Unleashing Photocarrier Transport in Mesoporous Single‐Crystalline LaTiO2N for High‐Efficiency Photocatalytic Water Splitting

Abstract LaTiO 2 N is a promising narrow‐bandgap semiconductor photocatalyst that shows great promise for water redox reactions. However, its performance is often hindered by fast photocarrier recombination events. Herein, LaTiO 2 N mesoporous single crystals (MSCs) are successfully fabricated via a topotactic conversion route by using the Ruddlesden–Popper compound NaLaTiO 4 as the precursor. The LaTiO 2 N MSCs are characterized by high crystallinity, abundant mesopores, no grain boundaries (GBs), and exposure of (010) and (101) crystal facets. A facet‐assisted photocarrier separation mechanism is identified for these LaTiO 2 N MSCs which contributes to the much better photocarrier separation than conventional counterparts. By loading proper cocatalysts, LaTiO 2 N MSCs serve as an efficient photocatalyst for water‐splitting half‐reactions and are capable of photocatalyzing overall water‐splitting reactions, delivering an impressive apparent quantum efficiency (AQE) as high as 65.07% at 420 ± 20 nm for O 2 ‐evolution and a solar‐to‐hydrogen (STH) efficiency as high as 0.012% for solar‐driven overall water splitting. These findings not only highlight the grain‐boundary‐free MSCs with peculiar crystal‐facet exposure as highly active photocatalysts for particulate photocatalysis but also provide a rational design approach for developing efficient photocatalysts.