An implantable electrode having a strong, adherent surface coating of iridium oxide or titanium nitride on a platinum surface, where the platinum surface has a surface area of at least five times that of a smooth shiny platinum surface of the same geometry. The iridium oxide coating may be formed on platinum by a physical deposition process, such as sputtering. A gradient coating of iridium oxide ranging in composition from pure platinum to pure iridium oxide is produced by sputtering.