Undoped Layered Perovskite Oxynitride Li₂LaTa₂O₆N for Photocatalytic CO₂ Reduction with Visible Light

Oxynitrides are promising visible‐light‐responsive photocatalysts, but their structures are almost confined with three‐dimensional (3D) structures such as perovskites. A phase‐pure Li 2 LaTa 2 O 6 N with a layered perovskite structure was successfully prepared by thermal ammonolysis of a lithium‐rich oxide precursor. Li 2 LaTa 2 O 6 N exhibited high crystallinity and visible‐light absorption up to 500 nm. As opposed to well‐known 3D oxynitride perovskites, Li 2 LaTa 2 O 6 N supported by a binuclear Ru II complex was capable of stably and selectively converting CO 2 into formate under visible light ( λ >400 nm). Transient absorption spectroscopy indicated that, as compared to 3D oxynitrides, Li 2 LaTa 2 O 6 N possesses a lower density of mid‐gap states that work as recombination centers of photogenerated electron/hole pairs, but a higher density of reactive electrons, which is responsible for the higher photocatalytic performance of this layered oxynitride.