KR20020058385A - Fabrication of bipolar plate using semiconductor materials for mini-fuel cells - Google Patents

Abstract

PURPOSE: Provided is a method for manufacturing a bipolar plate which is a component of small fuel cell, using semiconductor material instead of graphite which has been conventionally used. CONSTITUTION: The method comprises growing a thin film of silicon carbide with thickness of 10 nm to 100 micrometer(according to the purpose) on a silicon substrate, using silanes gas(SiH4, SiCl4, and so on), hydrocarbon gas(CH4, C2H4, C3H8, and so on), and organic silane compounds(CH3SiH3, CH3SiCl3, (CH3)6Si2, (CH3)4Si, and so on) as raw material by chemical vapor deposition, plasma chemical vapor deposition, sputtering, and liquid phase methods. In method for etching Si or SiC/Si, dry etching uses gases such as SF6, CF4, NF3, and CCl4, and wet etching uses gases such as KOH, NaOH, and HF.

Description

Fabrication of bipolar plate of small fuel cell using semiconductor material {Fabrication of bipolar plate using semiconductor materials for mini-fuel cells}

An object of the present invention is to develop a technology for manufacturing a bipolar plate, which is a component of a small fuel cell, using semiconductor materials instead of graphite. Photomicrographs and wet (or dry) etching processes are used to form microchannels through which gaseous (or liquid) fuel can flow over the semiconductor materials Si and SiC / Si. After depositing an insulator (SiO ₂ or SiN _x ) thin film on it, metal (Pt, Ru, Pd, Au) is bonded by metal bonding process to be used as a current collector, which is used in fuel cells (PEMFC, DMFC, etc.) Make a bipolar plate.

The present invention has the advantage that it is possible to manufacture a bipolar plate having a smaller volume and weight, excellent mechanical strength, and excellent interfacial bonding properties between an ion conductive membrane (membrane) and bipolar than a fuel cell made of conventional graphite.

Recently, many studies have been conducted on the development of a semi-permanent power source capable of long-term operation on a single charge due to the active development of small portable electronic devices. Since batteries are generally heavy, expensive and have a long lifespan, development of battery replacement power sources using solar energy and hydrogen energy has been actively studied [J. Stephens, Fuel Cells Bulletinsw, No. 12, 6 (1999). Among these alternative power sources, electrochemical devices using hydrogen fuel as an electricity source have been studied for about 30 years, mainly for use as thermal power generation replacement, transportation and field installation power sources. Recently, with the advent of portable electronic products such as mobile phones and laptops, the development of fuel cells with a long lifespan and high energy density has emerged as a concern [J. H. Hirschenbofer, et al. Fuel cell Handbook Fourth Edition, FETL, (1999).

The fuel cell is said to have been invented by Sir William R. Grove of England in the first half of the 19th century, and its principle is to convert the chemical energy (combustion energy) of a fuel directly into electrical energy. Typical cells supply energy through storage systems, but fuel cells serve as a generator. Energy can be used continuously while fuel is being supplied. Reaction equation and general reaction which take place at each electrode are as follows.

Fuel cells are alkaline fuel cells (AFCs), polymer electrolyte membranes (PEMFCs), phosphoric acid fuel cells (PAFCs), and molten carbonate fuel cells, depending on the type of electrolyte and operating temperature. (molten carbonate fuel cell, MCFC), solid oxide fuel cell (SOFC), and direct methanol fuel cell (DMFC) [Karl Kordesch, Simader, Fuel cell and Their Applications, VCH Publishers, Inc. New York, NY, USA, 52 (1996)]. Among them, fuel cells having a low operating temperature and convenient system miniaturization, movement and portability are polymer electrolyte fuel cells and direct methanol fuel cells. A polymer electrolyte fuel cell and a direct methanol fuel cell are composed of a support including a catalyst layer, a positive electrode, a negative electrode, a polymer electrolyte, and a bipolar plate. The part of the component that serves as a fuel passage and the current collector is called a "bipolar plate". The bipolar plate prevents gas mixing and connects electrical circuits between unit cells when stacking unit cells to increase the capacity of the fuel cell. Bipolar plates are classified as either porous or dense without pores. Bipolar plates require low electrical resistance, high mechanical strength and stability against electrolytes. Recently, many studies have been conducted to reduce weight and reduce volume for convenience of carrying and moving. Usually bipolar plate is prepared by mixing an appropriate amount of graphite powder on the thermosetting resin. Such graphite materials have high bipolar plate and angular poles (anode and cathode) and high interface resistance, resulting in voltage drop, low mechanical strength, low conductivity, and high cost. In order to overcome this problem, recently, high conductive carbon fibers and the like are added and manufactured as a binder. Los Alamos National lab. Is developing lightweight high-conductivity bipolar plates by adding reinforcing fibers or "X" or "Y" reinforcements to graphite materials [S. Chalk et al, Fuel Cell for Transportation Program National Laboratory Annual Progress Report, NS DOE Report vol. 2 No. 2, (1999). They studied to improve mechanical and electrical properties by adding reinforcing agents to existing graphite materials. Graphite fiber-reinforced plates are 50 S / cm lower than typical graphite materials with electron conductivity of 104 S / cm, while tensile strength and flexural strength are also 4100 psi higher than 3600 psi and 5300 psi of conventional graphite materials. And 8200 psi. However, it was not effective in reducing the weight and volume of the existing graphite material. Therefore, there is a big problem in manufacturing a fuel cell in a very small size. Therefore, the present invention is to solve the existing problems by using a semiconductor material (Si, SiC, SiC / Si) for the bipolar plate used in the production of small fuel cells (polymer electrolyte fuel cell, direct methanol fuel cell, etc.).

The present invention has been made to solve the above problems, and is a technique for manufacturing a bipolar plate of a small fuel cell (PEMFC, DMFC) using Si, or SiC / Si semiconductor materials. Si and SiC / Si, which are semiconductor materials, are used as blpolar plate materials, and the flow paths of raw materials (gas and liquid) are formed by forming a pattern using a wet or dry etching process on these semiconductor surfaces. A silicon nitride (SiN _x ) or silicon oxide (SiO _x ) thin film, which is an insulator, is formed on the flow path formed in this way, and a metal junction is performed thereon to complete a bipolar plate. A small fuel cell is manufactured using the prepared bipolar plate. When replacing graphite materials used in conventional bipolar plates with semiconductor materials, they are lighter and smaller in volume than graphite, increasing energy density and applying to small fuel cells. In addition, the corrosion resistance and mechanical strength is strong, it is possible to easily form a gas flow path through the wet etching and dry etching process compared to the conventional mechanical etching.

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The present invention provides a) bipolar plate material using Si and SiC / Si semiconductors, b) silicon carbide (SiC) thin film formation on the silicon surface, and c) photo process and wet (or dry) these semiconductor surfaces. (D) forming a flow path of a gas (or liquid) raw material using an etching process; d) forming a silicon insulator (SiN _x or SiO _x ) on the surface of the semiconductor; e) forming a metal junction on the substrate on which the flow path is formed; F) It consists of a technology for manufacturing fuel cells using bipolar plates made of these semiconductor materials.

Hereinafter, each technology will be described in detail with reference to examples of the present invention.

Example 1 Technique for Forming Silicon Carbide Thin Film on Silicon Substrate

As shown in FIG. 1, the substrate was cut to a size of 15 × 15 mm 2 to grow a SiC thin film on a silicon substrate. In order to remove impurities such as organic matter and natural oxide film that may exist on the surface of Si, and then ultrasonically washed with acetone for 3 minutes, and then treated with 5% diluted HF aqueous solution for 3 minutes and dried with N ₂ gas. After this pretreatment, the substrate was placed in a reactor, depressurized for 30 minutes, and purged with hydrogen gas for 10 minutes to completely remove residual gas in the reactor. In order to remove the oxide film which may occur during mounting, the temperature was raised to 1100 ° C. in a hydrogen atmosphere to maintain hydrogen etching for 5 minutes, and then cooled to room temperature. In order to grow SiC on the cooled Si substrate, the temperature was raised at a rate of 25 ° C./sec, and then, TMS (tetramethylsilane, (CH ₃ ) ₄ Si), which was a feed gas, was supplied to grow SiC having a thickness of 100 μm.

[Example 2] A technique for forming a flow path of raw materials (gas and liquid) using a wet (or dry) etching process on the surface of Si and SiC / Si semiconductors

In order to form the raw material flow path on the surface of Si, SiC, and SiC / Si semiconductors for the use of semiconductor materials in bipolar plates, photolithography process is performed as follows. As shown in FIGS. 2 and 3, the photoresist (P / R) is uniformly coated on the semiconductor surface, and the stripe line is etched on the P / R using a standard exposure process ([FIG. 4]. ] And [FIG. 5]). The line width is 500 μm, the line width is 300 μm, and the depth is 200 μm. The line width formed on the P / R is transferred to the surface of the semiconductor in the same size to perform an etching process to make a flow path. In this case, there are two methods of etching, wet etching and dry etching. Dry etching is etched using SF ₆ gas, wet etching is etched using a chemical etching solution of KOH. The photoresist remaining on the surface of the etched semiconductor is completely removed using an organic solvent or asher [Fig. And a semiconductor (Si, SiC / Si) substrate having a flow path as shown in FIG. 7.

Example 3 Technology of Forming Insulator Silicon Nitride or Silicon Oxide on Semiconductor Surface

An insulator (SiO _x or SiN _x ) thin film is grown on the semiconductor surface where the flow path is formed by etching using a chemical vapor deposition method at 1000 Å thickness as shown in FIGS. 8 and 9. The Si substrate was soaked in acetone for 5 minutes and ultrasonically immersed in dilute HF aqueous solution for 5 minutes and dried with N ₂ gas. To remove the native oxide film generated during the transfer to the reactor while the H ₂ flow to a 1000 sccm H ₂ etching for 5 minutes at 1000 ℃. In the case of nitriding treatment, NH ₃ and H ₂ gas were used, and in the case of oxidation treatment, each insulator thin film was grown at 1050 ° C. using O ₂ gas.

Example 4 Metal Bonding Technology

SiO ₂ (or SiN _x ) / Si, SiO ₂ (or SiN _x ) / SiC, SiO ₂ (or SiN _x ) / SiC / Si, SiC / SiO ₂ (or SiN _x ) / Si on the substrate [FIG. 10] As described above, the metals are bonded to form a current collector using chemical vapor deposition. The metal used at this time is Pt, Ru, Au, Pd, etc., the heat treatment temperature is 1050 ℃, the heat treatment time is 1 hour.

Example 5 Fabrication Technology with Fuel Cell

A fuel cell is fabricated by using a semiconductor material bonded with metal as a bipolar plate of anode and cathode and using Nafion as a membrane. Such a fuel cell can be manufactured in a very small size because it can reduce the volume and weight compared to the conventional graphite, and because of the high electronic conductivity by bonding a metal can solve the problem of the bipolar used in the conventional fuel cell.

Example 6 Comparative Example

After fabricating a fuel cell using commercially available graphite material as a bipolar plate, the characteristics of the fuel cell using the semiconductor material fabricated in this experiment were compared. Compared to the bipolar plate using graphite material, the electron conductivity increased from 104 S / cm to 1000 S / cm when the semiconductor material was used as the bipolar plate, and the tensile strength was 3.0 × 10 ⁶ lb / in ² of the existing graphite material. compared to the case of Si in the case of a little low ^{1.1 × 10 6 lb / in 2} , SiC has shown the same ^{3.0 × 10 6 lb / in 2} psi and a graphite material. In particular, the thickness of the bipolar plate has been reduced from 1.5 cm to <1 mm, making it possible to manufacture small fuel cells.

As described above, according to the present invention, if the semiconductor material used for the bipolar plate, which is a component of the conventional fuel cell, is used, the bulk and weight can be reduced, thereby making it possible to manufacture a micro fuel cell. In addition, by using Si and SiC / Si semiconductor as bipolar plate material, it has excellent corrosion resistance and mechanical strength, and has the advantage of reducing manufacturing cost by having opportunity of mass production by using semiconductor etching process, photo process, and metal bonding process. .

Claims (5)

Technology to manufacture bipolar plate using Si and SiC / Si semiconductor and use it for manufacturing fuel cell According to claim 1, a silane gas (SiH ₄ , SiCl _4, etc.) and a hydrocarbon gas (CH ₄ , C ₂ H ₄ , C ₃ H _8, etc.) are added to a silicon substrate as a raw material and an organosilane compound (CH ₃ SiH ₃ , CH ₃ SiCl ₃ , (CH ₃ ) ₆ Si ₂ , (CH ₃ ) ₄ Si, etc.) to the silicon carbide thin film using According to the technology to grow to a thickness of 10 nm ~ 100 ㎛. The method for etching Si or SiC / Si according to claim 1, wherein dry etching is performed using gases such as SF ₆ , CF ₄ , NF ₃ , CCl ₄ , and wet etching using chemical etching solutions such as KOH, NaOH, HF, etc. Technology to use. Silicon oxide and silicon nitride thin films in the temperature range of 100 ℃ to 1300 ℃ by using chemical vapor deposition, molecular beam deposition, plasma chemical vapor deposition, or sputtering method on the etched Si or SiC / Si thin film in a thickness of 1 ~ 10000 00 Technology to grow. The technique of joining Pt, Pd, Au, and Ru according to claim 1 using a chemical vapor deposition method, a molecular beam deposition method, a plasma chemical vapor deposition method, or a sputtering method for a heat treatment temperature of 20 to 1300 ° C. and a heat treatment time of 0 to 2 hours.