Gas Diffusion Substrate

• US 20080268297A1
• Filed: 06/15/2005
• Published: 10/30/2008
• Est. Priority Date: 06/15/2004
• Status: Active Grant

• Current Assignee: Technical Fibre Products Limited
• Original Assignee: Johnson Matthey PLC, Technical Fibre Products Limited
• Inventors: Rowe, Julia Margaret, Sharman, Jonathan David Brereton, Siodlak, Julian Andrew, Walker, Nigel Julian, Quayle, George Thomas
• Granted Patent: US 8,133,306 B2
• Time in Patent Office: Days
• US Class Current: 429/12
• CPC Class Codes: H01M 4/8605 Porous electrodes
• CPC Class Codes: H01M 4/8642 Gradient in composition
• CPC Class Codes: H01M 8/0234 Carbonaceous material
• CPC Class Codes: H01M 8/0243 in the form of mixtures
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

A gas diffusion substrate includes a non-woven network of carbon fibres, the carbon fibres are graphitised but the non-woven network has not been subjected to a graphitisation process. A mixture of graphitic particles and hydrophobic polymer is disposed within the network. The longest dimension of at least 90% of the graphitic particles is less than 100 μm. A process for manufacturing gas diffusion substrates includes depositing a slurry of graphitised carbon fibres onto a porous bed forming a wet fibre network, preparing a suspension of graphitic particles and hydrophobic polymer, applying onto, and pulling the suspension into, the network, and drying and firing the network. Another process includes mixing a first slurry of graphitic particles and hydrophobic polymer with a second slurry of graphitised carbon fibres and liquid forming a third slurry, depositing the third slurry onto a porous bed forming a fibre-containing layer, and drying and firing the layer.

Claims

1. A gas diffusion substrate comprising

a non-woven network of carbon fibres wherein the carbon fibres are graphitised but the non-woven network has not been subjected to a graphitisation process;

and

a mixture of graphitic particles and hydrophobic polymer disposed within the network, wherein the longest dimension of at least 90% of the graphitic particles is less than 100 μ

m.

2. A gas diffusion substrate according to claim 1, wherein the non-woven network has a grammage of between 10-50 g/m².

3. A gas diffusion substrate according to claim 1, wherein the longest dimension of at least 90% of the graphitic particles is between 20 and 0.1 μ

m.

4. A gas diffusion substrate according to claim 1, wherein the graphitic particles are small enough to be held in colloidal suspension.

5. A gas diffusion substrate according to claim 1, wherein the weight ratio of graphitic particles to hydrophobic polymer is between 50:

1 and 2;

1.

6. A gas diffusion substrate according to claim 1, wherein the weight ratio of graphitic particles to carbon fibres is between 1:

2 and 10;

1.

7. A gas diffusion substrate according to claim 1, wherein the substrate has a gradient in the concentration of the graphitic particles and hydrophobic polymer across the thickness of the non-woven network.

8. A gas diffusion substrate according to claim 1, wherein the graphitic particles and hydrophobic polymer are homogeneously disposed within the fibre network.

9. A gas diffusion substrate according to claim 1, comprising a carbonised phenolic resin binder.

10. A gas diffusion substrate according to claim 1, wherein a base layer of carbon black and hydrophobic polymer is present on at least one face of the substrate

11. A gas diffusion electrode comprising a gas diffusion substrate according to claim 1 and an electrocatalyst layer.

12. A gas diffusion electrode according to claim 11 wherein the substrate has a gradient in the concentration of the graphitic particles and hydrophobic polymer across the thickness of the non-woven network, wherein the electrocatalyst layer is adjacent to the face of the gas diffusion substrate and wherein there is a higher concentration of graphitic particles and hydrophobic polymer.

13. A membrane electrode assembly comprising a gas diffusion substrate according to claim 1.

14. A membrane electrode assembly comprising a gas diffusion electrode according to claim 11.

15. A process for preparing a gas diffusion comprising the steps of:

a) depositing a slurry of graphitised carbon fibres onto a porous bed to form a wet fibre network;

b) preparing a suspension of graphitic particles and hydrophobic polymer, wherein the longest dimension of at least 90% of the graphitic particles is less than 100 μ

m;

c) applying the suspension onto the wet fibre network;

d) pulling the suspension into the wet fibre network; and

e) drying and firing the wet fibre network at a temperature that does not exceed 1000°

C.

16. A process according to claim 15, wherein in step (d) the suspension is pulled into the wet fibre network using a suction system.

17. A process according to claim 16, wherein the suspension is applied to one face of the wet fibre network only, and the suction is applied to the other face of the wet fibre network.

19. A process for preparing a gas diffusion substrate according to claim 15, comprising a further step of applying a layer comprising carbon black and a hydrophobic polymer to at least one face of the fibre-containing layer.

20. A process for producing a gas diffusion electrode wherein a gas diffusion substrate is produced by a process according to claim 15 and an electrocatalyst layer is deposited onto the gas diffusion substrate.

18. A process for preparing a gas diffusion substrate comprising the steps of:

a) mixing graphitic particles, wherein the longest dimension of at least 90% of the graphitic particles is less than 100 μ

m, with a suspension of hydrophobic polymer to form a first slurry;

b) mixing graphitised carbon fibres and a liquid to form a second slurry;

c) mixing the first slurry with the second slurry to form a third slurry;

d) depositing the third slurry onto a porous bed to form a fibre-containing layer; and

e) drying and firing the fibre-containing layer at a temperature that does not exceed 1000°

C.

21. The process of claim 18 wherein step (b) further comprises mixing a binder with the carbon fibres and the liquid.