Gas diffusion substrate
A novel flexible non-woven carbon fibre gas diffusion substrate comprising a plurality of first carbon fibres orientated in the x-, y- and optionally z-directions, said first fibres being bonded with a thermoplastic polymeric substance, and a carbon based filler material, characterised, in that the flexible non-woven carbon fibre gas diffusion substrate has a total density of greater than 0.35 g/cm 3 , and a gas diffusion electrode obtained therefrom is disclosed. Also disclosed is a process for the manufacture of the substrate and electrode.
1. A flexible non-woven carbon fibre gas diffusion substrate comprising:
a plurality of first carbon fibres oriented in the x-, y- and optionally z-directions, said first fibres being bonded with a thermoplastic polymeric substance, and
a carbon based filler material, wherein the flexible non-woven carbon fibre gas diffusion substrate has a total density of greater than 0.35 g/cm 3 .
2. A flexible non-woven carbon fibre gas diffusion substrate according to claim 1 , wherein the total density is greater than 0.4 g/cm 3 .
3. A flexible non-woven carbon fibre gas diffusion substrate according to claim 1 , wherein the first carbon fibres are selected from the group consisting of longer fibres, shorter fibres, and a combination of longer and shorter fibres.
4. A flexible non-woven carbon fibre gas diffusion substrate according to claim 1 , wherein one or more continuous strands comprised of a plurality of second carbon fibres is embedded within the non-woven carbon fibre gas diffusion substrate.
5. A flexible non-woven carbon fibre gas diffusion substrate according to claim 1 , wherein the carbon based filler material comprises a mixture of a particulate carbon and one or more polymers.
6. A flexible non-woven carbon fibre gas diffusion substrate according to claim 1 , wherein the carbon based filler material further comprises a catalyst other than an electrocatalyst.
7. A flexible non-woven carbon fibre gas diffusion substrate according to claim 1 , wherein the carbon based filler material further comprises a modifier material or materials.
8. A process for the preparation of a flexible non-woven carbon fibre gas diffusion substrate according to claim 1 , said process comprising the steps of:
in-filling a flexible non-woven carbon fibre web with a carbon based filler material, and (ii) hotpressing said filled substrate under a high temperature and pressure.
9. A process for the preparation of a flexible non-woven carbon fibre gas diffusion substrate according to claim 1 , said process comprising the steps of:
dispersing first carbon fibres, thermoplastic polymeric material and carbon based filler material as a suspension, (ii) forming a substrate by the controlled deposition of the slurry onto a moving mesh belt, (iii) drying the substrate, and (iv) hotpressing the substrate under high temperature and pressure.
10. A process according to claim 8 , wherein the substrate is hotpressed at a temperature of from 150° C. to 320° C.
11. A process according to claim 8 , wherein the substrate is hotpressed at a pressure of from 2500 kPa to 12000 kPa.
12. A gas diffusion electrode comprising a flexible non-woven carbon fibre gas diffusion substrate according to claim 1 and an electrocatalyst material.
13. A membrane electrode assembly comprising a flexible non-woven carbon fibre gas diffusion substrate according to claim 1 .
14. A membrane electrode assembly comprising a gas diffusion electrode according to claim 12 .
15. A fuel cell comprising a flexible non-woven carbon fibre gas diffusion substrate according to claim 1 .
16. A fuel cell comprising a gas diffusion electrode according to claim 12 .
17. A fuel cell comprising a membrane electrode assembly according to claim 13 .