A method of making carbon nanotubes doped with iron, nitrogen and sulphur for an oxygen reduction reaction catalyst includes the steps of mixing an iron containing oxidising agent with a sulphur-containing dye to form a fibrous fluctuate of reactive templates and using these for in-situ polymerisation of an azo compound to form polymer-dye nanotubes, adding an alkali to precipitate magnetite, and subjecting the nanotubes to pyrolysis, acid leaching, and heat treatment.