JPS61193373A - Internally reformed type fuel cell laminate - Google Patents

Abstract

PURPOSE:To aim at obtaining electric output stable over a long term, by making electrochemical characteristics of unit fuel cells at the entrance part of gas flow smaller than those at other parts, when laminating plural number of unit fuel cells in which reforming catalysts are arranged in a gas passage on the fuel gas side adjacent to an electrode on the same fuel gas side. CONSTITUTION:At the fuel gas entrance part of a fuel gas side perforated plate 14 with a number of openings 14a, opening ratio is made smaller, while gas diffusion resistance being made bigger, than those at other parts, in order to make electrochemical characteristics of fuel cells at the entrance part smaller than those at other parts. Thus, in the fuel gas, consisting mainly of hydrocarbon or alcohol group and steam, to be supplied to laminate of internally reformed, molten carbonates type fuel cells, reaction consuming hydrogen takes place in parallel with gas decomposition etc at the gas side passage 8 adjacent to the gas side electrode 2 keeping current density of cells at the entrance part as small as it used to be, even when a large amount of electric current is taken out. Accordingly, the activity of reforming catalysts 10 is made stable and even a small amount of filling load comes to do well.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an internal reforming fuel cell stack, and more specifically, to a fuel gas flow path adjacent to a fuel gas side electrode. This invention relates to an internal reforming fuel cell stack in which an internal reforming catalyst is arranged.

[Conventional technology]

Figure 3 shows a conventional internally reformed molten carbonate fuel cell stack, in which (1) is an electrolyte (IJ),
(:1) is the fuel gas side electrode, and (3) is the oxidizing gas side electrode. (4') is a fuel gas side porous plate that supports the fuel gas side electrode (c) and separates a reforming catalyst, which will be described later, from the fuel gas side electrode (2). (Left) is the oxidizing gas side electrode (
3) is a perforated plate on the oxidizing gas side that supports. (6) separates and forms a fuel gas side flow path and an oxidant gas side flow path, and
Electrolyte matrix (/), fuel gas side electrode (ko).

When stacking multiple unit fuel cells consisting of an oxidizing gas side electrode (3), a fuel gas side perforated plate (3), and an oxidizing gas side perforated plate (3), the unit fuel cells (ri) are electrically connected to each other. This is a separator plate that serves to connect in series. (ff) is a gas flow path on the fuel gas side formed separately from the separator plate (4) VC, and (9) is a gas flow path on the oxidizing gas side. Fuel gas side Gas flow path (r) K is a reforming catalyst (10
) are placed.

With the above configuration, the fuel gas containing hydrocarbons or alcohols and steam as the main components, and the oxidizing gas containing oxygen and carbon dioxide as the main components, are fed into the internal reforming molten carbonate fuel cell in a cross-flow manner. and introduced into the fuel gas side gas flow path (1) and the oxidizing gas side gas flow path (9), respectively. Hydrocarbons or alcohols in the fuel gas supplied to the fuel gas side gas flow path (g) are converted into the following formula by the action of the reforming catalyst (10) disposed inside the fuel gas side gas flow path (ff). Through the chemical reaction shown below, it is reformed into a fuel gas whose main components are hydrogen and carbon monoxide.

The overall reaction is an endothermic reaction, and the unit fuel cell
directly utilizes the thermal energy that is produced as a by-product.

Hydrocarbon + H co0 → H co, Co, Co co, CH2X (/
17/Iz:lff-Ni kind+HJO→HayCO+CO
a+CH* (J)CH da + HJO-+CO
+,? H co (3) CO + H co O → C
The hydrogen generated inside the OJ + H (fuel gas side gas flow path tt) and the oxygen and carbon dioxide in the oxidizing gas are transferred to the fuel gas side porous plate (Il) and the oxidizing gas side porous plate (,1), respectively. The electrochemical reaction occurs at the fuel gas side electrode (C) and the oxidizing gas side electrode (J) as shown in the following formula.

(Fuel gas side electrode) HJ+CO-+ HaO+ COJ + 2e
(&) (Oxidizing gas side electrode) Nakako + CO + Ko θ → Co, (A) Through these series of chemical and electrochemical reactions, the chemical energy possessed by fuel gases such as hydrocarbons or alcohols is released. , converted into electrical energy and by-product thermal energy.

Here, the reforming catalyst (10) is, for example, alumina! An active material such as nickel is supported on a carrier mainly composed of gnesia, etc., and in order to maintain the activity of the reforming catalyst (lO), K is an active material such as nickel as shown in the formula below. It is necessary to operate while preventing the oxidation of substances N1 + HJO → N1'O' + H
There is a ko (ri).

For decomposition of hydrocarbons or alcohols and hydrogen production using a general reforming catalyst (10), formulas (1) to (4I) k
As shown in the figure, this is done by adding steam, but the generated hydrogen prevents oxidation of layer materials such as nickel, making stable operation possible over a long period of time.

However, internally reforming molten carbonate fuel cells
As shown in formula 1 (3), the formula Cl) ~ (4t
) is consumed in parallel to produce stinium, the hydrogen concentration decreases and oxidation of the active material of the reforming catalyst (10), such as nickel, occurs (Hiroshi). The activity of (10) is more likely to decrease.

The conditions under which such an active material is oxidized differ from K, such as the type of active material, the type of support, and temperature, but for example, in the case of a catalyst using nickel as the active material.

As a guideline, the ratio of water vapor concentration to hydrogen concentration is I
It is known that when θ~20 or more, oxidation of nickel occurs and the activity of the catalyst decreases.

The ratio of the water vapor concentration to the hydrogen concentration has a distribution in the flow direction of the fuel gas, but the amount is usually large at the fuel gas inlet, and the ratio of the urea concentration to the water vapor concentration at that part is the same as that of the reforming catalyst ('to). Most important for stability. The ratio increases as the electrochemical reaction in Equation (3) becomes more active, □In other words, as more current is extracted, and as the filling amount of the reforming catalyst (tO) decreases, ) to (ri) becomes larger as the chemical reactions become inactive.

Therefore, in a conventional fuel cell stack of this type, in order to prevent a decrease in the activity of the reforming catalyst (lO) disposed in the fuel gas side gas flow path (f) at the fuel gas inlet part, the extractable current, That is, the electrical output is limited to a small range, and in order to extract a larger current, it is necessary to fill a large amount of reforming catalyst (10).

[Problem that the invention seeks to solve]

With conventional internal reforming fuel cell stacks as described above, it is difficult to stably obtain large output over a long period of time because the activity of the reforming catalyst decreases due to oxidation. In order to achieve this, there was a problem in that it was necessary to fill the fuel gas side gas flow path with a large amount of a highly active reforming catalyst.

This invention was made to solve the above-mentioned problems, and it is possible to stably increase output over a long period of time with a small amount of reforming catalyst while preventing the activity from decreasing due to oxidation of the reforming catalyst. The purpose is to obtain an internally reforming fuel cell stack that can be used.

[Means for solving problems]

The internal reforming fuel cell stack according to the present invention changes the electrochemical activity of the unit fuel cells in the direction of flow of fuel gas.

[For production]

゛ In this invention, the electrochemical activity of the fuel cell at the fuel gas inlet portion is smaller than the electrochemical activity of the fuel cell at other portions, so even if a large current is drawn from the fuel cell as a whole, Most of it passes through the electrochemically highly active part of the fuel cell, and the current density flowing through the fuel cell in the fuel gas inlet part remains small.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows a fuel gas side perforated plate (ttI) that changes the electrochemical activity of the fuel cell in the fuel gas flow direction, and Figure 1 shows an internal reforming type melting using a fuel gas side perforated plate (ta). A carbonate fuel cell stack is shown.

Also, the same reference numerals as in FIG. 3 indicate the same parts.

As shown in Fig. 1, the fuel gas side perforated plate (t4t) in which a large number of openings (lIIa) are formed has a smaller opening ratio at the fuel gas inlet part than other parts, thereby increasing the diffusion resistance of the fuel gas. Thus, the electrochemical activity of the fuel cell in the fuel gas inlet portion is smaller than the electrochemical activity of the fuel cell in other portions.

With the above configuration, the fuel gas mainly composed of hydrocarbons or alcohols and steam supplied to the internally reformed molten carbonate fuel cell stack is transferred to the fuel gas side gas flow path (
ff) and the fuel gas side electrode (2), the formula (/1
～(4') Decomposition of fuel gas, hydrogen production reaction and formula (
61 electrochemical reactions, that is, hydrogen consuming reactions, are performed in parallel. Each unit fuel cell (with respect to the flow direction of fuel gas)
? ), in other words, how fast the electrochemical reaction of formula (&) (A) occurs depends on the electrochemical activity of each unit fuel cell (ri) and each part. Although it depends on the composition of the fuel gas and oxidizing gas, electrochemical activity has a large influence among them. In this embodiment, the electrochemical activity of each unit fuel cell at the fuel gas inlet section is made smaller than that at other sections, and as a result, when a large current is extracted from the fuel cell stack as a whole, but.

The current density flowing through the fuel cell at the fuel gas inlet portion remains small. Therefore, even when a large current is drawn as a whole, the amount of hydrogen consumed at the fuel gas inlet is small, that is, the ratio of water vapor concentration to hydrogen concentration remains small, and the activity of the reforming catalyst (10) remains stable. It is kept as it is. As a result, the amount of current that can be taken out is larger than that of conventional ones, and conversely,
It is also possible to reduce the filling amount of the reforming catalyst (10).

In the above example, the electrochemical activity of the fuel cell was changed by changing the aperture ratio of the fuel gas side porous plate (ta) in the flow direction of the fuel gas, but as is well known, the fuel gas side electrode The electrochemical activity of the fuel cell can be easily changed by changing the structure of (g), for example, porosity, pore distribution, electrode surface area, etc., and similar effects can be obtained.

〔Effect of the invention〕

As is clear from the above description, this invention changes the electrochemical activity of the fuel cell in the direction of the flow of fuel gas, resulting in long-term stability [large electrical output can be extracted, reforming] The amount of catalyst packed can also be reduced.

[Brief explanation of drawings]

FIG. 1 is a plan view of essential parts of the present invention, FIG. 2 is a partially front sectional view, and FIG. 3 is a front sectional view of a conventional internal reforming fuel cell stack. (j)-Φfuel gas side electrode, (ltI)e・fuel gas side porous plate, (/&B)@・opening, (ri)・unit fuel cell. (ff)...Fuel gas side gas flow path, (10)...Reforming catalyst. In each figure, the same reference numerals indicate the same or corresponding parts. (ll) Trout

Claims (5)

[Claims] (1) In an internal reforming fuel cell stack consisting of a plurality of unit fuel cells in which a reforming catalyst is arranged inside a fuel gas side gas flow path adjacent to a fuel gas side electrode, the electrochemical An internal reforming fuel cell stack characterized in that the activity is changed in the direction of flow of fuel gas. (2) The internal reforming fuel cell stack according to claim 1, wherein the internal reforming fuel cell is a molten carbonate fuel cell. (3) The internal reforming fuel cell stack according to claim 1, wherein the electrochemical activity of the unit fuel cell is smaller at the fuel gas inlet portion than at other portions. (4) The internal reforming fuel cell stack according to claim 1, wherein the aperture ratio of the fuel gas side porous plate supporting the fuel gas side electrode is changed in the flow direction of the fuel gas. (5) The internal reforming fuel cell stack according to claim 1, comprising a fuel gas side electrode in which at least one of porosity, pore distribution, and electrode surface area is changed in the flow direction of the fuel gas. .