Oxygen Evolution at Hematite Surfaces: The Impact of Structure and Oxygen Vacancies on Lowering the Overpotential

Abstract

Simulations of the oxygen evolution reaction (OER) are essential for understanding the limitations of water splitting. Most research has focused so far on the OER at flat metal oxide surfaces. The structure sensitivity of the OER has, however, recently been highlighted as a promising research direction. To probe the structure sensitivity, we investigate the OER at eleven hematite (Fe2O3) surfaces with density functional theory + Hubbard U (DFT + U) calculations. The results show that the O-O coupling (O-O bond formation via two adjacent terminal Os at dual site) OER mechanism at the (110) surface is competing with the mechanism of OOH formation at single site. We study the effects of surface orientation (110 vs. 104), active surface sites (bridge vs. terminal site), presence of surface steps and oxygen vacancy concentration on the OER and explore strategies to reduce the OER overpotential. It is found that the oxygen vacancy concentration is the most effective parameter in reducing the overpotential. In particular, an overpotential of as low as 0.47 V is obtained for the (110) surface with an oxygen vacancy concentration of 1.26 vacancies/nm 2 .

Highly Selective Electrochemical Reduction of Dinitrogen to Ammonia at Ambient Temperature and Pressure over Iron Oxide Catalysts

“…Furthermore, chronoamperometry tests of the four catalysts at more negative potentials were carried out. [34][35][36] In our case, the slight changes in crystal orientation may be acontributing factor in the higherN H 3 formation rates that were observedf or the hematite samples than fort he untreated hematite analogues after thermala nnealing (see the Supporting Information,T ableS2), yet they were unable to explain the large difference in NRR activity between the two hematite samples after thermala nnealing. All catalysts displayed the highest averageN H 3 formation rate at À0.9 Vv s. Ag/AgCl, with the highest rate (0.459 mgh À1 cm À2 )o btainedb yt he o-Fe 2 O 3 -Ar/ CNT catalyst.…”

Key Strategies to Advance the Photoelectrochemical Water Splitting Performance of α‐Fe2O3 Photoanode

“…This part of the review article is intended to provide mechanistic insight into the water oxidation reactions on α‐Fe 2 O 3 surface, and the origin of surface states . At the beginning of the year 2011, Liao et al .…”

“…In general, one oxygen vacancy generates two electrons which increase charge carrier concentrations and results in better conductivity. In 2016, Zhang et al ,. reported two exciting pieces of work where they explained the orientation sensitivity (Figure d), surface state, oxygen vacancies, etc ., on OER at the α‐Fe 2 O 3 surface.…”

Surface stabilities of 3C–SiC and H2O adsorption on the (110) surface

“…20,21 To assess the possible impact of water on 3C-SiC, it is always fundamentally important to investigate the adsorption behaviors of H 2 O on 3C-SiC surfaces. Moreover, the adsorption of H 2 O and the subsequent dissociation dictate the water splitting on these surfaces through a series of complex oxygen and hydrogen evolution reactions, 22,23 which can be of wider interests to surface catalysis. 24 Multiple theoretical studies have suggested that the surface termination of 3C-SiC have great influence on the H 2 O adsorption.…”