Enhanced photoelectrochemical water oxidation of WO3/R-CoO and WO3/B-CoO photoanodes with a type II heterojunction

Tungsten trioxide (WO3) has been conceived as a promising photoanode material for photoelectrochemical (PEC) water oxidation. Therefore, many efforts have been made to improve its PEC performances. Herein, a novel heterojunction is fabricated through combining rocksalt CoO (R-CoO) or blende CoO (B-CoO) nanosheets with WO3 nanoplates using a spin-coating method. The typical type II heterojunctions, e.g., WO3/R-CoO and WO3/B-CoO, both have exhibited higher photocurrent densities than pristine WO3 photoanode. The photocurrent densities of WO3/R-CoO, WO3/B-CoO and WO3 are 0.53 mA cm(-2), 0.45 mA cm(-2) and 0.31 mA cm(-2) at 1.23 V vs. reversible hydrogen electrode, respectively. For the WO3/R-CoO photoanode, the surface charge separation efficiency is 50.95% and the photoconversion efficiency is 0.062%, which are both higher than the WO3 and WO3/B-CoO photoanodes. The enhanced PEC performances are due to the type II heterojunction between WO3 and R-CoO (or B-CoO), which facilitates the absorption of visible light and charge transport. The better performance of WO3/R-CoO than that of WO3/B-CoO may be due to the deeper valence band position of R-CoO. Our work demonstrates that R-CoO (or B-CoO) can couple with WO3 to form a type II heterojunction to improve the PEC water oxidation performance.

Automated summary

By combining CoO nanosheets with WO3 to form heterojunctions, PEC performance of WO3 can be improved, with WO3/R-CoO heterojunction showing the best performance, possibly due to the lower valence band position of R-CoO.