JPS5834573A - Liquid fuel cell - Google Patents

Abstract

PURPOSE:To increase the voltage of a liquid fuel cell, and enhance the fuel utilizing efficiency of the battery by interposing between the anode and the cathode, either a layer prepared by stacking a plural number of ion exchange membranes, or a layer prepared by stacking an ion exchange membrane and a fuel-permeation preventing membrane. CONSTITUTION:A multi-layered film 1 prepared by stacking a plural number of ion exchange membranes prevents any direct contact between a cathode 7 and an anode 8. It also prevents any fuel contained in an anolyte chamber 2 from reaching to the cathode 7 through the anode 8. Air entering from an air inlet 5 is exhausted from an air outlet 6. Oxygen gas contained in an air chamber 4 reacts with hydrogen ions in the cathode 7 to produce water. Fuel undergoes reaction in the anode 8 to produce gas, which is exhausted from an exhaust hole 3. Hydrogen ions produced in the anode 8 reach to the cathode 7 through the ion exchange membranes. At this point, the chemical energy of the fuel is converted into electric energy. By stacking a plural pieces of ion exchange membranes as mentioned above, the fuel preventing effect and the fuel utilizing efficiency can be enhanced.

Description

[Detailed description of the invention] The present invention relates to liquid fuel cells.

In conventional fuel cells that use liquid fuels such as methanol, hydrazine, and aldehydes, an ion exchange plate is used between the anode and the cathode to separate the cathode and anode and prevent the fuel from reaching the cathode directly. There are structures that use membranes. Moreover, in this case,
The fuel blocking effect of the ion exchange membrane is small, and the liquid fuel passes through the ion exchange membrane and reacts with oxygen in the air at the air electrode, resulting in a decrease in fuel utilization efficiency and a decrease in the air electrode potential, i.e., the battery The disadvantage is that the voltage drops.

In the present invention, as the ion exchange membranes are stacked, the electrical resistance increases in proportion to the number of stacked membranes, but the fuel blocking effect is inversely proportional to the square of the number of stacked membranes, that is, as the membranes are stacked, the fuel blocking effect rapidly increases. The purpose of this is to prevent a drop in cell voltage and waste of fuel due to direct reaction of fuel with oxygen on the air electrode.

The voltage of a battery is the difference between the potential of the cathode and the potential of the anode (Figure 5). That is, to increase the cell voltage, it is necessary to raise the cathode potential or lower the anode potential, but as shown in FIG. 4, when the fuel comes into contact with the cathode, the cathode potential decreases. In other words, the battery voltage decreases. Therefore, in order to prevent a drop in battery voltage, it is necessary to use a diaphragm to prevent the fuel from coming into contact with the cathode, but since the diaphragm has electrical resistance, there is a voltage drop due to the resistance.

The present invention has confirmed through experiments that the increase in battery voltage due to fuel permeation inhibition 11-1 caused by overlapping membranes is superior to the decrease in battery voltage due to an increase in electrical resistance due to overlapping membranes. By interposing a stack of multiple ion exchange membrane layers or a stack of an ion exchange membrane and a fuel permeation blocking membrane between the anode and cathode of the fuel cell, the cell voltage can be increased and the fuel utilization efficiency can be improved. It is an enhanced version of

The present invention will be explained in detail below. A multilayer membrane 1 made by stacking a plurality of ion exchange membranes prevents the cathode 7 and anode 8 from coming into direct contact, and also prevents the fuel in the anode chamber 2 from reaching the cathode 7 through the anode. . Air entering from the air inlet can be exhausted from the outlet 6. Oxygen gas in the air chamber 4 reacts with hydrogen ions at the cathode to produce water. The fuel reacts at the anode to generate gas, which is discharged from the discharge port 3. Hydrogen ions generated at the anode pass through an ion exchange membrane and reach the cathode. At this time, the chemical energy of the fuel is converted into electrical energy. By stacking a plurality of ion exchange membranes, the fuel blocking effect can be increased and the fuel utilization efficiency can be improved. The authors particularly focused on liquid twist Q: liquid fuel permeating through the ion exchange membrane P: permeability coefficient S: ion exchange membrane area T: elapsed time ΔC: difference in fuel concentration on both sides of the ion exchange membrane N: methanol as the number of stacked ion exchange membranes. The relationship between the amount of methanol permeation and the number of stacked ion exchange membranes was measured. The ion exchange membrane used was Naf manufactured by DI Pont de Nemours.
ion425. As a result of the experiment, it was confirmed that the amount of methanol (fuel) permeated decreases in inverse proportion to the square of the number of membranes as the ion exchange membranes are piled up, as shown in equation (1) or Figure 2. On the other hand, electrical resistance increases in proportion to the number of sheets. When methanol reaches the cathode (air electrode), it reacts with oxygen, causing the air electrode potential to drop. Figure 3A shows the contribution of methanol to the battery voltage drop. As the number of membranes increases, the drop in battery voltage decreases, but this is because the ion exchange membrane prevents methanol from reaching the cathode, as shown in Figure 2. Another possible cause of battery voltage drop is ion exchange membrane resistance. As shown in FIG. 3B, the drop in battery voltage due to membrane resistance increases in proportion to the number of stacked layers. The two main causes of the battery voltage drop are considered to be the two mentioned above, and the values of the battery voltage drop due to both are shown in FIG. 3C. When used in Nafion 425', it was experimentally confirmed that when two ion exchange membranes were stacked, the drop in battery voltage was minimal. of course,
When using other ion exchange membranes, the optimum number of ion exchange membranes to be used may be different from that of Nafion 425.

The multilayer membrane according to the present invention does not necessarily have to consist only of ion exchange membranes, but may also be combined (superimposed) with other membranous substances having a methanol blocking effect.

According to the present invention, since the amount of methanol reaching the air electrode can be reduced, a drop in battery voltage can be suppressed and fuel utilization efficiency can be increased.

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional view of the fuel cell according to the present invention, Figure 2 is a diagram showing the relationship between the amount of methanol permeation through the membrane, the electrical resistance of the membrane, and the number of stacked ion exchange membranes, and Figure 3 is the decrease in cell voltage. FIG. 4 is a relationship diagram between the amount of ion exchange membranes, the membrane resistance which is the cause of the decrease, the magnitude of the battery voltage decrease due to methanol permeation, and the number of stacked ion exchange membranes. FIG. 4 is a graph showing a decrease in cathode potential due to methanol, and FIG. 5 is a diagram showing the relationship between battery voltage and cathode and anode potentials. 1...Ion exchange membrane, 2...Anolyte chamber, 3...
・Gas exhaust port, 4...Air chamber, End...Air inlet, 6.
・Both air ports, 7...Cathode (air electrode), 8...
Anode (fuel electrode), A... Decrease in battery voltage due to methanol, B... Decrease in battery voltage due to electrical resistance of the ion exchange membrane, C... Amount of battery voltage drop that is the sum of A and B. Spear Z Diagram Ion Length J Sara Ii Odor! - #2 books (Yuion length J Saramezato, Chichi, E No. 1J-Fig. 5

Claims (1)

[Claims] 1. It has a fuel electrode placed in contact with a mixture of liquid fuel and electrolyte, an ion exchange membrane and electrolyte placed on the opposite side, and an oxidizer electrode placed in contact with the electrolyte. A liquid fuel cell characterized in that the ion exchange membrane is composed of a plurality of closely stacked ion exchange membranes or an ion exchange membrane and a fuel permeation blocking membrane.