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

LaTaON2 is a photocatalyst with intense visible light absorption up to 650 nm, but exhibits low H2 evolution activity owing to uncontrolled facets and high defect densities. In this work, core–shell‐structured plate‐like LaKNaTaO5/LaTaON2 was synthesized by nitriding a layered perovskite‐type LaKNaTaO5. The volatilization of K and Na species during the nitridation promoted the rapid transformation of LaKNaTaO5 into LaTaON2 along [010] direction with the plate‐like shape retained. This yielded high‐quality LaTaON2 shells exposing (010) facets on the lattice‐matched LaKNaTaO5 cores. After loading with a Rh co‐catalyst, LaKNaTaO5/LaTaON2 showed photocatalytic H2 evolution activity four times greater than that obtained from conventional irregular‐shaped LaTaON2 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. Core–shell structured plate‐like LaKNaTaO5/LaTaON2 containing LaTaON2 shells exposing (010) facets and having a low defect density on the lattice‐matched LaKNaTaO5 cores was obtained by a brief nitridation process. When modified with a Rh co‐catalyst, LaKNaTaO5/LaTaON2 exhibited photocatalytic H2 evolution activity four times greater than that obtained from conventional LaTaON2 powders with uncontrolled facets.