Understanding the Catalytic Active Sites of Crystalline CoSbxOy for Electrochemical Chlorine Evolution

The chlorine evolution reaction (CER) is a key reactionin electrochemicaloxidation (EO) of water treatment. Conventional anodes based on platinumgroup metals can be prohibitively expensive, which hinders furtherapplication of EO systems. Crystalline cobalt antimonate (CoSb (x) O (y) ) was recentlyidentified as a promising alternative to conventional anodes due toits high catalytic activity and stability in acidic media. However,its catalytic sites and reaction mechanism have not yet been elucidated.This study sheds light on the catalytically active sites in crystallineCoSb (x) O (y) anodesby using scanning electrochemical microscopy to compare the CER catalyticactivities of a series of anode samples with different bulk Sb/Coratios (from 1.43 to 2.80). The results showed that Sb sites servedas more active catalytic sites than the Co sites. The varied Sb/Coratios were also linked with slightly different electronic statesof each element, leading to different CER selectivities in 30 mM chloridesolutions under 10 mA cm(-2) current density. Thehigh activity of Sb sites toward the CER highlighted the significanceof the electronic polarization that changed the oxidation states ofCo and Sb.