a cathode current collector for a sodium sulphur cell is formed of a metal substrate , for example of a nickel alloy such as inconel 600 , which is provided with a firmly adherent coating of carbon which is produced by decomposition of a carbon - containing gas in a glow discharge with the substrate heated to a temperature of 200 ° c . to 1000 ° c . in an electric field , conveniently a radio frequency field employed for inductively heating the substrate .