Enhanced Photoelectrocatalytic Water Splitting in Bi₂Mo_1–xW_xO₆ Solid Solutions: Understanding the Atomic Level Mechanism from the Experimental and First-Principles Approach

The second-order Jahn-Teller distortion (SOJT-D) is predominantly observed in the MO 6 octahedra of Aurivillius metal oxides such as Bi 2 MoO 6 and Bi 2 WO 6, due to the presence of both transition metal Mo 6+ (or W 6+ ) and Bi 3+ lone-pair cations. This effect leads to intraoctahedral distortion as the consequence of the mixing of empty d-orbitals and completely filled p-orbitals of the ligands that may affect the efficiency of photocatalysts. Herein, photoelectrocatalytic (PEC) water splitting performance of second-order Jahn-Teller distorted Bi 2 MoO 6, Bi 2 WO 6, and Bi 2 Mo 1– x W x O 6 solid solutions is investigated by the combined experimental and first-principles approach. Our theoretical study reveals that the SOJT-D parameter is monotonically decreased with increasing x value of Bi 2 Mo 1– x W x O 6 solid solutions, and this trend is well correlated with Raman analysis. The Bi 2 Mo 1– x W x O 6 (0 < x < 1) solid solutions show higher PEC activity as compared to both pristine materials, as experienced from our study that the Bi 2 Mo 0.9 W 0.1 O 6 photoanode delivered maximum efficiency, which is ∼4 and ∼17-fold higher than that of Bi 2 MoO 6 and Bi 2 WO 6, respectively. In the presence of both Mo and W cations, the recombination center of photoinduced charge carriers is suppressed due to their different conduction band levels and spatially separated, resulting in enhanced PEC water splitting activity in the solid solutions.