JPH03219564A - Fuel cell power generator device - Google Patents

Abstract

PURPOSE:To stop the generating operation of a fuel cell in the state where the deterioration of a formed oxidizing agent electrode catalyst is suppressed by connecting a water electrolytic device, utilizing electrode potential difference to electrolyze water, mixing the formed hydrogen with nitrogen, and supplying it to a fuel electrode. CONSTITUTION:The inert gas replacement of a fuel cell 1 is conducted, and a pair of electrodes of a water electrolytic device are electrically connected to the cell 1. At that time, the fuel electrode and oxidizing agent electrode 4A of the cell 1 generate potentials corresponding to the adsorption quantities of hydrogen and oxygen, and a potential difference exceeding the potential necessary for the electrolysis of water is applied between the electrodes of the water electrolytic device 11. Consequently, hydrogen and oxygen of the quantities corresponding to the remaining adsorbed gas quantities are formed by the electrolysis of water. As the quantity of hydrogen formed thereby is regularly larger than the remaining adsorbed oxygen on the oxidizing agent electrode 4A by a stoichiometric ratio or more, the formed hydrogen is mixed with nitrogen for inert gas replacement and supplied to a fuel electrode 3A through a fuel gas chamber 3, whereby the remaining adsorbed oxygen of the oxidizing agent electrode is consumed and removed on the bases of the electrostatic reaction of the fuel cell.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention mainly relates to a matrix type fuel cell power generation device,
In particular, the present invention relates to a fuel cell power generation device equipped with a stop device that actively consumes residual adsorbed oxygen remaining on the oxidizer electrode 1 when power generation operation is stopped.

[Conventional technology]

As is well known, a fuel cell is a cell stack consisting of multiple single cells in which a matrix holding an electrolyte is sandwiched between a pair of fuel electrodes and an oxidizer electrode, with a gas-impermeable plate interposed between the stacked surfaces. A hydrogen-rich fuel gas is supplied to the fuel gas chamber defined between the electrode and the gas impermeable plate, and a hydrogen-rich fuel gas is supplied as an oxidizer to the oxidizer chamber defined between the oxidizer electrode and the gas impermeable plate. It generates electricity by supplying air or oxygen. In addition, since fuel cells generate water on the oxidizer electrode side due to the power generation reaction, the operating temperature of batteries that use highly hygroscopic phosphoric acid as the electrolyte is 130°C.
to 190° C., generally about 190° C., to facilitate discharge of generated water, and to maintain the activity of the electrode catalyst for power generation operation.

When the current flowing to the external load circuit is cut off in order to stop or suspend the operation of a fuel cell operated in this way, a high temperature open circuit voltage is generated in each unit cell, and the electrode catalyst particles become coarse. A deterioration phenomenon in which the electrode surface area decreases (
(called sintering) occurs, leading to a decrease in power generation performance and shortened lifespan.As the battery temperature decreases, the phosphoric acid adsorbs moisture in the reaction gas, diluting the phosphoric acid, and the phosphoric acid solution expands in volume and is transferred from the matrix to the electrode. In addition, the gas separation function of the matrix from which the phosphoric acid solution leaked may deteriorate, causing the air as a reaction gas to mix with the fuel gas, resulting in explosion gas. Various obstacles occur, such as an increased risk of occurrence.

Therefore, in order to avoid these failures and stop the power generation of the fuel cell, the external load circuit is cut off, and the supply of fuel gas and oxidizing gas is stopped. A method is known to lower the temperature of a fuel cell while purging residual reaction gas (fuel gas or oxidizer) by supplying an inert gas such as dry nitrogen to each of the oxidizer chambers, oxidizer passages, and supply/discharge manifolds. It is being

[Problem to be solved by the invention]

In the conventional method described above, by supplying nitrogen gas from the outside, the reaction gas in both gas chambers can be purged at an early stage. It has been thought that the danger of gas mixture can be avoided.

However, on the oxidizer electrode side, there is residual adsorbed oxygen that is chemically adsorbed on the surface of the electrode catalyst particles, and this residual adsorbed oxygen cannot be desorbed only by purging with nitrogen gas.
Recent research has revealed that this is the reason why the oxidizer electrode maintains a high potential, and that exposing the oxidizer electrode to a high potential at high temperatures until it cools down can have an adverse effect on the catalyst layer. There are drawbacks that cannot be avoided.

An object of the present invention is to eliminate the adverse effects on the electrode catalyst layer of a fuel cell by adding a stop device that actively consumes residual adsorbed oxygen.

[Means to solve the problem]

According to the present invention, the above object is made of a stack of unit cells having a fuel electrode and an oxidizer electrode, and a fuel gas as a reaction gas is supplied to the fuel electrode and the oxidizer electrode via a fuel gas chamber and an oxidizer gas chamber. and an oxidizer to generate power, and supply the generated power to an external load via a power converter, and when power generation operation is stopped, the fuel gas and oxidizer are switched to an inert gas for gas replacement. The hydrogen electrode is electrically connected to the fuel electrode and the oxidizer electrode via a switch, and hydrogen generated by water electrolysis using the electromotive force of the fuel cell is mixed with the inert gas and supplied to the fuel gas chamber. This is achieved by providing a water electrolyzer.

[Effect]

In the above means, gas is replaced in the fuel cell, and a pair of electrodes of a water electrolyzer are electrically connected to the fuel cell. At this time, the fuel electrode and oxidizer electrode of the fuel cell generate a potential corresponding to the amount of adsorbed hydrogen and oxygen, and the potential difference between the electrodes of the water electrolyzer exceeds the potential required for water electrolysis. is applied, hydrogen and oxygen are generated by electrolysis of water in an amount commensurate with the amount of residual adsorbed gas. Since the amount of generated hydrogen is always greater than the stoichiometric ratio than the residual adsorbed oxygen on the oxidizer electrode side, by mixing this generated hydrogen with nitrogen for gas replacement and supplying it to the fuel electrode via the fuel gas chamber. , the residual adsorbed oxygen of the oxidizer electrode can be consumed and removed based on the electromotive reaction of the fuel cell. Note that if a discharge resistor is connected to the fuel cell as necessary, consumption of adsorbed oxygen can be promoted.

〔Example〕

This invention will be explained below based on examples.

FIG. 1 is a schematic configuration diagram showing an embodiment of the fuel cell power generation apparatus of the present invention. In the figure, 3A is a fuel electrode of the phosphoric acid fuel cell main body 1, 2 is a matrix, and 4A is an oxidizer electrode. A pair of electrodes 13A and 14A of a water electrolyzer 11 are electrically connected to both poles of the fuel cell main body 1 via a switch 7 of the water electrolyzer. The hydrogen generation chamber 13 of the water electrolyzer 11 is connected to the fuel supply line via the valve 8, while the oxygen generation chamber 14 is opened to the outside of the power generation system. Fuel gas chamber 3. A three-way valve 5 and a three-way valve 6, each having one end connected to the nitrogen gas side, are connected to each inlet of the oxidant gas chamber 4.

When the fuel cell main body is stopped, the electrical load on the fuel cell main body 1 is cut off, the three-way valve 5 and the three-way valve 6 are switched to the nitrogen side, and nitrogen is allowed to flow into both gas chambers 3.4 at a predetermined flow rate. At the same time, the switch 7 of the water electrolyzer is closed, and the pair of electrodes 13
A and 14A are electrically connected to the fuel electrode 3A and the oxidizer electrode 4A, respectively. In general, fuel cells consist of multiple single cells connected in series, each consisting of a fuel electrode, a matrix, and an oxidizer electrode, so the residual hydrogen and oxygen adsorbed on each cell generate a potential higher than that required for water electrolysis. A potential difference is obtained, water in the electrolyte chamber 12 is electrolyzed, and hydrogen and oxygen are each produced in amounts commensurate with the amount of residual adsorbed gas.

After a certain period of time, the valve 8 connected to the hydrogen generation chamber 13 of the water electrolyzer is opened, and the generated hydrogen is mixed with the nitrogen flowing to the fuel electrode 3A. On the other hand, oxygen generated in the oxygen generation chamber 14 is discharged to the outside of the fuel cell main body. Therefore, the amount of hydrogen adsorbed on the fuel electrode side is always in excess of the residual adsorbed oxygen on the oxidizer electrode side by more than the stoichiometric ratio, and the residual adsorbed oxygen on the oxidizer electrode side is efficiently removed. In order to further completely remove the residual adsorbed oxygen on the oxidizer electrode side,
A discharge resistor 21 is connected between the two poles via a switch 22,
When the voltage sensor 23 detects that the potential of the fuel cell has fallen below a certain level, a discharge resistor is turned on.

A discharge current flows through the fuel cell 1 through the discharge resistor 21, and the remaining adsorbed oxygen is completely and quickly consumed by an electromotive reaction, thereby making it possible to lower the electrode potential.

When the remaining adsorbed oxygen is consumed and the electrode potential of the fuel cell decreases accordingly, the amount of hydrogen generated by the water electrolyzer 11 also decreases and eventually approaches zero, which is detected by the voltage sensor 23.
The fuel gas chamber 3 and oxidizer gas chamber 4 are detected by
By closing a valve (not shown) disposed on the outlet side of the gas chamber, both gas chambers can be brought to a stopped state while being replaced with nitrogen gas.

〔Effect of the invention〕

As described above, this invention cuts off the external load when power generation operation is stopped, supplies nitrogen to the reaction gas chamber of the fuel cell to replace the gas, and connects a water electrolyzer to the fuel cell to remove any remaining adsorbed oxygen. Water is electrolyzed using the electrode potential difference caused by the above, and the generated hydrogen is mixed with the nitrogen and supplied to the fuel electrode. As a result, it becomes possible to consume the generated hydrogen and adsorbed oxygen corresponding to the amount of adsorbed oxygen using the electromotive reaction of the fuel cell, and the remaining adsorbed oxygen of the oxidizer electrode, which could not be removed by conventional gas replacement alone, is consumed. Since the electrode potential can be lowered by the electrode being exposed to a high potential, it is possible to stop the power generation operation of the fuel cell while suppressing deterioration of the oxidizer electrode catalyst caused by exposing the electrode to a high potential. Also,
If a load resistor is connected to the output circuit of the fuel cell to cause a discharge current to flow, the consumption of adsorbed oxygen is promoted and the adsorbed oxygen can be consumed more quickly.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the fuel cell power generation apparatus of the present invention. 1: Fuel cell, 2: Matrix, 3: Fuel gas chamber, 4
: Oxidizing gas chamber, 5, 6: Three-way valve, 7: Switch, 8:
Valve, 11: Water electrolyzer, 21: Discharge resistance, 3A
:Fuel electrode, 4A dioxide electrode. 0 Figure 1

Claims (1)

[Scope of Claims] 1) Consisting of a stack of single cells having a fuel electrode and an oxidizer electrode, fuel gas as a reaction gas and A device that supplies an oxidizing agent to generate electricity, supplies the generated power to an external load via a power conversion device, and when power generation operation is stopped, switches the fuel gas and oxidizing agent to an inert gas for gas replacement. Water is electrically connected to the fuel electrode and the oxidizer electrode via a switch, and is supplied to the fuel gas chamber by mixing hydrogen generated by water electrolysis using the electromotive force of the fuel cell with the inert gas. A fuel cell power generation device comprising an electrolyzer.