Introduction of oxygen vacancies into hematite in local reducing atmosphere for solar water oxidation

Inherent Oxygen Vacancies Boost Surface Reconstruction of Ultrathin Ni-Fe Layered-Double-Hydroxides toward Efficient Electrocatalytic Oxygen Evolution

“…0.3 eV) is further detected in the profile of Fe 2p (Figure d). These results together point out the increasing electron density around metal atoms (Ni and Fe) due to enriched V O . Accordingly, Ni-Fe LDH- V O shows the obviously decreased signal of O–H in its O 1s profile (Figure S2) but the increased ones for M–O and adsorbed H 2 O owing to V O .…”

“…To further inquire the local structures, molecular vibrational spectroscopies were carried out (Figure S1). In Raman spectra, the two samples show the peaks correlated with a representative carbonate-intercalated Ni-Fe LDH, such as v CO 3 2– at 1061 cm –1 , v Ni 2+ – O – Fe 3+ at 460 cm –1 , and v Fe 3+ – O – Fe 3+ at 530 cm –1 . , In comparison with Ni-Fe LDH, Ni-Fe LDH- V O shows a visible red-shift of the band ascribed to the O–M–O bending, which is likely caused by crystal defects. , In FT-IR spectra, the v M – O band in Ni-Fe LDH- V O is located at 650 cm –1 , lower than that of Ni-Fe LDH (764 cm –1 ), which suggests the weakened M–OH bonds due to rich V O . , …”

“…As shown in Figure b, ferric sites of high spin (3d 5 ) are evidenced by a strong signal in EPR with a Landé factor ( g ) of 1.97. , By contrast, the signal of Ni-Fe LDH- V O is visibly weakened, indicating the decreased concentration of electronic spin and unpaired ectrons . Rich V O in Ni-Fe LDH- V O brings about more electrons in Fe d-orbital manifolds for the counterbalance of charge, namely, Fe 2+ (3d 6 ) with the reduced resonance of electronic spin. , To be noted, the EPR peak signal at 1.97 was considered as an indicator for the presence of V O in TiO 2 because Ti 4+ had empty d orbitals, while Ti 3+ coexisting with V O had one unpaired electron . In this case, the peak signal intensities were positively correlated to the relative amount of V O , which is obviously distinct from our LDH involving Fe 3+ .…”

“…35 Rich V O in Ni-Fe LDH-V O brings about more electrons in Fe d-orbital manifolds for the counterbalance of charge, namely, Fe 2+ (3d 6 ) with the reduced resonance of electronic spin. 3,30 To be noted, the EPR peak signal at 1.97 was considered as an indicator for the presence of V O in TiO 2 because Ti 4+ had empty d orbitals, while Ti 3+ coexisting with V O had one unpaired electron. 36 In this case, the peak signal intensities were positively correlated to the relative amount of V O , 28 which is obviously distinct from our LDH involving Fe 3+ .…”

“…These results together point out the increasing electron density around metal atoms (Ni and Fe) due to enriched V O . 30 (hν) that are above the band gap of semiconductors can be absorbed. This is expressed as the following equation:…”