TWI445238B - Bipolar plate and fuel cell utilizing the same - Google Patents

Description

Bipolar plate and fuel cell

This invention relates to fuel cells, and more particularly to a bipolar plate in a fuel cell and a method of forming same.

Referring to FIG. 1 , a proton exchange membrane fuel cell (hereinafter referred to as PEMFC) is sandwiched between two catalyst layers 13 , a gas diffusion layer 15 , and a bipolar plate 17 by a proton exchange membrane 11 . ), a current collector 18 and an end plate 19 are formed. The two sides of the separation of the proton exchange membrane 11 are divided into an anode (hydrogen or recombinant gas) and a cathode (oxygen or air). The anode undergoes an oxidation reaction, and the cathode undergoes a reduction reaction. When the hydrogen of the anode contacts the catalyst 13 (generally platinum or platinum alloy) adjacent to the proton exchange membrane 11, the hydrogen molecules dissociate into hydrogen ions and electrons, wherein the electrons will Via the bridge connecting the anode and the cathode, and the device 16 connected in series with the bridge, the anode travels from the anode to the cathode, and the hydrogen ions pass directly from the anode through the membrane electrode group 11 to the cathode. It is particularly emphasized that the proton exchange membrane 11 is wet. The thin film allows only hydrogen ions to traverse water molecules, while other gas molecules cannot pass through. Under the action of the catalyst, the electrons and oxygen which are reached by the bridge are combined with oxygen to form oxygen ions, and hydrogen ions which pass through the proton exchange membrane 11 are synthesized to form water molecules, which is an electrochemical oxidation and reduction reaction.

The application of electrochemical reaction makes the PEMFC power generation system have high efficiency, no pollution, fast response, etc., and can increase the current by increasing the bridge voltage or increasing the reaction area of the electrode in series, especially in the continuous flow of hydrogen and oxygen (usually With the supply of air, the demand of the power supply device 16 can be continuously provided. Under such characteristics, PEMFC can be designed as a large-scale power plant, decentralized power and mobile power, in addition to being used as a small system power.

The bipolar plate is an important component in the fuel cell, and its weight accounts for about 80% of the entire battery pack, and the cost also accounts for 40% of the entire battery pack. At present, fuel cell bipolar plates are classified into three types such as high density graphite sheets, composite carbon sheets, and metal sheets. The cost of high density graphite sheets is too high and the pressure is brittle. The composite carbon sheet is light in weight, low in cost, and has excellent corrosion resistance, such as the bipolar plate disclosed in the Republic of China Patent Application No. 094116957. Although the composite carbon board has the above advantages, its mechanical strength and electrical conductivity are still not satisfactory, and the manufacturing process is complicated, which is time consuming and labor intensive. The thickness of the other metal bipolar plate is thinner, which can reduce the volume of the fuel cell, and has the advantages of high mechanical strength and excellent electrical conductivity. A metal wavy bipolar plate as disclosed in the Patent Application No. 01124228.0 of the People's Republic of China. The above-mentioned bipolar plate has a thin thickness, which can greatly reduce the size of the fuel cell. However, during the operation of the fuel cell, the metal bipolar plate is dissolved in metal ions due to acid corrosion resistance due to the high temperature and acidic environment. The above metal ions will hinder the proton proton membrane from conducting protons, resulting in a decrease in performance and service life of the fuel cell. If a bipolar plate is made of an acid-resistant precious metal, there is a problem that the cost is too high to be commercialized. At present, the acid corrosion resistance of metal bipolar plates is improved by plating a layer of metal nitriding which is resistant to acid corrosion and heat resistance. The film is titanium nitride or chromium nitride. However, these films themselves have poor electrical conductivity, and in order to achieve the effect of heat and acid corrosion resistance, it is necessary to have a thickness of several tens of micrometers, resulting in a decrease in the performance of the entire fuel cell stack. In the Republic of China Patent Application No. 094113066, a composite material layer is formed on a metal substrate. The above composite material layer has a large thickness, a complicated manufacturing process, and a high cost. In summary, there is a need for a bipolar plate that is thin in thickness, high in electrical conductivity, simple in production, and resistant to acid and acid corrosion.

The present invention provides a bipolar plate comprising a metal substrate; a metal layer on the metal substrate; a metal carbide layer on the metal layer; and a carbon layer on the metal carbide layer.

The invention also provides a fuel cell comprising a proton exchange membrane sandwiched between two end plates; wherein the proton exchange membrane and the end plate are sequentially a catalyst layer, a gas diffusion layer, the above bipolar plate, and a collector plate .

Fig. 2 is a cross-sectional view showing the structure of a bipolar plate in an embodiment of the present invention. The total thickness of the bipolar plate 17 is between about 1.0 mm and 1.5 mm. If it is larger than 1.5 mm, the fuel cell is too heavy and the cost is increased. If it is less than 1.0 mm, a flow path having a thickness of about 0.8 mm cannot be formed on the surface. The step of forming the bipolar plate 17 is as follows: First, a metal base 171 is provided, which may be made of aluminum, copper, magnesium, stainless steel, or an alloy thereof. Next, a metal layer 173 is formed on the metal substrate. The metal layer 173 has a thickness of between about 50 nm and 200 nm. The thickness of the metal layer 173 needs to take into account the electrical conductivity of the material. Metal materials with good electrical conductivity can have thicker thickness, while metal materials with poor electrical conductivity require thinner thickness. The metal layer 173 can be formed by an evaporation method such as a pulsed cathode vacuum arc method. The metal layer 173 needs to be in good bonding with the carbon and metal substrate 171. In an embodiment of the invention, the metal layer 173 may be titanium, nickel, vanadium, or lead. A metal carbide layer 175 is then formed over the metal layer. The metal carbide layer 175 has a thickness of between about 50 nm and 200 nm and can be formed by an evaporation method such as a pulsed cathode vacuum arc method. The metal carbide layer 175 may be titanium carbide, nickel carbide, vanadium carbide, or lead carbide. The metal carbide layer 175 has a corresponding relationship with the metal layer 173. For example, when the metal layer 173 is made of titanium, the metal carbide layer 175 is titanium carbide; when the metal layer 173 is made of nickel, the metal carbide layer 175 is nickel carbide. And so on. Finally, a carbon layer 177 is formed on the metal carbide layer. The thickness of the carbon layer 177 is between about 50 nm and 200 nm. The formation method can be a high energy ion plasma. The advantage is that a dense film surface can be formed at room temperature, thereby improving the carbon layer 177 and the metal carbide layer 175. Adhesion. The carbon layer 177 formed by the above method is mainly sp ² bonded graphite carbon, and a small part is sp ³ bonded carbon.

The metal layer 173, the metal carbide layer 175, and the carbon layer 177 are all electrically conductive materials, and the conductivity of the bipolar plate 17 is not lowered while taking into consideration the heat resistance and acid corrosion resistance of the bipolar plate 17. Since the metal layer 173 and the metal carbide layer 175 are interposed between the carbon layer 177 and the metal base 171, the problem of low adhesion between the carbon layer 177 and the metal base 171 can be effectively improved. The above-mentioned bipolar plate 17 has a surface roughness of between 200 nm and 300 nm, and its acid corrosion resistance acid current of 3.3×10 ^-7 to 6.3×10 ^-7 at a temperature of 0.5 M sulfuric acid at 70 ° C. A/cm ² and electrical conductivity between 1000 and 1300 S/cm.

In an embodiment of the present invention, the gas and liquid flow paths 31 can be further carved into the surface of the bipolar plate 17 by mechanical processing, as shown in FIG. Both ends of the flow path 31 are a fluid inlet 33 and a fluid outlet 35, respectively. Taking a bipolar plate having a thickness of between 1 mm and 1.5 mm as an example, the depth and width of the flow path are between about 0.5 mm and 1.0 mm, such as 0.8 mm.

The above-described bipolar plate 17 can be applied to the fuel cell shown in Fig. 1. In Fig. 1, the proton exchange membrane 11 is sandwiched between two catalyst layers 13, a gas diffusion layer 15, a bipolar plate 17, a current collector 18, and an end plate 19 of the present invention. Composed of.

The above and other objects, features, and advantages of the present invention will become more apparent and understood.

Example 1

A stainless steel piece (15 mm * 15 mm * 2 mm, size SS316L) was taken, and the flow path was drawn on the surface of the stainless steel piece by mechanical processing. The thickness of the stainless steel sheet is 2 mm, and the corrosion resistance at a temperature of 70 ° C and a concentration of 0.5 MH ₂ SO ₄ is 2.426 × 10 ^-6 A / cm ² ~ 9.145 × 10 ^-6 , and the conductivity is 1300 S. /cm.

Next, a 200 nm titanium metal layer was deposited on a stainless steel sheet by a pulsed cathode vacuum arc method. Next, a 200 nm titanium carbide layer was deposited on the titanium metal layer by a pulsed cathode vacuum arc method. Finally, a 200 nm carbon layer is deposited on the titanium carbide layer by high energy ion plasma to complete the bipolar plate.

The bipolar plate has a good appearance, the thickness of the vapor deposited film is 600 nm, the surface roughness is 100 to 200 nm, and the corrosion resistance at a temperature of 70 ° C and a concentration of 0.5 MH ₂ SO ₄ is 3.3 x 10 ^{-7 .} ~6.3x10 ^-7 A/cm ² and a conductivity of 1202.5 S/cm. Compared with untreated stainless steel sheets, the bipolar plates of the present invention greatly enhance the acid corrosion resistance without sacrificing electrical conductivity.

The present invention has been disclosed in several embodiments, and is not intended to limit the invention, and any one of ordinary skill in the art can make any changes and modifications without departing from the spirit and scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

11‧‧‧Proton exchange membrane

13‧‧‧ catalyst layer

15‧‧‧ gas diffusion layer

16‧‧‧ device

17‧‧‧ bipolar plates

18‧‧‧ Collector board

19‧‧‧End board

171‧‧‧Metal substrate

173‧‧‧metal layer

175‧‧‧Metal carbide layer

177‧‧‧carbon layer

31‧‧‧ flow path

33‧‧‧ fluid inlet

35‧‧‧ fluid outlet

1 is a cross-sectional view of a conventional proton exchange membrane fuel cell; FIG. 2 is a cross-sectional view showing a structure of a bipolar plate in an embodiment of the present invention; and FIG. 3 is an embodiment of the bipolar plate in an embodiment of the present invention. view.

171‧‧‧Metal substrate

173‧‧‧metal layer

175‧‧‧Metal carbide layer

177‧‧‧carbon layer

17‧‧‧ bipolar plates

Claims (9)

A bipolar plate comprising: a metal substrate; a metal layer on the metal substrate; a metal carbide layer on the metal layer; and a carbon layer on the metal carbide layer, wherein the carbon layer A dense film surface comprising sp ² bonded graphite carbon and sp ³ bonded carbon, and the carbon layer is formed by a high energy ion plasma. The bipolar plate of claim 1, wherein the metal substrate comprises copper, aluminum, magnesium, stainless steel, or an alloy thereof. The bipolar plate of claim 1, wherein the metal layer comprises titanium, nickel, vanadium, or lead. The bipolar plate of claim 1, wherein the metal carbide layer comprises titanium carbide, nickel carbide, vanadium carbide, or lead carbide. The thickness of the bipolar plate as described in claim 1 is between 1 mm and 1.5 mm. The bipolar plate according to claim 1, wherein the metal layer, the metal carbide layer, and the carbon layer each have a thickness of between 50 nm and 200 nm. For example, the bipolar plate described in claim 1 further includes a first-class track on the surface of the bipolar plate. The bipolar plate of claim 7, wherein the flow channel has a width and a depth of between 0.5 and 1.0 mm. A fuel cell comprising: a proton exchange membrane sandwiched between two end plates; wherein the proton exchange membrane and the end plate are sequentially a catalyst layer and a gas diffusion layer, as claimed in claim 1 The bipolar plate and a collector plate are described.