JP4683974B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system, and more specifically to a fuel cell system capable of removing gas such as carbon dioxide generated from a fuel electrode in a liquid fuel direct supply type fuel cell system.

  A fuel cell is a device that generates electrical energy from hydrogen and oxygen, and can achieve high power generation efficiency. The main feature of the fuel cell is direct power generation that does not go through the process of thermal energy and kinetic energy as in the conventional power generation system, so high power generation efficiency can be expected even on a small scale, and there is little emission of nitrogen compounds, etc. Noise and vibration are also small, so the environment is good. In this way, fuel cells can effectively use the chemical energy of fuels and have environmentally friendly characteristics, so they are expected to be energy supply systems for the 21st century, and are used on a large scale from space use to automobiles and portable devices. It is attracting attention as a promising new power generation system that can be used in various applications from power generation to small-scale power generation, and technological development is in full swing toward practical application.

  Among them, solid polymer fuel cells are characterized by low operating temperature and high power density compared to other types of fuel cells. In particular, as a form of solid polymer fuel cells, direct methanol A fuel cell (Direct Methanol Fuel Cell: DMFC) is attracting attention. In DMFC, an aqueous methanol solution as a fuel is directly supplied to the anode without modification, and electric power is obtained by an electrochemical reaction between the aqueous methanol solution and oxygen, and carbon dioxide is emitted from the anode to the cathode by this electrochemical reaction. The product water is discharged as a reaction product. Aqueous methanol solution has higher energy per unit volume than hydrogen, and is suitable for storage and has a low risk of explosion, so it can be used in automobiles and mobile devices (cell phones, notebook personal computers, PDAs, MP3 players, Use for power sources such as digital cameras or electronic dictionaries (books) is expected.

As described above, in a liquid fuel direct supply type fuel cell such as a DMFC, carbon dioxide is generated from the anode, and if mixed in the methanol aqueous solution as the fuel as carbonate ions or gas, the supply of fuel to the anode is inhibited. There are problems and various measures have been taken.
JP 2004-146387 A

  However, in the conventional method of removing carbon dioxide, it is possible to remove carbonate ions that are dissolved in an aqueous methanol solution as a fuel and exist as ions, but it is difficult to remove gaseous carbon dioxide. Further, when gaseous carbon dioxide is discharged out of the system, there is a risk that vaporized liquid fuel is discharged out of the system together with carbon dioxide.

  The present invention has been made in view of the above-described problems, and is a fuel cell capable of removing gas such as carbon dioxide generated from a fuel electrode in a liquid fuel direct supply type fuel cell system including DMFC. The purpose is to provide a system.

In order to achieve the above object, a fuel cell system of the present invention includes an electrolyte layer, a fuel electrode provided on one surface of the electrolyte layer, and an oxidant electrode provided on the other surface of the electrolyte layer. A fuel storage unit that supplies fuel to the fuel electrode and stores the fuel; and a fuel supply unit that is detachably attached to the fuel storage unit and replenishes the fuel storage unit with the fuel. In the system, the fuel supply unit includes a product removal unit that is connected to the fuel supply unit and removes a product generated from the fuel electrode, and the fuel storage unit includes a wick material that supplies the fuel to the fuel electrode. The fuel replenishment portion has a connection surface with the fuel storage portion inclined at 1 to 10 °, and one end of the wick material that becomes the upper portion of the wick material when the bottom surface of the housing of the fuel replenishment portion is installed as a bottom surface Fuel facing Wherein the the top of the compared and a product discharge port.

  Here, the product includes carbon dioxide, formaldehyde, formic acid and the like when methanol is used as the fuel as described above. The removal of these products may be performed so that the products generated from the fuel electrode are removed as much as possible from the outside of the fuel system. There are a method of removing by absorbing by some kind of substance such as mechanical adsorption and occlusion, and a method of chemically decomposing with a catalyst. According to the present invention, the product produced from the fuel electrode can be removed.

According to a second aspect of the present invention, in the fuel cell system according to the first aspect, the fuel is a liquid fuel. Liquid fuels, such as the methanol, isopropyl alcohol, ethylene glycol, dimethyl ether, etc. ethyl alcohol and the like, are suitable for storage, application to the portable device is facilitated.

  According to a third aspect of the present invention, in the fuel cell system according to the first or second aspect, the product removing means is provided in the fuel supply section. As a result, the product removing means can be replaced with the fuel replenishing unit.

  The invention according to claim 4 is the fuel cell system according to any one of claims 1 to 3, wherein the product removing means includes a substance that expands in volume by removing the product, According to a fifth aspect of the present invention, in the fuel cell system according to the fourth aspect, the fuel replenishing section replenishes the fuel storage section with the fuel as the material expands in volume. Thereby, fuel can be replenished from a fuel replenishment part to a fuel storage part, without using another motive power.

  A sixth aspect of the present invention is the fuel cell system according to any one of the first to fifth aspects, wherein the product removing means contains calcium oxide. As a result, carbon dioxide can be adsorbed as calcium carbonate, and an exothermic reaction is performed at that time, so that heat generated by the exothermic reaction can be used.

  The invention according to claim 7 is the fuel cell system according to any one of claims 2 to 6, wherein the gas generated from the fuel electrode is provided between the fuel storage section and the product removing means. A gas permeable membrane selectively permeable is provided. Thereby, the gas produced | generated from a fuel electrode can be selectively removed.

  The present invention can remove gas such as carbon dioxide generated from a fuel electrode in a fuel cell system, particularly a liquid fuel direct supply type fuel cell system.

  The basic configuration of the DMFC 10 of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an exploded perspective view schematically showing the internal structure of the DMFC 10. The DMFC 10 includes an anode side electrode 12 to which a methanol aqueous solution or pure methanol (hereinafter referred to as “methanol fuel”) is supplied by capillary action. A cathode side electrode 14 to which air is supplied and an electrolyte membrane 16 sandwiched between the anode side electrode 12 and the cathode side electrode 14 are provided, and an electrochemical reaction between methanol in methanol fuel and oxygen in air. Generate electricity. Reference numerals 18 and 20 denote current collectors provided in the respective cells 22, and the plurality of cells 22 can be connected in series by connecting the current collectors 18 and 20 by the wiring 24. A methanol fuel storage unit 26 for storing methanol fuel to be supplied to the anode side electrode 12 is provided at the bottom of the anode side electrode 12, and the methanol fuel filled in the methanol fuel storage unit 26 is a methanol fuel supply port. The anode side electrode base material 30 constituting the anode side electrode 12 is supplied to the anode catalyst layer 32 from the current collector 28 via the current collector 18. On the other hand, air is provided with an air intake port 36 in the upper part of the housing 34, and is supplied to the cathode catalyst layer 38 using the air flow that naturally occurs from the air intake port 36.

  FIG. 2 is a diagram schematically showing a cross section of the DMFC 10. As shown in FIG. 2, the anode side electrode 12 has carbon paper as an anode side electrode base material 30, and Pt-Ru black is formed on one surface thereof. And a catalyst paste mixed with 5 wt% Nafion solution (manufactured by DuPont). On the other hand, 14 is a cathode-side electrode, and the cathode-side electrode 14 is a cathode-side electrode base material 40 formed by filling carbon black (Vulcan XC-72: manufactured by CABOT) into carbon paper subjected to water repellent treatment. A catalyst paste in which Pt black and a 5 wt% Nafion solution (manufactured by DuPont) are mixed is applied to one surface thereof. In this embodiment, only the cathode side electrode 14 is filled with carbon black. However, when carbon black is filled into the carbon paper of both the anode side electrode 12 and the cathode side electrode 14, the amount of carbon black filled in the carbon paper is When the cathode side is larger than the anode side, the generated water generated from the cathode side is easily discharged, and even in a fuel cell system that does not have an air supply means for forcibly supplying air to the cathode side. Water can be discharged and air can be supplied smoothly.

A wick material 42 is disposed under the anode side electrode 12 (current collector 18), and methanol fuel is supplied from the methanol fuel storage unit 26 to the anode side electrode 12 regardless of the orientation of the DMFC 10. It has become so. The wick material 42 is generally made of a hydrophilic absorbing material that absorbs moisture, a porous material or a particulate material, specifically, a bridged polyacrylate, isobutylene / maleate, Starch / polyacrylate, PVA (polyvinyl alcohol) / polyacryl, acrylic fiber hydrolysis system, crosslinked PV
A polymer material such as A-type can be applied. In addition, it is desirable to have a function of moving the generated water to a predetermined isolated location and evaporating it. Examples of such materials include porous metals and porous minerals having concave portions on the surface, hydrophilic carbon, Examples include carbon paper, woven fabric, non-woven fabric, paper, pulp, polymer material, natural fiber, and synthetic fiber. Furthermore, a material having high water absorption that causes capillary action is also suitable. Synthetic fibers and the like such as polyester may be used.

In the present embodiment, the electrodes 12 and 14 are of the type in which the catalyst layers 32 and 38 are formed on the electrode base materials 30 and 40, but H ⁺ from methanol, and water from H ⁺ and oxygen. It is sufficient that the catalyst layers 32 and 38 having a catalytic function for generating the electrode exist, and the configuration of the electrode is not limited thereto. Moreover, although the particle | grains (Pt-Ru black and Pt black) which consist of Pt-Ru and Pt were used for the catalyst, you may use the catalyst carrying | support carbon which carry | supported the catalyst on carbon black.

  FIG. 3 is a cross-sectional view showing the basic configuration of the DMFC system 100 with the fuel cartridge 150 attached to the DMFC 110. The fuel cartridge 150 is filled with a methanol aqueous solution or pure methanol having a concentration higher than that of methanol fuel. Yes. The fuel cartridge 150 includes a fuel supply connection port 152 for replenishing methanol into the methanol fuel storage unit 126 of the DMFC 110. By inserting the fuel supply connection port 152 into a corresponding part on the DMFC 110 side, the fuel cartridge 150 and the fuel The cartridge 150 is connected.

  The methanol fuel in the methanol fuel storage unit 126 is sucked up from the methanol fuel supply port 128 via the current collector 118 by the capillary phenomenon of the anode-side electrode base material 130, and methanol is oxidized on the anode catalyst layer 132 ( Formula (1)). The reaction at the anode catalyst layer 132 is as follows.

メタノールが酸化されて得られるプロトンは、電解質膜１１６の中を拡散してカソード側電極１１４のカソード触媒層１３８へ到達し、アノード側電極１１２で発生した電気は、集電体１１８を介してカソード側電極１１４側の集電体１２０へ到達する。一方、筐体１３４の空気取込口１３６から取り込まれた空気中の酸素は、カソード側電極１１４のカソード触媒層１３８へ到達し、アノード側電極１１２から得られたプロトンと電子を受領することにより酸素を還元し、水を生成する（式（２））。カソード触媒層１３８での反応は次のようになる。

Protons obtained by oxidizing methanol diffuse through the electrolyte membrane 116 and reach the cathode catalyst layer 138 of the cathode side electrode 114, and electricity generated at the anode side electrode 112 passes through the current collector 118 to the cathode. It reaches the current collector 120 on the side electrode 114 side. On the other hand, oxygen in the air taken in from the air intake port 136 of the casing 134 reaches the cathode catalyst layer 138 of the cathode side electrode 114 and receives protons and electrons obtained from the anode side electrode 112. Oxygen is reduced to produce water (formula (2)). The reaction at the cathode catalyst layer 138 is as follows.

このようにセル１２２により取り出される電気を、携帯機器と接続することにより携帯機器を直接駆動することや、二次電池等の充電に使用することができる。

Thus, the electricity taken out by the cell 122 can be used to directly drive the portable device by connecting to the portable device or to charge the secondary battery or the like.

  As shown in Formula (1), carbon dioxide is generated in the methanol oxidation reaction in the anode catalyst layer 132. When the generated carbon dioxide reaches a certain concentration or more, it becomes a gas (bubble) 160 and enters the pores of the porous current collector 118, the anode-side electrode base material 130, and the wick material 142. In the anode electrode base material 130, countless holes having an average pore diameter of several μm to several tens of μm serve as a fuel supply path to the anode catalyst layer 132. The supply path is blocked, and the amount of methanol supplied to the anode catalyst layer 132 is reduced.

  Therefore, the upper surface of the fuel cartridge 150 is inclined by θ (about 1 to 10 °), and the bubbles 160 adhering to the current collector 118, the anode electrode base material 130, and the wick material 142 are removed from the upper part of the methanol fuel storage unit 126 (DMFC system). 100 is discharged from the product discharge port 144 formed at the upper position when the cartridge 100 is installed stably, that is, when the bottom surface 154a of the cartridge housing 154 forming the fuel cartridge 150 is used as the bottom surface. To do. A gas permselective membrane such as a porous membrane formed of a fluororesin is disposed at the product outlet 144, and liquid such as methanol fuel does not permeate, and gas such as carbon dioxide permeates selectively. Then, it is introduced into the product removing unit 156 as indicated by an arrow. It is better to arrange a gas selective permeable membrane at the inlet of the product removal unit 156 so that liquid does not enter the product removal unit 156.

  In this embodiment, the product removing section 156 is filled with particulate calcium oxide (CaO) having a diameter of 1 to 2 mm, and carbon dioxide is adsorbed by the calcium oxide. Calcium oxide changes to calcium carbonate when carbon dioxide is adsorbed as shown in formula (3).

このとき、気体の二酸化炭素は固体の炭酸カルシウムとなって除去されるので、生成物除去部１５６にて二酸化炭素分の体積が収縮する。従って、生成物排出口１４４近傍と生成物除去部１５６との間に圧力差ができ、矢印で表した流れが生じる。これにより、効率的に二酸化炭素を除去することが可能となる。

At this time, since the gaseous carbon dioxide is removed as solid calcium carbonate, the volume of carbon dioxide shrinks in the product removal unit 156. Accordingly, a pressure difference is generated between the vicinity of the product discharge port 144 and the product removal unit 156, and a flow indicated by an arrow is generated. Thereby, carbon dioxide can be efficiently removed.

  Further, when the water in the methanol fuel becomes water vapor together with carbon dioxide and permeates through the gas selective permeable membrane, the calcium oxide also adsorbs water and changes to calcium hydroxide as shown in the equation (4).

酸化カルシウムが水酸化カルシウムとなる反応は発熱反応（ΔＨ＝−６３ｋＪ／ｍｏｌ
）であるため、この生成物除去部１５６の温度が上昇し、膨張する可能性が考えられる。そこで、生成物除去部１５６と燃料カートリッジ１５０の濃度の高いメタノール水溶液あるいは純メタノールが貯蔵されている燃料タンク部１５８との間には、移動可能な仕切板１５４ｂを用いると良い。これにより、温度上昇により生成物除去部１５６が膨張したときに、この圧力が燃料タンク部１５８に伝わり、燃料カートリッジ１５０からＤＭＦＣ１１０のメタノール燃料貯蔵部１２６へ、燃料供給接続口１５２を通ってメタノールを補充することができる。また、酸化カルシウムが炭酸カルシウムあるいは水酸化カルシウムに変化することによる体積変化によっても、仕切板１５４ｂを介して燃料タンク部１５８へ圧力をかけることができる。さらに、この反応熱が、燃料タンク部１５８、メタノール燃料貯蔵部１２６を介してセル１２２に伝わることにより、セル１２２を温めることができ、セル１２２の反応促進に寄与し、ＤＭＦＣ１１０の性能を向上させることができる。

The reaction in which calcium oxide becomes calcium hydroxide is an exothermic reaction (ΔH = −63 kJ / mol).
Therefore, there is a possibility that the temperature of the product removing unit 156 rises and expands. Therefore, it is preferable to use a movable partition plate 154b between the product removing unit 156 and the fuel tank unit 158 in which the high concentration methanol aqueous solution or pure methanol in the fuel cartridge 150 is stored. As a result, when the product removal unit 156 expands due to a temperature rise, this pressure is transmitted to the fuel tank unit 158, and methanol is passed from the fuel cartridge 150 to the methanol fuel storage unit 126 of the DMFC 110 through the fuel supply connection port 152. Can be replenished. Further, pressure can be applied to the fuel tank portion 158 via the partition plate 154b also by a volume change caused by the change of calcium oxide to calcium carbonate or calcium hydroxide. Furthermore, the reaction heat is transmitted to the cell 122 via the fuel tank unit 158 and the methanol fuel storage unit 126, so that the cell 122 can be warmed, contributing to the reaction promotion of the cell 122 and improving the performance of the DMFC 110. be able to.

  If a porous membrane formed of a fluororesin is also disposed at the fuel supply connection port 152, a high concentration aqueous methanol solution or pure methanol has a lower surface tension than methanol fuel, so that the porous membrane is permeated. The methanol fuel is not supplied to the fuel cartridge 150 because the methanol fuel cannot permeate the porous membrane. One-way methanol supply from the fuel cartridge 150 to the methanol fuel storage 126 is performed. Is possible.

When calcium oxide is used for the product removal unit 156, the amount (mass) of calcium oxide required can be predicted from Equation (5), and spherical calcium oxide particles are ideal so that the filling rate is 74%. Assuming that the product removal unit 156 is packed into the product removal unit 156 (to be close-packed), the design product removal unit 156 has a volume (density: 3.25 g / cm) of the required amount of calcium oxide. It can be obtained by converting to ³ ) and multiplying by about 1.35.

ここで、Ｍ_CaOは酸化カルシウムの質量、Ｖ_meは燃料カートリッジに充填されたメタノール水溶液又は純メタノールの体積、Ｄ_meは燃料カートリッジに充填されたメタノール水溶液又は純メタノールの密度、Ｃ_meは燃料カートリッジに充填されたメタノール水溶液又は純メタノールの質量パーセント濃度、Ｗ_meはメタノールの分子量（約３２ｇ／ｍｏｌ）、Ｗ_CaOは酸化カルシウムの分子量（約５６ｇ／ｍｏｌ）である。

Here, M _CaO is the mass of calcium oxide, V _me is the volume of the methanol aqueous solution or pure methanol filled in the fuel cartridge, D _me is the density of the methanol aqueous solution or pure methanol filled in the fuel cartridge, and C _me is the fuel cartridge. The weight percentage concentration of the methanol aqueous solution or pure methanol filled in the vessel, W _me is the molecular weight of methanol (about 32 g / mol), and W _CaO is the molecular weight of calcium oxide (about 56 g / mol).

For example, if the fuel cartridge 50 wt% aqueous methanol solution (density of about 0.89 g / cm ³⁾ is 5 cm ³ filled, to adsorb all carbon dioxide generated, oxidation theoretically about 3.89g It is sufficient to introduce calcium into the product removing unit 156.

[Other matters]
Particles (beads) having a diameter of 100 μm to several mm (a clearance smaller than the height of the methanol fuel storage unit 126) made of a material having low reactivity with methanol and carbonate ions in the methanol fuel storage unit 126 When the DMFC 110 rotates and moves, the beads float, stir and collide in the methanol fuel storage unit 126 and adhere to the porous current collector 118, the anode-side electrode base material 130, and the wick material 142. Bubbles 160 are removed by the impact. If the beads are slightly smaller than the height of the methanol fuel storage unit 126, about 1 to 5 beads may be used, and if the size is about several hundred μm, about 10 to 100 beads may be used. Therefore, if the total volume of the beads is set to be less than 20% of the volume of the methanol fuel storage unit 126, preferably about 0.001% to 10%, the methanol fuel storage unit 126 The bubbles 160 attached to the current collector 118, the anode electrode base material 130, and the wick material 142 can be removed without wasting the volume.

  The material is preferably glass, metal such as gold having high corrosion resistance, ceramics, fluororesin, PET (polyethylene terephthalate), PC (polycarbonate), PP (polypropylene) or PE (polyethylene). In addition, when a plurality of kinds of beads having different materials and dimensions are introduced, the beads 160 moving in the methanol fuel move in various ways depending on the dimensions when the DMFC 100 is moved, so that the bubbles 160 can be more efficiently removed. Can do.

  The present invention does not require so much electromotive force, and can be used not only in a planar DMFC for portable equipment that is required to be as thin as possible, but also in a fuel cell for home use or automobile.

It is a disassembled perspective view which shows the basic composition of DMFC which concerns on this invention. It is sectional drawing which shows the basic composition of DMFC which concerns on this invention. It is sectional drawing which shows the DMFC system which concerns on the Example of this invention.

Explanation of symbols

10, 110 DMFC
12, 112 Anode-side electrode 14, 114 Cathode-side electrode 16, 116 Electrolyte membrane 18, 118 Anode-side current collector 20, 120 Cathode-side current collector 22, 122 Cell 24 Wiring 26, 126 Methanol fuel storage unit 28, 128 Methanol Fuel supply port 30, 130 Anode-side electrode base material 32, 132 Anode catalyst layer 34, 134 Housing 36, 136 Air intake port 38, 138 Cathode catalyst layer 40, 140 Cathode-side electrode base material 42, 142 Wick material 60, 160 Air bubbles 100 DMFC system 144 Product discharge port 150 Fuel cartridge 152 Fuel supply connection port 154 Cartridge housing 154a Bottom surface 154b Partition plate 156 Product removal unit 158 Fuel tank unit

Claims (7)

An electrolyte layer, a fuel electrode provided on one surface of the electrolyte layer, an oxidant electrode provided on the other surface of the electrolyte layer, and a fuel that supplies fuel to the fuel electrode and stores the fuel In a fuel cell system comprising: a storage unit; and a fuel supply unit that is detachably attached to the fuel storage unit and supplies the fuel to the fuel storage unit.
Connected to said fuel supply unit includes a product removing means for removing the product generated from the fuel electrode, the fuel storage portion is provided with a wick material for supplying the fuel to the fuel electrode, the fuel supply The part has a connecting surface with the fuel storage part inclined by 1 to 10 °, and faces one end of the wick material that becomes the upper part of the wick material when the bottom surface of the casing of the fuel supply part is installed. A fuel cell system comprising a product discharge port in an upper part of the fuel storage unit . The fuel cell system according to claim 1, wherein
The fuel cell system according to claim 1, wherein the fuel is a liquid fuel. The fuel cell system according to claim 1 or 2,
The fuel cell system, wherein the product removing means is provided in the fuel supply unit. The fuel cell system according to any one of claims 1 to 3,
The fuel cell system according to any one of claims 1 to 3, wherein the product removing unit includes a substance that expands by volume when the product is removed. The fuel cell system according to claim 4, wherein
5. The fuel cell system according to claim 4, wherein the fuel replenishment unit replenishes the fuel storage unit with the fuel in accordance with volume expansion of the substance. The fuel cell system according to any one of claims 1 to 5,
6. The fuel cell system according to claim 1, wherein the product removing unit includes calcium oxide. The fuel cell system according to any one of claims 2 to 6,
7. The gas selective permeable membrane is provided between the fuel storage unit and the product removing unit and selectively permeates gas generated from the fuel electrode. 8. The fuel cell system described in 1.

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