The Operando Optical Spectrum of Hematite during Water Splitting through a GW–BSE Calculation

Abstract

Hematite is a possible photoanode for photoelectrochemical cells (PECs) that is widely studied using density functional theory (DFT). In this paper we perform more accurate calculations of the absorption spectrum of hematite using the one-shot Green’s function (G 0 W 0) and Bethe–Salpeter equation (BSE) methods, which take excited states into account and compare the spectrum to experimental data. We found a match between our calculations and the observed absorption spectra in peak locations. Furthermore, there is anisotropy of the absorption spectra that is concurrent with the crystal structure. We also calculated the absorption spectrum of hematite intermediates during catalysis of the oxygen evolution reaction to better understand which intermediate is dominant during the reaction and the contribution of excited states to catalysis. The *O intermediate was found to be the most optically and chemically dominant species during catalysis.

Oxygen Evolution Catalysts at Transition Metal Oxide Photoanodes: Their Differing Roles for Solar Water Splitting

“…[ 100–102 ] Through computation, Toroker's group has been attempting to reproduce the absorption spectra of the four main OER intermediate species, i.e., *O, *OOH, *, and *OHH, with respect to the neutral *OH. [ 103,104 ] The feature at around 580 nm for *O displayed reasonable matches with experimental findings. Similar results have been also observed previously with potential modulated absorption spectroscopy and light modulated absorption spectroscopy, where these features are subdued upon Al 2 O 3 coating but unchanged with various bulk thicknesses.…”

Simulations to Cover the Waterfront for Iron Oxide Catalysis

“…The transition of *OH 2 and *OOH intermediates to *OH and *O is found to be a reason for the domination of *O on the surface, and this result is in agreement with experimental measurements. [11,32] With this work, we demonstrated how neighboring sites may use each other's presence as neighbors to reduce the energy required for catalytic steps. To the best of our knowledge, this work is the first to show the effects of neighbor-site species interactions that do not create a new intermediate.…”

Identifying the Spectroelectrochemical Characteristics of Hematite Photoanodes for Water Oxidation

“…3c). 36 The optical signals of OER intermediate for Ti1-Fe2O3 is identical to Fe2O3 but those of Ti5-Fe2O3 are slightly different due to the different surface chemical composition (Supplementary Fig. 9).…”

“…32,35 The gradient doping near the surface, and the concomitant upshifted local Fermi levels would therefore cause a downward band bending. As such, a more 36 anodic applied potential is needed to flatten the bands, causing shifts in Efb. The negative effect of this downward bending is substantially eliminated when an α-Fe2O3/Fe2TiO5 heterojunction is formed.…”

“…(c) Spectra of the main OER intermediate species under illumination calculated by subtracting the -0.2 VHg/HgO spectrum from all higher potential spectra in (b, i) for Fe2O3. For comparison, dashed black curve shows the calculated Fe(IV)=O spectrum relative to Fe(III)-OH by Snir et al36…”