JP5422302B2 - Gas heating device and fuel cell system using the same - Google Patents

Description

  The present invention relates to a gas heating device provided in the fuel cell so that the solid polymer fuel cell can be started without any trouble, and further relates to a fuel cell system using the device. In this specification, “metal” includes metalloids such as silicon.

  The operating temperature of the polymer electrolyte fuel cell is 80 to 100 ° C., and the power generation efficiency is lowered at a temperature lower than this, and the startability at a low temperature is a big problem. In particular, when it is used for a fuel cell vehicle, there is a problem that it takes a long time to start when it is started in a state where the outside air temperature is low, for example, below freezing. As a low-temperature start-up measure, a method has been proposed in which the reaction is promoted by supplying electric power to an external load of the fuel cell, and the start-up property is improved by raising the temperature by self-heating (Patent Document 1).

  When the fuel cell stack is warmed up by self-heating as described above, there is a method of promoting heat generation by flowing a large current through the fuel cell stack in order to shorten the warm-up time. However, if the output current is increased by shortening the warm-up time, the calorific value increases, and the amount of generated water generated inside the cell increases with power generation, and this generated water becomes a diffusion electrode layer, catalyst layer. As a result of freezing inside, there is a problem that the reaction gas cannot reach the solid polymer electrolyte membrane, causing a rapid voltage drop and consequently a rapid voltage drop. In other words, if the generated water freezes faster than the temperature rises due to self-heating due to an increase in output power, the generated water freezes in the cell before the temperature of the fuel cell stack rises, making it impossible to generate power. Cannot be achieved.

Special Table 2000-512068

  In order to improve the startability, it is sufficient that the warm-up time of the fuel cell can be shortened and that the temperature rise of the fuel cell stack can be made faster than the freezing of the produced water. One way to increase the temperature of the fuel cell stack faster than freezing of generated water is to heat the gas (hydrogen and air) supplied to the stack to 80-100 ° C, which is the operating temperature of the fuel cell. is there. As a method for heating the supply gas, a heating device such as an electric heater is generally used. However, in this case, since it takes time to heat to 80-100 ° C., it is impossible to shorten the warm-up time of the fuel cell. This invention makes it a subject to provide the gas heating apparatus which can solve such a problem.

  As a result of studying means for heating the gas supplied to the fuel cell stack to 80-100 ° C. in a short time, the present inventors have found that this is possible by installing the gas heating device of the present invention.

The invention according to claim 1 includes an oxidation reactor that raises the temperature of a mixed gas of hydrogen and air (or oxygen) by the oxidation heat of hydrogen in the presence of a hydrogen oxidation catalyst, and the hydrogen oxidation catalyst can be oxidized and reduced. a gas heating device, wherein the catalytically active metal on a carrier consisting of a metal oxide is a catalyst that has been reduced before or after filling the filling of the Li Kui oxidation reactor, such being carried.

  In the invention according to claim 2, a gas supply unit for supplying hydrogen and air (or oxygen) to the upstream side of the oxidation reactor is added, and a dilution gas for adjusting the temperature of the oxidation reaction gas is added to the downstream side. The gas heating device according to claim 1, further comprising a gas addition unit.

The invention according to claim 3 is characterized in that the catalyst charged in the oxidation reactor is divided into an upstream packed bed and a downstream packed bed, and hydrogen and air (or oxygen) are supplied to both packed beds. The gas heating device according to claim 1 or 2 .

The invention according to claim 4 is characterized in that the gas heating device according to any one of claims 1 to 3 is connected to a hydrogen electrode and an air (or oxygen) electrode of a proton exchange membrane fuel cell. It is a fuel cell system.

  The redox-capable metal oxide constituting the catalyst support charged in the oxidation reactor is preferably a composite oxide. The metal oxide is preferably a rare earth metal oxide. As the rare earth metal oxide, cerium oxide, lanthanum oxide, and samarium oxide are preferable. The metal oxide is a composite oxide of a rare earth metal and at least one metal selected from the group consisting of magnesium, titanium, zirconium, yttrium, aluminum, silicon, cobalt, iron and gallium, or a rare earth A composite oxide of a metal and at least two metals selected from the group consisting of magnesium, titanium, zirconium, yttrium, aluminum, silicon, cobalt, iron and gallium is preferable. The catalytically active metal of the hydrogen oxidation catalyst is preferably at least one metal selected from the group consisting of Group VIII metals, tin, copper, silver, manganese, chromium and vanadium. It is preferable that the hydrogen oxidation catalyst has been reduced before or after filling the oxidation reactor.

  As a preferred fuel cell system equipped with the gas heating device according to the present invention, a fuel cell system in which the gas heating device according to the present invention is installed upstream of the fuel cell air (or oxygen) electrode inlet, and the gas heating device according to the present invention include: Fuel cell system installed upstream of the fuel cell air (or oxygen) electrode inlet and upstream of the hydrogen electrode gas inlet, gas of the gas heating device installed upstream of the fuel cell air (or oxygen) electrode inlet A fuel cell system that supplies a mixed gas of hydrogen and air (or oxygen) to the supply unit, and supplies air (or oxygen) to the addition unit of the gas heating device, and a fuel cell hydrogen electrode gas inlet upstream portion A fuel cell system that supplies a mixed gas of hydrogen and air (or oxygen) to the gas supply section of the gas heating apparatus and supplies hydrogen to the addition section of the gas heating apparatus. Temu, and the like.

  A part or all of the hydrogen gas as fuel and air (or oxygen) are mixed and introduced into a catalyst layer that can be oxidized from a low temperature, and the hydrogen as fuel is heated to a predetermined temperature (eg, by the oxidation heat of hydrogen). Increase to 80 ℃) instantly. In addition, a part of hydrogen as a fuel is mixed with air (or oxygen) used for the cathode reaction, and this mixed gas is introduced into a catalyst layer that can be oxidized from a low temperature, thereby air used for the cathode reaction. (Or oxygen) can be instantaneously raised to a predetermined temperature. As described above, since the reaction gas instantaneously reaches the predetermined temperature, the fuel cell itself can be instantaneously heated to the predetermined temperature. As a result, the fuel cell can be quickly warmed up and started.

  A catalyst that can oxidize hydrogen from a low temperature uses an oxide capable of redox reduction as a support, and supports the active metal on the support. The catalyst is used in a reduced state. The reduction treatment may be performed before the reaction tube is installed and filled in the reaction tube, or after the catalyst that has not been reduced is installed in the reaction tube, the reduction treatment may be performed. By these reduction treatments, a part or all of the oxidized carrier used for the catalyst carrier is reduced. When hydrogen and air (or oxygen) are brought into contact with this catalyst at a low temperature of room temperature or lower, the reduced carrier reacts with oxygen to generate oxidation heat, and the catalyst layer temperature instantaneously becomes hydrogen and air (or oxygen). ) Rises to the temperature at which it reacts. Once the temperature of the catalyst layer rises to a temperature at which hydrogen and air (or oxygen) react, the reaction between hydrogen and air (or oxygen) proceeds autonomously thereafter. As a result, preheating with an electric heater or the like is not required at the time of starting the apparatus, and a fuel cell system having excellent startability can be constructed.

  Under the hydrogen-excess atmosphere, these catalysts react with air (or oxygen) at the time of start-up, and the oxidized carrier is reduced with hydrogen in the reaction gas in the region where the catalyst layer temperature exceeds 400 ° C. The system can be started later by supplying a mixed gas of air (or oxygen) and hydrogen again. Since the hydrogen electrode of the fuel cell is in an excess hydrogen atmosphere, it can be repeatedly activated.

  On the other hand, since the air (or oxygen) electrode is in an air (or oxygen) -excess atmosphere, the carrier oxidized by reacting with oxygen at the time of activation is not subjected to re-reduction treatment, so that it cannot be repeatedly activated. Therefore, the oxidation catalyst is divided into two stages, the first stage is supplied with air (or oxygen) that becomes a hydrogen-excess atmosphere, and the second stage has air between the first and second stages to burn the remaining hydrogen. (Or oxygen) is supplied. As a result, the first stage catalyst is subjected to a re-reduction process and can be repeatedly activated.

  As the number of times of activation of these catalysts increases, the re-reduction treatment becomes insufficient, and eventually, there is a possibility that the activation cannot be performed. The startability at a temperature below room temperature is due to the heat of oxidation when the metal oxide support in the reduced state is oxidized. This oxidation occurs in the upstream area of the catalyst layer, and the catalyst in the downstream area is reduced by excess hydrogen at a temperature of 400 ° C or higher, so that the carrier is oxidized in the upstream area of the catalyst layer but is reduced in the downstream area. Is preserved. At the next start-up, the carrier in this downstream region is oxidized, and start-up at room temperature or below becomes possible. As the number of start-ups increases, the area of the oxidized carrier upstream of the catalyst layer increases and the area of the carrier that maintains the reduced state decreases, and eventually the reduced state necessary to start up at a temperature below room temperature. It is considered that the region having the carrier does not exist and cannot be activated.

  Therefore, when the region of the carrier in the reduced state is reduced after starting a predetermined number of times, the supply of hydrogen and air (or oxygen) to the catalyst layer is reversed, and the carrier enters the region where the carrier is kept in the reduced state. By supplying the gas, activation at a temperature below room temperature is performed, and the carrier is re-reduced and regenerated to a reduced state in a region where the carrier in the reduced state is reduced.

  According to this method, even if the number of times of activation increases, it is possible to stably start from a low temperature below room temperature. In order to reverse the entrance gas to the catalyst layer, a valve mechanism for reversing the flow directions of hydrogen and air (or oxygen) is installed at the entrance and exit of the catalyst layer, and these are opened and closed as appropriate.

  According to the present invention, a part or all of hydrogen gas as a fuel and air (or oxygen) are mixed and introduced into a catalyst layer that can be oxidized from a low temperature, and hydrogen as a fuel is generated by the oxidation heat of hydrogen. Is immediately raised to a predetermined temperature. In addition, a part of hydrogen as a fuel is mixed with air (or oxygen) used for the cathode reaction, and this mixed gas is introduced into a catalyst layer that can be oxidized from a low temperature, thereby air used for the cathode reaction. (Or oxygen) can be instantaneously raised to a predetermined temperature. As described above, since the reaction gas instantaneously reaches the predetermined temperature, the fuel cell itself can be instantaneously heated to the predetermined temperature. As a result, the fuel cell can be quickly warmed up and started.

1 is a schematic view showing a gas heating device of Example 1. FIG. 6 is a schematic view showing a gas heating apparatus of Example 2. FIG. 6 is a schematic diagram showing a proton exchange membrane fuel cell system of Example 4. FIG.

  Next, in order to explain the present invention specifically, some examples of the present invention will be given.

Example 1
FIG. 1 shows a gas heating device (3) provided with an oxidation reactor (2) for raising the temperature of a mixed gas of hydrogen and air by the oxidation heat of hydrogen in the presence of a hydrogen oxidation catalyst (1). As a hydrogen oxidation catalyst, a catalyst in which platinum was supported on a cerium oxide support (noble metal type: 1 wt%, transition metal type: 5 wt%, 1 mmφ pellet) was used. The catalyst loading was 2 mL.

  The inlet gas temperature supplied to the gas heating device is -40 ° C to 20 ° C, the catalyst layer outlet temperature is 450 ° C, the gas heating device outlet temperature is 80 ° C or 100 ° C, and the hydrogen gas flow rate at the gas heating device outlet is 10 NL / The gas flow rate to the gas supply unit (4) and the gas addition unit (5) of the gas heating apparatus was set to be min. Table 1 shows the results of operation under conditions 1 to 14.

Example 2
In FIG. 2, the catalyst charged in the oxidation reactor (2) is divided into an upstream packed bed (1a) and a downstream packed bed (1b), and hydrogen heating and air are supplied to both packed beds. Device (3) is shown. As a hydrogen oxidation catalyst, a catalyst in which platinum was supported on a cerium oxide support (noble metal type: 1 wt%, transition metal type: 5 wt%, 1 mmφ pellet) was used. The amount of catalyst packed was 0.3 mL for both the upstream packed bed (1a) and the downstream packed bed (1b).

  The inlet gas temperature supplied to the gas heating device is -40 ° C to 20 ° C, the outlet temperature of the upstream packed bed and the temperature of the downstream packed bed are both 450 ° C, the outlet temperature of the gas heating device is 80 ° C or 100 ° C, The gas flow rates of the gas supply unit (4) and the gas addition unit (5) of the gas heating device were set so that the total air supply amount supplied to the gas heating device was about 24 NL / min. Table 2 shows the results of operation under conditions 1 to 14.

Example 3
Same as Example 1 except that the metal supported on the cerium oxide support was changed to iron, cobalt, nickel, ruthenium, rhodium, palladium, tin, copper, silver, manganese, chromium and vanadium as the hydrogen oxidation catalyst. The operation was performed.

Each gas flow rate was set such that the gas heating gas supply temperature was 20 ° C, the catalyst layer outlet temperature was 450 ° C, and the gas heater outlet temperature was 100 ° C.

Example 4
In FIG. 3, as a hydrogen oxidation catalyst, a metal oxide carrier supporting platinum is made of lanthanum oxide, samarium oxide, Ce-Zr composite oxide, Ce-Ti composite oxide, Ce-Mg composite oxide, Ce-Zr-Al. complex oxide, except that had use what was changed to Ce-Zr-Si composite oxide was carried out the same procedure as in example 1. Each gas flow rate was set so that the gas heating gas supply temperature was 20 ° C, the catalyst layer outlet temperature was 450 ° C, and the gas heater outlet temperature was 100 ° C. In FIG. 3, (6) is a proton exchange membrane fuel cell, (7) is its hydrogen electrode, (8) is an air electrode, (9) is an electrolyte membrane, and (10) is a plurality of valves constituting the valve mechanism. It is.

Table 3 shows the time required for the gas heater outlet gas temperature to reach 100 ° C. when the catalysts of Examples 1, 3, and 4 are used.

  As shown in Tables 1 and 2, it can be confirmed that the outlet temperature rises to 80 ° C. or 100 ° C. at an inlet temperature of −40 ° C. to 20 ° C.

  Further, from Table 3, the outlet temperature increased for any of the catalysts, and the time until the outlet temperature reached the predetermined temperature was 1.5 min or less, and it was confirmed that the startability was very high.

(1) Hydrogen oxidation catalyst
(1a) Upstream packed bed
(1b) Downstream packed bed
(2) Oxidation reactor
(3) Gas heating device
(4) Gas supply section
(5) Gas addition section
(6) Proton exchange membrane fuel cell
(7) Hydrogen electrode
(8) Air electrode
(9) Electrolyte membrane
(10) Valve

Claims (4)

An oxidation reactor that raises the temperature of a mixed gas of hydrogen and air (or oxygen) by the heat of hydrogen oxidation in the presence of a hydrogen oxidation catalyst is provided, and the hydrogen oxidation catalyst is supported on a support made of a metal oxide that can be oxidized and reduced. gas heating device, wherein the active metal is reduced treated catalyst before or after filling the filling of the supported by a Li Kui oxidation reactor. A gas supply unit for supplying hydrogen and air (or oxygen) to the upstream side of the oxidation reactor, and a gas addition unit for adding a dilution gas for adjusting the temperature of the oxidation reaction gas on the downstream side. The gas heating device according to claim 1, wherein Catalyst charged to the oxidation reactor is divided into an upstream zone packed layer and the lower basin filling layer, to claim 1 or 2, and hydrogen both filling layers and air (or oxygen) is characterized in that it is provided The gas heating apparatus as described. Fuel cell system gas heating device according to any one of claims 1 to 3, characterized in that it is connected to the hydrogen electrode and the air (or oxygen) electrode of the proton exchange membrane fuel cell.

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