Understanding the catalytic active sites of crystalline CoSb2O6 for electrochemical chlorine evolution

The chlorine evolution reaction (CER) is a key reaction in electrochemical oxidation (EO) water treatment. Conventional anodes based on platinum group metals (PGMs) can be prohibitively expensive, which hinders the further application of EO systems. Crystalline cobalt antimonate (CoSb2O6) was recently identified as a promising alternative to conventional anodes due to its 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 catalytic active sites in crystalline CoSb2O6 anodes by using scanning electrochemical microscopy (SECM) to compare the CER catalytic activities of a series of anode samples with different Sb/Co ratios. The results showed that Sb sites served as more active catalytic sites than the Co sites. The varied Sb/Co ratios were also linked with slightly different electronic states of each element, leading to different CER selectivity in chloride solutions. The high activity of Sb sites towards CER highlighted the significance of the electronic polarization that changed the oxidation states of Co and Sb.