WO₃/BiVO₄ Photoanodes: Facets Matching at the Heterojunction and BiVO₄ Layer Thickness Effects

Abstract

Photoelectrochemical solar energy conversion offers a way to directly store light into energy-rich chemicals. Photoanodes based on the WO3/BiVO4 heterojunction are most effective mainly thanks to the efficient separation of photogenerated charges. The WO3/BiVO4 interfacial space region in the heterojunction is investigated here with the increasing thickness of the BiVO4 layer over a WO3 scaffold. On the basis of X-ray diffraction analysis results, density functional theory simulations show a BiVO4 growth over the WO3 layer along the BiVO4 {010} face, driven by the formation of a stable interface with new covalent bonds, with a favorable band alignment and band bending between the two oxides. This crystal facet phase matching allows a smooth transition between the electronic states of the two oxides and may be a key factor ensuring the high efficiency attained with this heterojunction. The photoelectrochemical activity of the WO3/BiVO4 photoanodes depends on both the irradiation wavelength and the thickness of the visible-light-absorbing BiVO4 layer, a 75 nm thick BiVO4 layer on WO3 being best performing.

Enhanced Charge Carrier Separation in WO3/BiVO4 Photoanodes Achieved via Light Absorption in the BiVO4 Layer

“…A series of control photoanodes consisting of pure BiVO 4 on FTO (without WO 3 layer) with variable BiVO 4 thickness was also prepared. The absorption spectra of the two electrode series are shown in Figures S1 and S2; the thickness of the BiVO 4 layer was estimated using the absorption coefficient at 420 nm, 19 α 40 = 6.7 × 10 4 cm −1 . XRD analyses confirm the successful synthesis of WO 3 and BiVO 4 (Figure S3) and FESEM images demonstrate the uniform coating of the photoanodes (Figure S4).…”

“…A way to overcome this intrinsic flaw is to couple BiVO 4 with WO 3 in the WO 3 /BiVO 4 heterojunction where visible light harvesting BiVO 4 sensitizes wider band gap WO 3 . BiVO 4 photoanodes based on this heterojunction achieve the highest current densities among oxide-based photoanodes. , The suitable band gap alignment between the two oxides, the efficient electron and hole transport in WO 3 and BiVO 4 , respectively, and the spacial charge separation support the high performance of WO 3 /BiVO 4 photoanodes. − …”

Constructing a Two-Dimensional SnWO4 Nanosheet Array Film for Enhanced Photoelectrochemical Performance

“…At a wavelength of 500−620 nm, the SnWO 4 -NS photoanode has a higher IPCE value than the SnWO 4 -powder photoanode (Figure 7a) and SnWO 4 -flaking photoanode (Figure S8a), indicating a better photon-to-electron conversion ability due to the 2D array structure. To exclude the influence of light absorption, the absorbed photon-to-current conversion efficiency (APCE) was calculated (referring to the Supporting Information for detailed calculation), 46 and it also presents a high efficiency of the SnWO 4 -NS photoanode compared to the SnWO 4 -powder photoanode (Figure 7b) and SnWO 4 -flaking photoanode (Figure S8b). These results illustrate that the charge separation is accelerated by introducing a 2D sheet-like array structure SnWO 4 for film photoanodes.…”

Fabricating BiVO4/FeOOH/ZnFe-LDH hierarchical core–shell nanorod arrays for visible-light-driven photoelectrochemical water oxidation

“…Meanwhile, coupling with water oxidation electrocatalysts at the BiVO 4 photoanode, such as CoPi, 15 NiOOH, 16,17 FeOOH, 16,18,19 CoOOH, 20 and NiFe oxide/ hydroxide, [21][22][23][24] is also one of the most effective ways to improve the oxidation kinetics of BiVO 4 . In addition, appropriate interface matching, concluding the crystal lattice, 25,26 energy band level 27,28 or local structure of the semiconductor/electrocatalyst interface, [29][30][31] plays a vital role in effective charge separation and transport. The rational design and fabrication of the BiVO 4 /coca-talyst interface have grabbed plenty of attention and some constituents that are only used as cocatalysts have also been explored to optimize the interface properties.…”