JPS59211970A - Fuel cell generator - Google Patents

Abstract

PURPOSE:To obtain a fuel cell generator with stable cell performance by suppressing the cathode potential and preventing the growth of platinum grains on the cathode when the operation of the fuel cell is interrupted or stopped. CONSTITUTION:During the cell operation, methanol is fed from a fuel reservoir 15 to a cell proper 1 through a fuel feed valve 16, air is guided by an air blower 17 to the cell proper 1 through an air inlet valve 18, and steam and unreacted air is discharged outside the cell through an air outlet valve 19. When the cell is stopped, the connection of the cell proper 1 and a load circuit 2 is opened by a load switch 20, and in conjunction with it, the air inlet valve 18 and air outlet valve 19 are closed. As a result, the feed of oxygen to an air pole is cut off when the cell operation is stopped, and the potential increase at the air pole can be suppressed. The potential essentially suppressing the reaction at a positive electrode is preferably made 0.9V vs NHE or less.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a fuel cell power generation device, and particularly to a device that uses an acidic electrolyte and uses at least platinum as the catalytic active component of the positive electrode. The performance of the positive electrode is low when
The present invention relates to a fuel cell power generation device suitable for preventing.

[Background of the Invention] Among fuel cell power generation devices that use an acidic electrolyte such as sulfuric acid or sulfur/acid, and have a positive electrode that uses platinum as a catalyst and an oxidizing agent such as air or oxygen as a reactant, Conventionally, in types that operate at low temperatures, growth of platinum catalyst particles has rarely been a problem. This is because particle growth due to sintering between platinum catalyst particles is unlikely due to the low temperature. Therefore, when the fuel cell stops operating, the positive and negative values of the battery are 1! Inkuma is in an open circuit state, and the entire battery is in a state where it shows open circuit pressure. It was thought that stopping in such a state would be advantageous in terms of the efficiency of use of the healing material in liquid fuel cells where a large amount of reactants are accumulated within the cell.

However, growth of platinum particles was observed even in low-temperature operation of 100 C or less in air electrodes, oxygen electrodes, etc. of fuel cells that use acidic electrolytes such as sulfuric acid and phosphoric acid. The growth of such platinum particles reduces the effective surface area of the platinum catalyst,
This will reduce the activity of the platinum catalyst, which will reduce the performance of the electrode.

[Purpose of the invention]

An object of the present invention is to provide a fuel cell power generation device that eliminates the problems of the prior art described above, prevents the growth of platinum particles on the cathode (positive electrode), and has stable cell performance.

[Summary of the invention]

The present inventors have discovered that when the operation of a fuel cell is stopped or stopped, the cathode potential increases and the platinum catalyst comes into contact with an acidic electrolyte such as sulfuric acid or phosphoric acid, causing corrosion of platinum particles.

Regarding the corrosion of platinum catalysts in general, "At1as ofl
:lecirochemical p:Qu eye 1br
ia in Aqueous8o1uti□n, Pe
M in rgamon press (1966)
, Pourbaix states that corrosion of platinum progresses under the following mechanism under acidic conditions where P n =0 or less.

(1) Pt+Hg0-+PtO+2H”+26
(Eo=9.80V) (2) PtO+H*C))P
tOx+2H”+26 (E=1.045V) (1),
(2) is the oxidation reaction of pt. Thus, oxides of platinum are first formed at high potentials (>9.80 V) and in the presence of concentrated acids.

(3) Pt0z+4H"+2e--+Pt"+2H
*0 (Eo=0.837V) (3) is a process in which the surface of reeds and platinum particles becomes ions and dissolves into the electrolytic solution due to a dissolution reaction of oxides generated on the surface of platinum.

(4) Pt” +2 e−→Pt (EO=
1.188V) The dissolved platinum ions are reduced by (4) and precipitated on the platinum particles, thereby growing the platinum particles.

The potentials described in this document relate to the corrosion mechanism of giant particles of platinum, such as platinum plates. However, the platinum particles used in fuel cells are finely dispersed and supported on carbon powder, and the particle size is about 3OA.

Such fine particles have a higher proportion of atoms exposed on the surface of each particle, resulting in increased surface energy, and their chemical properties are generally more active than that of large particles.

The present invention is characterized in that it includes means for maintaining a potential that substantially suppresses the reaction at the positive electrode when the operation of the fuel cell is stopped or stopped. Considering the fact that platinum as the cathode ti is in the form of fine particles, it is particularly desirable to set it to 0, (jV vl NHE or less).

[Embodiments of the invention]

Hereinafter, the present invention will be explained in more detail based on a leprosy example.

FIG. 1 is a block diagram showing an embodiment of a fuel cell power generation device according to the present invention. In FIG. 1, reference numeral 1 denotes a main body of a fuel cell power generation apparatus, which includes a stacked battery which is a cell main body, a fuel and oxidizer supply system control system, and the like.

2 is a load circuit, and the output of the generator main body 1 is this 2
work in 3 is a short circuit, which is a circuit with substantially zero electrical resistance, or a low resistance circuit with almost the same resistance as the load circuit 2. Therefore, the short circuit 3 can be a non-resistance circuit, a low resistance circuit, a low resistance+capacitor circuit, or the like. The connection between the load circuit 2 and the short circuit 3 is switched by a switch section 4. That is, during load operation of the fuel cell, A-B, D-H
However, when the operation of the fuel cell for the intended load is stopped or stopped, A-C and D-F are connected.

As a result, when the operation is stopped or stopped, potential increase at the cathode is prevented, and growth of platinum particles at the cathode is suppressed.

Figure 2 shows acidic electrolyte type methanol used in fuel cells.
The basic structure of an air fuel cell is shown. In FIG. 2, 5 is a fuel electrode, that is, a methanol electrode, and 6 is an air electrode. An ion exchange membrane 7 is provided between both electrodes 5 and 6.
This prevents methanol, which is fuel, from diffusing into the air electrode 6. Exchange of electrons between the electrodes 5 and 6 is possible through contact between the current collector 14 and each electrode. Methanol, which is a fuel, becomes an aqueous solution together with sulfuric acid, which is an electrolyte, and is supplied from a fuel port 9 to a fuel chamber 8 as an anolite. Carbon dioxide generated by reaction on the methanol electrode 5 is discharged from the exhaust gas outlet 1.
Ejected from 0. The air electrode 6 is in contact with the air chamber 11, and air is supplied to the air chamber 11 through the air inlet 12, and the water generated on the air electrode 6 becomes water vapor and flows through the exhaust gas outlet 13 along with unreacted air. be discharged. Note that FIG. 2 shows the structure of a unit cell, which is the basic structure of a battery, and an actual stacked battery is formed by stacking many of these basic structures.

Here, for both the methanol electrode 5 and the air electrode 6, Cabot Carbon Black Coated on a porous carbon non-woven fabric substrate as a binder, at a temperature of 300 to 350 in nitrogen.
It was produced by firing at C for 0.5 to 2 hours. The amount of PTFE is 5 to 10% in the methanol electrode and 1% in the air electrode relative to the catalyst.
It was set at 5 to 30%. The obtained electrode was combined with a cation exchange membrane Nafion 425 manufactured by DuPont, and a single cell was constructed using a tank wire mesh or a graphite plate as a current collector. 3mO for anorite! ! ,//! An aqueous solution containing 1 mol/l of sulfuric acid and 1 mol/l of methanol was used and supplied by a liquid pump. Air was blown with an air pump.

In this way, the battery was maintained at 600 ℃ and operated in each operation mode described later, and changes in battery performance at that time were measured.

FIG. 3 shows each operation mode of the battery. In Figure 3, G is 1
This is a mode in which the engine is stopped for 90 hours out of 00 hours and operated for 10 hours.
In the mode that stops for 10 hours, ■ in Figure 3 is 60m.
This mode is a mode in which continuous discharge is performed at a constant discharge density of A/cm''.Also, regarding the G and H operation modes, the operation mode A-B in Fig. 1 is maintained even during the rest period.

This is a D-E connection. During the suspension of operation, A-C in Fig. 1.

The operating modes in which the positive and negative terminals of the battery are short-circuited by connecting D-F are designated as G' and H', respectively. Figure 4 shows changes in battery performance over time in each operating mode.

As shown in FIG. 4, it can be seen that the performance decrease in 9G and H is large, while the decrease in ■ is small. Furthermore, it can be seen that H' and G' also result in a small decrease in performance that is equal to or more than that of I. After this test, I disassembled the battery and examined it and found that Hl.
In G, growth of platinum particles was observed at the air electrode, reducing performance. Therefore, the decrease in the performance of G and H is mainly due to the decrease in the performance of the air electrode, and this is because the potential of the air electrode increases and platinum particles grow while the battery is open-circuited and discharged. . Furthermore, the fact that performance equivalent to or better than ■ was obtained for G' and H' is that by short-circuiting the positive and negative electrodes of the battery while the operation was stopped, it was possible to suppress the rise in potential of the air electrode and prevent the growth of platinum particles. This is especially true.

Next, instead of the acidic electrolyte methanol-air fuel cell, an acidic electrolyte hydrogen-air □ fuel cell was used to measure cell performance in each operation mode. In this case, the basic structure of the battery is generally the same as that shown in FIG. The difference is that the fuel electrode 5 is a gas electrode, so it is the same as the air electrode.
Two points are that the ion exchange membrane 7 between the positive and negative electrodes is unnecessary, and a separator that simply prevents contact between the two electrodes is sufficient. Using 3mot/4 sulfuric acid as the electrolyte,
Hydrogen was supplied to the fuel chamber 8 and air was supplied to the air chamber 11, and the battery was turned over. The driving mode is G as shown in Figure 3.
, H, I, and Examples 10G' and dH'.

Figure 5 shows the changes in battery performance over time in each operation mode. As in Figure 4, the performance decline in G is large, and in H
It can be seen that the performance deterioration of I, H', and G' is the next smallest.

From FIG. 5, it can be seen that even in the case of an acidic electrolyte type hydrogen-air fuel cell, by short-circuiting the positive and negative electrodes of the cell during operation stoppage, it is possible to suppress the increase in the potential of the air electrode and prevent the growth of platinum particles.

FIG. 6 is a diagram showing another embodiment of the fuel cell power generating apparatus according to the present invention. In FIG. 6, during battery operation, methanol is supplied from a fuel reservoir (methanol) 15 to the battery main body 1 via a fuel supply valve 16, and is also supplied to the battery body 1 by an air blower 17 via an air-inlet valve (electromagnetic valve) 18. Air is introduced into the battery body 1, and the rL1 water vapor and unreacted air are discharged to the outside of the battery body via an air outlet valve (electromagnetic valve) 19.

When battery operation is stopped, the load switch 20
The connection between the load circuit 2 and the load circuit 2 is opened. In this embodiment, the air inlet valve 18 is activated based on the actuation of the load switch 20.
A circuit is provided to automatically open and close the air outlet pulp 19. When the load switch 20 is opened, the air inlet pulp 18 and the air outlet pulp 19 are closed. As a result, when the battery stops operating, the supply of oxygen to the air electrode is cut off. When the pond is stopped, the cathode (air electrode) remains at a high level due to the presence of oxygen, which is the active material of the air electrode, so by cutting off the oxygen supply, the rise in potential at the air electrode is suppressed. be able to.

In the large embodiment shown in FIG. 6, the 1 part of the battery main body exhibits the same effect in both the acid injection liquid type methanol-air fuel cell and the acidic electrolyte type hydrogen-air j-thermal cell.

In the above examples, air was used as the oxidizing agent, but
It is also possible to use oxygen. In addition to sulfuric acid, phosphoric acid, trifluoromethanesulfonic acid, etc. can be used as the acid (11) electrolyte. In other words, this book can be applied to all types of acidic electrolyte fuel cells.

Further, means for shorting the positive and negative electrodes when the operation is stopped or for cutting off the supply of the oxidizing agent when the operation is stopped is an embodiment of the present invention,
The present invention provides P t at the positive electrode when the battery operation is stopped or stopped.
+ 2H*O−→PtOs+4H”+48 potential at which the reaction does not substantially occur, preferably 0.9V v8 N
All of these are included as long as there is a means to suppress HB or less.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to suppress the increase in d level at the positive electrode when the device is stopped or stopped for the intended load, and to prevent the growth of platinum particles at the positive electrode, thereby improving battery performance. is stable over the long term.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of the operation system of the fuel cell power generation device according to the present invention, J219 is a cross-sectional schematic diagram of the basic structure of a methane (12)-air fuel cell, and Fig. 3 is (G) ( H) (I) is a diagram showing the test operation mode of the battery, Figure 4 is a diagram showing changes in performance over time in each operation mode of an acidic electrolyte type methanol-air fuel cell, and Figure 5 is a diagram showing changes in performance over time in each operation mode of an acidic electrolyte type methanol-air fuel cell. FIG. 6 is a block diagram showing another example of the operation system of the fuel cell power generator according to the present invention. 1...Fuel cell power generation device main body, 2...Load circuit, 3
... Short circuit, 5... Methanol electrode, 6... Air electrode, 7... Ion exchange membrane, 14... Current collector, 18.
... Air inlet Robulp (Solenoid valve), 19... Air outlet Pulp (IT solenoid valve, 20... Load switch. Agent Patent attorney Tatsuyuki Unuma (13) Sheep l 2nd eye $39 Piece 71rl (/ L) Ginmachi (k) O1σθ 2ρθ 3ρθ ffrIt'I(h) Kaya 4me θ 16θ 2σσ Jσθ Nurai Il
(h) Kaya 5 eyes θ /lρ 2σρ J/θ埒 1”l
(h,) Rod 6 3-1-1 Saiwai-cho, Hitachi City Stock % formula % Hitachi Laboratories, Hitachi, Ltd. 3-1-1 Saiwai-cho, Hitachi City

Claims (1)

[Scope of Claims] In a fuel cell power generation device using a 1° acidic electrolyte and at least platinum as a catalytic active component of the positive electrode, when the device is stopped or stopped for its intended load, the positive electrode 1. A fuel cell power generation device characterized by comprising means for maintaining the potential at a potential that substantially suppresses the reaction of the fuel cell. 2. The fuel cell power generation device according to claim 1, wherein the means is means for suppressing the positive electrode potential to 0.9 V vs. NHE or less. 3.% Allowance The fuel cell power generation device according to claim 1, wherein the means is means for connecting the positive electrode and the negative electrode via a short circuit or a resistor. 4.% Permissible The fuel cell power generation system according to claim 1, wherein the means is means for cutting off the supply of the oxidizing agent.