Catalyst

1. A platinum alloy catalyst comprising a bulk alloy PtX, wherein the atomic percent of platinum in the bulk alloy is from 5 to 50 at %, the remaining at % being X, wherein the atomic percent of platinum at the surface of the alloy catalyst is from 10 to 80 at %, the remainder being X, provided that the at % of platinum at the surface of the alloy catalyst is at least 25% greater than the at % of platinum in the bulk alloy.

2. A platinum alloy catalyst according to claim 1 , wherein X is one or more metals selected from the group consisting of precious metals ruthenium, rhodium, palladium, iridium, osmium, gold and silver, and transition metals.

3. A platinum alloy catalyst according to claim 1 , wherein X is ruthenium or tin or ruthenium and tin.

4. A platinum alloy catalyst according to claim 1 , wherein the catalyst is unsupported or supported on a dispersed support material.

5. A platinum alloy catalyst according to claim 4 , wherein the catalyst is supported on a dispersed support material.

6. A platinum alloy catalyst according to claim 1 , wherein the catalyst consists essentially of the PtX alloy dispersed on a conductive carbon support.

7. An electrode comprising a catalyst according to claim 1 .

8. A catalysed membrane comprising a catalyst according to claim 1 .

9. A transfer substrate comprising a catalyst according to claim 1 .

10. A membrane electrode assembly comprising a catalyst according to claim 1 .

11. A fuel cell comprising a membrane electrode assembly according to claim 10 .

12. A fuel cell comprising an electrode according to claim 7 .

13. A portable device comprising a fuel cell according to claim 11 .

14. A portable device comprising a fuel cell according to claim 12 .