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 (eta(abs)), charge separation (eta(sep)) and charge transfer (eta(trans)) processes. In BiVO4 photoanodes, the eta(trans) has been greatly enhanced by integrating various low-price oxygen evolution electrocatalysts but improving eta(abs) x eta(sep) efficiency remains a great challenge. Considering this challenge, here, we fabricate inverse opal (IO)SnO2@BiVO4 type-II heterojunction photoanodes and investigate the nabs x n sep efficiency by tailoring the amount of BiVO4 on the IO-SnO2 nanostructures. The optimized IO-SnO2@BiVO4 photoanode exhibits eta(abs) x eta(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 eta(abs) x eta(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 eta(abs) x eta(sep) is high, the majority of the photogenerated holes are lost at the surface/electrolyte recombination, resulting in a very low eta(trans) of 24.93 % at 1.23 V vs. RHE. To improve the eta(tr)(ans) performance, an oxygen evolution catalyst is deposited on the surface of optimized IO-SnO2@BiVO4, and it greatly increases the eta(abs) (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.