WO2011139140A2

WO2011139140A2 - Metal-air cell and method of fabricating thereof

Info

Publication number: WO2011139140A2
Application number: PCT/MY2011/000042
Authority: WO
Inventors: Alva Sagir; Mohd Rais Ahmad
Original assignee: Mimos Berhad
Priority date: 2010-05-06
Filing date: 2011-05-05
Publication date: 2011-11-10
Also published as: WO2011139140A3; MY158578A

Abstract

The present invention provides a metal air-cell with low impedance bulk lipophilic membrane where methyl methacrylate [30] and tetrahydrofurfuryl acrylate [32] monomers are fabricated as the bulk co-polymer membrane, methyl methcrylate-tetrahydrofurfuryl acrylate (MT) [20] in a variety of ratio under reflux condition in toluene [34] in the presence of benzoyl peroxide [36], which is then installed with the anode, a fuel electrode [22] and the cathode, an air electrode [24] at each side of the membrane to complete the metal-air cell. The proposed bulk membrane of methyl methcrylate-tetrahydrofurfuryl acrylate (MT) offers economic benefits of low cost as well as ease of handling where the bulk co-polymer in the metal-air cell plays a role in effectively separating both the fuel and oxidant, preventing mixing and also transporting ions from the anode to the cathode to complete the redox reaction chemistry in generating micropower voltage that can be harnessed as a source of power.

Description

Title of Invention: METAL-AIR CELL AND METHOD OF FABRICATING THEREOF

Technical Field

[1] The present invention relates to metal-air cell for micropower voltage generation with low impedance bulk lipophilic membrane.

Background Art

[2] A fuel cell is an electrochemical cell that converts a source fuel into an electric

current. It generates electricity inside a cell through reactions between a fuel and an oxidant, triggered in the presence of an electrolyte. The reactants flow into the cell, and the reaction products flow out of it, while the electrolyte remains within it. Fuel cells can operate virtually continuously as long as the necessary flows are maintained.

[3] In a metal-air cell, the air electrode functions as cathode which then couple with a metal anode to produce a voltage potential that can be harnessed as a source of power. In this cell, the molecular oxygen is reduced to hydroxide at the cathode and the electrolyte is oxidized at the conductive metal anode. The assembly requires the air electrode to breathe air into the cell while at the same time contain the liquid electrolyte from leaking from the liquid chamber.

[4] There are several methods to produce metal-air cell. Presently, there are metal-air cell which are fabricated with polymer electrolyte as the membrane. A prior art listed a method of fabricating and characterizing cross linked membranes for alkaline fuel cells. This fuel cell also uses bulk polymer as the membrane and uses ammonium quartemary salt. This fuel cell is a type of alkaline fuel cell using poly (epichlorhydrin) as matrix.

[5] A prior art includes the use of a separator for the polymer electrolyte membrane fuel cell which comprises a resin substrate and an electro-conductive coating formed on the substrate. This fuel cell uses bulk polymer as the membrane containing methanol solution and the reaction is based on polyethylene sulfide, polyacetal. The anode catalyst is plutonium-rutherium and the cathode catalyst is plutonium.

[6] Another prior art listed the method to fabricate lithium air cell in which, the cell characteristics are improved compared to conventional ones in which a positive electrode containing a poly (tetramethyl piperidinyloxy methacrylate) radical as the redox catalyst of oxygen and a negative electrode composed of lithium metal which are set opposing each other via a separator and a non aqueous electrolytic solution is injected between the positive electrode and the negative electrode. A foamed nickel plate is put on the positive electrode and foamed nickel plate is pressed by a pressing member through which air is circulated to the positive electrode side. This invention is an air cell which uses methyl methacrylate as the catalyst of oxygen but uses no tetrahydrofurfuryl.

[7] The present invention is made in view of the prior arts described above where a low impedance bulk lipophilic membrane is proposed for the metal-air cell. As compared to prior arts, the proposed lipophilic bulk membrane cost only a fraction of the cost of commercially available membrane separator for hydrogen fuel cell such as Nafion. Summary of Invention

[8] The present invention proposes a metal-air cell for micropower voltage generation with low impedance bulk lipophilic membrane where in this process methyl methacrylate (M) and tetrahydrofurfuryl acrylate (T) monomers are fabricated as the lipophilic bulk polymeric membrane in a variety of ratio under reflux condition, which is then installed with the anode, a fuel electrode and the cathode, an air electrode at each side of the membrane to complete the metal-air cell. Methyl methacrylate (M) and tetrahydrofurfuryl acrylate (T) is proposed due to its chemical stability, compatibility with ionic liquid, high thermal stability, good mechanical strength and high polarity; as depended on the ratio of the monomers. The proposed bulk membrane of methyl methcrylate-tetrahydrofurfuryl acrylate (MT) also offers economic benefits of low cost as well as ease of handling.

Brief Description of Drawings

[9] Fig. 1 is a cross-sectional drawing of the metal-air cell with low impedance MT bulk co-polymer.

[10] Fig. 2 is a drawing showing the structure of methyl methacrylate-tetrahydrofurfuryl acrylate (MT) polymeric membrane.

[11] Fig. 3 is a drawing showing the structure of methyl methacrylate monomer.

[12] Fig. 4 is a drawing showing the structure of tetrahydrofurfuryl acrylate monomer.

[13] Fig. 5 is a drawing showing the bulk co-polymerization process of methyl

methacrylate and tetrahydrofurfuryl acrylate.

Description of Embodiments

[14] Hereinafter, the present invention is described in detail.

[15] The invention involves a method to fabricate metal-air cell using a low impedance bulk lipophilic membrane of methyl methcrylate-tetrahydrofurfuryl acrylate [20] (MT) as shown in Fig. 1. The structure of the low impedance bulk lipophilic methyl methcrylate-tetrahydrofurfuryl acrylate [20] (MT) membrane is shown in Fig. 2.

[16] In this metal-air fuel cell invention, the methcrylate-tetrahydrofurfuryl acrylate [20] (MT55) functions as low impedance bulk membrane which is doped with lipophilic ammonium salt, such as trioctylmethyl ammonium chloride, tetradodecyl ammonium chloride or tridodecyl hexadecyl ammonium bromide, to allow passage of ions. The anode [22] which is the fuel electrode and cathode [24], the oxygen or air electrode containing catalyst is installed at each side of the membrane as shown in Fig. 1.

[17] The chemical reactions involved in this metal-air cell are as follows.

[18] At the cathode [24], the air electrode, molecular oxygen is catalytically reduced to hydroxide by magnesium oxide, Mn0₂ [26].

[19] 0₂ + 2H₂0 + 4e- > 40H-

[20] In order to complete the cell, an electrode that produces electrons is required. This electrode is an anode [22] such as aluminium foil [28] or zinc plate, wherein the electrolyte such as 1M sodium hypophosphite (NaH₂P0₂) is catalytically oxidized to the dihydrogen phosphate species.

[21] 40H + 2Na⁺H₂P0₂- > 2H₂0 + 2Η₂Ρ0₃ ²" + 4e

[22] The overall cell reaction becomes:

[23] 0₂ + 2H₂P0₂- > 2H₂P0₃ ²- + electric energy + heat

[24] In this invention, the bulk co-polymer in the metal-air cell play a role in effectively separating both the fuel and oxidant, preventing mixing and also transporting ions from the anode [22] to the cathode [24] to complete the redox reaction chemistry.

[25] The copolymer membranes are fabricated from methyl methcrylate [30] and tetrahydrofurfuryl acrylate [32] monomers. The disclosed copolymer exhibits excellent properties as fuel cell membrane that includes clear and colorless appearance, good flexibility, not sticky and good adhesion onto surface. The polarity of this copolymer can vary, depending on the ratio between methyl methcrylate [30] and tetrahydrofurfuryl acrylate [32] and therefore can be used to fabricate a variety of sensors. The monomers of methyl methcrylate [30] and tetrahydrofurfuryl acrylate [32] are shown in Fig. 3 and Fig. 4 respectively.

[26] The key feature of this method is the ability of the bulk copolymer of methyl

methcrylate-tetrahydrofurfuryl acrylate [20] that can be prepared in a variety of ratio under reflux condition in toluene [34] in the presence of benzoyl peroxide [36]. Fig. 5 shows the bulk co-polymerization process of methyl methcrylate [30] and tetrahydrofurfuryl acrylate [32] to methyl methcrylate-tetrahydrofurfuryl acrylate [20].

[27] For example preparation of bulk copolymer methyl methcrylate-tetrahydrofurfuryl acrylate [20] (MT55) is conducted at a composition of 5 parts methyl methcrylate [30] to 5 parts tetrahydrofurfuryl acrylate [32]. Firstly, 5 mL of methyl methcrylate [30] and 5 mL of tetrahydrofurfuryl acrylate [32] are put into a 50 mL three-neck round bottom flask. 15 mL toluene [34] and 1 mg benzoyl peroxide [36] are added as initiator into the mixture of monomers. Reflux process is started and maintained at 95°C while being stirred under nitrogen gas flow for 7 hours. After 7 hours the heating would be discontinued and the mixture would be gradually cooled to room temperature. Then the viscous polymeric material was transferred to a 50 mL beaker where the solid material eventually becomes cloudy. The cloudy polymeric material would be washed three times with 5 mL portions of petroleum ether (80°C - 100°C) until it becomes clear. The bulk polymeric membrane would be air dried at ambient condition for over night. The final sold mass would appear white and elastic.

[28] Another example is preparation of bulk copolymer methyl methcrylate-tetrahy- drofurfuryl acrylate [20] (MT46) conducted at a composition of 4 parts methyl methcrylate [30] to 6 parts tetrahydrofurfuryl acrylate [32]. Firstly, 4 mL of methyl methcrylate [30] and 6 mL of tetrahydrofurfuryl acrylate [32] are put into a 50 mL three-neck round bottom flask. 15 mL toluene [34] and 1 mg benzoyl peroxide [36] are added as initiator into the mixture of monomers. Reflux process is started and maintained at 95°C while being stirred under nitrogen gas flow for 7 hours. After 7 hours the heating would be discontinued and the mixture would be gradually cooled to room temperature. Then the viscous polymeric material was transferred to a 50 mL beaker and added with petroleum ether (80°C - 100°C). The mixture is then transferred to a 50 mL three neck round bottom flask and continues with distillation until all solvent separates and viscous solution was found in the bottom of the 50 mL three neck round bottom flask. After the distillation process was discontinued, the mixture would be allowed to gradually cool to room temperature. Then the viscous polymeric material would be transferred to a 50 mL beaker and the solid material eventually becomes cloudy. The cloudy polymeric material would be washed three times with 5 mL portions of petroleum ether until it becomes clear. The bulk polymeric membrane would be air dried at ambient condition for over night. The final sold mass would appear white and elastic. The methy methacrylate [30] and tetrahydrofurfuryl acrylate monomers can also be prepared in the following ratio: 7 parts methyl methacrylate [30] and 3 parts tetrahydrofurfuryl acrylate [32] to produce bulk co-polymer (Bulk MT73); 8 parts methyl methacrylate [30] and 2 parts tetrahydrofurfuryl acrylate [32] to produce bulk co-polymer (Bulk MT82); or 9 parts methyl methacrylate [30] and 1 part tetrahydrofurfuryl acrylate [32] to produce bulk co-polymer (Bulk MT91).

[29] Once the polymeric membrane is ready, the metal-air fuel cell can be fabricated. The present invention uses methyl methcrylate-tetrahydrofurfuryl acrylate [20] typically of the methyl methcrylate-tetrahydrofurfuryl acrylate [20] (MT55) ratio to function as a low impedance lipophilic bulk membrane. As an example, firstly, 200 mg of methyl methcrylate-tetrahydrofurfuryl acrylate [20] (Bulk MT55) is mixed with 12 mg tri- octylmethyl ammonium chloride (TOMA-CI). Other ammonium salt such as tetradodecyl ammonium chloride or tridodecyl hexadecyl ammonium bromide can also be used. The mixture would then be dissolved with 4 mL of tetrahydrofuran (THF) and sonicated for 1 hour. The mixture would then be dropped on top of the magnesium oxide, Mn0₂ [26] sides at air electrode layer by layer until 1.2 mm dried thickness of the bulk MT as shown in Fig. 1. The air electrode was then placed into the cell and 1M NaH₂P0₂ was dropped too into the cell. The anode and cathode is then connected to a voltmeter and readings of voltage could then be obtained which signifies the functioning of the metal-air cell in producing a voltage potential that can be harnessed as a source of power.

[30] Accordingly, the invention disclosed a method to fabricate metal air-cell with low impedance bulk lipophilic membrane where in this process methyl methacrylate [30] and tetrahydrofurfuryl acrylate [32] monomers are fabricated as the bulk co-polymer membrane, methyl methcrylate-tetrahydrofurfuryl acrylate (MT) [20] in a variety of ratio under reflux condition in toluene [34] in the presence of benzoyl peroxide [36], which is then installed with the anode [22], a fuel electrode and the cathode [24], an air electrode at each side of the membrane to complete the metal-air cell.

[31] It is the combination of the above features and its technical advantages give rise to the uniqueness of such invention. Although the descriptions above contain much specificity, these should not be construed as limiting the scope of the embodiment but as merely providing illustrations of some of the presently preferred embodiments.

Claims

A metal air-cell comprising: a fuel electrode [22], a catalyzed air electrode [24], and a bulk lipophilic membrane [20] between the electrodes, characterized in that methyl methacrylate [30] and tetrahydrofurfuryl acrylate [32] monomers, and doping salt are fabricated as the bulk co-polymer membrane, methyl methcrylate-tetrahydrofurfuryl acrylate (MT) [20].

A cell according to claim 1, wherein the composition of lipophilic bulk co-polymer, methyl methcrylate-tetrahydrofurfuryl acrylate (MT) [20], can be prepared from methyl methacrylate [30] and tetrahydrofurfuryl acrylate [32] monomers in the following ratio:

5 parts methyl methacrylate [30] and 5 parts tetrahydrofurfuryl acrylate [32] to produce bulk co-polymer (Bulk MT55).

A cell according to claim 1, wherein the composition of the lipophilic bulk co-polymer, methyl methcrylate-tetrahydrofurfuryl acrylate (MT) [20], can be prepared from methyl methacrylate [30] and tetrahydrofurfuryl acrylate [32] monomers in the following ratio:

6 parts methyl methacrylate [30] and 4 parts tetrahydrofurfuryl acrylate [32] to produce bulk co-polymer (Bulk MT64);

7 parts methyl methacrylate [30] and 3 parts tetrahydrofurfuryl acrylate [32] to produce bulk co-polymer (Bulk MT73);

8 parts methyl methacrylate [30] and 2 parts tetrahydrofurfuryl acrylate [32] to produce bulk co-polymer (Bulk MT82); or

9 parts methyl methacrylate [30] and 1 part tetrahydrofurfuryl acrylate [32] to produce bulk co-polymer (Bulk MT91).

A cell according to claim 1, wherein the doping salt used is of lipophilic ammonium salt type such as trioctylmethyl ammonium chloride, tetradodecyl ammonium chloride or tridodecyl hexadecyl ammonium bromide.

A cell according to claim 1, wherein the anode [22], the fuel electrode is of metal type such as aluminium foil or zinc plate.

A method of fabricating lipophilic bulk co-polymer of metal-air cell, wherein the lipophilic bulk co-polymer, methyl methcrylate- tetrahydrofurfuryl acrylate (MT) [20] is formed under reflux in toluene[34] in the presence of benzoyl peroxide [36].

A method according to claim 6, wherein the formation of the composition of the lipophilic bulk co-polymer, methyl methcrylate- tetrahy drofurfuryl acrylate (MT) [20] in varying ratio comprises:

putting the required ratio parts of methyl methacrylate [30] and tetrahy- drofurfuryl acrylate [32] monomers into flask;

adding toluene and benzoyl peroxide as initiator into the mixture of monomers;

starting the reflux process of the mixtures which is maintained at 95°C while stirring under nitrogen gas flow for 7 hours;

allowing mixture to cool to room temperature after heating process; adding of petroleum ether (80°C - 100°C) for distillation to separate solvent and viscous solution, if necessary;

allowing mixture to cool to room temperature and until the solid material becomes cloudy;

washing of the cloudy polymeric material with petroleum ether until the material becomes clear; and

air drying bulk polymeric membrane at ambient condition overnight. [Claim 8] A method of fabricating metal-air cell according to any of the

proceeding claims, comprises:

mixing co-polymer methyl memcrylate-tetrahydrofurfuryl acrylate

(MT) [20] with lipophilic ammonium salt as doping salt;

dissolving mixture with tetrahy drofuran (THF);

applying sonication towards mixture for 1 hour;

dropping mixture on top of catalyst [26] sides at air electrode, layer by layer until achieving the required dried thickness of MT;

placing of cathode, air electrode [24] into the cell;

dropping electrolyte into the cell; placing of anode, fuel electrode [22] into the cell; and

connecting the anode [22] and cathode [24] for micropower voltage power generation.