Constructing ordered paths to improve the charge separation and light harvesting capacity towards efficient solar water oxidation performance

Photoelectrochemical (PEC) water-splitting performance can be expressed as the product of efficiencies of light absorption (η_abs), charge separation (η_sep) and charge transfer (η_trans) processes. In BiVO₄ photoanodes, the η_trans has been greatly enhanced by integrating various low-price oxygen evolution electrocatalysts but improving η_abs×η_sep efficiency remains a great challenge. Considering this challenge, here, we fabricate inverse opal (IO)-SnO₂@BiVO₄ type-II heterojunction photoanodes and investigate the η_abs×η_sep efficiency by tailoring the amount of BiVO₄ on the IO-SnO₂ nanostructures. The optimized IO-SnO₂@BiVO₄ photoanode exhibits η_abs×η_sep of 62.91 % at 1.23 V vs. reversible hydrogen electrode (RHE), which is much higher than that of the bare BiVO₄ (16.14 %). The significantly improved η_abs×η_sep is attributed to the introduction of IO-SnO₂, which provides a high solar light-harvesting capability by diffuse scattering and coherent multiple internal scattering. Moreover, it greatly improves the intrinsic charge transport and reduces interface contact resistance due to ordered paths for electron migration. Even though η_abs×η_sep is high, the majority of the photogenerated holes are lost at the surface/electrolyte recombination, resulting in a very low η_trans of 24.93 % at 1.23 V vs. RHE. To improve the η_trans performance, an oxygen evolution catalyst is deposited on the surface of optimized IO-SnO₂@BiVO₄, and it greatly increases the η_trans (96.29 %) and achieves J_H2O of 3.57 mA∙cm⁻² with excellent stability for 10 h. In addition, we achieve an applied bias photon‐to‐current efficiency of nearly 1.02 % at 0.72 V vs. RHE. Overall, the obtained results and fabrication process are considered a significant step toward achieving sustainability.