KR20040089951A - Electrode of alkaline fuel cell - Google Patents

Abstract

PURPOSE: Provided is an electrode for an alkaline fuel cell, which uses alloys having excellent hydrogen storage characteristics to permit hydrogen storage in the electrode itself, and has improved activity so as to increase initial starting capability and operation quality of a fuel cell. CONSTITUTION: The alkaline fuel cell includes an anode and a cathode, wherein the anode comprises an electrode sheet(11) formed of Ni-based hydrogen storage alloy, and a catalyst layer(12) laminated on one surface of the electrode sheet(11) and forming a metallic bond with the electrode sheet(11) through interfacial contact. Particularly, the electrode sheet(11) comprises base alloy including 0.1-60 wt% of Ti, 0.1-40 wt% of Zr, 0-60 wt% of V, 0.1-0.57 wt% of Ni and 0-56 wt% of Cr, the base alloy being mixed with 0-7.5 wt% of Co, 13-17 wt% of Mn, 0-3.5 wt% of Fe, 0-1.5 wt% of Sn and 0.01-0.003 wt% of B, based on 100 wt% of the total weight of the mixture.

Description

Alkaline fuel cell electrode {Electrode of alkaline fuel cell}

The present invention relates to an electrode material of an alkaline fuel cell, and more particularly, to an Ni-Al, Ni-Pt, Ni-Pd, and Ni-Ir alloy on one surface of an electrode sheet made of a Ni-based alloy having excellent hydrogen storage characteristics. Alkaline-type fuel that has been coated with one of the catalyst materials to impart hydrogen storage capacity to the electrode itself and at the same time increase the activity of the electrode, thereby improving the initial maneuverability of the fuel cell and increasing the operating performance of the fuel cell. It relates to an electrode of a battery.

As the world's population grows and industrializes, a large amount of energy sources are needed, and fossil fuels are expected to be depleted in the near future because most energy sources use fossil raw materials. It is inadequate.

In addition, the fossil fuel, which is the main energy source of today, generates a large amount of harmful substances such as carbon monoxide and dioxin during combustion, which causes problems of global warming and serious environmental pollution.

Therefore, methods to effectively use energy such as wind power, tidal power, and solar power are being researched to solve environmental problems such as global warming and secure clean energy sources that can replace fossil fuels. Fuel cells that convert chemical reactions into electricity have been widely studied as energy sources of automobiles, which are vehicles for transportation.

The fuel cell is a battery that converts chemical energy generated by a chemical reaction of gaseous fuel into electrical energy. The fuel cell is the same as a conventional chemical cell in that it uses an oxidation / reduction reaction, but a chemical reaction is performed in a closed system. Unlike batteries, the reactants are continuously supplied from the outside, which serves as a power generation device in which the reaction products are continuously removed out of the system.

That is, a fuel cell is a means for obtaining electricity by an electrochemical reaction in which oxygen and hydrogen supplied to a cathode and an anode correspond to reverse electrolysis reactions of water, and are a pollution-free energy generator in which heat and water are incidentally generated besides electricity.

Representative of the fuel cell is a hydrogen-oxygen fuel cell used in Gemini and Apollo spacecraft, which is a first generation fuel cell using an alkaline aqueous solution as an electrolyte and using pure hydrogen and oxygen as reactants. In contrast, a high temperature molten carbonate fuel cell that does not use a noble metal catalyst is a second generation, and a solid electrolyte fuel cell capable of generating higher efficiency is called a third generation fuel cell.

Among the various types of fuel cells, the closest practical use is the first generation fuel cell, which is an alkaline fuel cell using a phosphate electrolyte, and most fuel cells mainly include hydrogen gas mainly composed of hydrogen reformed fossil fuel. And oxygen in the air are used as reactants.

In addition, although research and development of PEM fuel cells using acid as an electrolyte have been widely conducted, the fuel cell has low electric conversion efficiency, and the acid is used as an electrolyte. As it is a precious metal, it is not only expensive but also has a disadvantage of generating harmful substances such as carbon monoxide.

In order to make a fuel cell with high energy conversion efficiency and no pollution factor, it is necessary to increase the capacity of the fuel cell and to improve the performance of the fuel cell. The most basic element for improving the performance of the fuel cell is the improvement of the performance of the fuel cell electrode. .

However, the conventional alkaline fuel cell is advantageous in terms of efficiency and cost compared to the PPM fuel cell, but the carbonate generated during the reaction accumulates on the electrode surface using nickel alloy or platinum, thereby degrading the activity of the electrode. As a result, the performance of the fuel cell is reduced as the operating time increases.

In addition, conventionally, as disclosed in US Pat. No. 6,242,260, since the electrode and the catalyst are separated, there is a disadvantage in that the reaction area is small and the activity of the electrode is low.

The present invention was devised to solve all the problems of the electrode of the conventional alkaline fuel cell as described above, by using an alloy having excellent hydrogen storage characteristics directly as an electrode to store hydrogen in the electrode itself, An object of the present invention is to provide an electrode of an alkaline fuel cell having excellent initial starting performance and operating performance by improving the activity of the electrode by combining the catalyst layer with the effective use of hydrogen as a fuel and increasing the reactivity of the electrode.

1 is a perspective view of an embodiment of the present invention electrode.

Figure 2 is a cross-sectional view of one embodiment electrode of the present invention.

3 is a schematic cross-sectional view of a unit cell.

((Explanation of symbols for main part of drawing))

1. Embodiment of the Invention Electrode 11. Electrode Sheet

12. Catalyst layer 31. Anode

32. Electrolytes 33. Cathode

E. Turning

The above object of the present invention is achieved by an electrode sheet made of Ni-based alloy powder having a hydrogen storage capability, and a Ni-based catalyst laminated on one surface of the electrode sheet.

An anode electrode, which is a fuel electrode of an alkaline fuel cell of the present invention, has a laminated structure in which a Ni-based catalyst layer is coated on one surface of an electrode sheet made of the Ni-based alloy powder and integrated by metal bonding at an interface thereof. Unevenness obtained by using a Ni-based alloy having excellent hydrogen storage ability as a sheet forming material to smoothly supply hydrogen as fuel and protruding a plurality of protrusions on the surface of the catalyst layer laminated on one surface of the electrode sheet. The technical feature of the present invention is that the performance of the electrode can be further improved by expanding the reaction area by the surface and increasing the activity.

Ni-based alloy having excellent hydrogen storage ability as a material of the electrode sheet constituting the electrode of the present invention is 0.1 to 60wt% Ti, 0.1 to 40wt% Zr, 0 to 60wt% V, 0.1 to 0.57wt% Ni, 0 to 0 to 7.5 wt% Co, 13 to 17 wt% Mn, 0 to 3.5 wt% Fe, 0 to 1.5 wt% Sn and 0.01 to 0.003 wt% to the base alloy having a composition of 56 wt% Cr so that the total weight ratio is 100 wt% B has a composition to be added, where 0wt% of the composition range may mean that it may not be contained in the alloy, if necessary.

In addition, the catalyst layer material laminated and coated on the surface of the Ni-based alloy electrode sheet constituting the anode, which is the anode, is a Ni-Al alloy composed of 35 to 65 wt% Ni, 35 to 65% Al, and 0 to 1.5 wt% Cr. , 3 to 20 wt% Ni-Pt alloy, 3 to 20 wt% Ni-Pd alloy, and 3 to 20 wt% Ni-Ir alloy are used. Use

In this case, in the case of the Ni-based binary alloy used for the catalyst layer, Pt, Pd, Ir, and Ag, rather than Ni, act as a catalyst, but theoretically, Ni does not matter, but it is used as the Ni alloy as described above. It is for forming metal bond between two interfaces at the interface of catalyst layer. If the content of Ni is less than 3wt%, the interfacial bonding force between electrode and catalyst layer is weak so that durability can be separated or separated, and if it exceeds 20wt%, catalytic metal The absolute amount of is insufficient and the reactivity and activity of the whole electrode is reduced.

Details of the effects and the resulting effects, including the object and technical configuration of the present invention will be clearly understood by the following description with reference to the drawings showing a preferred embodiment of the present invention.

Figure 1 is a perspective view of an embodiment of the present invention electrode, Figure 2 is a cross-sectional view thereof.

As shown, the positive electrode of the present invention includes a thin plate-shaped electrode sheet 11 made of a Ni-based alloy which is a hydrogen storage alloy; Stacked on the upper surface of the electrode sheet 12, a plurality of regular projections (E) is composed of a catalyst layer 12 protruding on the surface.

In this case, although it is not necessary to form protrusions on the surface of the catalyst layer, by forming the protrusions to improve the performance of the electrode, it is more preferable to form the protrusions.

After fabricating the electrode for a fuel electrode according to the present invention having the laminated structure as described above, the performance of the conventional electrode was compared with that of the conventional electrode.

Materials for forming the electrode sheet for the positive electrode is 6.9wt% Ti, 5.1wt% V, 25.7wt% Zr, 38.4wt% Ni, 3.1wt% Cr, 15.7wt% Mn, 0.7wt% Sn, 1.3wt% Co, Ni-based hydrogen storage alloy powder composed of 0.5wt% Al, 2.6wt% Fe and particle size of 2 ~ 8㎛, 61.5wt% Pt-38.5wt% Ni or 5wt% Pd-40wt% Pt- Two kinds of powders, each composed of 55 wt% Ni and having a particle diameter of 10 to 20 μm, were prepared.

After shaping rolling the hydrogen storage alloy powder to make a primary green sheet having a thickness of 0.6 mm and a width of 150 mm, the catalyst layer powder is rolled on one surface of the primary green sheet to form a catalyst layer. Secondary green sheets laminated to have a thickness of 0.2 mm were prepared.

At this time, the roll used for the die-rolling of the catalyst layer powder has a smooth surface and grooves are formed in the protrusion (E) having a bottom diameter (c) of 2 mm, a protrusion period (d) of 3 mm, and a height (e) of 0.35 mm. Four types of catalyst layers were formed by using two types of each of the uneven surface.

As described above, four kinds of secondary green sheets prepared in two surface shapes of the catalyst layers of each composition component were sintered for 60 minutes in a hydrogen atmosphere at 900 ° C., followed by hot rolling at 700 ° C. to increase the porosity of 0.6 mm. The electrode plate was manufactured.

At this time, the diameter of the pores formed in the electrode sheet made of a hydrogen storage alloy was 0.08 ~ 6㎛, the pore size formed in the catalyst layer was 10 ~ 18㎛, the bottom diameter (c) 2mm, which was formed in the catalyst layer of the secondary green sheet, The surface irregularities of the protrusion period (d) 3mm and the height (e) 0.35mm were changed to 1.8mm, 2.5mm and 0.19mm after hot rolling, respectively.

Potentiometer / Galvanostat after preparing a half cell using each electrode to investigate the electrode activity (mass activity) of the porous electrode according to the present invention prepared as described above (Potentiostat / Galvanostat) ) Was connected to a computer to measure the electrode activity, and RHE (Reference Hydrogen Electrode) was used as a reference electrode.

The area where the electrode and the electrolyte contact each other was 1 cm 3, and the rugged capillary of the reference electrode was brought into close contact with the working electrode as close as possible to minimize the inter-liquid contact potential removal and IR enhancement.

In addition, the correction of the IR drop was automatically corrected in the potentiator / galvanostat, the operating temperature of the half cell was 85 ° C. in the electrochemical measurement, and 6N KOH was used as the electrolyte.

As the electrode activity measurement specimens, four kinds of electrode plates (Pt coated nickel alloy, Pd coated nickel alloy, Pt coated nickel alloy with irregularities on the coating part, Pd with irregularities on the coating part) were prepared according to the embodiment of the present invention. Coated nickel alloy) and Raney nickel, which is most often used as a catalyst for hydrogen electrodes, was used as a comparative material.

The results of measuring electrode activity of each specimen are shown in Table 1 below.

division Type of electrode Mass activity (A / g) Comparative material Raney Nickel Catalyst 3.26 Example Hydrogen Storage Alloy + Pt-Ni Alloy Coating + Flat Surface 3.45 Hydrogen Storage Alloy + Pd-Pt-Ni Alloy Coating + Flat Surface 3.59 Hydrogen Storage Alloy + Pt-Ni Alloy Coating + Uneven Surface 3.58 Hydrogen Storage Alloy + Pd-Pt-Ni Alloy Coating + Uneven Surface 3.75

From Table 1, it can be seen that the four types of electrode according to the present invention showed 5.8 to 15.0% higher activity than the electrode manufactured with Raney nickel catalyst as a comparative material in the case of hydrogen electrode activity.

In addition, the electrode having the same composition and surface irregularities in the catalyst layer of the inventive examples appeared 0.13 to 0.16 A / g higher than the surface irregularities in the electrode activity, which is due to the surface irregularities of the catalyst layer. This is because the reaction area was enlarged by widening.

In addition to the battery performance of the alkaline fuel cell using the half-cell, as shown in FIG. 3, a unit having a platinum dispersed carbon (Pt / C) electrode as the anode electrode 31 as the electrode and the comparative material of the present invention, respectively, as shown in FIG. A battery was constructed to measure electrode activity. At this time, a Ni-Ag alloy electrode was used as the anode 33 facing the cathode 31 while the electrolyte 32 was interposed therebetween.

The unit cell is supplied with a humidification gas having a ratio of hydrogen and oxygen of 2: 1, and the pressure of the reaction gas is 5 atm, under conditions of a battery temperature of 80 ° C, a hydrogen electrode temperature of 90 ° C, and an oxygen electrode temperature of 85 ° C. In this case, the performance test results of each unit cell are shown in Table 2 below.

division Type of electrode Mass activity (mA / mg-Pt) Comparative material Platinum dispersed carbon electrode 70 Example Hydrogen Storage Alloy + Pt-Ni Alloy Coating + Flat Surface 145 Hydrogen Storage Alloy + Pd-Pt-Ni Alloy Coating + Flat Surface 172 Hydrogen Storage Alloy + Pt-Ni Alloy Coating + Uneven Surface 167 Hydrogen Storage Alloy + Pd-Pt-Ni Alloy Coating + Uneven Surface 213

It can be seen from Table 2 that the use of the inventive electrodes of the present invention increased the activity 2 to 3 times higher than that of the conventional Pt / C electrode, and the unevenness of the catalyst layer is the case of the unevenness of the catalyst layer among the example electrodes. It was higher than 22 ~ 41mA / mg.

As described above, the electrode of the present invention is believed to be due to the combination of a catalyst material having a catalytic properties with a nickel alloy excellent in hydrogen storage alloy excellent in hydrogen activity to increase the activity of the electrode. In addition, since hydrogen is stored in the electrode itself, the reaction rate of the battery is high when the battery is restarted after being shut down.

As described above, the electrode of the present invention has the advantage that the catalyst is bonded to the surface of the nickel alloy electrode having excellent hydrogen storage ability, thereby improving the activity of the electrode, and can store the hydrogen in the electrode to produce electricity immediately after operation There is this.

Claims (5)

An alkaline fuel cell comprising an anode and a cathode, the anode comprising: an electrode sheet (11) made of a Ni-based hydrogen storage alloy; Alkaline fuel cell electrode, characterized in that consisting of a catalyst layer (12) laminated on one surface of the electrode sheet (11) through a contact interface. The method of claim 1, wherein the electrode sheet 11 is a total of a base alloy having a composition of 0.1 ~ 60wt% Ti, 0.1 ~ 40wt% Zr, 0 ~ 60wt% V, 0.1 ~ 0.57wt% Ni, 0 ~ 56wt% Cr 0 to 7.5 wt% Co, 13 to 17 wt% Mn, 0 to 3.5 wt% Fe, 0 to 1.5 wt% Sn, and 0.01 to 0.003 wt% B are added so that the weight ratio is 100 wt%. Alkaline fuel cell electrode. The catalyst layer 12 of claim 1, wherein the catalyst layer 12 is made of 35-65 wt% Ni, 35-65% Al, and 0-1.5 wt% Cr, 3-20 wt% Ni-Pt alloy, 3 An alkali fuel cell electrode, which is one of a -20 wt% Ni-Pd alloy and a 3-20 wt% Ni-Ir alloy. 2. The alkaline fuel cell electrode as claimed in claim 1, wherein a plurality of protrusions protrude from the surface of the catalyst layer. An alkaline fuel cell comprising an anode and a cathode, wherein the cathode is a 3-20 wt% Ni-Ag alloy.