Cathodic Electrodeposition of Stoichiometric Cobalt Chalcogenide Thin Films

Abstract

Here, we demonstrate a two-step electrochemical approach for the synthesis of cobalt chalcogenides, CoQ (Q = S or Se) based on the prior modification of a substrate with S or Se, followed by electrochemical reduction in a Co2+-complexing electrolyte to afford CoS or CoSe in film form. The two-step strategy circumvents a common problem with the electrodeposition of metal chalcogenides, namely admixture of the target material with undesired phases such as excess metal or the chalcogen. The strategy was combined with complexation to shift the free metal deposition regime to more negative potentials. Compositional analysis showed that as-synthesized films retain a stoichiometric ratio of Co and S or Se and XPS analysis confirmed the formation of CoS and CoSe. The electrodeposited films were successfully used as electrocatalysts for the triiodide/iodide redox system and showed comparable (or even, superior) performance to a Pt electrode. As also demonstrated both by the present work and by companion studies in our laboratories, the two-step strategy is generally applicable to a variety of other metal chalcogenides.