Ternary platinum alloy catalyst

A platinum alloy catalyst PtXNb, wherein X is nickel, cobalt, chromium, copper, titanium or manganese, characterised in that in the alloy the atomic percentage of platinum is 46-75at%, of X is 1-49at% and of Nb is 1-35at% is disclosed. The catalyst has particular use as an oxygen reduction catalyst in fuel cells, and in particular in phosphoric acid fuel cells.