JPH01154467A - Liquid fuel cell - Google Patents

Abstract

PURPOSE:To make a cell lightweight, to heighten cell voltage, and to lengthen the life by giving supply and exhaust functions of liquid fuel and oxidizing agent to electrodes and by combining them with impermeable separators. CONSTITUTION:Electrodes 1, 2 are formed by installing grooves 4 for supplying and exhausting fuel and oxidizing agent on the one side of a conductive porous substrate and applying a catalyst such as platinum onto its other side. An electrolyte 3 consists of an ion exchange membrane into which a sulfuric acid aqueous solution is impregnated. Separators 5 are flat plates comprising a mixture of expanded graphite and water repellent material. By using the electrodes 1, 2 having electrochemical reaction conducting parts and fuel and oxidizing agent supply and exhaust parts and the electrolyte impermeable separators 5, a cell is made compact and cell voltage is heightened, and the life is lengthened.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a liquid fuel cell, and in particular, the present invention provides an excellent method for liquid fuel cells, in which the electrodes have both an electrochemical reaction part and a function of supplying and discharging fuel and oxidizing agent. The present invention relates to liquid fuel cells manufactured using the same, which have excellent battery characteristics and light weight.

[Conventional technology]

Fuel cells, which are capable of continuously converting the chemical energy of fuel into electrical energy by supplying fuel and oxidizer, are attracting attention as a new power source due to their advantages such as high efficiency and non-pollution. has been done. Among these, those that use liquid as a fuel flow are expected to be put into practical use due to their ease of handling fuel, miniaturization of batteries, etc. An example of the structure of a single cell of this liquid fuel cell is shown in FIG. 1, and a battery is constructed by stacking a plurality of these cells.

That is, it is comprised of a fuel electrode 1, an oxidizer electrode 2, and an electrolyte 3 having ion conductivity located therebetween, and a separator 5 having grooves 4 for supplying and discharging liquid fuel and oxidizer to and from each electrode. As mentioned above, the battery is a repetition of the single cell shown in FIG. 1, and is stacked with the separator 5 in between. Therefore, such a separator 5 is not only a current collector that extracts electrical energy from an electrode, but also an interconnector that electrically connects unit cells, a separator that separates fuel and oxidizer, and a separator that separates fuel and oxidizer. It is also a means for supplying an oxidizing agent and discharging reaction products at each electrode. Since such functions are required, carbon materials are generally used in large numbers due to their chemical and electrochemical stability, economical efficiency, and light weight. Conventional separators using carbon materials can be roughly divided into those made by cutting a carbon block by mechanical processing, and those made by putting it in a mold and press-forming.Machined products include impermeable high-density separators. There are graphite ones. This is made into a graphite block at a high temperature of 2000° C. or higher, and after cutting, it is impregnated with phenol resin or the like to make it impermeable, which serves to separate liquids and gases. For this reason, productivity is low and it is expensive.
Since it is a hard material, it is brittle and has problems with mechanical strength. Another problem is that it is heavy due to its high density.

One example of pressure molding with good productivity is a resin mold made of carbon powder and thermosetting resin. Although this material is easy to manufacture, inexpensive, dense, and has excellent impermeability, it has problems such as high mechanical strength and high electrical resistance (including contact resistance with electrodes). In addition, some use expanded graphite as the carbon material for reasons of economy and weight reduction.

(Japanese Patent Laid-Open No. 59-27476) Expanded graphite has flexibility and elasticity, and when laminated, it makes good contact with other members and has low contact resistance.

However, it has problems in density and uniformity compared to those described above, and cannot be said to have sufficient separation functions such as absorption of liquid fuel, electrolyte, etc., and permeation of fuel and oxidizer.

In order to improve this problem, there are proposals to coat the surface with a water-repellent material or to mix the water-repellent material with expanded graphite. (Japanese Patent Application No. 61-96785) Although this proposal is good for liquid impermeability, since it contains a water-repellent substance, it is heavier than one that does not contain it. In addition, although it is good for flat plates, when it comes to structures with grooves as shown in Figure 1, when trying to reduce the density and weight,
There are problems with liquid impermeability, such as insufficient uniformity and the presence of pinholes.

[Problem that the invention seeks to solve]

As described above, it has been a difficult problem to satisfy both the weight reduction and liquid impermeability (gas-liquid separation function) of the battery.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid fuel cell that is lighter in weight and has an improved gas-liquid separation function, thereby reducing the weight of the battery, improving the battery voltage, and extending the life of the battery.

[Means for solving problems]

The above purpose is to reduce weight by equipping the electrode, which is lighter than the separator described above, with the function of supplying and discharging liquid fuel and oxidizing agent, and to achieve impermeability by combining this with a flat separator. Ru.

[Effect]

Here, the present invention will be explained by detailing the characteristics of a methanol fuel cell that uses sulfuric acid as an electrolyte and methanol as a liquid fuel.

In the present invention, a single cell is configured as shown in FIG. 2, for example. The electrode is made of a conductive porous substrate having grooves 4 on one side for supplying and exhausting fuel and oxidizing agent, and on the other side,
For example, the electrolyte 3 is made of an ion exchange membrane impregnated with an aqueous sulfuric acid solution. Further, the separator 5 uses expanded graphite. The reactions at the electrodes of a methanol fuel cell are as follows: Fuel electrode: CHaoH + H20 → 6H++CCh+6 Q
-(1) Oxidizer electrode: 6H++3/20z+6Q→
3H20...(2) and so on. Since the reaction that produces water proceeds at the oxidizing agent electrode, the produced water must be discharged from the electrode, and the oxidizing agent must have water repellency to the extent that diffusion does not become rate-limiting. In the conventional electrode (flat plate type in Figure 1), the water repellency of the catalyst layer is 10 for both the fuel electrode and the air electrode.
Amount of polytetrafluoroethylene (hereinafter referred to as PTFE) of wt% to 50 wt%, preferably 20 to 30% of the fuel electrode
It has been found that excellent electrode performance is exhibited in 30 to 40 wt% PTFE as an oxidizer electrode. Therefore, the amount of PTFE and electrode performance of the electrode base material having grooves on one side of the present invention were investigated. As a result, Fig. 3 shows the monopolar performance of the fuel electrode, and Fig. 4 shows the monopolar performance of the oxidizer electrode.
It can be seen that good performance is exhibited when the amount of FE is 50 wt% or less. From Fig. 4, PTFE content of 10 to 50 wt% indicates high oxidizing agent electrode performance. Considering the strength of the electrode, the PTFE content of the base material should be 10 to 50 wt%, preferably 20 to 40 wt%. It can be seen that unipolar characteristics can be obtained.

The separator is of a flat plate type and is made of a mixture of expanded graphite and a water-repellent material. This is expanded graphite from 30 to 3
In addition to expanded graphite powder, 10 to 50 w of PTFE or fluorocarbon is added as a water repellent material in the process of forming a sheet-like molded product (laminate sheet) with a press pressure of 0.00 kg/aJ.
t% is added, and then a plurality of these laminate sheets are stacked and pressed under a press pressure of 100 to 500 kg/ad to form a molded product. When we measured the amount of liquid permeation through this separator with an aqueous sulfuric acid solution, it was found to be 0.01 ma/a after 100 hours.
# and liquid permeation were substantially zero. Other impermeable carbon materials (resin mold, impermeable high-density graphite, etc.) can also be applied.

A fuel cell to which the present invention can be applied uses methanol as a fuel,
Some use liquid fuels such as formalin and formic acid, and others use gaseous fuels such as hydrogen and hydrogen-containing gas. Regarding those using gaseous fuel, there is a proposal for using phosphoric acid as an electrolyte (Japanese Patent Laid-Open No. 154771/1983).

No proposal similar to the present invention has been found in fuel cells that use liquid fuel.

In this way, the present invention provides a fuel cell using liquid fuel, in which an electrochemical reaction part is provided at the electrode, and fuel and edging agent are supplied and
By using a separator that has a discharge function and is permeable to adults, it is possible to reduce the weight of the battery, improve the battery voltage, and extend the life of the battery.

〔Example〕

Hereinafter, the present invention will be explained by examples, but the present invention is not limited to the following examples.

<Example-1> A 100×120mm carbon base material (density 0.4g/a1) with a thickness of 4 mm and a flat surface on one side and a groove with a depth of 2cm and a width of 3mm on the other side. , polytetrafluoroethylene liquid (PTFE, Polyflon Dispersion D-1 = manufactured by Daikin) was 40 wt% as PTFE.
After drying, it was baked at 380°C for 15 minutes.

On this flat side, 1.15 g of catalyst powder, in which 50 wt% of platinum and ruthenium were supported on carbon powder (Furnace Black: Cabot Corporation), was coated with Polyflon dispersion D1.
and water to obtain a paste of 25 wt % as PTFE, which was uniformly applied. After drying, it was fired at 280° C. for 1 hour to obtain fuel electrode 1.

Furthermore, 0.77 g of catalyst powder in which 30 wt% of platinum was supported on carbon powder was taken, and polyflon dispersion D1 was prepared.
A paste containing 35 wt % of PTFE was uniformly applied to the flat side of the carbon base material, dried, and then baked at 280° C. for 1 hour to obtain an oxidizer electrode 2.

Next, expanded graphite powder and polyflon dispersion D1
2 as expanded graphite (80 wt%) and PTFE.
0 wt% was mixed uniformly and press-formed at a temperature of 370°C to obtain a laminate sheet with a thickness of about 3 cm.Furthermore, 5 sheets of this were laminated and molded at a press pressure of 150 kg/cd to form a flat plate. Separator A (110×114 nn) was obtained.

Considering the configuration of the single cell shown in FIG. 2, the total weight of fuel electrode 1, oxidizer electrode 2, and separator A (two sheets) was measured. Its weight was 72.8g.

Comparative Example-1> Carbon vapor (E-
715: Kureha Chemical) 100X120m.

Water repellency was made using PTFE4+'t to a content of 40 wt% in the same manner as in Example-1. Thereafter, a fuel electrode and an oxidizer were obtained in the same manner as in Example-1. They are respectively referred to as a fuel electrode 3 and an oxidizer electrode 4.

The separator was made by laminating 15 laminate sheets and had the shape shown in FIG. 1, with 20 rows of horizontal counterflow type grooves on each of the front and back sides. This will be referred to as separator B.

Considering the configuration of the single cell shown in FIG. 1, the fuel f42. The total weight of oxidizer electrode 3 and separator B (two sheets) was measured. Its weight was 113.8g.

<Example-2> Using fuel electrode 1 and oxidizer electrode 2, 3 was used as an electrolyte between the electrodes.
A single cell (1) of the type shown in Fig. 2 was constructed using a separator A with an ion exchange membrane (CMV: M glass layer) holding an aqueous solution of mon/Q sulfuric acid interposed therebetween. The results of measuring the current density-voltage (i-V) characteristics of the single cell (1) are shown in FIG. 5 (1).

The measurement conditions were 2Q of anolite (1 mon/Q methanol + 1.5 moQ/Q sulfuric acid aqueous solution) as fuel at 500 m
Q/m1nf is circulated, and air is used as an oxidizing agent at 1rnQ.
/rnin. The battery temperature was kept constant at 60°C.

<Comparative Example-2> A single cell of the type shown in FIG. The results are shown in Figure 5 (II
).

<Example-3 and Comparative Example-3> Single cell using fuel electrode 1, oxidizer electrode 2, and separator A (
A battery (m) consisting of 33 stacked cells of 1), 3 fuel electrodes, 3 oxidizer electrodes, and 4. A battery (IV) is constructed by stacking 33 single cells (II) using separator B, and the current density is 60 mA.
The battery was operated continuously for 1000 hours at /al. The relationship between output power and operating time is shown in Figure 6 (m).
The operating conditions shown in (IV) are 7nolite (1mo
Circulate Q/Q methanol + 1.5mo Q/Q sulfuric acid aqueous solution) 1.59 to the battery, adjust the methanol concentration to 1moQ/Q±0,3moQ/Q, and keep the liquid level at ±5. Adjust it so that it is %.

Air was supplied by a fan. Battery temperature was 55±2°C.

Further, when the weights of the batteries were compared, the weight of the battery (m) was 63% of that of the battery (IV).

〔Effect of the invention〕

The electrode according to the present invention has an electrochemical reaction layer and gas/liquid supply/
By configuring a battery that also has a discharge function and is combined with a flat separator, the following effects can be achieved.

(1) The battery components are light, and the battery can be made lighter.

(2) Highly productive and inexpensive separator materials (expanded graphite,
Resin-molded graphite can be used, and since it is a flat plate type, it has good permeability to adults (improved battery voltage and extended life).

(3) When using expanded graphite, the contact resistance is low because both the separator and the electrode are flexible.
(Improved battery voltage, longer life).

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a single cell of a fuel cell, Figure 2 is a configuration diagram of a single cell of the present invention, Figure 3 is the amount and potential diagram of the base material PTFE of the fuel electrode, and Figure 4 is the diagram of the base material PTFE of the oxidizer electrode. Fig. 5 is a current density-voltage characteristic diagram of a single cell, and Fig. 6 is a continuous operation diagram of a 33-cell stacked battery. 1... Fuel electrode, 2... Oxidizer electrode, 3... Electrolyte,
4...Groove, 5...Separator. ＋12] Figure 2 Figure 3 Figure 27 F' F4 Quantity (wt Z) 4□
□□ -J! Material MFh amount (wt%) Figure 5 L degree of electric current (-/C mutually

Claims (1)

[Claims] 1. A fuel cell in which a plurality of single cells each having a pair of electrodes arranged with an electrolyte sandwiched therein are stacked with a separator in between, wherein the electrodes are based on a mixture of a conductive material and a water-repellent substance. One side has an electrochemical reaction layer containing a conductive material, a water repellent substance, and one or more white metal elements, and the other side has one or more groove structures for supplying and discharging fuel and oxidizing agent. A liquid fuel cell characterized by: 2. The liquid fuel cell according to claim 1, wherein the electrolyte comprises an ion exchange membrane containing an electrolytic solution. 3. The liquid fuel cell according to claim 1, wherein the separator is a flat plate made of a pressure-molded mixture of expanded graphite and a water-repellent material or an impermeable carbon material. 4. The liquid fuel cell according to claim 1, wherein the conductive material comprises a carbon base material and/or a carbon carrier. 5. Claim 1, wherein the water-repellent substance is one or more of fluororesin and fluorocarbon.
The liquid fuel cell according to item 1 or 3. 6. The liquid fuel cell according to claim 1 or 3, wherein the amount of the water-repellent substance mixed is 10 to 50 wt%.