CN109935851B

CN109935851B - Flow field for reducing mass transfer polarization of cathode of direct methanol fuel cell

Info

Publication number: CN109935851B
Application number: CN201711370618.7A
Authority: CN
Inventors: 孙海; 张盟; 孙公权
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2017-12-19
Filing date: 2017-12-19
Publication date: 2020-12-15
Anticipated expiration: 2037-12-19
Also published as: CN109935851A

Abstract

The invention provides a bipolar plate flow field, which is provided with an inlet, an outlet and a flow channel, wherein the flow channel is in a multi-unit symmetrical comb shape; each unit is composed of a pair of tooth combs which are mirror-symmetrical and mutually crossed; the flow field can promote axial mass transfer of the electrode, reduce mass transfer polarization of the cathode, improve the performance of the fuel cell, and is easy to process and convenient for large-scale production. Compared with the traditional interdigital flow field, the invention has small resistance and greatly reduces the energy consumption of the fuel cell system. The invention further arranges the branch flow channels under the branch flow channels, namely the two-stage branch flow channels are arranged in a staggered manner, and the length of the channel under the ridge is shorter, so that the air resistance of the flow field is smaller.

Description

Flow field for reducing mass transfer polarization of cathode of direct methanol fuel cell

Technical Field

The present invention belongs to an improved technology of fuel cell device. In particular to a cathode flow field improvement technology of a direct methanol fuel cell.

Background

At present, the bipolar plate structure of the direct methanol fuel cell has a snake shape, an interdigital shape, leaves and the like, wherein the snake-shaped groove has a simple structure, the groove stroke is longer, the great on-way loss causes the pressure drop to be higher, thus great burden is brought to the air pump for cathode air supply, and the longer ridge has great adhesion to water drops, so that the water drops are easy to gather on a diffusion layer under the ridge and are difficult to discharge, and the axial mass transfer effect of the cathode is poor. The traditional interdigital flow field has larger resistance than a snake-shaped flow field, because the inlet and the outlet of the snake-shaped flow field are communicated by a groove, but the interdigital flow field is not communicated by a groove, the gas can be transmitted only through a diffusion layer under a ridge. Therefore, the cathode must be provided with a novel flow field with simple structure, small flow resistance and good drainage.

Disclosure of Invention

The invention aims to provide an interdigital flow field for reducing the mass transfer polarization of a cathode of a direct methanol fuel cell, which can promote the axial mass transfer of an electrode, reduce the mass transfer polarization of the cathode, improve the performance of the fuel cell, is easy to process and is convenient for large-scale production.

The bipolar plate flow field is provided with an inlet, an outlet and a flow channel, wherein the flow channel is in a multi-unit symmetrical comb shape; each unit is composed of a pair of tooth combs which are mirror-symmetrical and mutually crossed; the plurality of cells are arranged in sequence in a direction from the inlet to the outlet.

The number of the units is 4-8.

Each tooth comb is composed of a comb handle and a plurality of comb teeth, and the number of the comb teeth is 2-20.

The depth of the comb teeth is 0.2-2 mm, the width of the comb handle is 0.4-4 mm, and the width of the comb teeth is 0.1-0.4 mm.

The flow passages are spaced by ridges.

The width of the flow channel is equal to the width of the ridge.

The width of the ridge is 0.1-0.4 mm

The invention also provides a preparation method of the bipolar plate flow field, which is characterized in that graphite is used as a raw material to prepare a plate, a groove is carved on the graphite plate by utilizing a carving machine, and the groove forms the tooth comb.

The present invention may also provide a methanol fuel cell comprising any of the bipolar plate flow fields described above.

Advantageous effects

(1) The width of ridge and groove as flow field is 0.1 ~ 0.4 mm's capillary structure, and it plays the effect of capillary, and liquid surface tension, cohesion and adhesive force combined action make the water droplet can creep in the groove, the liquid column height of representation capillary force

Gamma is the surface tension coefficient, theta is the contact angle between the liquid surface and the solid surface, r is the radius of the capillary tube, and theoretically, the smaller r is, the larger the capillary force is. Theoretical calculation shows that when the width of the capillary structure is at least less than 0.4mm, the capillary force has obvious absorption effect on the diffusion layer and good drainage effect, but the width of the capillary structure is not less than 0.1mm, and the air resistance is obviously increased.

(2) Compared with the traditional interdigital flow field, the invention has small resistance and greatly reduces the energy consumption of the fuel cell system. The traditional interdigital flow channel mainly comprises two main flow channels and two branch flow channels, wherein the branch flow channels are arranged in a staggered manner; the invention further arranges the branch flow channels under the branch flow channels, namely the two-stage branch flow channels are arranged in a staggered manner, and the length of the channel under the ridge is shorter, so that the air resistance of the flow field is smaller.

(3) Under the working condition of high current density, mass transfer polarization is easy to occur in a serpentine flow field, as shown in figure 2, but the bipolar plate flow field has better drainage effect under ridges, and is 350-400 mA/cm²Mass transfer polarization still does not appear in the current density interval, and the bipolar plate flow field mass transfer polarization limit current density is higher.

Drawings

Figure 2 of the invention;

FIG. 1 is a graphite plate for a bipolar plate flow field of the present invention;

FIG. 2 is a comparison of the performance of a prior art serpentine flow field and a bipolar plate flow field of the present invention;

in the figure, 1, comb teeth; 2. a comb handle.

Detailed Description

The polar plate takes graphite as raw material, and a groove can be carved on the graphite plate by utilizing a carving machine, as shown in figure 1. The flow field structure is a flow field of a plurality of pairs of tooth comb type structures, the comb teeth of each pair of tooth combs are mutually crossed to form a unit, and each tooth comb type structure consists of comb teeth and a comb handle; in the upstream, gas firstly enters the comb handle and then is dispersed to each comb tooth, but must enter the downstream comb tooth structure through the diffusion layer, and water drops gathered under the spine are swept in the process, so that the purpose of mass transfer enhancement is achieved; in the downstream, the gas-liquid mixed medium is converged to the comb handle by the comb teeth and flows out of the outlet; a plurality of groups of units are required to be arranged, 4-8 units can be arranged, the number of comb tooth structures is 2-20, and the width of a flow field

d＝4×n×m×d，

Wherein n is the comb handle quantity, and m is the broach quantity, and d is the broach width, and the broach width equals with the ridge width.

n is greater than 4, m is greater than 2, the depth of the comb teeth is 0.2-2 mm, the width of the comb handle is 0.4-4 mm, the width of the comb teeth is 0.1-0.4 mm, and the width of the ridge is 0.1-0.4 mm.

Examples

1. The bipolar plate takes graphite as a raw material, and a groove can be carved on the graphite plate by utilizing a carving machine.

2. The flow field structure is a flow field composition of a 4-pair comb type structure, as shown in fig. 1. Each pair of flow field comb teeth (1) with the comb-shaped structure are mutually crossed to form a unit; in the upstream, gas firstly passes through an inlet main channel, then enters a comb handle (2) through a bend, then is dispersed to 3 comb teeth (1), and enters a downstream 3 comb tooth (1) structure through a diffusion layer; in the downstream, the gas-liquid mixed medium is converged to the comb handle (2) by the comb teeth and flows out of the outlet; the depth of the comb teeth can be set to be 0.3mm, the width of the comb handle (2) is 1.2mm, the width of the comb teeth is 0.35mm, and the width of the ridge is 0.35 mm.

Claims

1. The bipolar plate flow field is provided with an inlet, an outlet and a flow passage and is characterized in that,

the flow channel is in a plurality of unit symmetrical comb-shaped shapes;

each unit is independently provided with an inlet and an outlet;

the plurality of units are arranged in sequence in the direction from the inlet to the outlet;

each unit consists of two tooth comb structures, each tooth comb structure consists of a comb handle and a plurality of comb teeth, and the comb teeth of the two tooth comb structures of each unit are oppositely and crossly arranged;

one of the two comb handles of each unit is connected with the inlet, and the other comb handle of each unit is connected with the outlet; fluid enters the plurality of tooth comb units through the plurality of comb handles arranged in parallel at the same time, and directly enters another comb tooth in each unit after being guided between the primary comb teeth, and then enters the other opposite comb handle, and the other comb handle of each unit is communicated with the flow field outlet.

2. The bipolar plate flow field as in claim 1, wherein the number of said cells is 4 to 8.

3. The bipolar plate flow field as in claim 1, wherein the number of said teeth is 2 to 20.

4. The bipolar plate flow field as claimed in claim 1, wherein the depth of the comb teeth is 0.2-2 mm, the width of the comb handle is 0.4-4 mm, and the width of the comb teeth is 0.1-0.4 mm.

5. A bipolar plate flow field as claimed in claim 1, wherein said flow channels are interspersed by ridges.

6. The bipolar plate flow field of claim 5, wherein the flow channels have a width equal to the width of the ridges.

7. The bipolar plate flow field as in claim 5, wherein the ridge has a width of 0.1 to 0.4 mm.

8. The method of making a bipolar plate flow field as in any one of claims 1-7, wherein the plate is made from graphite, and grooves are engraved in the graphite plate by an engraving machine, the grooves forming said comb teeth.

9. A methanol fuel cell comprising the bipolar plate flow field of any one of claims 1-7.