JPS61225776A - Operation of fuel cell - Google Patents

Abstract

PURPOSE:To obtain high output voltage in the early stage of operation as high hydrophobic nature is maintained by discharging a cell at high temperature exceeding a rated operation temperature for a specified period before transferring to rated operation after starting. CONSTITUTION:Before transferring to rated operation after starting, a fuel cell is preliminarily discharged at high temperature exceeding a rated operation temperature, preferably at temperature 20 deg.C or more higher than the rated operation temperature, for a specified period. When operation temperature is increased, an affinity between electrode and electrolyte is increased, and wettability of electrolyte to electrode is accelerated and electrode reaction becomes active. High initial voltage is rapidly obtained as high hydrophobic nature is maintained without sacrifice of the life of electrode.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

This invention has a fuel electrode and an oxidizer electrode facing each other with an electrolyte layer in between, and by continuously supplying fuel, M, and other agents to each electrode from the outside, the chemical energy of the fuel can be directly converted into electricity. This invention relates to a method of operating a fuel cell that converts energy into electric power and generates electricity.

[Prior art and its problems]

Fig. 1 shows the change in battery voltage over time when the fuel cell is operated continuously under the rated operating conditions. This pattern of output voltage change over time, which shows a tendency for the output voltage to increase and reach a peak voltage, remain stable for a certain period of time, and then gradually start to decrease, is due to the affinity of the electrode for the electrolyte, in other words. The strength of the hydrophobicity of the electrode, especially the strength of the hydrophobicity of the oxidizer electrode, which influences the characteristics of the fuel cell, has a great influence. In other words, if the oxidizer electrode has strong hydrophobicity, it has a weak affinity with the electrolyte, and this results in a long electrode life (on the other hand, the electrode reaction at the beginning of operation is insufficient, resulting in a low output voltage and the peak voltage is reached). On the other hand, if the hydrophobicity of the oxidizer electrode is weak, the electrode reaction will occur actively from the beginning of operation, so the time it takes for the output voltage to reach the peak voltage will be shortened; This shows contradictory trends in terms of output characteristics, such as shortening the life of the battery and accelerating the drop in output voltage after reaching the peak voltage. Hydrophobicity has been adjusted by changing the type and mixing ratio of electrode materials such as TA and water agents, and by changing the manufacturing method of electrodes. In many cases, hydrophobicity is adjusted by adjusting the amount of hydrangea and the method of adding it.When constructing electrodes using this method, it has traditionally been desirable to have strong hydrophobicity from the viewpoint of electrode life. First, in order to obtain the specified output voltage early after the start of operation, the electrodes are manufactured by sacrificing some electrode life to slightly lower the hydrophobicity of the electrodes.As a result, the fuel cell There was a problem that would shorten the lifespan of the

[Purpose of the invention]

This invention was developed in consideration of the above points, and while adopting an electrode with high hydrophobicity, it also achieves high output voltage characteristics within an early period after the start of operation without impairing the life of the battery. The object of the present invention is to provide a method of operating a fuel cell that can be obtained.

[Key points of the invention]

The above object is achieved by the present invention, when starting the operation of a fuel cell, prior to transition to rated operation, a preliminary operation in which discharge is performed for a predetermined period at a high temperature that exceeds at least the rated operating temperature, preferably at least 20°C higher than the rated operating temperature. This is accomplished by performing an operation. In other words, it is well known that the lifespan of fuel cell electrodes generally tends to be shorter as the operating temperature increases, but on the other hand, the time it takes for the battery's output voltage to reach its peak value after the start of operation also depends on the operating temperature. It has been confirmed from the results of experiments conducted by the inventor that the higher the temperature, the shorter the time. Figure 2 shows this situation, and the vertical axis shows the change over time in the battery's output voltage when returning to the rated operating temperature from operation under each operating temperature condition shown in the figure, as is clear from the characteristics shown. The higher the operating temperature, the faster the initial output voltage rises.The reason for this is that when the operating temperature is raised, the
This increases the affinity between the electrode and the electrolyte, which promotes the electrolyte to become accustomed to the electrode so that the electrolyte penetrates into the electrode in a short period of time from the dry state before operation starts, and as a result, the electrode reaction becomes active. It is speculated that this is to make the world more popular. Therefore, as mentioned above, only at the beginning of fuel cell operation, a preliminary operation is performed under high temperature conditions exceeding the rated temperature, and after the output voltage reaches the peak voltage, the cell temperature is returned to the rated temperature and steady operation is performed. By doing so, it is possible to maintain the high hydrophobicity of the electrode and quickly obtain a predetermined initial voltage without impairing the life of the electrode.

[Embodiments of the invention]

Next, this invention will be explained in detail. First, as the fuel electrode that constitutes the fuel cell, a palladium-added activated carbon catalyst and a sufficient amount of polytetrafluoroethylene are mixed and formed into a thin film on the electrode base, and one oxidizer electrode is made of a platinum-added carbon blank catalyst. A sufficient amount of polytetrafluoroethylene is added and mixed to give it high hydrophobicity, and the mixture is formed into a thin film to form the fuel electrode and the oxidizer electrode, and the fuel cell is placed in an electrolyte of 7N potassium hydroxide aqueous solution. Raise the operating temperature to 85℃ (rated operating temperature is 65℃) and
A preliminary operation was performed for 0 hours, and then the temperature was returned to the rated operating temperature and steady operation was performed. Note that the operating temperature of the battery can be increased by adjusting the preheating temperature of the reaction gas supplied to the electrodes of the battery. Figure 3 shows the change in output voltage over time (solid line A) when the preliminary operation under the above-mentioned high-temperature condition was performed, and the change in output voltage over time (solid line A) when the same highly hydrophobic electrode was used but the preliminary operation was not performed as described above. This shows the output voltage change over time (dotted line) obtained from experimental results when operating at the rated temperature.
As can be seen from the illustrated characteristic diagram, by performing the preliminary operation under high temperature conditions, the time required for the voltage to reach the peak value Vo is significantly shortened. In addition, Figure 4 shows the case where the operation was performed with the above-mentioned preliminary operation, and the case where the electrode was configured to have low hydrophobicity by adjusting the amount of lJi water agent added to the oxidizer electrode in advance, and the case where the preliminary operation described above was performed. This is a fuel cell output characteristic diagram that shows the voltage change over time due to long-term continuous operation, determined from the results of experiments conducted by the inventor, in the case of the conventional operation method in which operation is started at the rated temperature from the beginning without performing a discharge operation. The solid line 8 in the figure shows the characteristic line according to the embodiment of this invention, and the dotted line 2 shows the characteristic line according to the conventional operating method.As is clear from this characteristic diagram, the characteristic line due to the operating method of this invention No decrease in the life of the battery was observed, and good results were obtained with a longer life when the high-temperature preliminary operation described above was performed using a highly hydrophobic electrode.

【Effect of the invention】

As described above, according to the present invention, when starting the operation of the fuel cell, a preliminary operation is performed in which discharge is performed for a predetermined period at a high temperature condition that exceeds the rated operating temperature at least before shifting to rated operation. A practical effect that can significantly shorten the time from the start of operation until the output voltage reaches its peak value compared to conventional operation methods, while maintaining the high hydrophobicity imparted to the electrode in advance and without impairing the electrode life. It is possible to provide a highly efficient driving method.

[Brief explanation of drawings]

Fig. 1 is an output characteristic diagram showing general changes in cell voltage over time during continuous operation of a fuel cell, Fig. 2 is a characteristic diagram showing the relationship with operating temperature, and Fig. 3 is a characteristic diagram showing the relationship with operating temperature. A temporal change characteristic diagram of the output voltage comparing the case where the preliminary operation operation is performed and the case where the preliminary operation operation is not performed,
FIG. 4 is a characteristic diagram of voltage change over time during continuous operation, comparing the operating method of the present invention and the conventional operating method. In the figure, A and C: Output characteristics of the battery obtained by the example of this invention. Tatsu Todoroki, Director of the Institute of Industrial Science and Technology

Claims (1)

[Claims] 1) A method of operating a fuel cell, which has a fuel electrode and an oxidizer electrode facing each other with an electrolyte layer in between, and generates electricity by supplying fuel and oxidizer reaction gas to each electrode, the method of operating a fuel cell. 1. A method of operating a fuel cell, which comprises performing a preliminary operation of discharging for a predetermined period at a high temperature condition exceeding at least a rated operating temperature before transitioning to rated operation.