Incipient adsorption of water and hydroxyl on hematite (0001) surface

Abstract

The adsorption of submonolayer coverages of water and hydroxyl molecules on hematite (0001) surface is investigated using density functional theory with Hubbard correction U (DFT+U). The effect of adsorption on the structural, energetic, and electronic properties of both iron and oxygen terminated hematite surfaces is examined. The influence of the van der Waals interactions on the adsorption binding energy and geometry is also considered. It is found that tilted orientations of molecules are energetically more favored than planar ones, because the hydrogen bond stabilizes molecules on the surface. Bonding of H 2 O is more than twice weaker than that of OH. For both molecules adsorption on the iron-rich termination is much stronger than on the oxygen-terminated surface. The differences in bonding properties of water and hydroxyl molecules to the hematite surfaces are explained by different character of the charge transfer in the molecule-oxide system.

Single Crystalline α-Fe2O3 Nanosheets with Improved PEC Performance for Water Splitting

“…The same was observed experimentally by Li et al, where hematite crystallites with the (012) surface were found to have higher OH coverage, which play a positive role in PEC water oxidation reaction . The (0001) surface in hematite is a naturally occurring and thermodynamically stable surface. , Moreover, the electrical conductivity in the (0001) plane is four times higher than that along [001] direction. , Both these features of the (0001) surface are advantageous to water splitting . It is worth noting that the α-Fe 2 O 3 NSs presented in this work possess the widest surface of (0001).…”

“… 49 , 50 Moreover, the electrical conductivity in the (0001) plane is four times higher than that along [001] direction. 51 , 52 Both these features of the (0001) surface are advantageous to water splitting. 51 It is worth noting that the α-Fe 2 O 3 NSs presented in this work possess the widest surface of (0001).…”

Boosting Charge Transfer Efficiency by Nanofragment MXene for Efficient Photoelectrochemical Water Splitting of NiFe(OH)x Co-Catalyzed Hematite

“…The work function of α-Fe 2 O 3 (5.0 eV) was larger than that of NFMX (4.7 eV), indicating that it formed an undesirable Ohmic contact, as shown in Figure S16b,c. However, the surface of α-Fe 2 O 3 was not fully covered by NFMX and absorbed H 2 O molecules might reduce the surface dipole moment, lowering the work function of α-Fe 2 O 3 to ∼ −0.78 eV, as reported by Pabisiak et al This resulted in the band edge shift of α-Fe 2 O 3 , turning the Ohmic contact into a Schottky contact, which is beneficial for PEC water oxidation (Figure S16d). , …”

“…As shown in Figure 4a, the charge trapping resistance to surface states (R trap ) and the charge transfer resistance (R ct ) from surface states to the electrolyte are presented in the Nyquist plot, fitted by the equivalent circuit model, as shown in the inset circuit of Figure 4a. 60 In Figure 4b,c 61 This resulted in the band edge shift of α-Fe 2 O 3 , turning the Ohmic contact into a Schottky contact, which is beneficial for PEC water oxidation (Figure S16d). 62,63 In Figure 4d, the density of the mid-gap surface states (Nss), which are related to OH− and O− terminated surfaces, was calculated from C trap (Figure S17).…”