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

Abstract

LaTiO2N 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, LaTiO2N mesoporous single crystals (MSCs) are successfully fabricated via a topotactic conversion route by using the Ruddlesden–Popper compound NaLaTiO4 as the precursor. The LaTiO2N 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 LaTiO2N MSCs which contributes to the much better photocarrier separation than conventional counterparts. By loading proper cocatalysts, LaTiO2N 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 O2‐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.

Synthesis and photocatalytic activity of LaTiO2N using titanium oxide nanosheet/La3+ hybrids as a precursor

“…[40][41][42][43] On the other hand, in the case of the photocatalyst with few defects, the photocatalytic activity is not so much dependent on particle size, as recombination is suppressed even with large crystal sizes. 44,45 Fig. 8 Thus, photocatalytic activity is rarely determined by a single factor.…”

Stability and degradation of (oxy)nitride photocatalysts for solar water splitting

“…52,74,82,96–98 For example for LaTiO 2 N Kasahara et al estimated that 12% of the generated holes went into N 2 evolution (for 440 μmol O 2 , 40 μmol N 2 ), 52 while for various morphologies with and without cocatalyst decoration achieving a broad range of O 2 evolution rates (15–736 μmol h −1 ), N 2 evolution in the order of 2–8 μmol was reported during the first hours. 68 Also Wang et al observed substantial N 2 evolution during the first two of four 5 h photocatalytic full water splitting cycles performed by LaTiO 2 N. 95 This observation is attributed to the corrosion via photo-oxidation of the material which is correlated to the loss of nitrogen from the structure, that seems to stop after one or two hours. Similar observations were reported for BaTaO 2 N. 96 During chronoamperometric PEC measurements of LaTiO 2 N containing electrodes, small quantities of N 2 evolution were detected as well.…”

“… 94 Concerning long term stability a slight drop in hydrogen evolution rate for Pt decorated LaTiO 2 N catalysts in the course of four 25 min measurement cycles was reported 52 and no drop in oxygen and hydrogen evolution rate for RhCrO y and CoOOH decorated LaTiO 2 N in the course of four 5 h measurements. 95 Hence, one of the difficulties to assess consistently and comparably O 2 or H 2 evolution rates, and therefore indirectly stability, is that even when fixing the material composition there is still a large parameter space which needs to be controlled and reported to assure reproducibility. Some performance indicators of oxynitride photocatalysts have been summarized in Table 1 .…”