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  Cell and power generation methodRelated Patent Categories: Chemistry: Electrical And Wave Energy, Apparatus, ElectrolyticThe Patent Description & Claims data below is from USPTO Patent Application 20070181418. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a cell and a method of power generation using the same. More particularly, the present invention relates to a cell and a method of power generation making use of an acidic medium and a basic medium being kept into contact with the acidic medium (i.e., a bipolar-type reaction field). BACKGROUND ART [0002] A cell is a device that converts chemical energy of a substance directly into electric energy. Further, cells can be classified into primary cells that discharge electric power until their chemical energy is used up, secondary cells capable of being reused by storing chemical energy again by a charging operation after being used up, and fuel cells that obtain electric energy by continually being supplied with a substance having chemical energy from outside. Currently, numerous-types of cells have been developed. Each cell has different advantages and disadvantages with respect to each item of environmental safety, economy, amount of electric energy that can be supplied, portability, storage properties, adaptation to an environment of use, recycling performance, and the like, so that cells are selected and put to practical use in accordance with an intended use. Critical technical factors that are common to all cells are what chemical substances are used for reaction, how the reaction is promoted, and in what form the chemical substances are stored, supplied and collected. [0003] A cell makes use of two kinds of chemical substances, namely, a reducing agent that causes a reduction reaction (donating electrons to the opposing party or drawing oxygen therefrom) and an oxidizing agent that causes an oxidation reaction (drawing electrons from the opposing party or giving oxygen thereto). By causing these reactions separately at two electrodes that oppose each other, the energy of generated electrons is taken to the outside (ions produced at the two electrodes accompanying the generation of electrons are neutralized within the cell). Reaction efficiency depends on the kind and reaction style of the chemical substances to be used, material and activity of electrodes, and the environment of reaction fields including electrolytes. Further, what substances are to be selected to constitute a cell is a point affecting whether the whole cell system will be good or bad not only at the time of use but also at the time of manufacturing and at the time of discarding after use. [0004] For example, manganese system or mercury system primary cells are excellent in economical efficiency and storage properties of the chemical substances. However, when harmful heavy metals are let alone after using the manganese system or mercury system primary cells, it adversely affects the environment, so that they must be collected strictly. Since the manganese system or mercury system primary cells cannot be reused by self-charging, problems are caused in that discarding of cells after use and reuse of resources are expensive. [0005] For example, lithium ion secondary cells are sufficient in the amount of electrical energy, and can be reused by self-charging. However, lithium is an extremely unstable flammable dangerous substance with respect to water or oxygen in the air. For this reason, in order to prevent such danger, sufficient safety countermeasures should be taken for packaging the cells or for protecting the environment at the time of use of the cells. Collection and reuse of the resource of the cells after expiration are also essential thus boosting the entire cost for implementing the processes of manufacturing, using, and discarding the cells. The same problem may occur in lead system storage cells, and from manufacturing cost and electric energy supply points of view, status quo is such that a large amount of the lithium ion system secondary cells is used for vehicle batteries or the like. [0006] On the other hand, among fuel cells, cells are mainly known in which hydrogen or methanol is used as a reducing agent (fuel) or oxygen or hydrogen peroxide is used as an oxidizing agent. For example, so-called direct methanol cells have been proposed in which methanol is used as a reducing agent (fuel) and an aqueous solution of hydrogen peroxide is used as an oxidizing agent (see U.S. Pat. No. 6,485,851, for example). [0007] In the case of these cells, since methanol and an aqueous solution of hydrogen peroxide are in a liquid state at an ordinary temperature and under a normal pressure, they are excellent in portability or storage properties. However, there is a critical problem in that the cells produce carbon dioxide which is a substance that causes green house phenomenon to occur accompanying the reaction and imposes burden on the environment. Further, methanol as a fuel is flammable, so that its leakage results in a serious danger. Moreover, problems are still arisen in that use of a large amount of noble metal reaction catalyst for causing reactions makes the manufacturing cost higher, methanol fuel at the side of a cathode moves, through a solid electrolyte film, to the side of an anode, and methanol crossover may occur thus deteriorating reaction efficiency. [0008] Further, hydrogen-oxygen system fuel cells can supply a large amount of electric energy and produces only water as a reaction product, so that the hydrogen-oxygen system fuel cells are extremely excellent in environmental safety. However, hydrogen as a fuel is flammable, so that its leakage results in a serious danger. [0009] Moreover, the cited document (see Electrochemistry 71, No. 5 (2003) 313-317) discloses a cell of a bipolar-type, as a hydrogen-oxygen fuel cell, in which a strong acidic high polymer membrane is provided at an anode (negative electrode) side and a strong basic high polymer membrane is provided at a cathode (positive electrode) side. Further, the cited document also described that the fuel cells have such advantages that oxidization reaction which is a rate reaction at the anode is initiated comparatively well, and electrode catalysts have high option, and water produced by the reaction is hard to affect the electrodes, and the like. [0010] By the way, in the bipolar-type cells, a reduction reaction is provoked at the side of a strong acidic high polymer membrane, and an oxidation reaction is provoked at the side of a strong basic high polymer membrane. However, the bipolar-type cells are structured such that potentials due to the neutralization of hydrogen ions H.sup.+ and hydroxide ions OH.sup.- at the center of the cells occupy a larger part of the electromotive force than the electromotive force due to the oxidation and reduction reactions of the bipolar-type cells. This is because the potential due to the neutralization of hydrogen ions H.sup.30 and hydroxide ions OH.sup.- is generally higher than one due to other ions. [0011] For this reason, the electromotive properties of this-type of the bipolar-type cell depend on the neutralizing reaction of water produced in the vicinity of a border between the acidic high polymer membrane and the basic high polymer membrane. However, a region where hydrogen ions H.sup.30 and hydroxide ions OH.sup.- come across cannot be a border portion between both high polymer membranes, and is actually dispersed into a wide region where the border is principally located. Further, water produced in accompanying with the neutralization makes it difficult to move hydrogen ions H.sup.+ and hydroxide ions OH.sup.-. Accordingly, since the site where the neutralizing reaction of hydrogen ions H.sup.+ and hydroxide ions OH.sup.- is actually taken place tends to fluctuate, the bipolar-type cell of this-type has a property of having difficulty in generating electromotive force stably. [0012] Further, water produced in this bipolar-type cell has a possibility of being accumulated into the interface between both high polymer membranes to form a water layer. The existence of the water layer may hinder the neutralization reaction between hydrogen ions H.sup.+ and hydroxide ions OH.sup.- thereby resulting in difficulty in supplying electric energy in accordance with the formation or the increase of water layer with time. [0013] Accordingly, an object of the present invention is to provide a bipolar-type cell which is a cell having a novel structure which is able to generate power stably, and a method of power generation using the same. [0014] According to some aspects of the present invention, one object of the present invention is to provide a novel cell for meeting various needs, and solving various problems, which have been caused by the conventional cells, such as occurrence of danger due to the use of flammable and ignitable fuels, discharge of carbon dioxide, complicated storage properties, and a complicated structure of the cell. DISCLOSURE OF THE INVENTION [0015] The above-described problems can be solved by the inventions as follows: [0016] A cell of the present invention comprises an acidic medium, a first electrode which is disposed in the acidic medium, a basic medium which is kept in contact with the acidic medium, and a second electrode which is disposed in the basic medium, wherein the acidic medium contains a first substance which causes a reaction of removing electrons from the first electrode, accompanied by hydrogen ions contained therein, and the basic medium contains a second substance which causes a reaction of donating electrons to the second electrode, accompanied by hydroxide ions contained therein. [0017] In accordance with the cell of the present invention, when hydrogen ions H.sup.+ and hydroxide ions OH.sup.- are involved in the reaction at the electrodes, the first substance in the acidic medium, accompanied by the hydrogen ions H.sup.+ in the acidic medium, causes an oxidation reaction that removes electrons from the first electrode, and the second substance in the basic medium, accompanied by the hydroxide ions OH.sup.- in the basic medium, causes a reduction reaction that donates electrons to the second electrode. At this time, the electromotive force by oxidation reaction in an acidic medium becomes, in principle, larger than the electromotive force by oxidation reaction generated in a basic medium. This is due to the following reason. Since hydrogen ions H.sup.+ are a substance of the reactant, the chemical equilibrium tends to be shifted to the product in an acidic medium having a high hydrogen ion concentration, thereby raising the oxidation potential. Also, the electromotive force by reduction reaction generated in a basic medium becomes, in principle, larger than the electromotive force by reduction reaction generated in an acidic medium. This is due to the following reason. Since hydroxide ions OH.sup.- are a substance of the reactant, the chemical equilibrium tends to be shifted to the product in a basic medium having a high hydroxide ion concentration, thereby lowering the oxidation potential. [0018] For this reason, according to the structure of the bipolar-type cell of the invention, the electromotive force generated by the oxidation-reduction reaction at the electrodes is a principal source of the voltage obtained from the cell, so that the cell of the invention can generate electric power more stably than a different bipolar-type cell in which the electromotive force is generated principally in an area having a property such that the site where the neutralizing reaction is generated within the cell tends to fluctuate as described in the aforementioned non-patent document 2. [0019] Further, a method of power generation by using a cell comprises an acidic medium, a first electrode which is disposed in the acidic medium, a basic medium being kept into contact with the acidic medium, and a second electrode which is disposed in the basic medium, [0020] wherein a first substance which is contained in the acidic medium causes a reaction of removing electrons from the first electrode, accompanied by hydrogen ions contained therein, and a second substance which is contained in the basic medium causes a reaction of donating electrons to the second electrode, accompanied by hydroxide ions contained therein. [0021] In accordance with a method of power generation of the present invention, as described above, the electromotive force due to the oxidation and reduction reactions at the electrodes can be a subjective source of a voltage that can be obtained from the cell. Consequently, a power force can be generated more stably. Continue reading... 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