Enhanced photoelectrochemical water oxidation on WO3 nanoflake films by coupling with amorphous TiO2

High surface states induced photoelectrochemical (PEC) activity and stability issue is the major performance bottleneck for nanostructured WO 3 photoanode. Here we report that amorphous TiO 2 ( α -TiO 2 ) be used as passivator to modify the surface states of WO 3 nanoflakes film for improving its PEC water oxidation performance. In comparison with bare WO 3 film, the α -TiO 2 -coupled WO 3 ( α -TiO 2 /WO 3 ) film is of higher PEC water oxidation activity and stability. The photocurrent on α -TiO 2 /WO 3 film photoanode is improved by 2 times that reached 1.4 mA/cm 2 in 0.1 M Na 2 SO 4 solution at 0.8 V ( vs. SCE). After α -TiO 2 coupling, the UV–vis absorption edge and intensity of WO 3 film do not change obviously, but the formation and oxidation kinetics of H 2 O 2 on WO 3 photoanode are modified. The density functional theory calculations indicate the monoclinic WO 3 (002) has a surface energy of 1.17 J/m 2 , whereas the α -TiO 2 /WO 3 (002) with a much lower surface energy of 0.3 J/m 2 . Additionally, the length of Ti O bond of α -TiO 2 is changed from the initial 1.929 Å to a shorter length of 1.886 Å and a longer length of 2.290 Å in α -TiO 2 /WO 3 (002) through the O 2- -W 6+ bonding effect at α -TiO 2 /WO 3 interface. Therefore, the enhanced PEC water oxidation performance on α -TiO 2 /WO 3 film can be attributed to that α -TiO 2 passivates the surface states of WO 3 nanoflakes film, and the formation of H 2 O 2 from the photoexcited-electrons/dissolved-oxygen route is depressed and the PEC oxidation of H 2 O 2 is accelerated.