.
- the present invention is directed to an improved electrolytic cell having a new electrolyte and or a new electrode composition for water electrolysis or other type of electrochemical reaction.
- the invention also encompasses pre-treatment protocols for electrodes which produce a more efficient electrolytic cell.
- the electrolytic cell is useful as a gas generator in a drug delivery device.
- the improved cell allows for rr ⁇ aturization of the electrolytic cell and any device incorporating such a cell.
- the novel electrolytic cell is one of the smallest electrolytic cells comprising a liquid electrolyte.
- the mir ⁇ aturization or micronization is possible because the cell delivers a large amount of gas volume as compared to the size and quantity of components.
- the miniaturized electrolytic cell can be used in human applications, such as for administering drugs to be applied either externally or internally.
- the electrolytic cell of the invention can be scaled-up and used in commercial rnanvtfacturing settings.
- the improved electrolytic cell exhibits a constant rate of gas production over a prolonged period of time.
- the anode must be insoluble in an anodic dissolution process, which is an electrochemical reaction (this is distinguishable from chemical or other types of dissolution); the cathode can be chosen from a wide variety of materials. Steady state production over an extended period of time, as shown below, is highly desirable as such a constant rate produces a constant rate of drug delivery when the electrolytic cell is employed in a drug delivery device.
- the electrolytic cell can be designed to have a controlled variable rate of gas production, as shown below.
- the anode is soluble, such as brass or copper.
- Such a variable rate is desirable for certain types of applications, such as delivering pain medication, in which it is preferred that an initial high delivery rate is followed by a lower constant rate.
- the electrolytic cell is designed to have an pulsatile rate of gas production, as shown below.
- the anode is insoluble material in an anodic dissolution process, which is an electrochemical reaction (this is distinguishable from chemical or other types of dissolution); the cathode can be chosen from a wide variety of materials.
- Such an intermittent rate of gas production is useful for certain types of applications, such as for irrigation systems, for the addition of fertility materials to irrigation water, and for adrriinistering insulin or hormones to mammals.
- An electrolytic cell of the invention is dramatically superior to prior art cells in that it is simple and cost effective to manufacture, it is composed of materials that are safe and non-toxic, and it can be used in a variety of applications.
- an electrolytic cell according to the invention can be used in a drug delivery device to administer a steady and controlled amount of drug over an extended period of time.
- the an electrolytic cell according to the invention can be used to adrninister a high amount of medication immediately following use, followed by a lower steady rate of administration, or the electrolytic cell can be used to administer a drug at intermittent periods of time.
- the new electrolyte and/or electrode composition are useful in an electrolytic cell comprising the electrolyte and at least two electrodes (anode and cathode) connected to an external source of electrical current, such as a battery, for generating gas.
- the electrolyte conducts electrical current between the electrodes and, as a result of an electrochemical reaction, gas is generated-
- the rate of gas production corresponds to the electrical current supplied to the electrolytic cell, and the total amount of gas produced is related to the electrical current supplied to the cell during the time of operation.
- the new electrolyte is di-potassium hydrogen phosphate solution, K ⁇ EPO,,.
- Less alkaline phosphate buffer i.e. , j HPO, + KHjPO,, may also be used as an electrolyte.
- the preferred pH of the electrolyte is about 8.0 to about 11.0, and the preferred concentration of the electrolyte is from about 1 to about 6 M.
- the pH of 5.50 - 5.55 M KjHPO, solution is 10.5 to 11.0.
- the pH of the solution can be reduced to any desired value, such as reducing the pH from 11.0 to 8.0, by adding a proper amount of phosphoric acid of the same molarity. Such a method does not change the concentration of the electrolyte solution-
- the electrolyte With the use of a low level of current, i.e., less than about 2 mA, the electrolyte is preferably present at a concentration of about 5.50 to 5.55 M. With the use of a high level of current, i.e., greater than 7 mA, the concentration of the electrolyte is preferably from about 1 M to about 2 M.
- the new electrolyte is inexpensive, non-toxic, safe, and simple to produce.
- An electrochemical gas generator having the new electrolyte delivers gas for an extended period of time.
- the presence of reactants in suitable amounts and the volume of electrolyte solution are two of the factors which determine the life of the electrolytic cell.
- large scale electrolytic cells can operate for years as long as a sufficient quantity of electrolyte solution is present in the cell.
- the practical limitation of tie life span of a micronized or miniaturized cell is the time it takes the electrolyte solution to dry. This is because the electrochemical reaction consumes a relatively negligible amount of water compared with the volume of gas produced. Thus, if water is added to the cell it can be re-used almost indefinitely.
- the new electrolyte can be used in any water-electrolysis based electrolytic cell operating at low currents, as well as other types of electrolytic cells operating at high or low currents.
- the cells can be used, for example, in drug delivery devices, such as those described in U.S. Patent Nos.5,242,406; 5,062,834; 5,704,520; 5,090,963; and 5,186,805, which are specifically incorporated by reference.
- a drug delivery device mcorr ⁇ raring the new electrolyte can be used, for example, in low-cost disposable devices for one-time use and in devices that may be fixed to a band or strap for attachment to the body, e.g., the arm, of the person to receive the medicament dispensed from the device.
- Yet another aspect of the invention is directed to the use of various materials for the electrode. Modification of electrode materials can result in a modification of the rate of gas production, which can thereby control the rate of a substance being delivered.
- Preferred anode compositions for producing a steady rate or pulsatile rate of gas production are certain noble metals, stainless steel, and nickel.
- Useful noble metals are, for example, platinum, iridium, rhodium, ruthenium, osmium, and alloys thereof.
- Gold, or alloys thereof can also be used, although gold is not preferred because it can cause high overvoltage.
- Alloys of noble metals for use in anodes of electrolytic cells having steady rate or pulsatile rate of gas production do not contain metals which are soluble in an electrochemical reaction. Stainless steel is preferred as it is inexpensive.
- Preferred anode compositions for producing an initial high rate of gas production, followed by a lower steady rate of gas production are brass and copper.
- Cathode compositions for all three types of gas rate production can be selected from a wide range of materials.
- the anode and cathode for all three types of applications can be made of the same or different materials. If the shelf life of the electrolytic cell is to be short, then different materials can be used for the anode and cathode compositions. However, if the shelf life of the electrolytic cell is to be long, then it is preferred that the anode and cathode are made of the same material to avoid potential corrosion during storage.
- a device having an electrolytic cell and controlled changes in gas evolution can be used, for example, for pain treatment. Such a device could be used for the delivery of morphine.
- a patient requiring pain treatment requires a high rate of drug delivery. After the initial treatment period, however, the rate of drug delivery must decay.
- a drug delivery device can provide a high rate of initial delivery followed by a steady lower rate of delivery.
- Such a drug delivery device is dramatically superior to prior art delivery devices, as it does not require smart electronics or any other complicated mechanism, and therefore, is simple, efficient, and cost-effective.
- One of the critical parameters of an electrochemical reaction is the initial condition of the electrode surface area. If the electrode surface area is clean and free of an organic or other film or adsorbed species, it is active and electrochemical reactions using the electrode will have high current efficiency.
- pre-treating electrode surfaces there are many different methods of pre-treating electrode surfaces, such as mechanical, thermal, chemical, and electrochemical treatments. The method chosen depends upon the intended use of the cell, the electrode design, the nature of the electrolyte, and the cell design.
- One papular chemical pretreatment method for platinum electrodes uses a "piranha" solution, consisting of a mixture of sulfuric acid and hydrogen peroxide.
- the initial electrode surface is significant as the efficiency of gas delivery is critical. If the electrode surface in such a device was not pretreated, the gas evolution of the device maybe unstable (i.e., a non-linear drug delivery curve), the drug delivery may be initially delayed because the current would have to penetrate the electrode surface film, and the repeatability of the results would be poor because the initial electrode surface would not be controlled- This is most significant for drug devices, as regulatory approval of such devices requires that results are repeatable and consistent.
- the pretreatment process of the invention comprises pretreating stainless steel, copper, or brass electrodes by washing with ethyl alcohol and rinsing, dipping the electrodes in citric acid and rinsing, followed by activating the electrodes with the electrolyte.
- a pretreatment process for nickel electrodes is also disclosed.
- FIGURES Figure 1 : Shows a graphical comparison of gas delivery over time for three different electrolytic cells having stainless steel electrodes and 5.5 M an electrolyte;
- Figure 2 Shows a graphical comparison of Faradaic current efficiency over time for three different electrolytic cells having stainless steel electrodes and 5.5 M KjHPO, as an electrolyte;
- Figure 3 Shows a graphical comparison of cell potential over time for three different electrolytic cells having brass electrodes and an electrolyte composition of; (1) 5.5 M K j HPO,; (2) 5.5 M K > HP ,and EDTA and (3) 5.5 M.
- Figure 4 Shows a graphical comparison of cell current over time for three different electrolytic cells having brass electrodes and electrolyte compositions of: (1) 5.5 M. K j HPO,; (2) 5.5 M. KJSPO, and EDTA; and (3) 5.5 M. K 2 HPO 4 and sulfamic acid
- Figure 5 Shows a graphical comparison of gas delivery over time by three different electrolytic cells having brass electrodes and electrolyte compositions of: (1) 5.5 M. K j H O,; (2) 5.5 M. K ⁇ HPO ⁇ n EDTA; and (3) 5.5 M. KjHPO, and sulfamic acid;
- Figure 6 Shows a graphical comparison of a normalized reaction rate for gas for three different electrolyte cells having brass electrodes and electrolyte compositions of: (i) 5.5 M. K*HPO 4 ; (2) 5.5 M. 2 HPO 4 and EDTA; and (3) 5.5 M.
- FIG. 7 Shows a graphical comparison of gas delivery over time for three different electrolytic cells having copper electrodes and electrolyte compositions of: (I) 5.5 M K 2 HPO 4 and 40 mM EDTA; (2) 5.5 M 2 HPO 4 and 20 mM EDTA; and (3) 5.5 M K ⁇ HPO, and 10 mM EDTA;
- Figure 8 Shows a graphical comparison of the normalized reaction rate for gas over time for three different electrolytic cells having copper electrodes and electrolyte compositions of: (1) 5.5 M K- 2 HP ,and 40 mM EDTA; (2) 5.5
- Figure 9 Shows a graphical comparison of the normalized reaction rate for gas over time for two different electrolytic cells having copper electrodes and electrolyte compositions of: (1) 5.5 50 mM sulfamic acid; and (2) 5.5 M K j HPO, and 20 mM sulfamic acid;
- Figure 10 Shows pulsatile gas delivery for an electrolytic cell having 1 M an electrolyte
- Figure 11 Shows pulsatile gas delivery for an electrolytic cell having 3 M KjHP , as an electrolyte.
- the present invention is directed to an improved electrolytic cell having a new electrolyte and/or a new electrode composition for water electrolysis or other type of electrochemical reaction, and a pre-treatment protocol for electrodes which produces a more efficient electrolytic cell.
- the electrolytic cell delivers gas at a stable rate and a relatively high Faradaic current efficiency of, for example, about 70 to about 95%.
- gas is produced at a rate of from about 0.001 mg hr up to about 24 ml hr.
- the electrolytic cell of the invention comprises at least two electrodes and the electrolyte of the invention.
- the two electrodes can be made of the same or different materials, and the electrodes can be made of coated or composite materials.
- the cathode can be made of a wide variety of metals.
- the problematic electrode is the anode due to potential corrosion with certain types of metals.
- Di-potassium hydrogen phosphate, jHPO,, or less alkaline phosphate buffer electrolyte is completely safe. Furthermore, in contrast to many prior art electrolytes, the novel electrolyte of the invention does not contain chloride ions. This is significant as an electrolyte containing chloride ions promotes corrosion of the anode if the electrodes are not made of a noble metal.
- the new electrolyte is superior to prior art electrolytes as it has a significant buffer capacity that prevents electrode corrosion. Corrosion is one possible side reaction if the anode used in the electrolytic cell is not made from a noble metal. To ensure the stability of gas evolution and high current efficiency, it is desirable to avoid side reactions (except when the electrolytic cell is designed to deliver a controlled variable rate of gas production).
- electrolyte there are natural pH changes in electrolyte near the electrodes. The pH near the anode decreases because the electrolyte near the electrode consumes OH " ions due to the electrochemical reaction of oxygen evolution- As a result, anode media becomes more acidic, thereby causing anode corrosion.
- an electrolyte can prevent such pH changes if it has a buffer capacity pH remaining constant near the electrodes. This was demonstrated in U.S. Patent Nos. 5,186,805 and 5,090,963, in which the only electrolyte tested having a buffer capacity, sodium bicarbonate, showed the best results.
- the novel electrolyte is superior to the prior art NaHCO 3 electrolyte in that the buffer capacity of KjHPO, is significantly greater than that of NaHCOj.
- the new electrolyte of the invention also prevents corrosion due a build up of a protecting film of phosphates on the electrodes. Specifically, high concentrations of phosphate ions cause polyphosphate creation in the electrolyte solution and on the electrode surface. See Cotton et al., Advanced Inorganic Chemistry; A Comprehensive Text, Pan 2, page 370 (Interscience Publishers, 1969). This is significant as the phosphate ions protect the surface of both electrodes from contamination and prevent anode corrosion. This superior property of the novel electrolyte of the invention is not found with prior art electrolytes, as it is a characteristic typically only found with phosphates.
- sodium bicarbonate a common prior art electrolyte
- sodium bicarbonate a common prior art electrolyte
- the amount of dissolved oxygen in the electrolyte is negligible as shown by electrochemical measurements. This is significant as dissolved oxygen can promote anode corrosion.
- tCjHPO functions to rrunimize the dissolution of oxygen in the electrolyte.
- the novel electrolyte is very conductive, with measurements showing conductivity of 112.5 mS/cm at 5.5 M, and 176.5 mS/crn at 2 M.
- the natural limitation of the reaction time of an electrolytic cell of the invention is the quantity of electrolyte.
- An electrochemical reaction can be represented schematically by the following equation: rnA i- nB ->pC ⁇ -qD
- a and B are reactants and C and D are products; m, n, p, and q are stoichiometric coefficients.
- Consuming the reactants over time leads to an increase in diffusion overvoltage, decrease of reaction rate, possibly pH changes, and in the case of a soluble anode, possible contamination of the electrolyte with sludge. Therefore, it may be necessary to add compounds to commercial electrolytic baths to correct the pH, filter electrolyte, etc. This allows the electrolytic cell to operate for an additional period of time. Replacing the anodes or all of the electrolyte is usually only required after months or years of operation for industrial-size electrolytic cells.
- electrochemical decomposition of water There are two possible time limitations for the length of operation of micronized cells due to the lack of water: electrochemical decomposition of water and drying of the electrolyte.
- electrochemical decomposition of water is schematically written as follows:
- the current density should be kept constant for the same reaction conducted in different types of cells.
- the required current density can restrict the rninimal electrode surface area required for an electrolytic cell.
- Cell overvoltage is the difference between the cell voltage (with a current flowing) and the open-circuit voltage (ocv) (which is the cell voltage under zero current conditions).
- the cell overvoltage is the sum of overvoltages of both electrodes plus the IR drop.
- the overvoltage represents the extra energy needed (an energy loss) to force a slow reaction to proceed at a required rate.
- a high overvoltage is undesirable, as it represents a high energy loss.
- High reaction overvoltage results in an unstable electrolytic cell, a loss of electrical energy, shorter time of battery discbarge, and a decrease of the current. Funhermore, high reaction overvoltage can result in a cell which is more susceptible to contamination of the electrolyte.
- Electrode Composition When the current density increases, the overvoltage increases. Thus, in designing an electrolytic cell it is desirable to keep the current density relatively low to avoid high overvoltage. This can be done by choosing a electrodes rraving a sufficient surface area in relationship to the intended voltage to result in a low current density. A lower intended current allows for the use of electrodes having a lower surface area, and conversely, a higher current requires the use of electrodes having a greater surface area, to obtain a desired low current density.
- the anode and cathode for steady state, pulsatile, or a controlled variable rate of gas production can be made of the same or different materials.
- metals that chemically react with water such as alkali or alkaline-earth metals, should not be used for electrode materials.
- metals having a low standard electrochemical potential such as zinc, aluminum, tin, etc., should not be used as electrode materials as they will corrode with exposure to the electrolyte.
- Highly toxic materials, such as lead r cadmium should not be used as anode materials, although they can be used as cathode materials.
- Metals or metal alloys, electrodes with modifications made to the surface, or carbon electrodes, operating as each electrode at lower overvoltages are preferred.
- the anode is insoluble, and can be certain noble metals, stainless steel, or pure nickel.
- Useful noble metals are, for example, gold, platinum, indium, rhodium, ruthenium, osmium, and alloys thereof.
- Stainless steel is preferred as it is inexpensive.
- metals capable of dissolving anodically such as brass, zinc, copper, cobalt, bright nickel, lower grades of steels, silver, etc., should be avoided as anode materials because an insoluble anode is required for water electrolysis.
- e anode is soluble, such as brass or copper.
- While the cathode for steady state, pulsatile, and controlled variable rate of gas delivery may be selected from a wide range of materials, certain materials should not be used.
- Metals capable of absorbing hydrogen such as palladium and niobium, or reducing to hydrides, such as titanium, zirconium, and tantalum, should not be used as cathodes as they will critically decrease the current efficiency of the cell operation.
- Tungsten, molybdenum, and titanium should not be used as cathode materials because oxides of these materials can absorb hydrogen, which can decrease the current efficiency of the cell.
- the anode is made of brass or copper (soluble anodes) as described above, and the cathode can be made of the cathode materials given in the following table.
- the anode and cathode for all three types of applications can be made of the same or different materials. If the shelf life of the electrolytic cell is to be short, then different materials can be used for the anode and cathode compositions. However, if the shelf life of the electrolytic cell is to be long, then it is preferred that the anode and cathode are made of the same material to avoid potential corrosion during storage. If both the anode and cathode are made of a noble metal or noble metal alloy (gold and all metals from the platinum group), then the anode and cathode can be made of different materials, regardless of the intended shelf life of the cell.
- a noble metal or noble metal alloy gold and all metals from the platinum group
- Electrodes are made from noble metals (cases 3-8 in the Table), then there are more possibilities for the choice of electrolyte.
- Noble metals do not dissolve anodically, so the requirements for the electrolyte may be reduced: i.e., it is not required that the electrolyte be a buffer and the electrolyte may have a neutral, acidic, or alkaline pH-
- the electrolyte in the cell must be hygroscopic and safe and it must contain compounds suitable for evolution of safe gases during electrochemical performance. Several examples of such compounds are:
- Aluminum salts - sulfates or nitrate, or potassium alum KAl(SO ⁇ . These salts are very hygroscopic and potassium alum is extremely inexpensive.
- the pH is slightly acidic
- the electrochemical reaction is electrolysis of water.
- the new electrolyte can be used in electrolytic cells having varying levels of current.
- the JKPO, electrolyte can be used in an electrolytic cell having a high level of current, i.e., above about 7 rnilUAropers.
- a relatively low concentration of electrolyte should be used, i.e., less than about 2 M.
- an electrolyte solution of about 5.50 to about 5.55 M solution of KjHPO was used in the high current cell.
- a high current results in a high rate of gas production.
- Use of such a high concentration electrolyte in a high current electrolytic cell required an enlarged electrode surface sufficient for performance at high current.
- it was discovered that such a high concentration electrolyte produced a slow coalescence of creating gas bubbles, forming a solution that resembled an emulsion.
- the high viscosity of the electrolyte solution prevented the transfer of gas bubbles out of the cell, and resulted in a significant increase in the cell potential at a constant current, without reaching a plateau.
- a relatively low concentration K j HPO, electrolyte ⁇ .e., an about 1 M to about 2 M solution of ⁇ HPO ⁇ is preferably used in an electrolytic cell having a high level of current.
- a 2 M solution of jHPO, used in an electrolytic cell operating at a high current lacked any coalescence problems.
- a lower concentration of the electrolyte allows operation of an electrolytic cell at a higher current.
- the KjHPO 4 electrolyte is extremely conductive, with a conductivity of 176.5 mS/cm at 2 M. This is important when operating an electrolytic cell at a high current, as this is when IR drop becomes significant.
- the lower concentration KjHPO, electrolyte is even more conductive than the high concentration jHPO electrolyte: at 25°C and a 2 M solution, the conductivity is 176.5 raS/cm, while at the same temperature a 5.5 M solution is 112.5 raS/cm. The difference in conductivity is likely caused by a more complete dissociation of ions for the lower concentration ICJTPO, electrolyte.
- the present invention also encompasses electrolytic cells which deliver gas at a controlled variable rate over a period of time.
- electrolytic cells which deliver gas at a controlled variable rate over a period of time.
- the rate of gas generation starts off high followed by a lower steady rate of gas generation.
- the rate of gas generation of this type of electrolytic cell is shown in Figs. 6 and 9.
- the rate of gas delivery depends upon: (I) the current flowing through the cell, and (2) the current efficiency of the particular gas evolution reaction, i.e., the presence or absence of side reactions.
- the rate of gas delivery can be controlled by choosing a combination of electrochemical reactions.
- the reactions can be chosen by changing the electrolyte, the electrode material, or both, as well as the resistor.
- a pump having controlled changes in drug delivery can be obtained by designing such an electrolytic cell. For example, with the use of brass electrodes, zinc and copper provide anodic dissolution producing anode salt passivation, which occurs when the anode surface is coated and blocked by a salt film.
- the cell potential will be high enough for water electrolysis, i.e., about 2N.
- Water electrolysis starts but has a very low current efficiency because of significant side reactions on both electrodes: on the anode, zinc and copper are dissolving and oxygen is evolving, while on the cathode, copper is being deposited and hydrogen is evolving. This is in contrast to the initial period of operation of the cell, in which zinc and copper anodic dissolution occurs, while only a high rate of hydrogen evolution occurs at the cathode.
- the length of the initial time period of a high rate of gas production prior to anode salt passivation depends upon the level of current used in the cell. Higher current produces a faster rate of phosphate production in the electrolyte, resulting in a faster onset of salt passivation and a consequent increase of cell potential.
- the theoretical limit of maximum time of cell operation is very prolonged
- the present invention also encompasses electrolytic cells which deliver gas at a pulsatile rate over a period of time.
- the rate of gas generation starts and stops as the current starts and stops.
- the rate of gas generation of this type of electrolytic cell is shown in Figs. 10 and 11.
- the best performance of hormones, such as human growth hormone or fertility hormones, is obtained with pulsatile delivery rather than continuous dehvery. (This is a characteristic of hormones.)
- a pulsatile insulin delivery device utilizing the electrolytic cell of the invention can be designed to delivery insulin at a specified time schedule, i.e.. rate level I during the day and rate level II at night.
- the pulsatile delivery is obtained by starting and stopping the current run through the device.
- the time of starting and stopping can be triggered by a timing device incorporated into the delivery device.
- the new electrolyte and/or the new electrodes can be used in electrolytic cells which function as gas generators for continuous or pulsatile drug dehvery devices.
- an electrolytic cell according to the invention can be used in a low-cost disposable device for single use.
- Such devices can be fixed to a band or strap for attachment to the body, e.g., the arm, of the person to receive the medicament dispensed from the device.
- Such a device comprises a power supply for energizing the electrodes.
- the power supply preferably includes a battery and an electrical control circuit for controlling the rate of energization of the electrode, and thereby the rate of dispensing the Uquid from the container.
- Such an electrical control circuit preferably includes presettable means for presetting the rate of energization of the electrodes, and an electrical switch for conrro Ung the energization of the electrodes.
- a miniaturized cell for use in the human body preferably has a minimum of Vz to I ml of electrolyte solution.
- Commercial size electrolyte cells can have 100's of liters of electrolyte solution.
- a typical rru aturized electrolytic cell for use in an external drug dehvery device has a minimum of about 0.15 ml of electrolyte solution.
- the use of about 0.15 ml of electrolyte solution in a cell utilizing conventional electrodes resulted in a cell having a high potential. Therefore, electrolytic cells having quantities of electrolyte less than about 0.2 ml preferably employ special electrodes having a larger surface area than conventional electrodes.
- a rruniaturized electrolytic cell having about 0.2 ml of electrolyte solution can produce gas for a period of over 200 hours, i. e. , for a week or longer.
- Electrode Pretreatment Method The electrode pretreatment method of the invention is useful for electrodes to be used in electrolytic cells. The pretreatment produces cells having consistent and repeatable results.
- the electrodes can be made of, for example, stainless steel, copper, brass, or nickel.
- the electrodes are first washed in a solution of absolute or 95% ethyl alcohol.
- the electrodes are washed in an ultrasonic bath in a closed glass vial for about 30 to about 40 minutes. This step removes fats and organic materials (dirt) from the electrode surface.
- the electrodes are then rinsed in deionized or RO (reverse osmosis) water.
- RO reverse osmosis
- the electrodes are dipped at 40-45°C for about 30 to about 40 in. This step removes oxides or other remaining film from the electrodes.
- the electrodes are then rinsed in deionized or RO (reverse osmosis) water.
- the electrodes are stored in the electrolyte solution ( ⁇ H OO for less than about 10 minutes to up to several days.
- the purpose of this step is to keep the electrode surface active and to prevent oxidation and contamination of the surface from exposure to the air.
- the process used for stainless steel electrodes is slightly modified for copper and brass electrodes.
- the dipping step was performed without the addition of heat and for a period of about 15 to about 20 minutes.
- the dipping step was performed without the addition of heat and for a period of about 5 to about 10 minutes.
- nickel electrodes The washing and storage steps for nickel electrodes are the same as for stainless steel electrodes. The two processes differ in the dipping process. Pure nickel exposed to air has an oxide film on its surface (as does stainless steel). However, the nickel film is much more stable than that present on stainless steel.
- the first solution comprises citric acid, ammonium acetate, and EDTA at an acidic pH.
- the citric acid is present at about 0.5 M
- the ammonium acetate is present at about 0.2 M
- the EDTA is added until dissolution.
- the second dipping solution comprises citric acid, ethylenediarriine, and a reducing agent, such as NaHSO 3 .
- a reducing agent such as NaHSO 3 .
- the citric acid is present at a concentration of about 1 to about 2 M
- the ethylenediarnine is added until the pH remains acidic (pH of about 5)
- the reducing agent is present at a concentration of about 0.01 M, depending upon the agent used.
- the third dipping solution comprises ammonium nitrate, citric acid, triethariolarnine, and a reducing agent, such as NaHSO 3 or sodium formaldehyde bisulfite.
- a reducing agent such as NaHSO 3 or sodium formaldehyde bisulfite.
- the ammonium nitrate is present at a concentration of about 2.5 M
- the citric acid is present at a concentration of about 0.01 M
- the triethanolarnine is present at a concentration of about 0.05 M
- the reducing agent is present at a concentration of about 0.01 M, depending upon the agent used.
- the purpose of this example was to demonstrate the rate of gas production of an electrolytic cell having a solution of KjHPO 4 as an electrolyte.
- Stainless steel electrodes (316 L) were used with a 5.5 M solution of
- K j HPO ⁇ an electrolyte in three electrolytic cells.
- the electrodes had a diameter of 0.8 nun, a length immersed in solution of 9 mm, for a total surface area of each electrode of 0.23 cm 1 .
- 316 L stainless steel was used because it is highly resistant to corrosion. "L” represents low carbon concentration in the steel, which is preferable because of possible electrolyte contamination with "sludge”. Sludge in ele uochemistry refers to particles of anode falling into electrolyte due to un-uniform anodic corrosion. Low carbon content in the stainless steel minimizes the amount of insoluble sludge.
- the pH of the electrolyte used in each cell was 10.8. No additives were used with the electrolyte.
- the electrolytic cells generated gas at constant rates for a period of about 111 hours, with a Faradaic current efficiency of about 80 to about 100%.
- the resistance of the circuit was 10.2 kOhm.
- the constant rate of gas generation for over 4 Vx days for the three cells is shown in Fig. 1, and the current efficiency of the three cells is shown in Fig. 2.
- the delivery rate for gas generation was measured as follows: evolving hydrogen and oxygen gas entered a water reservoir, pushing water via a tube into a vial on an analytical balance measuring continually on a time basis. The weight corresponded to the volume of gas generated (the y axis of Figure 1).
- results of this example demonstrate the efficiency and effectiveness of an electrolyte for an electrolytic cell. Moreover, this example demonstrates the successful preparation of a simple, cost-effective, delivery device incorporating an electrolytic cell, in which the rate of gas generation is steady and constant over an extended period of time. This is significant as the rate of gas generation governs the rate of dehvery of the substance contained in the device.
- the purpose of this example was to construct an electrolytic cell that initially delivers a high rate of gas production followed by a lower steady rate of gas production.
- Brass electrodes were used with a an electrolyte in three electrolytic cells, having a pH of ahout 10.5 to about 11.0: Cell A,
- Figs.3-6 The results are summarized in Figs.3-6.
- the cell potential of the three cells was rather low, at 0.85 to 0.95 V and, therefore, current was rather high See Figs.3 and 4.
- the resistance used was 10.9 kOhm.
- the delivery rate of hydrogen gas is high, as the current is initially high.
- the delivery rate of hydrogen gas is initially high as at the start of the reaction there is no side reaction on the cathode (where hydrogen gas evolves). This initial period of a high rate of gas production lasts for about 7 to about 11 hours. See e.g., Fig. 5, which shows the rate of delivery over time, including the break point, for the three cells.
- This example demonstrates the successful preparation of a dehvery device incorporating an electrolytic cell in which the rate of gas generation, which governs the rate of delivery of the substance contained in the device, is initially high followed by a lower steady rate of gas production.
- the purpose of this example was to construct an electrolytic ceil that initially delivers a high rate of gas production followed by a lower steady rate of gas production.
- Copper electrodes were used with a 5.5 M electrolyte in five electrolytic cells, having a pH of about 10.5 to 11.0: Cell D, Cell E,
- Fig. 7 shows the rate of delivery over time for the three EDTA cells
- Figs. 8 and 9 show the normalized reaction rate over time for the three EDTA cells and the sulfamic acid cells, respectively.
- Example 2 There are two primary differences between a cell having brass electrodes (Example 2) and a cell having copper electrodes. First, there is no break point in the delivery curve because salt passivation does not occur with copper electrodes. Second, water electrolysis starts immediately.
- copper electrode cells having EDTA or sulfamic acid as additives oxygen evolution and anodic dissolution of copper until it complexes occurs at the anode, and hydrogen evolution and electrodeposition of copper from complexes occurs at the cathode.
- oxygen evolution and anodic dissolution of copper until CuO (black powder) formation occurs at the anode
- hydrogen evolution occurs at the cathode.
- Cells having copper electrodes and EDTA or sulfamic acid as an additive have increased anodic dissolution of copper, creating soluble copper complexes. This enables an additional cathodic reaction of electrodeposition of copper from the created complexes.
- the second primary difference between cells having brass and copper electrodes is that with copper electrodes the cell potential is high enough at the beginning of cell operation to effect water electrolysis (about 2V). This is because copper anodes do not contain zinc.
- Anodic dissolution of zinc occurs at significantly lower anodic potential than anodic dissolution of copper or oxygen evolution.
- the anodic dissolution of zinc which occurs with brass electrodes (followed by anodic dissolution of copper), leads to an initial cell potential of loss than 0.95 V, which is too low for water electrolysis.
- This example demonstrates the successful preparation of a delivery device corrr ⁇ rating an electrolytic cell in which the rate of gas generation, which governs the rate of delivery of the substance contained in the device, is initially high followed by a lower steady rate of gas production.
Abstract
Description
Claims
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
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AU58337/01A AU5833701A (en) | 2000-04-13 | 2001-04-12 | Improved electrolytic cell |
EP01931602A EP1282453A2 (en) | 2000-04-13 | 2001-04-12 | Electrolytic cell |
JP2001577073A JP5581561B2 (en) | 2000-04-13 | 2001-04-12 | Improved electrolyzer |
CA002405925A CA2405925A1 (en) | 2000-04-13 | 2001-04-12 | Electrolytic cell |
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US19690700P | 2000-04-13 | 2000-04-13 | |
US60/196,907 | 2000-04-13 |
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WO2001079706A2 true WO2001079706A2 (en) | 2001-10-25 |
WO2001079706A3 WO2001079706A3 (en) | 2002-05-30 |
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PCT/EP2001/004265 WO2001079706A2 (en) | 2000-04-13 | 2001-04-12 | Electrolytic cell |
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US (1) | US6572740B2 (en) |
EP (1) | EP1282453A2 (en) |
JP (1) | JP5581561B2 (en) |
AU (1) | AU5833701A (en) |
CA (1) | CA2405925A1 (en) |
WO (1) | WO2001079706A2 (en) |
Cited By (2)
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WO2003037406A2 (en) * | 2001-10-26 | 2003-05-08 | Massachusetts Institute Of Technology | Transdermal transport device with an electrolytic actuator |
US7740984B2 (en) | 2004-06-04 | 2010-06-22 | Rovcal, Inc. | Alkaline cells having high capacity |
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BR0314111A (en) * | 2002-09-12 | 2005-07-26 | Childrens Hosp Medical Center | Method and device for painless medication injection |
US20040267240A1 (en) * | 2003-01-29 | 2004-12-30 | Yossi Gross | Active drug delivery in the gastrointestinal tract |
JP2006517827A (en) * | 2003-01-29 | 2006-08-03 | イー−ピル・ファーマ・リミテッド | Delivery of active drugs in the gastrointestinal tract |
US7670314B2 (en) * | 2004-02-17 | 2010-03-02 | Children's Hospital Medical Center | Injection device for administering a vaccine |
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EP2315862A2 (en) * | 2008-06-18 | 2011-05-04 | Massachusetts Institute of Technology | Catalytic materials, electrodes, and systems for water electrolysis and other electrochemical techniques |
US20100286628A1 (en) * | 2009-05-07 | 2010-11-11 | Rainbow Medical Ltd | Gastric anchor |
US20100286587A1 (en) * | 2009-05-07 | 2010-11-11 | Yossi Gross | Sublingual electrical drug delivery |
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US20110066175A1 (en) * | 2009-05-07 | 2011-03-17 | Rainbow Medical Ltd. | Gastric anchor |
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US20150329978A1 (en) * | 2014-05-15 | 2015-11-19 | Mohammed Muslim Chaudhry | Method of Producing Hydrogen Gas from Water |
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- 2001-04-12 CA CA002405925A patent/CA2405925A1/en not_active Abandoned
- 2001-04-12 AU AU58337/01A patent/AU5833701A/en not_active Abandoned
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WO2003037406A2 (en) * | 2001-10-26 | 2003-05-08 | Massachusetts Institute Of Technology | Transdermal transport device with an electrolytic actuator |
WO2003037406A3 (en) * | 2001-10-26 | 2004-01-29 | Massachusetts Inst Technology | Transdermal transport device with an electrolytic actuator |
US7645263B2 (en) | 2001-10-26 | 2010-01-12 | Massachusetts Institute Of Technology | Impedance sensor |
US7651475B2 (en) | 2001-10-26 | 2010-01-26 | Massachusetts Institute Of Technology | Microneedle transport device |
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US7740984B2 (en) | 2004-06-04 | 2010-06-22 | Rovcal, Inc. | Alkaline cells having high capacity |
Also Published As
Publication number | Publication date |
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JP5581561B2 (en) | 2014-09-03 |
JP2004538360A (en) | 2004-12-24 |
AU5833701A (en) | 2001-10-30 |
WO2001079706A3 (en) | 2002-05-30 |
US6572740B2 (en) | 2003-06-03 |
US20020027068A1 (en) | 2002-03-07 |
EP1282453A2 (en) | 2003-02-12 |
CA2405925A1 (en) | 2001-10-25 |
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