Photocatalytic Facet Selectivity in BiVO₄ Nanoparticles: Polaron Electronic Structure and Thermodynamic Stability Considerations for Photocatalysis

Abstract

Selective charge separation among different crystal facets of a semiconductor is an intriguing phenomenon for which there is no firm and full theoretical foundation currently. In this work, we report on a density functional theory + U characterization of band alignment and electron and hole polaron stabilities among the (010), (110), and (011) facets of bismuth vanadate BiVO 4 (BVO). Computation-derived band alignment indicates that the conduction band minima are at nearly the same level among the three facets but that the valence band maxima exhibit a shift. We also modeled electron and hole polarons as localized electrons and holes on vanadium and oxygen, respectively, and determined their relative stabilities from a "bulk" region to a surface region. Calculated stabilities reveal similar stability profiles across the various facets, with electron polarons most stable when localized on subsurface V atoms and hole polarons most stable on surface O atoms. Calculations indicate a small stability preference for electron polarons toward the (011) facet and for hole polarons toward the (110) facet, whereas, experimentally, interfacial reduction is observed to take place selectively on the (010) facet and oxidation on the (110) and (011) facets. Facet selectivity could be occurring on the basis of thermodynamics (electron or holes showing a stronger affinity for some facets over others) or kinetics (electron or hole transport and/or redox processes being more efficient toward/on some facets over others) or a combination of both. This work establishes that thermodynamic stability alone is not responsible for the observed facet selectivity in BVO. Therefore, we surmise that polaron transport kinetics and interfacial redox kinetics are likely to have a role in facet selectivity in BVO. These issues will be the subject of future publications.

Dynamics of Photoexcited Small Polarons in Transition-Metal Oxides

“…It can quench by recombining with the opposite charges. While the dynamics of charge-doping-induced ground-state polarons has already been studied in many TMOs, ,− due to the complexity, the behavior of photoexcited polarons in TMOs is still unclear.…”

Tuning Selectivity of Photoelectrochemical Water Oxidation via Facet-Engineered Interfacial Energetics

“…Here, two typical (010) and (110) crystal facets of BiVO 4 (BVO) are demonstrated because (1) BVO has a sufficient VB position to drive both the 2e − and 4e − WOR 45 and (2) the charge separation occurring between the (010) and (110) crystal facets is unexplored WOR activity. 46 against ΔG OH* . Data for several oxides reported in the literature were also included for comparison (Figure S2).…”

Z-scheme CdS/BiVO4 Photocatalyst for Highly Efficient Photodegradation of Organic Pollutants and DFT Calculation

“…To determine the charge transfer between CdS and BiVO4, we carried out DFT calculations using the Vienna Ab initio Simulation Package (VASP) code [36,37]. Meanwhile, the generalized gradient approximation (GGA) of the Perdew-Burke-Ernzerhof (PBE) is adopted for the exchange and correlation potential [38].…”

“…And the electron-hole transfer path was probed by the calculation of the electrostatic potential. Then, the surfaces of (010) and (100) were cleaved from BiVO4 cell and CdS cell (Figure 8 According to previous report, the difference in the electrostatic potential can be used to judge the migrating of photo-generated electrons [37]. As a result, the photo-generated electrons on the CdS can be more easily transferred to the BiVO4 at the CV-x (x=1~4) heterojunction.…”