CN109546160B

CN109546160B - Composite bipolar plate for fuel cell and preparation method and application thereof

Info

Publication number: CN109546160B
Application number: CN201811409532.5A
Authority: CN
Inventors: 邵志刚; 吕波; 何良; 覃博文; 苟勇; 高正远
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2018-11-23
Filing date: 2018-11-23
Publication date: 2021-01-05
Anticipated expiration: 2038-11-23
Also published as: CN109546160A

Abstract

The invention belongs to the field of fuel cells, and discloses a preparation method of a composite bipolar plate. The bipolar plate is a carbon-plastic composite plate consisting of polymethyl methacrylate resin, polystyrene resin, hydrogenated ethylene-butylene-styrene triblock copolymer, conductive filler and fiber reinforced material. The composite bipolar plate has good machining performance, excellent conductivity and durability. The bipolar plate can reduce the body resistance and the contact resistance of the bipolar plate and improve the performance of the full battery on the premise of ensuring the assembly of the galvanic pile.

Description

Composite bipolar plate for fuel cell and preparation method and application thereof

Technical Field

The invention belongs to the technical field of fuel cells, and particularly relates to a carbon/polymer-based composite bipolar plate and a preparation method and application thereof.

Background

A Fuel Cell (FC) is an energy conversion device capable of directly converting chemical energy into electrical energy. The power supply has the advantages of high energy conversion efficiency (40-60%), environmental friendliness, high starting speed, long service life and the like, is concerned more and more widely, and is hopefully applied to power supplies of portable power supplies, electric automobiles, unmanned aerial vehicles, underwater vehicles and the like. Currently, the main goals of PEMFC research are to reduce system cost and improve cell performance and stability. However, the high cost of the fuel cell greatly restricts the commercial application of the fuel cell, and the cost of the bipolar plate accounts for 30 to 45 percent of the cost of the fuel cell stack.

The current commercial bipolar plates are mainly non-porous graphite plates and modified metal plates, and the non-porous graphite plates are obtained by mixing graphite and graphitizable resin and performing complex graphitization process treatment. The bipolar plate prepared by the method has low strength, needs the thickness of 3-5mm to keep good mechanical property, and in addition, in order to ensure good air tightness, the graphite plate needs to be impregnated with resin for many times, and the machining process of a flow field is time-consuming, labor-consuming and high in cost. The metal plate is easy to produce in batches, has good mechanical property, but has the characteristics of poor corrosion resistance in an acid medium and large contact resistance with a gas diffusion layer. The carbon-plastic composite bipolar plate has the advantages of wide material source, simple processing technology, low cost, realization of batch production, great reduction of cost, direct compression molding of the flow field and avoidance of expensive machining technology. In addition, the carbon/polymer composite bipolar plate can reach the use standard in most application occasions through component modulation and structure modulation.

Chinese patent publication CN103746131A proposes a method for preparing a composite board by melting soluble resin into an organic solvent and then pouring graphite worms. The bipolar plate prepared by the method can be formed under lower pressure, and has better bending strength and electrical conductivity. However, the secondary mould pressing process is adopted in the experimental process, so that the process complexity in the preparation process is increased, and the production efficiency is reduced. Chinese patent publication No. CN106486683A proposes a preparation method of a magnesium phosphate cement-based composite bipolar plate, and the composite plate prepared by the method has low gas permeability and excellent corrosion resistance. However, the bipolar plate prepared by the process needs a curing time as long as 1 day, has low production efficiency and is not beneficial to reducing the cost of the bipolar plate. Daniel Adams et al (Energy Fuels2017,31, 14320-one-step 14331) adopt a method of adding a carbon felt intermediate transition layer to prepare a composite bipolar plate with a sandwich structure, wherein the composite bipolar plate has high bending strength and electrical conductivity, but the preparation process is relatively complex and the preparation cost is relatively high.

Disclosure of Invention

Therefore, in order to solve the problems of the composite bipolar plate, the invention develops the composite bipolar plate for the fuel cell, which can reduce the cost of the bipolar plate while maintaining the performances of good conductivity, mechanical strength, corrosion resistance and the like.

In order to achieve a higher power density, the fuel cell must effectively reduce the ohmic resistance of the bipolar plate itself and the contact resistance with the diffusion layer. In order to ensure that the bipolar plate is not easy to break and break in the using process, the polymer which plays the role of a binder is usually required to be more than 20%, so that the composite plate has low conductivity, high ohmic resistance and poor full battery performance.

Therefore, the invention aims to provide a preparation method and application of a carbon-based/polymer composite bipolar plate which has higher conductivity, good mechanical property and low cost. The bipolar plate prepared by the method has lower ohmic polarization loss, good mechanical strength and full battery performance. In order to achieve the purpose, the invention adopts the technical scheme that:

the invention provides a carbon-plastic composite bipolar plate, which consists of PMMA resin (polymethyl methacrylate resin), PS resin (polystyrene resin), SEBS resin (hydrogenated ethylene-butylene-styrene triblock copolymer), conductive filler and fiber reinforced material; in the bipolar plate, the mass fraction of PMMA resin is 3-30%, the mass fraction of PS resin is 3-25%, the mass fraction of SEBS resin is 2-8%, the mass fraction of conductive filler is 50-90%, and the mass fraction of fiber reinforced material is 1-15%.

Based on the technical scheme, preferably, the molecular weight of the PMMA resin is 8-12 ten thousand; the molecular weight of the PS resin is 20-45 ten thousand; the SEBS resin contains 15-25% of styrene, and has a melt index of 5-15g/10min at 200 DEG C

Based on the above technical scheme, preferably, the conductive filler is at least one of natural crystalline flake graphite, expanded graphite, acetylene black or graphene.

Based on the technical scheme, preferably, the purity of the natural crystalline flake graphite is 85-99.95%, the particle size is 200-1500 meshes, the particle size of the expanded graphite is 500-3000 meshes, the particle size of the acetylene black is 2-50 nm, the number of layers of graphene is N, and N is more than or equal to 1 and less than or equal to 5.

Based on the technical scheme, preferably, the fiber reinforced material is at least one of carbon fiber, carbon nanotube and glass fiber; the diameter of the carbon fiber or the glass fiber is 1-15 μm, and the length-diameter ratio is 10-50; the diameter of the carbon nano tube is 20-100nm, and the length-diameter ratio is 20-80.

The bipolar plate is prepared by pretreating and uniformly mixing raw materials and adopting a compression molding process.

Based on the above technical solution, preferably, the method for manufacturing a bipolar plate includes the following steps:

(1) the PMMA resin, the PS resin, the SEBS resin, the conductive filler and the fiber reinforced material which are weighed according to the proportion are stirred and mixed at room temperature to obtain a mixed material, the stirring and mixing speed is 20-100r/min, and the stirring and mixing time is 5-45 min. The materials are uniformly dispersed at room temperature, so that the material phase splitting caused by direct heating and melting is avoided;

(2) transferring the mixed material into a mold with a flow field, wherein the prepressing pressure is 40-80MPa,

the molding time is 1-40 min. Residual air in the material is removed by a high-force prepressing mode, so that the material has high bulk density. The compact network structure is formed;

(3) and (3) cooling the mold in the step (2) to room temperature by adopting an air cooling or circulating water cooling or hydraulic oil cooling mode, and releasing pressure and demolding to obtain the bipolar plate. The mode of air cooling or circulating water cooling has low cost, simple operation and no damage to the composite board.

In another aspect, the present invention provides an application of the bipolar plate, wherein the application is as follows: the bipolar plate is applied to proton exchange membrane fuel cells, alkaline anion exchange membrane fuel cells and methanol fuel cells.

Advantageous effects

Compared with the prior art, the invention has the following advantages:

1. the polymethyl methacrylate and polystyrene resin selected by the invention have high mechanical strength, and in addition, the melting points of the polymethyl methacrylate and the polystyrene resin are close, the melt compatibility is good, and the polymethyl methacrylate and the polystyrene resin do not phase separate. The composite board can achieve higher mechanical performance under the condition of lower resin content;

2. the SEBS resin selected by the invention belongs to a thermoplastic elastomer, and can form a good elastic part in PMMA and PS resin melts, so that the defect of high brittleness of high-strength resin is effectively overcome; besides, the SEBS can also reduce the porosity of the composite board and improve the air tightness.

3. The die pressing process designed by the invention has simple equipment requirement, the flow field can be directly formed by die pressing, the composite board with high conductive filler is produced, and the product quality is good.

Drawings

Fig. 1 is a graph of power density versus current density for a composite bipolar plate fabricated in example 1 and comparative examples 1-3 after cell assembly.

Fig. 2 is a contact angle test chart of composite bipolar plates of examples 1-3 of the present invention and comparative example 1.

Detailed Description

The present invention is further illustrated by the following specific examples, but the present invention is not limited to the following examples.

Example 1

0.8kg of PMMA resin (with the molecular weight of 8.5 ten thousand), 0.6kg of PS resin (with the molecular weight of 20 ten thousand), 0.2kg of SEBS resin (with the styrene content of 15 percent and the melt index of 5g/10min at 200 ℃), 9.4kg of graphite powder (with the purity of 99.95 percent and the 400 meshes) and 0.4kg of carbon fiber (with the diameter of 5 mu m and the length-diameter ratio of 20) are respectively weighed and added into a ball mill, the ball milling temperature is room temperature, the ball milling speed is 30r/min, and the ball milling time is 10 min. Then transferring the uniformly mixed materials into a mold with a flow field, wherein the prepressing pressure is 40MPa,

the molding time was 15 min. And finally, cooling the temperature of the die to room temperature by adopting a circulating water cooling mode, releasing the pressure and demoulding to obtain the carbon/polymer composite bipolar plate.

Example 2

0.6kg of PMMA resin (with the molecular weight of 10 ten thousand), 0.8kg of PS resin (with the molecular weight of 20 ten thousand), 0.2kg of SEBS resin (with the styrene content of 10 percent and the melt index of 9g/10min at 200 ℃), 9.6kg of graphite powder (with the purity of 99.95 percent and the 400 meshes) and 0.4kg of carbon fiber (with the diameter of 5 mu m and the length-diameter ratio of 20) are respectively weighed and added into a ball mill, the ball milling temperature is room temperature, the ball milling speed is 50r/min, and the ball milling time is 8 min. Then transferring the uniformly mixed materials into a die with a flow field, wherein the prepressing pressure is 80MPa,

the molding time was 20 min. And finally, cooling the temperature of the die to room temperature by adopting a circulating water cooling mode, releasing the pressure and demoulding to obtain the carbon/polymer composite bipolar plate.

Comparative example 1

Without PMMA: 1.5kg of PS resin (with the molecular weight of 20 ten thousand), 0.4kg of SEBS resin (with the styrene content of 10 percent and the melt index of 9g/10min at 200 ℃), 9.6kg of graphite powder (with the purity of 99.95 percent and the 400 meshes) and 0.2kg of carbon fiber (with the diameter of 5 mu m and the length-diameter ratio of 20) are respectively weighed and added into a ball mill, the ball milling temperature is room temperature, the ball milling speed is 50r/min, and the ball milling time is 8 min. And transferring the uniformly mixed materials into a mold with a flow field, wherein the prepressing pressure is 80MPa, the mold pressing temperature is 280 ℃, the mold pressing pressure is 100MPa, and the mold pressing time is 20 min. And finally, cooling the temperature of the die to room temperature by adopting a circulating water cooling mode, releasing the pressure and demoulding to obtain the carbon/polymer composite bipolar plate.

Comparative example 2

Without the addition of PS: 1.6kg of PMMA resin (with the molecular weight of 10 ten thousand), 0.5kg of SEBS resin (with the styrene content of 15 percent and the melt index of 12g/10min at 200 ℃), 9.4kg of graphite powder (with the purity of 99.95 percent and the 400 meshes) and 0.4kg of carbon fiber (with the diameter of 5 mu m and the length-diameter ratio of 20) are respectively weighed and added into a ball mill, the ball milling temperature is room temperature, the ball milling speed is 50r/min, and the ball milling time is 8 min. And transferring the uniformly mixed materials into a mold with a flow field, wherein the prepressing pressure is 80MPa, the mold pressing temperature is 280 ℃, the mold pressing pressure is 100MPa, and the mold pressing time is 20 min. And finally, cooling the temperature of the die to room temperature by adopting a circulating water cooling mode, releasing the pressure and demoulding to obtain the carbon/polymer composite bipolar plate.

Comparative example 3

Without SEBS: 0.8kg of PMMA resin (with the molecular weight of 10 ten thousand), 0.8kg of PS resin (with the molecular weight of 20 ten thousand), 9.8kg of graphite powder (with the purity of 99.95 percent and the 400 meshes) and 0.4kg of carbon fiber (with the diameter of 5 mu m and the length-diameter ratio of 20) are respectively weighed and added into a ball mill, the ball milling temperature is room temperature, the ball milling speed is 50r/min, and the ball milling time is 8 min. And transferring the uniformly mixed materials into a mold with a flow field, wherein the prepressing pressure is 80MPa, the mold pressing temperature is 280 ℃, the mold pressing pressure is 100MPa, and the mold pressing time is 20 min. And finally, cooling the temperature of the die to room temperature by adopting a circulating water cooling mode, releasing the pressure and demoulding to obtain the carbon/polymer composite bipolar plate.

The following table shows the comparison of physical property parameters of the composite bipolar plates of examples 1-2 of the present invention and comparative examples 1-3, and it can be seen from the table that the bipolar plates prepared according to the present invention have good electrical conductivity, bending strength and low contact resistance.

Referring to fig. 1, which is a graph showing the relationship between the power density and the current density of the assembled battery of the composite bipolar plates prepared in examples 1-2 and comparative examples 1-3, it can be seen that examples 1 and 2 have the best full battery performance, and thus it can be seen that the composite of three resins of PMMA, PS and SEBS has better effect than that of a single resin-based composite plate.

As shown in fig. 2, which is a graph showing the results of the surface contact angle test of the composite bipolar plates prepared in examples 1-2 and comparative examples 1-3, it can be seen that examples 1 and 2 have the highest contact angles, which is advantageous for the rapid drainage of liquid water and water management in fuel cells.

Claims

1. A carbon-plastic composite bipolar plate is characterized in that: the bipolar plate is composed of PMMA resin, PS resin, SEBS resin, conductive filler and fiber reinforced material; in the bipolar plate, the mass fraction of PMMA resin is 3-30%, the mass fraction of PS resin is 3-25%, the mass fraction of SEBS resin is 2-8%, the mass fraction of conductive filler is 50-90%, and the mass fraction of fiber reinforced material is 1-15%; the molecular weight of the PMMA resin is 8-12 ten thousand; the molecular weight of the PS resin is 20-45 ten thousand; the SEBS resin contains 15% -25% of styrene, and the melt index of the SEBS resin at 200 ℃ is 5-15g/10 min.

2. The bipolar plate of claim 1, wherein the conductive filler is at least one of natural flake graphite, expanded graphite, acetylene black, or graphene.

3. A bipolar plate as set forth in claim 1, wherein: the fiber reinforced material is at least one of carbon fiber, carbon nanotube and glass fiber; the diameter of the carbon fiber and the glass fiber is 1-15 μm, and the length-diameter ratio is 10-50; the diameter of the carbon nano tube is 20-100nm, and the length-diameter ratio is 20-80.

4. A bipolar plate as set forth in claim 2, wherein: the purity of the natural crystalline flake graphite is 85% -99.95%, the particle size is 200 meshes-1500 meshes, the particle size of the expanded graphite is 500 meshes-3000 meshes, the particle size of the acetylene black is 2nm-50nm, the number of layers of the graphene is N, and N is more than or equal to 1 and less than or equal to 5.

5. A method of manufacturing a bipolar plate according to any one of claims 1 to 4, wherein: the bipolar plate is prepared by pretreating and uniformly mixing raw materials and then adopting a compression molding process; the uniformly mixing is to stir and mix PMMA resin, PS resin, SEBS resin, conductive filler and fiber reinforced material weighed according to a certain proportion at room temperature to obtain a mixed material, wherein the stirring and mixing speed is 20-100r/min, and the stirring and mixing time is 5-45 min.

6. The method of manufacturing a bipolar plate according to claim 5, wherein: after the raw materials are evenly mixed, the mixture is stirred,

transferring the mixed material into a mold with a flow field, wherein the pre-pressing pressure is 40-80MPa, the mold pressing temperature is 230-;

cooling the mold in the step b) to room temperature by air cooling or circulating water cooling or hydraulic oil cooling

And (4) warming, releasing the pressure and demolding to obtain the bipolar plate.

7. Use of a bipolar plate according to claim 1, wherein: the bipolar plate is applied to proton exchange membrane fuel cells, alkaline anion exchange membrane fuel cells and methanol fuel cells.