Oxygen-deficient WO3−x@TiO2−x core–shell nanosheets for efficient photoelectrochemical oxidation of neutral water solutions

Preparation of highly active, stable and earth-abundant photoanodes for water oxidation is an important strategy to meet the demand of developing clean-energy technologies. In this paper, efficient and stable photoanodes based on oxygen-deficient black WO3−x@TiO2−x core–shell nanosheets with precisely controlled shell thickness have been fabricated for photoelectrochemical (PEC) conversion from neutral water solutions. The black WO3−x@TiO2−x core–shell nanosheet photoanode with the shell thickness of ∼15 nm achieved around 8 times higher photocurrent density (∼3.20 mA cm−2) than the pure WO3 photoanode at 1.23 V vs. the RHE. An improved onset potential with long-term PEC durability was also realized with the obtained black WO3−x@TiO2−x core–shell nanosheet photoanodes. The promoted PEC water oxidation performance was likely to be originated from enhanced light absorption, interfacial charge transfer and charge separation in these WO3−x@TiO2−x nanosheets which were revealed by finite-difference time-domain simulations and specific band alignment, along with optical and electrochemical spectroscopic evidence. In a word, such black WO3−x@TiO2−x nanosheet photoanodes suggest many exciting opportunities for PEC water splitting toward highly efficient solar fuel generation and many other PEC sensing applications.