Facile Fabrication of N‐Doped K₂Nb₂O₆ Nanocrystals with Defective Pyrochlore Structure for Improved Visible‐Light Photocatalytic Hydrogen Production

Semiconductor‐based photocatalytic water splitting is one of the effective ways for future hydrogen (H 2 ) production. However, the wide bandgap of most semiconductors severely limits the solar spectral absorption range, which seriously hinders their practical applications. Herein, porous N‐doped K 2 Nb 2 O 6 nanocrystals with defective pyrochlore structure are rationally designed to extend the absorption range from ultraviolet to visible region around 550 nm by NH 3 heat treatment. The obtained 6N–K 2 Nb 2 O 6 shows the highest visible‐light activity with an H 2 evolution rate of 20.4 μmol h −1 g −1 . More detailed exploration demonstrates that NH 3 heat treatment can promote the substitutional nitrogen doping in K 2 Nb 2 O 6 crystals while accompanied by the formation of oxygen vacancies or Nb 4+ species. The hybridization of N 2 p and O 2 p orbitals in the valence band (VB) of the nitrogen‐doped K 2 Nb 2 O 6 makes the VB maximum move more negatively, whereas the conduction band minimum shifted more positively due to the role of defective Nb 4+ species. Such a synergistic effect endows the samples with visible‐light absorption and greatly enhances charge separation and transfer efficiency, resulting in the excellent H 2 production performance. This study provides additional insights into the understanding of the effect of nitrogen doping on photocatalysts with excellent visible‐light‐driven photocatalytic activity.