Chemical, Structural, and Electronic Characterization of the (010) Surface of Single Crystalline Bismuth Vanadate

Abstract

We have structurally, chemically and electronically characterized the most stable (010) surface of a Mo-doped BiVO 4 single crystal. Low energy electron diffraction (LEED) reveals that the surface is not significantly reconstructed from a bulk termination of the crystal. Synchrotron based X-ray spectroscopies indicate no surface enhancement of any of the crystal constituents and that the Mo dopant occupies tetrahedral sites by substituting for V at the surface. Using resonant photoemission to study the valence band structure as the V L 3 edge is scanned we observe an intra-band gap state associated with reduced vanadium formed by the Mo doping. This state is likely associated with small polaron formation at the surface. This feature is enhanced at a photon energy that is not resonant with any of the main features in the absorption spectrum of the pristine BiVO 4. This indicates that the additional electron from Mo doping likely induces further distortion of the VO 4 tetrahedral units and generates a new conduction band state either by splitting of the V dz 2 states or by hybridization of V d zx and V dz 2 states. We measure a work function of 5.15 eV for the BiVO 4 (010) surface. Measurement of the work function allows us to recast the electronic energy levels onto the normal hydrogen electrode scale for comparison to the standard reduction and oxidation potentials of water. This detailed study should provide a basis for future work aimed at a molecular level understanding of BiVO 4 /electrolyte interfaces used for photoelectrochemical water splitting.

The role of ultra-thin MnOx co-catalysts on the photoelectrochemical properties of BiVO4 photoanodes

“…To further conrm this explanation, we calculated the extent of band bending in our BiVO 4 lms, assuming the core level peak position values of the BiVO 4 single crystal as those of the bulk (159.3 eV for Bi 4f 7/2 and 516.9 eV for V 2p 3/2 ). 48 The values for BiVO 4 lms with various MnO x thicknesses are listed in Table S1; † the values calculated using the Bi 4f 7/2 peak position agree very well with those calculated using V 2p 3/2 . Indeed, the extent of band bending increases with the increasing lm thickness.…”

Revealing Nanoscale Chemical Heterogeneities in Polycrystalline Mo‐BiVO4 Thin Films

“…We provide the analysis and comparison of these spectra with existing literature on un‐doped and doped Mo‐BiVO 4 , as well as V 2 O 5 . [ 2b,12 ] While in V 2 O 5 the coordination geometry of the oxygen ligands is octahedral, in Mo‐BiVO 4 is tetrahedral. In detail, the V spectrum comprises the L 3 ‐ (515–520 eV) and L 2 ‐edge (521–528 eV), which are separated by ≈6.8 eV due to the spin‐orbit coupling of the 2p core hole.…”

“…In detail, the V spectrum comprises the L 3 ‐ (515–520 eV) and L 2 ‐edge (521–528 eV), which are separated by ≈6.8 eV due to the spin‐orbit coupling of the 2p core hole. [ 2b,12 ] The L 3 ‐edge arises from dipole‐allowed transition from V 2p 3/2 core levels to the unoccupied V 3d states of the conduction band (CB). Within the V L 3 ‐region, three main peaks are discernable at 516.3 eV (t 2 , Peak 2), 517.3 eV (Peak 3), and 518.5 eV (e, Peak 4) originating from the ligand field splitting of V 3d states.…”

“…Within the V L 3 ‐region, three main peaks are discernable at 516.3 eV (t 2 , Peak 2), 517.3 eV (Peak 3), and 518.5 eV (e, Peak 4) originating from the ligand field splitting of V 3d states. [ 2b,12 ] Specifically, the peak at 516.3 eV (Peak 2) is composed of V 3 and 3 states, and the peak at 518.5 eV (Peak 4) of V 3d xy , 3d yz , and 3d zx states. [ 13 ] A small shoulder is observed at a photon energy of ≈515.3 eV (Peak 1), which can be attributed to core hole exciton or to excitation of an electron into a small polaronic state at V 4+ sites generated by Mo‐doping.…”

“…[ 13 ] A small shoulder is observed at a photon energy of ≈515.3 eV (Peak 1), which can be attributed to core hole exciton or to excitation of an electron into a small polaronic state at V 4+ sites generated by Mo‐doping. [ 12,14 ] An additional feature at 519.7 eV (Peak 5) is a consequence of mixing of anisotropic Bi 6p states with O 2p states. [ 12 ] The V L 2 ‐region corresponds to excitation from 2p 1/2 core levels to unoccupied CB V 3d states, which is further split into two peaks at 523.5 eV (Peak 6) and 525.3 eV (Peak 7) corresponding to t 2 and e states, respectively.…”