Flux‐Assisted Synthesis of Prism‐like Octahedral Ta3N5 Single‐Crystals with Controllable Facets for Promoted Photocatalytic H2 Evolution

Crystal facet engineering has emerged as one of the most important strategies for designing highly efficient photocatalysts with improved charge separation efficiency. Tantalum nitride (Ta 3 N 5 ) is one of the most popular visible‐light‐responsive photocatalysts, but the controllable synthesis of well‐shaped Ta 3 N 5 single‐crystals with clear facets is still challenging due to the harsh synthesis conditions. Herein, the first demonstration is given that prism‐like octahedral Ta 3 N 5 single crystals with preferential exposure of {001}, {010}, and {102} facets can be synthesized via the mixed KCl–LiCl flux. Meanwhile, the effects of flux type (KCl, LiCl, and KCl–LiCl), flux ratio, nitridation time, etc. on the phase composition, crystallinity, and morphology of Ta 3 N 5 are studied. Detailed structural characterizations verify its high crystallinity and relatively low defect density. Furthermore, growth of the Ta 3 N 5 single crystal with controllable facets is demonstrated to follow a bottom‐up growth mechanism involving dissolution, recrystallization, and precipitation processes. As a probe test, the as‐obtained Ta 3 N 5 single crystals exhibit about five times the promoted photocatalytic H 2 evolution rate with respect to the conventional Ta 3 N 5 nanoparticles, demonstrating the advantages of the specific facet‐defined structure. This finding offers a new avenue to prepare (oxy)nitrides with facets exposed for promising solar energy conversion.