CN102856567A - Gas diffusion layer for unitized regenerative fuel cell, and its preparation method - Google Patents

Abstract

The invention provides a gas diffusion layer for unitized regenerative fuel cell, and its preparation method. The gas diffusion layer comprises nonconductive organic synthetic fiber cloth as a support body, and conductive corrosion-resistance metal/metal oxide network formed on the support body and filled in the pores of the organic fibers. The gas diffusion layer further comprises a hydrophobic agent and a binder for achieving proper hydrophilic-hydrophobic property and good pore structure, so as to ensure mass transfer balance of the URFC in different work modes. The invention solves the corrosion problem of existing URFC support body, increases gravimetric specific power, and lowers electrode cost.

Description

Integrated renewable fuel cell gas diffusion layer and preparation method thereof

technical field

The invention relates to a fuel cell key material and a preparation method thereof, in particular to an integrated renewable fuel cell gas diffusion layer and a preparation method thereof.

Background technique

A regenerative fuel cell (RFC) is an energy storage system. In water electrolysis mode, water is electrolyzed into hydrogen and oxygen under the action of an external power supply; in fuel cell mode, hydrogen and oxygen are generated by The electrochemical reaction generates water and releases electrical energy at the same time, that is, the RFC energy storage system is composed of two components: a fuel cell (FC for short) and a water electrolyzer (WE for short). According to different combinations, RFC can be divided into separate type, integrated type and integrated type (Unitized Regenerative Fuel Cell, referred to as URFC).

URFC combines water electrolysis technology (electrical energy + 2H ₂ O-2H ₂ +O ₂ ) with fuel cell technology (2H ₂ +O ₂ -H ₂ O+electrical energy), and realizes two working modes on the same component through a bifunctional catalyst When performing the function of fuel cell, URFC realizes the recombination of hydrogen and oxygen and outputs electric energy; when performing the function of water electrolysis, URFC electrolyzes water into hydrogen and oxygen under the condition of external electric energy to achieve the purpose of energy storage.

Membrane electrode is the core component of URFC, and the porous gas diffusion layer is a crucial part of URFC membrane electrode. For the diffusion layer in the URFC membrane electrode, suitable hydrophilic and hydrophobic properties are required to ensure the mass transfer balance in different working modes. At the same time, in the water electrolysis working mode, the active oxygen species will seriously corrode the material at a higher anode potential. It has high electrochemical and chemical stability, that is, it must meet the requirements of corrosion resistance.

Traditional fuel cells use carbon paper or carbon cloth as the diffusion layer material, but the carbon material diffusion layer cannot be directly used in URFC, because the anodic oxidation reaction of carbon material will occur when URFC performs water electrolysis operation:

C+H ₂ O=CO ₂ +4H ⁺ +4e ^-

E ⁰ =0.118V vs. SHE at 25℃

Traditional diffusion layer supports (such as: carbon paper, carbon cloth, metal foam, metal woven/stretched mesh, metal fiber, etc.), in the working environment of URFC, have defects such as easy corrosion, high resistance, and high price. . Requirements for support materials in URFC working environment: 1. Stable at high potential; 2. Oxidation and corrosion resistance under acidic conditions; 3. Excellent strength and toughness; 4. Low price. At present, there are few reports on the diffusion layer of URFC, basically following the idea of membrane electrode diffusion layer of proton exchange membrane water electrolysis cell, mostly made of titanium material after hydrophobic treatment. For example, the sintered titanium plate, titanium mesh and other titanium material substrates are impregnated with PTFE to achieve hydrophobicity as the diffusion layer of URFC. However, titanium metal will form a surface oxide film with very low conductivity in the state of oxygen evolution. With the progress of water electrolysis, the oxide film on the surface of the titanium diffusion layer will gradually thicken, resulting in a gradual decrease in conductivity. If it works for a long time, the electrolytic cell The internal resistance will gradually increase. Although it can be solved by electroplating or electroless Pt plating on the surface, it greatly increases the manufacturing cost of URFC, and the weight of the battery is relatively large, which weakens the advantage of high mass specific energy of URFC.

Some organic fibers have the advantages of low price, light and soft material, acid and alkali corrosion resistance, aging resistance, stability at high potential, and easy construction of a suitable pore structure on the surface of the material. However, there is a problem that the material itself is an insulating material and does not conduct electricity. If the conductivity can be solved, it will greatly solve the corrosion problem of the URFC support, increase the weight specific power, reduce the electrode cost, and make URFC one step closer to practicality.

Contents of the invention

The purpose of the present invention is to provide an integrated renewable fuel cell gas diffusion layer and its preparation method.

In order to achieve the above purpose, the technical solution adopted by this party is as follows:

The integrated renewable fuel cell gas diffusion layer includes an organic fiber cloth support body; the upper and lower surfaces of the organic fiber cloth support body are coated with a mixed material layer composed of a conductive corrosion-resistant leveling material and a hydrophobic binder material.

The material of the organic fiber cloth is polyester fiber, polyolefin fiber, polyamide fiber, polyacrylonitrile fiber or polyvinyl alcohol fiber; the porosity of the organic fiber cloth is 30-90%, and the thickness is 50-90%. 500 microns.

Polyester fibers such as PET, PBT, polyolefin fibers such as PP, PE, polyamide fibers such as PA, polyacrylonitrile fibers PAN, polyvinyl alcohol fibers PVA, etc.

The mass ratio of the conductive corrosion-resistant leveling material to the hydrophobic binder material is (1-10):1, and the loading capacity of the corrosion-resistant leveling material on the organic fiber cloth is 3-8 mg/cm ² .

The conductive and corrosion-resistant leveling material is a corrosion-resistant metal material Pt, Ir or Ti, or an oxide, carbide or nitride of W, Mo, Ir or Ti;

Or use the above materials as a carrier to support an oxygen evolution catalyst, and the oxygen evolution catalyst is a mixture of oxides, carbides or nitrides of noble metals Pt, Pd, Au, Ru, Rh, Ir, or a mixture of noble metals Pt, Pd, Mixture or alloy of Au, Ru, Rh, Ir and transition metal elements Os, Ta, W, Ni.

The hydrophobic binder is polyvinylidene fluoride or polyvinylidene fluoride.

The preparation method of the above-mentioned integrated renewable fuel cell gas diffusion layer is as follows:

(1) Pretreatment of the support body

Soak the organic fiber cloth in deionized water, after ultrasonic vibration, let it stand, filter, and dry it for use;

(2) Preparation of conductive microporous layer:

1) Blend the hydrophobic binder and the organic solvent in a mass ratio (1-10): 100, stir at 20-80°C until completely dissolved to form solution A;

2) Add corrosion-resistant leveling material to solution A and stir for 10-60 minutes to make a hydrophobic conductive coating, wherein the mass ratio of corrosion-resistant leveling material to hydrophobic binder is (1-10):1;

3) Apply the hydrophobic conductive paint evenly to the surface of both sides of the organic fiber cloth, and make it penetrate into the fiber body under pressure, and repeat the coating after drying until the loading capacity of the corrosion-resistant leveling material reaches 3 -8 mg/cm ² .

The organic solvent is acetone or N,N dimethylformamide.

In order to investigate the performance of the URFC diffusion layer, it was made into a URFC membrane electrode, the method is as follows:

1. Preparation of catalytic membrane (CCM, catalyst coated membrane)

The oxygen evolution catalyst is supported on the oxygen reduction catalyst or the oxygen evolution catalyst and the oxygen reduction catalyst are mechanically mixed to obtain a double-effect oxygen electrode catalyst, and the double-effect oxygen electrode catalyst is mixed with a hydrophilic binder, and the double-effect electrocatalyst: hydrophilic adhesive The binding agent is (10-90%): (10-90%), and the mixture is prepared on the polymer electrolyte membrane (such as perfluorosulfonic acid membrane) by known methods such as spraying, printing or turning pressure, to obtain double-effect Oxygen electrode catalytic membrane.

2. Preparation of MEA

The double-effect oxygen electrode catalytic membrane, the diffusion layer and the traditional hydrogen electrode are hot-pressed together to obtain an integrated renewable fuel cell membrane electrode. The hot-pressing temperature is 120°C-180°C and the pressure is 0.01-10MPa.

Starting from the idea of preparing the fuel cell diffusion layer, the present invention adopts non-conductive organic synthetic fibers as the base of the diffusion layer, constructs a conductive corrosion-resistant metal/metal oxide network on it, fills the pores of the organic fibers, and combines A certain hydrophobic binder can make the diffusion layer achieve suitable hydrophilic and hydrophobic properties and a suitable pore structure, so as to ensure the mass transfer balance of URFC in different working modes.

The beneficial effects of the present invention are:

1. The diffusion layer prepared by the present invention solves the high potential corrosion problem of traditional electrode support materials by adopting non-conductive organic synthetic fibers as the substrate of the diffusion layer;

2. The diffusion layer prepared by the present invention has suitable hydrophilic and hydrophobic properties and a suitable pore structure, which can ensure the mass transfer balance of URFC under different working modes;

3. The diffusion layer prepared by the present invention has the characteristics of low price, light material and strong flexibility, which improves the weight specific power of URFC, reduces the cost of electrodes, and makes URFC one step closer to practicality.

Description of drawings

The microscope pictures of different supports of Fig. 1;

Fig. 2 I-V curves of URFC electrodes prepared on different supports.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Example 1

1) Hydrophobic treatment of the substrate

Cut out 2×2.5cm ² carbon paper, soak it in 1wt% PTFE emulsion multiple times for hydrophobization treatment, and then bake it at 360°C for 1 hour to obtain the hydrophobization treatment carbon paper;

2) Add ethanol to the 50mg IrO2/Ti leveling material, add 200mg20wt% PTFE emulsion after mixing evenly, obtain leveling layer slurry after mixing evenly, apply the slurry evenly on the carbon paper after hydrophobization treatment, and then Calcined at 360° C. for 1 hour to obtain a hydrophobic diffusion layer supported by carbon paper.

Example 2

1) Hydrophobic treatment of the substrate

Cut out 2×2.5cm ² titanium fiber mesh, dip it in 1wt% PTFE (polytetrafluoroethylene) emulsion for several times to carry out hydrophobic treatment, and then bake it at 360°C for 1 hour to make it hydrophobic;

2) Add ethanol to the 50mg IrO2/Ti leveling material, add 200mg20wt% PTFE emulsion after mixing evenly, obtain leveling layer slurry after mixing evenly, apply the slurry evenly on the carbon paper after hydrophobization treatment, and then Calcined at 360° C. for 1 hour to obtain a hydrophobic diffusion layer supported by carbon paper.

Example 3

Select polyethylene terephthalate synthetic fiber cloth (PET) as the support of the diffusion layer, and the preparation method of the diffusion layer is as follows:

1) Pretreatment of the support body:

Soak a 2×2.5cm ² organic fiber cloth in deionized water and oscillate ultrasonically for 30 minutes to remove surface impurities.

2) Preparation of conductive microporous layer:

a. Take a certain amount of PVDF resin, add organic solvent DMF, and make a 7% solution;

b. Put the PVDF solution in a constant temperature water bath at 60°C, and stir continuously for 30 minutes until the PVDF is completely dissolved, and place it for defoaming for later use;

c. Add the conductive cross-linking material IrO2/Ti into the PVDF solution, the ratio of IrO2/Ti to PVDF is 3:1, put it on the stirrer and stir for 30min to make a paste hydrophobic conductive coating;

d. On the 80°C heating plate, fix the organic fiber cloth as the support body, apply the hydrophobic conductive coating agent evenly on the fiber, and at the same time ensure that part of the hydrophobic conductive coating penetrates to the other side of the fiber;

e. After drying in an oven at 130°C, turn the support fiber 180°, and repeat step d;

f. Coating the conductive leveling material on the front and back sides several times, when the loading capacity of the leveling material reaches 3-8mg/cm ² , bake it at 200°C for 4 hours.

In order to investigate the performance of the diffusion layer of Examples 1, 2, and 3, they were respectively made into URFC membrane electrodes, and the method was as follows:

1. Preparation of catalytic membrane (CCM, catalyst coated membrane)

Mix Pt black and _IrO2 mechanically to obtain a double-effect oxygen electrode catalyst, mix the double-effect oxygen electrode catalyst with a hydrophilic binder, the double-effect oxygen electrode catalyst:hydrophilic binder ratio is 7:3, and use spraying, printing or The mixture is prepared on a polymer electrolyte membrane (such as a perfluorosulfonic acid membrane) by known methods such as rotating pressure, that is, a double-effect oxygen electrode catalytic membrane is obtained.

2. Preparation of MEA

The double-effect oxygen electrode catalytic membrane is hot-pressed together with the diffusion layer and the traditional hydrogen electrode to obtain an integrated renewable fuel cell membrane electrode. The hot pressing temperature is 140°C, and the pressure is 8kg/cm ² .

It can be seen from Figure 1 that the three materials have similar fiber structures and appropriate porosity, which facilitates us to better control the porosity and pore distribution when preparing the microporous layer;

The polarization curve test result of Fig. 2 shows: take non-conductive organic fiber as the diffusion layer of support body, has reached the consistent performance of carbon paper and metal fiber, illustrates that the preparation method of the diffusion layer of conductive modification of the present invention is successful .

Claims (7)

1. An integrated renewable fuel cell gas diffusion layer, characterized in that: the diffusion layer includes an organic fiber cloth support body; the upper and lower surfaces of the organic fiber cloth support body are coated with conductive corrosion-resistant leveling materials and hydrophobic bonding materials. A mixed material layer composed of agent materials. 2. The gas diffusion layer according to claim 1, characterized in that: the material of the organic fiber cloth is polyester-like fiber, polyolefin fiber, polyamide fiber, polyacrylonitrile fiber or polyvinyl alcohol fiber; The porosity of the organic fiber cloth is 30-90%, and the thickness is 50-500 microns. 3. The gas diffusion layer according to claim 1, characterized in that: the mass ratio of the conductive corrosion-resistant leveling material and the hydrophobic binder material is (1-10): 1, and the corrosion-resistant leveling material is formed on an organic fiber cloth The loading amount on is 3-8 mg/cm ² . 4. The gas diffusion layer according to claim 1 or 3, characterized in that: the conductive and corrosion-resistant leveling material is a corrosion-resistant metal material Pt, Ir or Ti, or an oxide of W, Mo, Ir or Ti compounds, carbides or nitrides; Or use the above materials as a carrier to support an oxygen evolution catalyst, and the oxygen evolution catalyst is a mixture of oxides, carbides or nitrides of noble metals Pt, Pd, Au, Ru, Rh, Ir, or a mixture of noble metals Pt, Pd, Mixture or alloy of Au, Ru, Rh, Ir and transition metal elements Os, Ta, W, Ni. 5. The gas diffusion layer according to claim 1, characterized in that: said hydrophobic binder is polyvinylidene fluoride or polyvinylidene fluoride. 6. A preparation method of the gas diffusion layer according to claim 1, characterized in that: it is prepared according to the following process, (1) Pretreatment of the support body Soak the organic fiber cloth in deionized water, after ultrasonic vibration, let it stand, filter, and dry it for use; (2) Preparation of conductive microporous layer: 1) Blend the hydrophobic binder and the organic solvent in a mass ratio (1-10): 100, stir at 20-80°C until completely dissolved to form solution A; 2) Add corrosion-resistant leveling material to solution A and stir for 10-60 minutes to make a hydrophobic conductive coating, wherein the mass ratio of corrosion-resistant leveling material to hydrophobic binder is (1-10):1; 3) Apply the hydrophobic conductive paint evenly to the surface of both sides of the organic fiber cloth, and make it penetrate into the fiber body under pressure, and repeat the coating after drying until the loading capacity of the corrosion-resistant leveling material reaches 3 -8 mg/cm ² . 7. The method for preparing a gas diffusion layer according to claim 6, characterized in that: the organic solvent is acetone or N,N dimethylformamide.

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