JPS62278766A - Operating method for phosphoric acid fuel cell - Google Patents

Abstract

PURPOSE:To remove excess phosphoric acid to prevent performance deterioration of a fuel cell by supplying a gas humidified with steam to an electrode when the phosphoric acid retaining amount in a catalyst layer of a fuel electrode or an oxidizing agent electrode becomes excess. CONSTITUTION:A phosphoric acid fuel cell 10 is operated by supplying hydrogen- rich fuel to a space 4 through a fuel gas supply line 19 and an oxidizing agent to a space 5. The partial pressure of oxygen in the air in the space 5 is measured and the content of pbosphoric acid in a catalyst layer on an oxidizing agent electrode 3 side is monitored based on the measured value. When the phosphoric acid retaining amount in the catalyst layer is excess, the air serving as oxidizing agent is introduced into a humidifier 11 to humidify the air, then supplied to the fuel cell 10. Since excess phosphoric acid is removed by the fumidified air, decrease in output voltage is prevented and the life of the cell can be lengthened.

Description

[Detailed description of the invention]

3. Detailed description of the invention

[Technical field to which the invention pertains]

The present invention relates to a method of operating a phosphoric acid fuel cell that prevents deterioration of the characteristics of the fuel cell and extends the life of the cell.

[Prior art and its problems]

First, the structure of the alliterative phosphoric acid fuel cell sheep cell is shown in Figure 2. In the figure, l is a matrix impregnated with almost 100% pure phosphoric acid as an electrolyte, and the matrix l is sandwiched between On both sides thereof, porous fuel Ti supporting the electric bridge catalyst, electrode 2 and oxidizer electrode 3 face each other, and further outside thereof, a reaction gas space 4.5 is formed which serves as a supply path for the fuel gas 5 and oxidizer gas. A unit cell 8 is constructed by laminating gas-diffusing electrode base materials 6.7. Further, a cell stack is constructed by stacking a large number of such jtl i cells with gas separators 9 interposed between them. With this configuration, by operating the fuel cell by supplying reactant gases such as fuel gas and A2 converting gas to each electrode, the fuel electrodes 2. As is well known, a three-phase interface is formed within the catalyst layer of the oxidizer electrode 3, and power is generated by the electrode reaction that takes place here. By the way, when operating such a fuel cell, the fuel electrode 2. If the retained amount of phosphoric acid impregnated into the catalyst layer of the oxidizer electrode 3 becomes excessive, the diffusion of hydrogen and &1 elements to the active sites of the catalyst layer will be inhibited, the three-phase interface will become unstable, and the battery characteristics will deteriorate significantly. It is known to do. For this purpose, powder of fluororesin, such as polytetrafluoroethylene, is usually dispersed and mixed in the catalyst layer of each electrode to give it an appropriate (θ) aqueous property.
Measures are taken to prevent excessive migration of phosphoric acid from the matrix I side to the electrode 2.3. However, during long-term operation of a fuel cell, the 18
Due to phenomena such as a decrease in aqueous properties or phosphoric acid absorbing moisture and causing its volumetric expansion, the phosphoric acid held in the matrix 1 gradually moves to the electrode 2°3 and becomes the electrode catalyst layer. It has been found from the course of operation of fuel cells that an excessive amount of rophosphoric acid is often impregnated into the fuel cells, resulting in a decrease in cell performance. Note that when the electrode catalyst layer is impregnated with excess phosphoric acid,
:Hydrogen in the reaction gas that directly participates in the l-electrode reaction. As is clear from Figure 3, the partial pressure characteristics of the oxygen gas component decreases, and the output voltage of the battery becomes H, which is the partial pressure (concentration) of the reformed gas, hydrogen in the air, and oxygen gas component in the parentheses state. In addition, it has been confirmed from experimental considerations that the amount of phosphoric acid retained in the catalyst layer is lower than when it is appropriate. The horizontal axis in Figure 3 shows the ratio of phosphoric acid impregnation in the oxidizer electrode catalyst layer, with the impregnation amount at the initial stage of operation being 1, and the vertical axis shows the voltage as the oxidant utilization rate changes from 40 to 60%. Indicates the amount of decrease. Moreover, as mentioned above, when the amount of phosphoric acid retained in the electrode catalyst layer became excessive, conventionally there was no effective means to actively remove phosphoric acid from the catalyst layer, and the operation of the fuel cell had to be stopped. We had no choice but to adopt the northern method of decomposing the upper part and removing excess phosphoric acid. However, this method stops the fuel cell,
This takes a lot of effort, including restarting, and reduces the operating rate of the fuel cell.

[Purpose of the invention]

This invention was developed in consideration of the above points, and when the amount of phosphoric acid retained in the TL electrode catalyst layer becomes excessive during operation, the excess phosphoric acid is removed from the electrode catalyst layer during operation by a non-toxic operation. It is an object of the present invention to provide a method of operating a phosphoric acid fuel cell, which can restore the battery output and extend the life of the battery by removing the phosphoric acid fuel from the battery.

[Key points of the invention]

In order to achieve the above object, this invention has additional features! We focused on the fact that when dry gas is supplied to the electrode, the amount of phosphoric acid impregnated and held in the electrode catalyst layer increases in scattering amount compared to when dry gas is supplied. When the phosphoric acid retention meter to the electrode or oxidizing agent electrode becomes excessive, by supplying humidified gas to the electrode using a water stem method, the excess phosphoric acid is taken into the added gas and the battery is charged together with the humidified gas. The purpose is to prevent the life of the Pr4i battery from decreasing by removing it from the outside to restore the battery's output characteristics.

[Embodiments of the invention]

FIG. 1 shows a gas supply system diagram of a fuel cell for implementing the operating method of the present invention attached to the oxidizer electrode side of the fuel cell. 8 is a fuel cell main body schematically showing a cell stack which is a multi-stone structure; 11 is a gas humidifier inserted in an oxidant gas supply path 12 passing through an oxidant gas space 5; 13 is a bypass of the gas humidifier 11. 14 is a source of inert gas such as nitrogen, 15 to 18 are on-off valves, and 19 is a fuel gas supply system. The gas humidifier 11 either discharges a gas to be heated into the water in a water tank and bubbles it to humidify the water, or generates a water mist by applying ultrasonic vibration to the water stored in the water tank. In addition, it is equipped with functions such as passing gas to be humidified into this water mist to perform humidification. During normal operation in such a system circuit, the fuel gas supply system 1
9, the hydrogen-rich fuel gas generated through the fuel reformer enters the fuel gas space 4 of the fuel cell main body 10,
Furthermore, air as an oxidizing gas is directly supplied to the oxidizing gas space 5 through the oxidizing gas passage 12 without passing through the gas humidifier 11, and power generation is performed in this state. Here, the partial pressure of the oxygen gas component in the air in the gas space of the fuel cell main body 10 is measured and monitored, and based on the relationship between the amount of phosphoric acid retained in the electrode catalyst layer and the oxygen partial pressure, the oxygen content is determined. Oxidizing agent 1 based on pressure measurement! If it is detected that the catalyst layer of the three electrodes is impregnated with excess phosphoric acid and the battery output voltage is reduced, the bypass valve I5 is closed and the valve 16.
17 is opened and air, which is an oxidant gas, is transferred to the gas humidifier 11.
The fuel is supplied to the oxidizer electrode 3 of the fuel cell main body 10 after being humidified. As a result, the phosphoric acid retained in excess in the catalyst layer of the oxidizer electrode 3 is taken into the humid air and expelled from the battery body 10 to the outside. The reason why phosphoric acid is scattered and eliminated by this heating operation is that phosphoric acid molecules have strong hygroscopicity, so when they come into contact with humidifying gas, phosphoric acid molecules adhere to water mist, and use the water mist as a carrier to combine with air. It is estimated that this will be eliminated from the battery body. By removing the excess phosphoric acid impregnated into the oxidizer electrode in this manner, the output voltage of the fuel cell is restored and the fuel cell returns to its normal operating state. Note that instead of humidifying and supplying air as an oxidant gas, the inert gas i#1 shown in the figure is supplied in an open circuit state of the fuel cell.
Excess phosphoric acid can also be removed in the same manner as described above by adjusting nitrogen gas by 4 and then supplying it to the oxidizing agent space 4 of the fuel cell main body. Also, the above description was about removing the excess phosphoric acid held on the oxidizer electrode side, but even if there are two τ on the fuel electrode side, the fuel gas should be heated in the same way, or the inert gas should be heated. Excess phosphoric acid retained in the catalyst layer of the fuel gas electrode 2 can be removed by supplying the phosphoric acid to the fuel gas space 4 of the fuel cell main body IO. Note that when humidifying and supplying the above-mentioned inert gas, it is effective to supply the heated inert gas to the oxidizing agent electrode, which has a high electrode potential, preferentially to the fuel gas electrode, which has a low electrode potential.

【Effect of the invention】

As described above, according to the present invention, when the amount of phosphoric acid retained in the catalyst layer of the fuel electrode or oxidizer electrode becomes excessive during operation, the 11t8i! By supplying gas humidified with water and air to remove excess phosphoric acid, the phosphoric acid distribution in the electrode catalyst layer is maintained well, the three-phase interface is maintained stably, and output voltage drop is prevented. It is possible to extend the life of the fuel cell. Moreover, the operation simply involves supplying heated gas to the reaction gas space of the fuel cell body, and excess phosphoric acid can be removed even while the fuel cell is in operation. There is no need to stop the operation of the fuel cell and disassemble the main body of the cell, thereby increasing the operating rate of the fuel cell.

[Brief explanation of drawings]

Fig. 1 is a gas supply system diagram including a fuel cell for carrying out the operating method of the present invention, Fig. 2 is a cross-sectional view of the structure of a 111 cell of a phosphoric acid fuel cell, and Fig. 3 is a diagram of the inside of the catalyst layer. 3 is a graph showing the amount of voltage drop with respect to changes in phosphoric acid retention. In each figure, 1: Matrinox, 2: Fuel electrode, 3. Oxidizer electrode, 4
: Fuel gas space, 5 Dioxide gas space, 6. '
ltl base electrode, 8: single cell, 10: fuel cell main body, 11:
Gas humidifier, 12; Oxidizing gas supply passage, 14: Inert gas source. Figure 111 (mv)

Claims (1)

[Scope of Claims] 1) A method of operating a phosphoric acid fuel cell comprising a matrix impregnated with phosphoric acid as an electrolyte and a fuel electrode and an oxidizer electrode disposed on both sides of the matrix, wherein the fuel electrode or the oxidizer A method for operating a phosphoric acid fuel cell, characterized in that when the amount of phosphoric acid held in a catalyst layer of an electrode becomes excessive, gas humidified with water vapor is supplied to the electrode to remove the excess phosphoric acid. 2) A method of operating a phosphoric acid fuel cell according to claim 1, characterized in that a humidified reaction gas is supplied to the electrodes. 3) A method of operating a phosphoric acid fuel cell according to claim 1, characterized in that a humidified inert gas such as nitrogen is supplied to the electrodes. 4) The operating method according to claim 1, characterized in that the state of phosphoric acid permeation within the electrode catalyst layer is detected by measuring the partial pressure of hydrogen or oxygen gas components in the reaction gas. How to operate a phosphoric acid fuel cell.