Highly improved photoelectrocatalytic efficiency and stability of WO photoanodes by the facile in situ growth of TiO branch overlayers.

The development of highly efficient and stable visible-light-responsive photoanode materials is essential for practical photoelectrocatalytic (PEC) applications. In this work, a novel method was proposed to enhance the PEC efficiency and stability of WO3 photoanodes by the facile in situ growth of TiO2 branch overlayers on WO3 nanoplates (TWNP) based on the lattice match between monoclinic WO3 and anatase TiO2. The WO3 nanoplates (WNP) with a fluted body and a thickness of 160 nm were first prepared on tungsten foil by a hydrothermal method. Then, numerous 001-oriented anatase TiO2 branches were directly grown in situ on the WNP with an average thickness of 50 nm and a length of 35 ± 5 nm. TWNP exhibited a photocurrent of ∼2.37 mA cm-2, which is 157% of that of WNP, and showed no obvious decay over 100 h continuous testing, compared to only 11.8% that remained for WNP. During the PEC degradation of phenol, the rate constant was 0.322 h-1 for TWNP while it was only 0.131 h-1 for WNP, and the activity of TWNP remained at 97.2% after 10 repeat tests compared to only 67.4% for WNP. According to the transient photovoltage and transient photocurrent measurements, these improvements can be attributed to the TiO2 branches which enhanced the charge separation efficiency and surface reaction kinetics, and hindered the inactivation of TWNP by providing an atomic-level protective cover. Overall, the in situ wet chemical growth of the TiO2 branches is a meaningful way to overcome WO3's drawbacks, i.e., sluggish surface reaction kinetics, rapid charge recombination and gradual loss of photoactivity, to improve the PEC activity and stability of WO3 photoanodes.