Synergetic Surface Sensitivity of Photoelectrochemical Water Oxidation on TiO₂ (Anatase) Electrodes

Abstract

The paper compares photoelectrocatalytic activity and selectivity of nanocrystalline anatase dominated by {110}, {101}, and {001} faces in photo(electro)catalytic water splitting. Although the anodic half-reaction of water splittingoxygen evolutiondominates the overall photoelectrochemical behavior of the photoexcited anatase, simultaneous reduction under photoelectrochemical conditions is also observed on some anatase faces. The activity of individual facets in anodic half-reaction of water splitting (oxygen evolution) increases in the order {101} < {110} < {001}. The increasing oxidation activity tracks the tendency of the surface to generate the OH • radical producing intermediates (H 2 O 2 , ozone) on the trapped hole states. The activity in reduction processes increases in the reversed order. Particularly, the reduction activity of the {101} oriented anatase can be attributed to pronounced hydrogen evolution by a charge transfer of photogenerated electrons. The observed trends agree with DFT-based models which confirm the possibility of a rational design of the photocatalysts.

Photo‐electrochemical activity and selectivity of nanocrystalline BaTiO3 electrodes in water oxidation

“…This type of the response is difficult to attribute to any recombination process and most likely reflects a gradual dominance of the electron transfer at the electrode/electrolyte interface. Similar behavior was reported previously for TiO 2 anatase [34] and SrTiO 3 [26] and might be facilitated by the proton transfer in the solution. One may reflect the fact that the protons formed in the anticipated oxidation of water may affect the charge transfer process as they need to be transported away from the electrode (i.e.…”

“…The experimental trends reflected in the DEMS data can be rationalized if one adopts the model reported in. [26,34,35] This model assumes that the photocurrent recorded in the experiments is, in fact, an integral of all charge transfer processes proceeding at the illuminated surface.…”

“…The photocurrent onset in alkaline media also shows little to no sensitivity to the actual particle size. It needs to be noted that a similar behavior when the photocurrent needs to be driven by significantly higher bias in alkaline than in acid is a native behavior of oxides based on tetravalent Ti [ 26,34 ] and most likely reflects a shift of protonation/deprotonation equilibria of the surface Ti‐O bonds.…”

Electronic Structure and Band Alignments of Various Phases of Titania Using the Self-Consistent Hybrid Density Functional and DFT+U Methods

“…However, due to the sensitivity of electronic structures, to the surface state (e.g., defects or molecular adsorptions, particle size, dielectric environment, etc.) (Diebold, 2003; Yu et al, 2003; Stevanovic et al, 2012; Ronca et al, 2013; Amano et al, 2016; Macounová et al, 2017), a complete understanding of the electronic and optical properties of TiO 2 remains elusive, despite a number of experimental and theoretical studies that have been conducted. For example, the relative band edge positions between the rutile and anatase phases are still under debate (Li and Gray, 2007; Scanlon et al, 2013; Zhang et al, 2014; Nolan et al, 2016).…”

Electrochemical Doping as a Way to Enhance Water Photooxidation on Nanostructured Nickel Titanate and Anatase Electrodes

“…As shown in Figure 2, the behavior that we observe for the nanoporous electrodes is clearly different. [23,39] Under these conditions, the photogenerated charge carrier separation and transport are dominated by the kinetics at the semiconductor-electrolyte interface which depends on the exposed facets [42] and the charge diffusion inside the nanostructure, which is tuned by the substrate potential. Considering the electrolyte composition, and the fact that the material is stable in 1 M NaOH in this potential range, the only possible reactions associated with the photocurrents are water photooxidation (oxygen evolution) and water photoreduction (hydro-gen evolution) (See SI, Figure S.1).…”