Revealing Nanoscale Chemical Heterogeneities in Polycrystalline Mo‐BiVO₄ Thin Films

Abstract

The activity of polycrystalline thin film photoelectrodes is impacted by local variations of the material properties due to the exposure of different crystal facets and the presence of grain/domain boundaries. Here a multi‐modal approach is applied to correlate nanoscale heterogeneities in chemical composition and electronic structure with nanoscale morphology in polycrystalline Mo‐BiVO4. By using scanning transmission X‐ray microscopy, the characteristic structure of polycrystalline film is used to disentangle the different X‐ray absorption spectra corresponding to grain centers and grain boundaries. Comparing both spectra reveals phase segregation of V2O5 at grain boundaries of Mo‐BiVO4 thin films, which is further supported by X‐ray photoelectron spectroscopy and many‐body density functional theory calculations. Theoretical calculations also enable to predict the X‐ray absorption spectral fingerprint of polarons in Mo‐BiVO4. After photo‐electrochemical operation, the degraded Mo‐BiVO4 films show similar grain center and grain boundary spectra indicating V2O5 dissolution in the course of the reaction. Overall, these findings provide valuable insights into the degradation mechanism and the impact of material heterogeneities on the material performance and stability of polycrystalline photoelectrodes.

Solution-based synthesis of wafer-scale epitaxial BiVO4 thin films exhibiting high structural and optoelectronic quality

“…28 Therefore, this step was performed in a confined volume, which helped to maintain the desired stoichiometry. Consistent with prior reports of metalorganic decomposition-derived BiVO 4 , 20,29 X-ray photoelectron spectroscopy (XPS) reveals a Bi-rich surface (Fig. S7†).…”

Review on BiVO4-Based Photoanodes for Photoelectrochemical Water Oxidation: The Main Influencing Factors

“…The improvement of electrical conductivity can improve the transfer and separation of charge carriers in BiVO 4 . As mentioned above, doping is considered to be an effective method to boost the conductivity of semiconductors, mainly by changing the electronic structure. − Various elements including nonmetals and metals have been successfully doped into BiVO 4 to improve the PEC performance. , Representative examples include W and Mo doping. , Replacing V 5+ in BiVO 4 with W 6+ or Mo 6+ has been confirmed to be the most promising method to improve the PEC activity, which effectively improves the electronic conductivity. , Park et al used DFT+U to clarify that W 6+ or Mo 6+ replaces the V location and causes the localized state of BiVO 4 band gap. The W- and Mo-doped BiVO 4 displays higher photocurrent than pristine BiVO 4 , because the carrier separation efficiency was enhanced by doping.…”

Designing multifunctional CoOx layers for efficient and stable electrochemical energy conversion

“…In this regard, interfacing semiconductor light absorbers with conformal and ultra-thin catalytic layers is a promising strategy to overcome the poor efficiency and material stability of the semiconductor photoelectrodes under harsh photoelectrochemical operating conditions. [9][10][11][12][13][14][15][16] These multifunctional layers provide protection against corrosion in chemical environments and at the same time activate the desired catalytic reaction, while still permitting efficient interfacial charge transport and minimizing losses due to parasitic light absorption. However, simultaneously fulfilling each of these criteria requires precise control over film properties, often down to the sub-nm length scale.…”