The KCaSrTa₅O₁₅ photocatalyst with tungsten bronze structure for water splitting and CO₂ reduction

KCaSrTa₅O₁₅ with tungsten bronze structure and a band gap of 4.1 eV showed activity for water splitting without cocatalysts. The activity was improved by loading the NiO cocatalyst. The apparent quantum yield of optimized NiO-loaded KCaSrTa₅O₁₅ was 2.3% at 254 nm for water splitting. When CO₂ gas was bubbled into the reactant aqueous solution, Ag cocatalyst-loaded KCaSrTa₅O₁₅ produced CO and H₂ as reduction products of CO₂ and H₂O, respectively, and O₂ as an oxidation product of H₂O. The carbon source of CO was confirmed to be CO₂ molecules by using ¹³CO₂. The ratio of the number of electrons to that of holes calculated from the amounts of products (CO, H₂ and O₂) was almost unity. Additionally, the ratio of the turnover number of electrons consumed for CO production to the total number of an Ag atom of the cocatalyst that was the active site for CO₂ reduction was 8.6 at 20 h. These results indicate that water was consumed as an electron donor for this photocatalytic CO₂ reduction in an aqueous medium. Thus, KCaSrTa₅O₁₅ with tungsten bronze structure has arisen as a new photocatalyst that is active for water splitting and CO₂ reduction utilizing water as an electron donor.