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LaTiO2N photocatalysts are attractive because they are responsive to visible light up to a wavelength of 600 nm. However, during the nitridation process to produce LaTiO2N from La2Ti2O7, the introduction of defects can cause a reduction in the hydrogen evolution activity of the photocatalyst, which limits its application to overall water splitting. Such defects can arise due to the change in crystal structure and the occurrence of overnitridation. Herein, it is demonstrated that nitridation of a metastable La–Ti oxide obtained by flame spray pyrolysis (FSP) can suppress the formation of such defects. A detailed analysis of the transition pathway during nitridation reveals that a combination of FSP and Al doping is essential for suppressing mesopore formation resulting from the volume change and Ti4+ reduction due to overnitridation. This leads to an increase in the apparent quantum yield for Al‐doped LaTiO2N during the visible‐light‐driven hydrogen evolution reaction, compared to that for undoped LaTiO2N. In the present study, insights are provided into the importance of minimizing structural changes during the synthesis of oxynitride photocatalysts by designing isostructural precursors for enhanced photocatalytic activity. Flame spray pyrolysis enables the synthesis of La–Ti oxides with a simple perovskite‐type structure, and Al doping promotes the formation of the simple perovskite‐type La–Ti oxides. The Al‐doped LaTiO2N obtained by nitridation has a reduced defect concentration due to suppressed structural change, which contributes to the improvement of hydrogen evolution activity.

LaTiO 2 N photocatalysts are attractive because they are responsive to visible light up to a wavelength of 600 nm. However, during the nitridation process to produce LaTiO 2 N from La 2 Ti 2 O 7 , the introduction of defects can cause a reduction in the hydrogen evolution activity of the photocatalyst, which limits its application to overall water splitting. Such defects can arise due to the change in crystal structure and the occurrence of overnitridation. Herein, it is demonstrated that nitridation of a metastable La–Ti oxide obtained by flame spray pyrolysis (FSP) can suppress the formation of such defects. A detailed analysis of the transition pathway during nitridation reveals that a combination of FSP and Al doping is essential for suppressing mesopore formation resulting from the volume change and Ti 4+ reduction due to overnitridation. This leads to an increase in the apparent quantum yield for Al‐doped LaTiO 2 N during the visible‐light‐driven hydrogen evolution reaction, compared to that for undoped LaTiO 2 N. In the present study, insights are provided into the importance of minimizing structural changes during the synthesis of oxynitride photocatalysts by designing isostructural precursors for enhanced photocatalytic activity.

Graphene exhibits zero-gap massless-Dirac fermion and zero density of states at E = 0. These particles form localized states called edge states on finite width strip with zigzag edges at E = 0. Naively thinking, one may expect that current is also concentrated at the edge, but Zarbo and Nikolic numerically obtained a result that the current density shows maximum at the center of the strip. We derive a rigorous relation for the current density, and clarify the reason why the current density of edge state has a maximum at the center.