Cascading Alignment of Multilayered SnO₂/WO₃/BiVO₄ Inverse Opal Skeletons in Photoelectrochemical Water Splitting

Tin dioxide (SnO₂) inverse opals (IOs) having a pore size of approximately 260 nm in the 370 nm sized polystyrene bead (PS) templates were developed by a spin-coating-assisted sol−gel process. Upon this template, the SnO₂/WO₃ core-shell IOs were developed by the facile electrodeposition under a constant potential (−0.47 V vs. sat. Ag/AgCl), where the thickness of WO₃ layer depended on the applied charge amount for WO₃ electrodeposition (200−800 mC/cm²). As a control sample, a pure WO₃ IO film with the same thickness of ∼3.1 μm and a band gap (E_g) of 2.6 eV was also prepared in the same method. The pore diameter of the SnO₂ IO structure declined noticeably as the charge amount of the deposited WO₃ layer increased from 200 to 800 mC/cm², leading to eventual coverage of the SnO₂ IO structure in the WO₃ (800 mC/cm²) layer. The optimum photoelectrochemical (PEC) response was achieved with the SnO₂/WO₃ (600 mC/cm²) IO electrode, which exhibited the highest photocurrent density (J_sc) of 2.8 mA/cm² (0.5 V_Ag/AgCl) under full-sun conditions and 0.91 mA/cm² (0.5 V_Ag/AgCl) under visible light, indicating that the enhancement of the J_sc under visible light contributed significantly to the improvement of the total J_sc, compared with the values for the pure SnO₂, SnO₂/WO₃ (200, 400, and 800 mC/cm²), and WO₃ IO electrodes. Furthermore, considering that the favorable cascading band alignment can boost the fast charge separation and transport through the conductive SnO₂ IO skeleton, we try to develop the multilayered SnO₂/WO₃/BiVO₄ IOs structure showing the well-matched band alignment. And then, the dual doped (W and Mo) BiVO₄ layer was adapted in the surface layer due to the more narrowing E_g of ~ 2.4 eV. Herein, the PEC performance and other results would be presented.

Figure 1