Towards better photocatalysts: first-principles studies of the alloying effects on the photocatalytic activities of bismuth oxyhalides under visible light

Via density functional theory computations, we investigated the photocatalytic activities of pure and alloyed bismuth oxyhalides (BiOXs). The dipole moments of the majority of pure and alloyed BiOXs are larger than 2.00 Debye, which can ensure their high photocatalytic efficiencies. Both the redox potentials of the photon-induced holes and the band gaps increase with an increasing content of lighter halogen atoms in the BiOXs, which competitively affects the photocatalytic efficiency. The hole mobility decreases a lot due to the hybridization of the halogen n p states, while the electron mobility is not affected by such hybridization. Therefore, the alloying effect in BiOXs brings about a substantially lower electronhole recombination rate and, accordingly, a much higher photocatalytic efficiency. Our investigation also suggests that O vacancies, which are energetically more favorable in alloyed BiOXs, could act as capture centers for excited electrons and, consequently, improve the separation of the electronhole pairs. Our findings present a reasonable explanation for the recent experimental reports and provide some guidance for the design of alloyed BiOX photocatalysts. Via density functional theory computations, we compared the photocatalytic activities of pure and alloyed BiOXs. Alloyed BiOXs have higher photocatalytic efficiencies due to much lower e h + recombination rate and easier formation of O vacancies. Our findings provide guidance for designing better BiOX photocatalysts.