A catalytic electrode has an electrically conductive substrate such as titanium with a coating comprising a platinum-group metal catalyst finely dispersed in a matrix consisting of a semi-conducting polymer formed in situ on the substrate. The catalyst may be a platinum-group metal oxide such as iridium oxide formed in situ together with the semi-conducting polymer by the application of a uniform liquid mixture followed by a controlled heat treatment.The semi-conducting polymer is preferably formed from polyacrylonitrile, polybenzimidazo-pyrrolone or an adamantane based polybenzoxazole.