Core–Shell‐Structured LaTaON₂ Transformed from LaKNaTaO₅ Plates for Enhanced Photocatalytic H₂ Evolution

LaTaON 2 is a photocatalyst with intense visible light absorption up to 650 nm, but exhibits low H 2 evolution activity owing to uncontrolled facets and high defect densities. In this work, core–shell‐structured plate‐like LaKNaTaO 5 /LaTaON 2 was synthesized by nitriding a layered perovskite‐type LaKNaTaO 5 . The volatilization of K and Na species during the nitridation promoted the rapid transformation of LaKNaTaO 5 into LaTaON 2 along [010] direction with the plate‐like shape retained. This yielded high‐quality LaTaON 2 shells exposing (010) facets on the lattice‐matched LaKNaTaO 5 cores. After loading with a Rh co‐catalyst, LaKNaTaO 5 /LaTaON 2 showed photocatalytic H 2 evolution activity four times greater than that obtained from conventional irregular‐shaped LaTaON 2 powders and utilized visible light up to 620 nm. This work provides a novel strategy yielding oxynitrides with well‐defined facets and low defect densities by selecting lattice‐matched oxide precursors containing volatile components.