Dynamics of Photogenerated Charge Carriers in WO₃/BiVO₄ Heterojunction Photoanodes

Abstract

Bismuth vanadate (BiVO4) with a band gap of ∼2.4 eV has emerged as one of the visible photocatalysts that can absorb light below 520 nm. The electron/hole pairs that are generated following BiVO4 band gap excitation are effective for water splitting, especially when BiVO4 is combined with other metal oxides such as WO3. We report a solution processed method for designing transparent WO3/BiVO4 heterojunction electrodes and observe a synergistic effect on the photoelectrochemical activity of WO3/BiVO4, with the combined system performing dramatically better than either individual component. Using ultrafast transient absorption spectroscopy, we elucidated the electronic interaction between WO3 and excited BiVO4. Moreover, the photocatalytic reduction of thionine by WO3/BiVO4 as well as by each individual oxide component is used to track electron injection processes and determine the energetics of the studied systems. In the composite WO3/BiVO4 film a shifted quasi-Fermi level results, due to electronic equilibration between the two materials. The better performance of WO3/BiVO4 heterojunction electrodes is thus a consequence of the electron injection from BiVO4 into WO3, followed by back electron transfer from WO3 to the holes in BiVO4.

New Insights into Mn1−xZnxFe2O4 via Fabricating Magnetic Photocatalyst Material BiVO4/Mn1−xZnxFe2O4

“…The characteristic spectra of monoclinic crystal BiVO 4 was well indexed with the standard card (JCPDS file 14-0688), corresponding to the characteristic diffraction phases of (110), (011), (121), (040), (200), (002), (211), (150), (132), and (042) [12,13]. The diffraction pattern of Mn 1-x Zn x Fe 2 O 4 was fully matched with the standard card (JCPDS file 74-2400), with the characteristic reflection phases (220), (311), (222), (400), (422), (511), (440), (620), and (622) [10].…”

Size-Dependent Ultrafast Charge Carrier Dynamics of WO3 for Photoelectrochemical Cells

“…[4][5][6][7] Tungsten (VI) oxide (WO 3 ) is of particular interest because it has a relatively small band gap energy of 2.6 eV (corresponding to a wavelength of 475 nm), enabling it to absorb light in the visible spectrum without the need for sensitizer dyes. 8,9 Its electrochemical properties 10,11 and spectroscopic properties, including transient absorption [12][13][14] and time-resolved microwave spectroscopy, 15 have been studied previously. However, ultrafast photoinduced charge carrier dynamics in WO 3 have not yet been investigated on the picosecond timescale.…”

WO3 mesocrystal-assisted photoelectrochemical activity of BiVO4

“…These results indicate that the photoexcited carriers in BVO transfer from BVO to WO across the heterointerface. 21 Interestingly, the amplitude of the oscillation signals is significantly raised upon further increasing V WO to 20% (see Figures 4b and c), which implies that the charge-transfer efficiency across the heterointerface would not be enhanced more by further increasing the interface-to-volume ratio. Consequently, V WO = 10% is the optimal value for charge-transfer efficiency in the BVO-WO heterostructures.…”