GAS DIFFUSION SUBSTRATE
A gas diffusion substrate comprising a non-woven fibre web, thermally conductive materials and a carbonaceous residue, wherein the thermally conductive materials and carbonaceous residue are embedded within the non-woven fibre web and wherein the thermally conductive materials have a maximum dimension of between 1 and 100 μm and the gas diffusion substrate has a porosity of less than 80% is disclosed. The substrate has particular use in phosphoric acid fuel cells.
1 . A gas diffusion substrate comprising a non-woven fibre web, thermally conductive materials and a carbonaceous residue, wherein the thermally conductive materials and carbonaceous residue are embedded within the non-woven fibre web and wherein the thermally conductive materials have a maximum dimension of between 1 and 100 μm and the gas diffusion substrate has a porosity of less than 80%.
2 . A gas diffusion substrate according to claim 1 , wherein the thermally conductive materials are particles having a d90 of 6-100 μm.
3 . A gas diffusion substrate according to claim 2 , wherein the particles are graphite (natural or synthetic).
4 . A gas diffusion substrate according to claim 1 , wherein the thermally conductive materials are selected from the group consisting of: fibrous or tubular materials;
disc-shaped materials; or any other form of thermally conductive carbon.
5 . A gas diffusion substrate according to claim 1 , wherein the carbonaceous residue is obtained from a carbonisable binder.
6 . A gas diffusion substrate according to claim 5 , wherein the carbonisable binder comprises a phenolic binder, a pitch-based resin or other high-yield carbonisable resin.
7 . (canceled)
8 . A gas diffusion substrate according to claim 1 wherein the thermally conductive materials and carbonaceous residue are present in the substrate at a combined weight of 5-700% compared to the weight of the non-woven fibre web.
9 . A gas diffusion substrate according to claim 1 , wherein the through-plane thermal conductivity of the substrate is at least 3 W/m.k at a pressure of 1000 kPa.
10 . A process for preparing a gas diffusion substrate as claimed in claim 1 , said process comprising the steps of:
(i) impregnating a non-woven fibre web with a mixture of thermally conductive materials and carbonisable binder to give an impregnated web;
(ii) curing the carbonisable binder within the non-woven fibre web at a temperature of 100-250° C.;
(iii) a first heat treatment step of the impregnated web at 600-1000° C. to carbonise the carbonisable binder to leave a carbonaceous residue; and
(iv) a second heat treatment step at 1800-3000° C. to provide the gas diffusion substrate.
11 . A process according to claim 10 , wherein before step (iii), two or more impregnated non-woven fibres webs are laminated.
12 . A gas diffusion electrode comprising a gas diffusion substrate as claimed in claim 1 and an electrocatalyst applied to the gas diffusion substrate.
13 . A membrane electrode assembly comprising a gas diffusion substrate as claimed in claim 1 and a catalyst-coated proton exchange membrane.
14 . A membrane electrode assembly comprising a gas diffusion electrode as claimed in claim 12 , and a proton exchange membrane.
15 . A fuel cell comprising a gas diffusion substrate as claimed in claim 1 .
16 . A phosphoric acid fuel cell comprising a gas diffusion substrate as claimed in claim 1 .
17 . A fuel cell comprising a gas diffusion electrode as claimed in claim 12 .
18 . A fuel cell comprising a membrane electrode assembly as claimed in claim 13 .
19 . A fuel cell comprising a membrane electrode assembly as claimed in claim 14 .
20 . A phosphoric acid fuel cell comprising a gas diffusion electrode as claimed in claim 12 .