KR101170487B1 - Method of driving direct methanol fuel cell system at low temperature - Google Patents

Abstract

The present invention relates to a low temperature starting method of a direct methanol fuel cell system. A low temperature startup method of a direct methanol fuel cell system of the present invention comprises a stack comprising a membrane-electrode assembly comprising an anode electrode and a cathode electrode positioned opposite each other, and an electrolyte membrane positioned between the anode electrode and the cathode electrode. A low-temperature start-up method of a direct methanol fuel cell system comprising at least one, wherein the stack temperature reaches 30 to 80 ° C. under constant voltage conditions while supplying a hydrocarbon fuel and an oxidant at a freezing point lower than an external temperature. Driving to; It includes, The electrolyte membrane provides a low-temperature start-up method of a direct methanol fuel cell system, characterized in that the ion conductivity is 0.1S / cm or more and the relative selectivity is 5 to 200. Here, relative selectivity refers to [selectivity of the electrolyte membrane / selectivity of Nafion electrolyte membrane], and selectivity refers to [ion conductivity / methanol transmittance].

Description

Low Temperature Start-up Method of Direct Methanol Fuel Cell System {METHOD OF DRIVING DIRECT METHANOL FUEL CELL SYSTEM AT LOW TEMPERATURE}

The present invention relates to a low temperature start-up method of a direct methanol fuel cell system, and more particularly, it is possible to activate a fuel cell system by itself without an external heating device at a low temperature and to protect the stack without damaging the stack. A low temperature start-up method for a direct methanol fuel cell system.

A fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxygen contained in hydrocarbon-based materials such as methanol, ethanol and natural gas into electrical energy.

This fuel cell is a clean energy source that can replace fossil energy, and has the advantage of generating a wide range of outputs by stacking unit cells, and having an energy density of 4-10 times that of a small lithium battery. It is attracting attention as a compact and mobile portable power source.

In such fuel cell systems, the stack that substantially generates electricity comprises several unit cells consisting of a membrane-electrode assembly (MEA) and a separator (also called a bipolar plate). It has a structure laminated to several tens. The membrane-electrode assembly is called an anode electrode (also called a “fuel electrode” or an “oxidation electrode”) and a cathode electrode (also called “air electrode” or “reduction electrode”) with a polymer electrolyte membrane containing a hydrogen ion conductive polymer therebetween. ) Is located.

The principle of generating electricity in a fuel cell is that fuel is supplied to an anode electrode, which is a fuel electrode, adsorbed to a catalyst of the anode electrode, and the fuel is oxidized to generate hydrogen ions and electrons. Reaching the cathode electrode, hydrogen ions pass through the polymer electrolyte membrane and are delivered to the cathode electrode. An oxidant is supplied to the cathode, and the oxidant, hydrogen ions, and electrons react on the catalyst of the cathode to generate electricity while producing water.

Representative examples of the fuel cell include a polymer electrolyte fuel cell (PEMFC) and a direct methanol fuel cell. When methanol is used as the fuel in the direct methanol fuel cell, it is called a direct methanol fuel cell (DMFC).

The polymer electrolyte fuel cell has an advantage of having a high energy density and a high output, but requires attention to handling hydrogen gas and reforms fuel for reforming methane, methanol, natural gas, etc. to produce hydrogen as fuel gas. There is a problem that requires additional equipment such as a device.

In contrast, the direct methanol fuel cell has a lower energy density than the polymer electrolyte fuel cell, but it is easy to handle fuel and has a low operating temperature, and thus can be operated at room temperature.

In addition, direct methanol fuel cells can operate at low temperatures, and can generate large amounts of electricity while being light and small in size. Recently, the portable power source has attracted attention.

Recently, many companies such as Samsung, LG, Hitachi, Sony and MTI have announced a direct methanol fuel cell system for ramtop computers and mobile phones.

In order to use a direct methanol fuel cell in a portable electronic device, operation must begin at cold temperatures, such as below zero. However, since water generated during operation of the fuel cell is cooled at sub-zero temperatures, there is a problem that the fuel cell is difficult to start operation at sub-zero cold temperatures.

Therefore, in order to operate a fuel cell, especially a direct methanol fuel cell at a subzero temperature without an external heating device, the fuel cell must be heated by the heat generated from the fuel cell and the fuel cell temperature must increase rapidly to an operational temperature. There is an urgent need for research on the technologies that can be realized.

One embodiment of the present invention is to provide a low-temperature start-up method of a direct methanol fuel cell system that can activate the fuel cell system by itself without an external heating device at low temperature, and can safely protect the stack without damaging the stack. will be.

According to one embodiment of the invention, a direct comprising at least one stack comprising an anode electrode and a cathode electrode located opposite each other, and a membrane-electrode assembly comprising an electrolyte membrane located between the anode electrode and the cathode electrode. A low temperature start-up method of a methanol type fuel cell system, comprising: driving the stack at a constant voltage condition until the stack temperature reaches 30 to 80 ° C. while supplying a hydrocarbon fuel and an oxidant having a freezing point lower than an external temperature; It includes, The electrolyte membrane provides a low-temperature start-up method of a direct methanol fuel cell system, characterized in that the ion conductivity is 0.1S / cm or more and the relative selectivity is 5 to 200. Here, relative selectivity refers to [selectivity of the electrolyte membrane / selectivity of Nafion electrolyte membrane], and selectivity refers to [ion conductivity / methanol transmittance].

The constant voltage condition is preferably 0.3 to 0.5 V per unit cell.

The hydrocarbon fuel and the oxidant are preferably supplied at a stoichiometric ratio of 2.5 to 4.0 lambda, respectively.

The hydrocarbon fuel is preferably selected from the group consisting of methanol, ethanol, propanol, natural gas, and combinations thereof, of which methanol fuel may be most effectively utilized.

As the electrolyte membrane, a polymer electrolyte membrane or a hydrocarbon electrolyte membrane having hydrogen ion conductivity may be used.

The stack can be used coated with a thermal insulating material.

The anode electrode and the cathode electrode may include a platinum-based catalyst.

The platinum-based catalyst is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu , At least one transition metal selected from the group consisting of Zn, Sn, Mo, W, Rh and Ru), and combinations thereof.

According to an embodiment of the present invention, there is provided a stack including at least two membrane-electrode assemblies including an anode electrode and a cathode electrode positioned opposite to each other, and an electrolyte membrane positioned between the anode electrode and the cathode electrode. A method of activating a direct methanol fuel cell system, the method comprising: driving the stack at constant voltage conditions until the stack temperature reaches 30 to 80 ° C. while supplying a hydrocarbon fuel and an oxidant having a freezing point lower than an external temperature; Wherein the electrolyte membrane has an ion conductivity of 0.1 S / cm or more and relative selectivity (here, relative selectivity refers to [selectivity of the electrolyte membrane / selectivity of Nafion electrolyte membrane], and selectivity refers to [ion conductivity / methanol transmittance]). ) Is 5 to 200 provides a low temperature activation method of a direct methanol fuel cell system.

The hydrocarbon fuel and the oxidant are preferably supplied at a stoichiometric ratio of 2.5 to 4.0λ.

According to the low-temperature start-up method and the activation method of the direct methanol fuel cell system according to an embodiment of the present invention, the fuel cell system can be activated at its low temperature without an external heating device, thereby improving the energy efficiency of the fuel cell system. Can be improved. In addition, there is an advantage that can safely protect the stack without damaging the stack.

1 shows a schematic structure of a fuel cell system of the present invention.
2 is a graph showing a voltage change with time driven under the conditions of Experimental Examples 2 and 3. FIG.
3 is a graph showing a voltage change with time driven under the conditions of Experimental Examples 2 and 3. FIG.
4 is a graph showing changes in voltage, current, and temperature with time driven under the conditions of Experimental Example 4. FIG.
5 is a graph showing changes in voltage, current, and temperature with time driven under the conditions of Experimental Example 5. FIG.
Figure 6 is a graph showing the voltage change with time driven under the conditions of Experimental Example 6.
7 is a graph showing changes in voltage, current, and temperature with time driven under the conditions of Experimental Example 8. FIG.
8 is a graph showing changes in voltage, current, and temperature with time driven under the conditions of Experimental Example 9. FIG.
9 is a graph showing a change in voltage over time driven under the conditions of Experimental Example 10;
10 is a graph showing changes in voltage, current, and temperature with time driven under the conditions of Experimental Example 11. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

One embodiment of the present invention is to provide a low temperature start-up method of a direct methanol fuel cell system.

In the present specification, the stack means a unit cell including a membrane electrode assembly and a separator.

The cold start method includes driving a stack at a constant voltage condition until the stack temperature reaches 30 to 80 ° C. while supplying a hydrocarbon fuel and an oxidant at a freezing point lower than an external temperature.

Hereinafter, the low temperature starting method will be described in more detail. In the present specification, the low temperature start-up method means a method capable of driving the fuel cell system at a low temperature of -5 ° C or lower. In particular, the present invention is more effective in harsh environments below -10 ° C. However, this temperature range refers to the temperature of the range that can utilize the present invention most effectively, and does not limit the scope of the present invention for a range outside of this.

In order to operate the stack at a low temperature, it is preferable to use a hydrocarbon fuel having a freezing point lower than the external temperature, for example, a high concentration hydrocarbon fuel having a concentration of 3 to 8 M may be used, but is not limited thereto. In addition, in the case of using a high concentration hydrocarbon fuel in this way, the hydrocarbon fuel penetrates the electrolyte membrane, moves from the anode electrode to the cathode electrode, and is oxidized at the cathode electrode to cause poisoning of the cathode catalyst, a decrease in fuel efficiency, and a decrease in electrode potential. Since there may be a crossover problem, it is preferable to use a methanol permeation reduction membrane. The methanol permeation reduction membrane will be described later.

The constant voltage condition may be performed at 0.3 to 0.5 V per unit cell. When the voltage under the constant voltage condition is in the above range, the output of the DMFC unit battery can be obtained stably, which is preferable.

It is appropriate to feed the hydrocarbon fuel and the oxidant to the stack in stoichiometry of 2.5 to 4λ.

The hydrocarbon fuel may be appropriately selected from the group consisting of methanol, ethanol, propanol, natural gas and combinations thereof. In particular, the hydrocarbon fuel may more preferably use methanol.

The oxidant can use air suitably.

In addition, the stack may be coated with a thermal insulating material. Thus, if the stack is coated with a thermal insulating material, it is possible to further improve the rate of temperature increase in the stack, to more effectively prevent the heat loss of the stack, and to further improve the stack performance.

When the methanol fuel cell is directly started at a low temperature in the above manner, the stack temperature can be stably reached to 30 to 80 ° C., which is a driving temperature at which an appropriate output (power) can be obtained.

The increase in the stack temperature to the above range is caused by the heat generated while generating electricity by the electrochemical reaction of the stack of the fuel cell system. When the above method is applied, the stack temperature is stably maintained without deterioration of the system. The temperature can be raised to the appropriate drive temperature range.

In the present invention, the membrane-electrode assembly includes a membrane-electrode assembly including an anode electrode and a cathode electrode positioned opposite each other, and an electrolyte membrane positioned between the anode electrode and the cathode electrode. Hereinafter, the structure of the membrane-electrode assembly will be described.

A methanol permeation reduction membrane is used as the electrolyte membrane, and a methanol permeation reduction membrane refers to an electrolyte membrane having an ion conductivity of 0.1 S / cm or more and a relative selectivity of 5 to 200. Here, relative selectivity refers to [selectivity of the electrolyte membrane / selectivity of Nafion electrolyte membrane], and selectivity refers to [ion conductivity / methanol transmittance].

When methanol passes through the electrolyte membrane from the anode to the cathode, it meets and oxidizes directly with oxygen at the cathode, resulting in a voltage loss due to the mixed potential, and poisoning the catalyst of the cathode to deteriorate performance and reduce fuel efficiency. Results in deterioration. In other words, when a high concentration of methanol is applied to the DMFC, the performance decreases, and when about 5 M or more, operation is almost impossible.

In the present invention, since 3 to 8 M of methanol fuel is used for stable starting under low temperature conditions, a methanol permeation reducing membrane having the above properties is used to have sufficient hydrogen ion conductivity and to reduce methanol crossover.

As the methanol permeation reducing membrane, for example, a polymer electrolyte membrane and a hydrocarbon electrolyte membrane having the above properties may be used.

The polymer electrolyte membrane can be made of a polymer resin having, for example, a cation exchange group selected from the group consisting of sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, phosphonic acid groups and derivatives thereof in the side chain.

Representative examples of the polymer resin include a fluorine polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer and a polyether ketone It may include one or more selected from polymers, polyether-etherketone-based polymers or polyphenylquinoxaline-based polymers. More preferably poly (perfluorosulfonic acid) (generally marketed as Nafion), poly (perfluorocarboxylic acid), copolymers of tetrafluoroethylene and fluorovinyl ethers containing sulfonic acid groups, defluorination Sulfide polyether ketones, aryl ketones, poly [(2,2'-m-phenylene) -5,5'-bibenzimidazole] [poly (2,2 '-(m-phenylene) -5,5 '-bibenzimidazole] or poly (2,5-benzimidazole) may be mentioned.

As the hydrocarbon electrolyte membrane, a hydrocarbon electrolyte membrane having hydrogen ion conductivity may be used, and examples of the hydrogen ion conductive group may include a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a phosphonic acid group, or a combination thereof.

The hydrocarbon of the hydrocarbon electrolyte membrane may include polyether ether ketone, polypropylene oxide, polyacrylic acid, polyarylene ether, or a combination thereof.

The cathode electrode and the anode electrode include an electrode substrate and a catalyst layer.

In the catalyst layer, any catalyst that can be used as a catalyst may be used as a catalyst in the reaction of a fuel cell, and a platinum-based catalyst may be used as a representative example. The platinum-based catalyst may be platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy or platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, At least one catalyst selected from the group consisting of Cu, Zn, Sn, Mo, W, Rh and Ru). As described above, the anode electrode and the cathode electrode may use the same material, but in order to prevent the catalyst poisoning caused by CO generated during the anode electrode reaction in the direct oxidation fuel cell, a platinum-ruthenium alloy catalyst is used as the anode. It is more preferable as an electrode catalyst. Specific examples include Pt, Pt / Ru, Pt / W, Pt / Ni, Pt / Sn, Pt / Mo, Pt / Pd, Pt / Fe, Pt / Cr, Pt / Co, Pt / Ru / W, Pt / Ru One or more selected from the group consisting of / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Ni, and Pt / Ru / Sn / W can be used.

In addition, such a metal catalyst may be used as the metal catalyst (black) itself, or may be supported on a carrier. As the carrier, carbonaceous materials such as graphite, denka black, ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanoballs or activated carbon may be used, or alumina, silica, zirconia, Inorganic fine particles such as titania may be used, but carbon-based materials are generally used. In the case of using the noble metal supported on the carrier as a catalyst, a commercially available commercially available product may be used, or the noble metal supported on the carrier may be prepared and used. Since the process of supporting the precious metal on the carrier is well known in the art, detailed descriptions thereof will be readily understood by those skilled in the art even if the detailed description is omitted.

The catalyst layer may further include a binder resin for improving the adhesion of the catalyst layer and the transfer of hydrogen ions.

It is preferable to use a polymer resin having hydrogen ion conductivity as the binder resin, more preferably a cation exchange group selected from the group consisting of sulfonic acid group, carboxylic acid group, phosphoric acid group, phosphonic acid group and derivatives thereof in the side chain. Any polymer resin which has can be used. Preferably, a fluorine polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer, a polyether ketone polymer, a polyether One or more hydrogen ion conductive polymers selected from ether ketone polymers or polyphenylquinoxaline polymers, more preferably poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), Copolymers of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, sulfide polyether ketones, aryl ketones, poly (2,2'-m-phenylene) -5,5'-bibenzimidazoles [poly ( 2,2'-m-phenylene) -5,5'-bibenzimidazole] or poly (2,5-benzimidazole) may be used including one or more hydrogen ion conductive polymers.

The hydrogen ion conductive polymer may replace H with Na, K, Li, Cs or tetrabutylammonium in a cation exchanger at the side chain terminal. In case of replacing H with Na in the side chain terminal ion exchanger, NaOH is substituted for the preparation of the catalyst composition, and tetrabutylammonium hydroxide is substituted for tetrabutylammonium, and K, Li or Cs may be substituted with appropriate compounds. It can be substituted using. Since this substitution method is well known in the art, detailed description thereof will be omitted.

The binder resin may be used in the form of a single substance or a mixture, and may also be optionally used with a nonconductive compound for the purpose of further improving adhesion to the polymer electrolyte membrane. It is preferable to adjust the usage-amount so that it may be suitable for a purpose of use.

Examples of the non-conductive compound include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer (PFA), and ethylene / tetrafluoro Ethylene / tetrafluoroethylene (ETFE), ethylenechlorotrifluoro-ethylene copolymer (ECTFE), polyvinylidene fluoride, copolymer of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), dode At least one selected from the group consisting of silbenzenesulfonic acid and sorbitol is more preferred.

The electrode substrate plays a role of supporting the electrode and diffuses the fuel and the oxidant to the catalyst layer, thereby serving to easily access the fuel and the oxidant to the catalyst layer. The electrode substrate is a conductive substrate, and representative examples thereof include carbon paper, carbon cloth, carbon felt, or metal cloth (porous film or polymer fiber composed of metal in a fibrous state). The metal film is formed on the surface of the formed cloth) may be used, but is not limited thereto.

In addition, it is preferable to use a water-repellent treatment with a fluorine-based resin as the electrode base material because it can prevent the reactant diffusion efficiency from being lowered by water generated when the fuel cell is driven. Examples of the fluorine-based resin include polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxy vinyl ether, and fluorinated ethylene propylene ( Fluorinated ethylene propylene), polychlorotrifluoroethylene or copolymers thereof can be used.

In addition, a microporous layer may be further included to enhance the reactant diffusion effect in the electrode substrate. These microporous layers are generally conductive powders having a small particle diameter, such as carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotubes, carbon nanowires, and carbon nanohorns. -horn or carbon nano ring.

The microporous layer is prepared by coating a composition comprising a conductive powder, a binder resin and a solvent on the electrode substrate. The binder resin may be polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride, alkoxy vinyl ether, polyvinyl alcohol, cellulose acetate Or copolymers thereof and the like can be preferably used. As the solvent, alcohols such as ethanol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, water, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, etc. may be preferably used. The coating process may be screen printing, spray coating, or coating using a doctor blade according to the viscosity of the composition, but is not limited thereto.

In the present invention, a fuel cell system includes the stack, a fuel supply part and an oxidant supply part.

The fuel supply unit serves to supply fuel to the electricity generation unit, and the oxidant supply unit serves to supply an oxidant such as oxygen or air to the electricity generation unit.

A schematic structure of the fuel cell system of the present invention is shown in FIG. 1, which will be described in more detail with reference to the following. Although the structure shown in FIG. 1 shows a system for supplying fuel and oxidant to an electric generator using a pump, the fuel cell system of the present invention is not limited to such a structure, and a fuel cell using a diffusion method without using a pump is shown. Of course, it can also be used for system architecture.

The fuel cell system 1 of the present invention includes at least one electricity generation unit 3 for generating electrical energy through an oxidation reaction of a fuel and a reduction reaction of an oxidant, a fuel supply unit 5 for supplying the fuel, And an oxidant supply unit 7 for supplying an oxidant to the electricity generation unit 3.

In addition, the fuel supply unit 5 for supplying the fuel may include a fuel tank 9 storing fuel and a fuel pump 11 connected to the fuel tank 9. The fuel pump 11 serves to discharge the fuel stored in the fuel tank 9 by a predetermined pumping force.

The oxidant supply unit 7 for supplying the oxidant to the electricity generating unit 3 includes at least one oxidant pump 13 for sucking the oxidant with a predetermined pumping force.

The electricity generator 3 is composed of a membrane-electrode assembly 17 for oxidizing and reducing a fuel and an oxidant, and a separator 19 and 19 'for supplying fuel and an oxidant to both sides of the membrane-electrode assembly. At least one of these electricity generating units 3 constitutes a stack 15.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

[Example]

All experiments were conducted in an environmental chamber (JEIO-Tech, TH-G 180, Korea) that can control temperature and humidity to maintain the same sub-zero temperature.

Experimental Example 1 Manufacture of Stack

A loading amount of the PtRu / C anode catalyst (HISPEC 12100, Johnson Matthey, UK) was 2.0 mg / cm ₂ to mix Nafion / H ₂ O / 2-propanol binder liquid to prepare a catalyst composition for the anode electrode. The catalyst composition was applied to a carbon paper electrode substrate (TGP-H060, Toray carbon, Japan) treated with 5% by weight polytetrafluoroethylene to prepare an anode electrode. At the anode electrode, the loading of the PtRu / C anode catalyst was 2.0 mg / cm 2.

In addition, SGL carbon paper ( ^® SIGRACET GDL 25BC, SGL Carbon Germany) having a microporous layer was used as the gas diffusion layer for the cathode. At this time, the loading amount of Pt / C cathode catalyst (HISPEC 12100, Johnson Matthey, UK) was 2.0 mg / cm 2 based on the weight of platinum.

The active electrode area of each electrode was 30 cm 2.

150 ° C. using a Carver Laboratory Press (Carver, Model M, USA) using the prepared anode electrode and cathode electrode and a hydrocarbon electrolyte membrane (PF DM-1-20-HB-o, Polyfuel) having a thickness of 20 μm. The membrane-electrode assembly was prepared by hot-pressing under a pressure of less than 50 kg for 1 minute at.

A stack was prepared by stacking 10 unit cells including the membrane-electrode assembly and the graphite bipolar plate.

(Experimental Example 2)

The stack prepared in Experimental Example 1 and 3M methanol were maintained at -5 ° C in the chamber, respectively, and 3M methanol and air maintained at -5 ° C were injected into the stack at stoichiometric ratios of 3.0 and 3.5λ, respectively. , It was driven under a constant current condition of 0.5A.

Experimental Example 3

The same procedure as in Experiment 2 was carried out except that the device was driven under a constant current condition of 1.0 A instead of a constant current condition of 0.5 A.

The voltage change with time driven under the conditions of Experimental Examples 2 and 3 is shown in FIG. 2, and the temperature change is shown in FIG. 3.

As shown in Fig. 2, when the currents of 0.5A and 1.0A were supplied to the stack at -5 ° C, the stack voltage was lowered from about 8.0V to 3.38V in the case of Experimental Example 2 which supplied the 0.5A current instantaneously. , Experimental Example 3, which was supplied with a 1.0A current, is reduced from about 8.0V to 2.16V, and gradually recovered to 5.14V and 4.63V for 30 minutes.

As a result, it can be seen that the output characteristics started with low outputs of 1.7 W and 2.16 W at −5 ° C., and increased to 2.57 W and 4.43 W after about 30 minutes, respectively.

In addition, as shown in FIG. 3, when 0.5A and 1.0A of current were applied to the stack at -5 ° C, the stack temperature was increased to 34 ° C (Experimental Example 2) and 39 ° C (Experimental Example 3), respectively. Can be. This increase in power is thought to be due to an increase in stack temperature. In addition, since there is no external heat source, it can be predicted that this temperature increase is due to an internal exothermic reaction.

Experimental Example 4

Instead of the constant current condition of 0.5A, it was carried out in the same manner as in Experiment 2 except that the step was increased while increasing from 0.5A to 4A.

Voltage, current, and temperature change with time driven under the conditions of Experimental Example 4 were measured, and the results are shown in FIG. 4. As shown in Fig. 4, when driven while changing the current, the voltage suddenly decreases initially and then gradually increases, but still shows a low voltage.

In addition, even if the stack temperature is also driven for 20 minutes, it can be seen that the temperature increase is not large compared to the result shown in FIG.

In addition, as shown in FIG. 4, as the temperature of the stack increases, the voltage of the stack shows a steady-state, which means that at low temperatures below zero, the voltage of the stack is greatly influenced by the stack temperature. It can be seen that.

Experimental Example 5

Instead of a constant current condition of 0.5A, it was carried out in the same manner as in Experimental Example 2 except that it was driven at a constant voltage of 4V.

Voltage, current, and temperature change with time driven under the conditions of Experimental Example 5 were measured, and the results are shown in FIG. 5. As shown in FIG. 5, a very low current of about 0.3 A was initially obtained, but it can be seen that as the stack temperature increases, the current improves. As a result, the stack temperature increased from -5 ° C to 52 ° C and the output showed 9.7W.

It can be seen from the results shown in FIGS. 4 and 5 that once the stack temperature reaches room temperature, the stack performance is maintained. In addition, in Experimental Example 5 driven in the constant voltage mode, the output characteristic is about 9.7W, and when driven in the constant current mode, it can be seen that the output characteristic is higher than 8.2W.

Experimental Example 6

The stack prepared in Experimental Example 1 and 5 M methanol were maintained at -10 ° C. in the chamber, respectively, and 5 M methanol and air maintained at −10 ° C. were injected into the stack at stoichiometric ratios of 3.0 and 3.5λ, respectively. , It was driven under a constant current condition of 0.5A.

The voltage change with time driven under the conditions of Experimental Example 6 is shown in FIG. 6. Initially, the voltage slightly decreased to 2.69V, which is greater than the voltage drop of 3.38V occurring at -5 ° C, but the voltage rose again and increased to 5.12V. In addition, as shown in FIG. 6, the stack temperature increased very high up to 51 ° C., which is expected due to the crossover due to the use of 5M methanol.

Experimental Example 7

Except for driving under a constant current condition of 1.0A was carried out in the same manner as in Experiment 6.

When driven under the conditions of Experimental Example 7, the voltage was too low, less than 0.1V, further experiments were meaningless.

Experimental Example 8

Instead of the constant current condition of 0.5A, it was carried out in the same manner as in Experiment 6 except that the step was increased while increasing from 0.5A to 2.5A.

Voltage, current, and temperature change with time driven under the conditions of Experimental Example 8 were measured, and the results are shown in FIG. 7.

As shown in FIG. 7, although the stack voltage initially dropped sharply to 2.22 V, it can be seen that the stack temperature increased with time, and the stack voltage was improved again. In addition, it can be seen that when the current is increased to more than 1.5 A, the characteristics appearing at almost room temperature are obtained.

In addition, the stack temperature was increased to about 60 ℃ even without a separate heat source, it can be seen that the output was 8.93W.

 Experimental Example 9

Instead of the constant current condition of 0.5A, it was carried out in the same manner as in Experimental Example 6 except that it was driven at a constant voltage of 4V.

Voltage, current, and temperature change with time driven under the conditions of Experimental Example 9 were measured, and the results are shown in FIG. 8. As shown in FIG. 8, it started at a low output of 0.51W at the beginning of driving, but increased to 8.7W, and the temperature increased to 63 ° C. In addition, the constant voltage mode showed better results than the constant current mode.

Experimental Example 10

After maintaining the stack prepared in Experimental Example 1 and 8M methanol at -15 ° C in the chamber, respectively, 8M methanol and air maintained at -15 ° C were injected at stoichiometric ratios of 3.0 and 3.5λ, It was driven under a constant current condition of 0.5A.

9 is a graph showing a change in voltage over time driven under the conditions of Experimental Example 10. FIG. As shown in FIG. 9, it can be seen that the voltage rapidly decreases to about 0.1V from the time when the driving is started until 52 seconds have elapsed.

Experimental Example 11

Instead of the constant current condition of 0.5A, it was carried out in the same manner as in Experimental Example 6 except that it was driven at a constant voltage of 4V.

The voltage change with time driven under the conditions of Experimental Example 10 is shown in FIG. 9.

Voltage, current, and temperature change with time driven under the conditions of Experimental Example 11 were measured, and the results are shown in FIG. 10. As shown in FIG. 10, it can be seen that when the stack temperature starts to increase, the current also increases to increase the output and the temperature increases to 51 ° C.

In summary, the experimental results in Experimental Examples 1 to 11 above, in the case of the constant current type that starts by maintaining a constant current, the voltage drops rapidly to the extent that damage to the stack due to a sudden decrease in voltage with the starting It can be seen that, as the temperature is lowered and the current is increased, it reaches a state where driving is impossible at all.

The start-up method of stepping up the current had some effect of limiting the voltage drop, but due to the sudden voltage reduction at the initial stage of operation, it was expected that the stack would be damaged or impossible to operate under low temperature conditions.

On the other hand, in the case of the constant voltage method which starts the voltage by keeping the voltage constant, the temperature can be increased to the proper driving temperature range by the stable temperature rise and the current rise, and the output is also excellent.

All simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

Claims (10)

Cold start-up of a direct methanol fuel cell system comprising a stack comprising at least two membrane-electrode assemblies comprising an anode electrode and a cathode electrode positioned opposite each other and an electrolyte membrane positioned between the anode electrode and the cathode electrode As a method,
Driving the stack until the stack temperature reaches 30 to 80 ° C. under constant voltage conditions, while supplying a hydrocarbon fuel and an oxidant having a freezing point lower than an external temperature; Including;
The electrolyte membrane has an ion conductivity of 0.1 S / cm or more and relative selectivity (here, relative selectivity refers to [selectivity of the electrolyte membrane / selectivity of Nafion electrolyte membrane], and selectivity refers to [ion conductivity / methanol transmittance]). A low temperature start-up method for a direct methanol fuel cell system, characterized in that 200.
The method of claim 1,
The constant voltage condition is a low-temperature start-up method of a direct methanol fuel cell system is 0.3 to 0.5 V per unit cell.
The method of claim 1,
The hydrocarbon fuel and the oxidant is supplied at a stoichiometric ratio of 2.5 to 4.0 lambda is a low temperature start-up method of a direct methanol type fuel cell system.
The method of claim 1,
The electrolyte membrane is a low temperature starting method of a direct methanol fuel cell system, characterized in that the polymer electrolyte membrane having a hydrogen ion conductive group.
The method of claim 1,
The electrolyte membrane is a low temperature start-up method of a direct methanol fuel cell system, characterized in that the hydrocarbon electrolyte membrane having a hydrogen ion conductive group.
The method of claim 1,
Wherein said stack is coated with a thermal insulating material.
The method of claim 1,
And said anode electrode and said cathode electrode comprise a platinum-based catalyst.
The method of claim 7, wherein
The platinum-based catalyst is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy, platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu At least one transition metal selected from the group consisting of Zn, Sn, Mo, W, Rh, and Ru), and combinations thereof.
A method of activating a direct methanol fuel cell system comprising a stack comprising at least two membrane-electrode assemblies comprising anode and cathode electrodes positioned opposite one another and an electrolyte membrane located between the anode and cathode electrodes As
Driving the stack until the stack temperature reaches 30 to 80 ° C. under constant voltage conditions, while supplying a hydrocarbon fuel and an oxidant having a freezing point lower than an external temperature; Including;
The electrolyte membrane has an ion conductivity of 0.1 S / cm or more and relative selectivity (here, relative selectivity refers to [selectivity of the electrolyte membrane / selectivity of Nafion electrolyte membrane], and selectivity refers to [ion conductivity / methanol transmittance]). Low temperature activation method of a direct methanol fuel cell system, characterized in that 200.
10. The method of claim 9,
The hydrocarbon fuel and the oxidant is supplied at a stoichiometric ratio of 2.5 to 4.0 lambda low temperature activation method of the direct methanol type fuel cell system.

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