KR101208159B1 - Fuel Cell - Google Patents

Abstract

The present invention relates to a fuel cell, wherein the fuel cell includes an anode electrode using an oxidation reaction of a fuel and a cathode electrode using a reduction reaction of an oxidant, and an electrolyte or an ion exchange membrane positioned between the anode electrode and the cathode electrode. In a fuel cell comprising, the cathode comprises at least one selected from the group consisting of a pure substance, a compound of a nonmetallic element selected from the group consisting of N, F, I, S, Cl and Br or an ion of the pure substance or a compound as an oxidizing agent. .

When the oxidant is used as described above, the fuel cell can obtain high energy conversion efficiency regardless of the presence or absence of a platinum catalyst used for the cathode electrode. Therefore, the platinum catalyst, which is a noble metal catalyst used in the conventional cathode electrode, may not be used, or the platinum catalyst may be replaced with another low-cost catalyst.

Non-platinum catalysts, cathode electrodes, fuel cells

Description

Fuel cell

The present invention relates to a fuel cell.

In general, 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. Such a fuel cell typically includes an anode electrode supplied with fuel, a cathode electrode supplied with an oxidant, and a cation exchange membrane positioned between the anode electrode and the cathode electrode. The oxidant in the fuel cell typically uses oxygen or air.

The fuel cell is attracting attention as a clean energy conversion device because of its high efficiency and low emission of pollutants. However, due to high cost and technical reliability limitations, it is difficult to commercialize. In particular, the oxygen reduction reaction at the cathode electrode (also known as 'air electrode' or 'reduction electrode') is 10 ⁶ times slower than the hydrogen oxidation reaction at the anode electrode (also called 'fuel electrode' or 'anode'). As it occurs, the oxygen reduction reaction of the cathode is not only a major factor in determining the overall reaction rate, but also a major factor in determining fuel cell performance.

In order to increase the rate of the oxygen reduction reaction, a platinum catalyst is used at the cathode of most fuel cells. Platinum catalysts, however, have high electrical conductivity and excellent catalytic properties, but are expensive and have limitations in increasing the surface area on which catalysis occurs. In order to reduce the cost, it is required to reduce the platinum content or to develop a non-noble metal catalyst as an alternative catalyst.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel cell of high efficiency capable of increasing energy conversion efficiency by exhibiting high power density regardless of the presence or absence of a platinum catalyst of a cathode electrode.

In order to achieve the above object, the present invention provides a fuel cell including an anode electrode using an oxidation reaction of a fuel and a cathode electrode using a reduction reaction of an oxidant, and an electrolyte or an ion exchange membrane positioned between the anode electrode and the cathode electrode. For example, the cathode may include at least one selected from a pure material, a compound of a nonmetallic element selected from the group consisting of N, F, I, S, Cl, and Br or an ion of the pure material or a compound as an oxidizing agent. Provide a fuel cell.

The compound may be at least one selected from hydrides, oxides or hydroxides.

The oxidant may be a compound selected from hydride of nitrogen, oxide of nitrogen, hydroxide of nitrogen, nitrogen hydride in ionic form, nitrogen oxide in ionic form or nitrogen hydroxide in ionic form.

The oxidant may be a pure substance or compound selected from chlorine, hydride of chlorine, oxide of chlorine, hydroxide of chlorine, chlorine hydride in ionic form, chlorine oxide in ionic form, and chlorine hydroxide in ionic form.

The oxidant may be a pure substance or a compound selected from iodine, hydride of iodine, oxide of iodine, hydroxide of iodine, iodine hydride in ionic form, iodine oxide in ionic form, and iodine hydroxide in ionic form.

The oxidant may be a compound selected from sulfur hydride, oxide of sulfur, hydroxide of sulfur, sulfur hydride in ionic form, sulfur oxide in ionic form, and sulfur hydroxide in ionic form.

The oxidizing agent may be a compound selected from hydride of bromine, oxide of bromine, hydroxide of bromine, bromine hydride in ionic form, bromine oxide in ionic form, and bromine hydroxide in ionic form.

The oxidant may be a compound selected from hydride of fluorine, oxide of fluorine, hydroxide of fluorine, fluoride hydride in ionic form, fluorine oxide in ionic form, and fluorine hydroxide in ionic form.

It is preferable that the said ion exchange membrane is a cation exchange membrane.

The anode electrode includes a catalyst, and the cathode electrode may or may not include a catalyst.

The fuel cell may include a fuel supply port for supplying a fuel used for an oxidation reaction to an anode electrode, and the fuel cell may include an oxidant supply port for supplying an oxidant used for a reduction reaction to a cathode electrode. Furthermore, the fuel cell may be provided with a transfer line for transferring the reactant at the cathode electrode with oxygen to oxidize the oxidant supply port.

The fuel cell according to the present invention uses a pure material or a compound of a nonmetallic element selected from the group consisting of N, F, I, S, Cl and Br as an oxidant instead of oxygen or air conventionally used as an oxidant for a cathode. It is possible to obtain a high energy conversion efficiency regardless of the presence or absence of a platinum catalyst used in the cathode of the fuel cell. In particular, the oxidants used in the present invention can reduce the manufacturing cost of the existing fuel cell and improve the energy conversion efficiency because the reaction rate is very fast and the activity loss is low. Therefore, when constructing a fuel cell, a platinum catalyst, which is a noble metal catalyst, may not be used for the cathode, or the platinum catalyst may be replaced with another low-cost catalyst.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings, but the accompanying drawings are provided only to assist in understanding the present invention, but the present invention is not limited thereto.

1 is a view schematically showing the configuration of a fuel cell according to an embodiment of the present invention.

As shown in FIG. 1, a fuel cell according to the present invention includes an anode electrode 10 using an oxidation reaction of a fuel and a cathode electrode 20 using a reduction reaction of an oxidant, and the anode electrode 10 and the cathode electrode 20. It comprises an electrolyte or ion exchange membrane 30 positioned between.

The anode electrode 10 may include a substrate and a catalyst layer.

The substrate serves to support the electrode and to diffuse the fuel into the catalyst layer to help the fuel easily accessible to the catalyst layer.

The substrate may be 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 cloth 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, since the substrate 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, polypolyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxy vinyl ether, and fluorinated ethylene propylene ( Fluorinated ethylenepropylene), polychlorotrifluoroethylene or copolymers thereof can be used.

The catalyst layer helps the oxidation reaction of the fuel to proceed efficiently, and includes a catalyst.

The catalyst is applicable without limitation as long as it is generally used in the art. Specifically, the catalyst may be a platinum-based catalyst. As the platinum-based catalyst, 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, A catalyst selected from the group consisting of Cu, Zn, Sn, Mo, W, Rh, Rh and combinations thereof) and mixtures thereof. In general, in order to prevent the catalyst poisoning phenomenon caused by CO generated in the reaction in the anode electrode 10 of the fuel cell, it is more preferable to use a platinum-ruthenium alloy catalyst. As the platinum-ruthenium alloy (-> platinum-based alloy) catalyst, Pt, Pt / Ru, Pt / W, Pt / Ni, Pt / Sn, Pt / Mo, Pt / Pd, Pt / Fe, Pt / Cr, Pt / Co, Pt / Ru / W, Pt / Ru / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Ni and Pt / Ru / Sn / W, each of which may be exemplified It can be used individually or in combination of 2 or more types.

The anode electrode 10 including the substrate and the catalyst layer can be formed by various known methods. For example, the slurry containing a catalyst can be apply | coated to a base material, and can be manufactured. If necessary, it may be prepared by applying a slurry containing a catalyst to the electrolyte or ion exchange membrane (30). However, the present invention does not limit their formation method.

The cathode electrode 20 includes a substrate. Since the description may be the same as described above with respect to the anode electrode 10, a detailed description thereof will be omitted.

According to the present invention, the cathode electrode 20 may further include a catalyst layer. That is, the cathode electrode 20 according to the present invention may include a catalyst layer and exhibit high energy conversion efficiency without including the catalyst layer. This is because the fuel cell according to the present invention uses an oxidant different from the conventional method using oxygen or air as the oxidant, which will be described later.

Therefore, when the cathode electrode 20 of the present invention is manufactured, it is not necessary to form or form a catalyst layer formed using a catalyst layer, in particular, a platinum-based noble metal catalyst, and in particular, even when the catalyst layer is formed, the content of the expensive platinum catalyst is reduced or Alternative low cost catalysts will be available.

In the case of further including a catalyst layer, a catalyst as described in the above-described anode electrode 10 may be used as the catalyst. In addition, since the catalyst layer may be formed in the same manner as the anode electrode 10 described above, a detailed description thereof will be omitted.

An electrolyte or an ion exchange membrane is provided between the anode electrode 10 and the cathode electrode 20.

The electrolyte refers to a material having ion conductivity such as hydroxide ions, phosphates, molten carbonates, solid oxides, and polymer electrolytes used in various types of fuel cells, and it is suitable to use an electrolyte having good ion conductivity, and generally used in the art. You can apply what is used.

The electrolyte or ion exchange membrane 30 serves as an insulator for electrically separating the anode electrode 10 and the cathode electrode 20, and the hydrogen from the anode electrode 10 to the cathode electrode 20 during operation of the fuel cell. It acts as a medium for transporting ions or hydroxide ions, and simultaneously serves to separate oxidants or fuels.

Therefore, the electrolyte or the ion exchange membrane 30 is preferably manufactured using a polymer having excellent hydrogen ion conductivity, it is applicable to those commonly used in the art.

The ion exchange membrane may be a cation exchange membrane or an anion exchange membrane.

Specifically, the cation exchange membrane may be 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. , Polyether-etherketone-based polymer, polyphenylquinoxaline-based polymer can be prepared using at least one selected.

Specifically, the anion exchange membrane may be selected from an electrolyte having a functional group exhibiting a cation capable of transferring hydroxide ions in the fluorine-based polymer and the hydrocarbon-based polymer.

If necessary, the electrolyte or ion exchange membrane 30 may further include an electrically conductive layer to ensure sufficient electrical conductivity, but the present invention is not limited thereto.

The anode electrode 10 undergoes an oxidation reaction of the fuel. Such fuels include hydrogen or hydrocarbon fuels in gas or liquid state as are commonly used in the art. Representative examples of the hydrocarbon fuel include methanol, ethanol, propanol, butanol or natural gas.

If necessary, the fuel cell may further include a fuel supply port 11 to supply fuel to the anode electrode 10. The fuel can be supplied easily by using a known transport means such as a pump.

In the cathode electrode 20, a reduction reaction of an oxidant occurs.

The oxidizing agent according to the present invention uses a different kind of oxidizing agent. Most fuel cells in the related art use a platinum catalyst for the cathode electrode 20 and the anode electrode 10. In particular, since the hydrogen oxidation reaction rate of the anode electrode 10 is relatively faster than the oxygen reduction reaction rate of the cathode electrode 20, a large amount of platinum catalyst is typically used for the cathode electrode 20. However, the present invention can provide a fuel cell having higher efficiency than conventional fuel cells without using a platinum catalyst. To this end, the present invention supplies a predetermined oxidant having a fast reaction rate to the oxidant instead of oxygen having a slow reaction rate.

According to the present invention, as the oxidizing agent used in the reduction reaction of the cathode, a pure substance, a compound of a nonmetallic element selected from the group consisting of N, F, I, S, Cl and Br or an ion of the pure substance or compound is used. In this case, the compound may be at least one selected from hydride, oxide or hydroxide. In addition, the oxide has a general meaning including hypooxide, suboxide, oxide, peroxide, and the like. These can be used individually or in combination of 2 types or more, respectively.

As described above, an oxidant selected from a pure substance, a compound of a nonmetallic element selected from the group consisting of N, F, I, S, Cl, and Br or an ion of the pure substance or a compound has a higher potential than a hydrogen reduction electrode and is reduced. The reaction rate is much faster than oxygen. For this reason, the fuel cell according to the present invention has many advantages over conventional fuel cells using oxygen as an oxidant because the voltage loss is small in the electrochemical reaction. In addition, since most of the oxidizing agents according to the present invention have low activation energy, there is no need to use an expensive noble metal catalyst used in the past. In addition, since the oxidizing agents according to the present invention have a low activity loss, there is an advantage that the activity loss is smaller than that of the conventional oxygen reduction reaction.

If necessary, the fuel cell according to the present invention may include an oxidant supply port 21 to supply an oxidant to the cathode electrode 20. The supply of the oxidant can be easily carried out by applying a known conveying means such as a pump.

In this case, the reactants generated through the reduction reaction in the cathode electrode 20 may be easily oxidized when contacted with oxygen, and thus may be supplied back to the cathode electrode 20. To this end, it is preferable that a transfer line (not shown) is provided to transfer the reactant discharged from the cathode electrode 20 to oxygen and then to the oxidant supply port 21. At this time, the contact with the oxygen may be carried out by connecting a separate oxygen supply line in the transfer line.

According to one embodiment of the present invention, the oxidant may be a compound selected from hydride of nitrogen, oxide of nitrogen, hydroxide of nitrogen, nitrogen hydride in ionic form, nitrogen oxide in ionic form or nitrogen hydroxide in ionic form.

For example, in the case of using nitric acid as the oxidizing agent, nitric acid can obtain a potential of 1.246 V when reduced to nitrogen, and this reaction occurs quickly without using a noble metal catalyst. This reaction can be used to operate the fuel cell. However, a small amount of nitrogen oxides such as NOx may be generated by the reduction reaction. They can be transferred back to the cathode electrode 20 of the fuel cell for use and exhibit more useful properties because they have a larger reduction potential (1.68 V). Through this reaction, hydrogen energy can be converted into electric energy.

The oxidant may be a pure substance or compound selected from chlorine, hydride of chlorine, oxide of chlorine, hydroxide of chlorine, chlorine hydride in ionic form, chlorine oxide in ionic form, and chlorine hydroxide in ionic form.

For example, hydrochloric acid may form chloric acid, perchloric acid, or the like through an oxidation process such as electrolysis. In particular, perchloric acid has a reduction potential of 1.287 V when reduced to chlorine ions. This reaction may be utilized for the cathode electrode 20 of the fuel cell, and may use no catalyst, reduce the amount of catalyst used, or use a noble metal catalyst other than platinum catalyst.

The oxidant may be a compound selected from sulfur hydride, oxide of sulfur, hydroxide of sulfur, sulfur hydride in ionic form, sulfur oxide in ionic form, and sulfur hydroxide in ionic form. In addition, the oxidizing agent may be a compound selected from hydride of bromine, oxide of bromine, hydroxide of bromine, bromine hydride in ionic form, bromine oxide in ionic form, and bromine hydroxide in ionic form. In addition, the oxidizing agent may be a compound selected from hydride of fluorine, oxide of fluorine, hydroxide of fluorine, fluoride hydride in ionic form, fluorine oxide in ionic form, and fluorine hydroxide in ionic form.

Specifically, sulfuric acid, sulfur oxide, and the like have a reduction potential of about 0.3 to 0.45 V when reduced to solid sulfur. Through this reaction, energy can be produced, and sulfur can be reduced and removed to solid sulfur.

As described above, the oxidants according to the present invention have a high reduction potential at the cathode electrode 20 of the fuel cell. Since these oxidants have less activity loss than oxygen reduction, they have high energy conversion efficiency and do not need to use expensive noble metal catalyst because of fast reaction speed.

In particular, in order to apply the fuel cell according to the present invention where a high-density output is required, such as an automobile, it is preferable to use a regeneration system that can oxidize the reduced nonmetallic compound again as an oxidant. For example, NO ₃ ⁻ ions may be reduced to NO ₂ ⁻ ions using a suitable catalyst. The reduced NO ₂ ⁻ ions can be easily oxidized to NO ₃ ⁻ ions in the presence of oxygen, thereby providing a reusable oxidant.

The fuel cell according to the present invention described above can be used by connecting a plurality as needed.

Hereinafter, the present invention will be described through the following examples, but the following examples are only exemplified to aid the understanding of the present invention, and the scope of the present invention is not limited to the following examples.

≪ Comparative Example 1 &

A 5% Nafion solution (NafionTM, manufactured by DuPont) was added to a carbon black (Basf-Pt / Vulcan XC72R) catalyst loaded with 20% platinum so that the weight ratio of the catalyst and Nafion solution was 80:20, and the catalyst 100 30 parts by weight of ultrapure water and isopropyl alcohol were added to prepare a catalyst slurry. This catalyst slurry was applied onto carbon paper (manufactured by Toray Industries, Inc.) so that the Pt / carbon catalyst was 1 mg / cm ² to prepare a cathode electrode.

Subsequently, an anode electrode was manufactured in the same manner as in the preparation of the cathode electrode. This catalyst slurry was applied on carbon paper (manufactured by Toray Industries, Inc.) so as to have a catalyst of 0.5 mg / cm ² to prepare an anode electrode.

The cation exchange membrane Nafion 212 (manufactured by DuPont) was placed between the cathode electrode and the anode electrode prepared above, followed by heat compression for about 3 minutes while applying a pressure of 100 kg / cm ² at a temperature of 120 ° C. Using this, a fuel cell as shown in FIG. 1 was constructed.

Comparative Example 2

After dispersing carbon black in distilled water, cobalt salt and polypyrrole were dissolved. After sufficiently stirring, a reducing agent (sodium borohydride) was added to reduce the metal salt. Through this, a catalyst in which the nitrogen of Co and the pyrrole group was coordinated was prepared. A unit cell was manufactured in the same manner as in Comparative Example 1, except that the cathode was manufactured using the catalyst slurry. At this time, hydrogen and pure oxygen were used to increase the concentration of the reactants, and the unit cell performance was measured at 2 atmospheres.

≪ Example 1 >

A catalyst in which iron was fixed on carbon black was prepared as a catalyst suitable for the electrochemical reduction of nitric acid. Iron nitrate 10 mM and melamine (Melamin) 30 mM in ethylene glycol solvent was supported on carbon black (Vulcan-XC72R). At this time, the weight ratio of iron and carbon black was 10:90. The prepared sample was heat-treated at 700 ° C. for 3 hours in a nitrogen atmosphere to fix iron on carbon black. A cathode electrode was prepared using a catalyst slurry in which iron was fixed to carbon black, and the same procedure as in Comparative Example 1 was carried out.

<Experimental Example>

Hydrogen was supplied at 20 ml / min to the anode electrode of the fuel cell of the embodiment, and nitric acid at a concentration of 5 M was supplied at 1 ml / min to the cathode. At this time, the active area of the unit cell is 2cm ² , the current density was measured at an atmospheric pressure of 80 ℃, the results are shown in Table 1 and Figures 2 and 3.

1.0 V 0.9 V 0.8 V 0.7 V 0.6 V Comparative Example 1
(Pt / C catalyst) 20 20 80 220 445 Comparative Example 2
(Co-PPy catalyst) - - - 20 70 Example 1
Nitrate oxidant 60 250 460 500 520

As shown in Table 1, when comparing Comparative Example 1 using the platinum catalyst and Comparative Example 2 using the non-platinum catalyst instead of the platinum catalyst, the power conversion efficiency of Comparative Example 1 using the platinum catalyst was excellent. You can check it.

However, it can be seen that the present invention can obtain a maximum power density of 520 mW / cm ² at a normal pressure of 80 ° C. using a nitrate reduction reaction without using a catalyst. Compared with the performance of the fuel cell of Comparative Example 1 using the oxygen reduction reaction of the conventional platinum catalyst it can be confirmed that the efficiency of the fuel cell in the high potential region. That is, the fuel cell of Comparative Example 1 using the existing platinum catalyst shows a power density of 445mW / cm ² at 0.6V, but the present invention shows a power density of 460mW / cm ² at 0.8V. Therefore, it can be seen that the present invention can operate at a higher potential when producing the same power, thereby increasing the energy conversion efficiency by about 16 to 20%.

<Experimental Example 2>

A stability test was performed at 80 ° C. for 100 hours while supplying nitric acid at a concentration of 5M to the cathode electrode of the fuel cell, and the results are shown in FIG. 3.

As can be seen in Figure 3 it can be seen that the fuel cell according to the present invention shows a stable cell performance even after a stability test for 100 hours.

1 is a view schematically showing the configuration of a fuel cell according to an embodiment of the present invention.

2 is a unit cell test result measured when 5M nitric acid is used as an oxidant in a cathode of a fuel cell according to the present invention.

3 is a result of measuring stability by leaving the fuel cell according to the present invention at 80 ℃ for 100 hours.

Claims (13)

A fuel cell comprising an anode electrode using an oxidation reaction of hydrogen or a hydrocarbon fuel, a cathode electrode using a reduction reaction of an oxidant, and an electrolyte or ion exchange membrane positioned between the anode electrode and the cathode electrode, The cathode electrode comprises nitric acid as an oxidizing agent, The cathode electrode is a fuel cell, characterized in that made of carbon black fixed iron. delete delete delete delete delete delete delete The fuel cell of claim 1, wherein the ion exchange membrane is a cation exchange membrane. delete The fuel cell of claim 1, wherein the fuel cell includes a fuel supply port for supplying a fuel used for an oxidation reaction to an anode electrode. The fuel cell of claim 1, wherein the fuel cell includes an oxidant supply port for supplying an oxidant used in a reduction reaction to a cathode electrode. The fuel cell of claim 1, wherein the fuel cell comprises a transfer line for oxidizing the reactant at the cathode by contacting with oxygen and then transferring the reactant to an oxidant supply port.

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