Environmental Engineering Reference
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FIGURE 3.8 (a) Overlay of Fe 2p XPS spectra of air annealed hematite (denoted as: A-hematite) and
oxygen-deficient hematite (denoted as: N-hematite), together with their different spectrums. The dashed
lines highlight the satellite peaks of Fe 2+ and Fe 3+ . (b) Mott-Schottky plots measured for A-hematite and
N-hematite. Inset: magnified Mott-schottky plot of N-hematite. (c) Linear sweep voltammograms col-
lected on A-hematite and N-hematite under a simulated solar light of 100 mW cm −2 and dark condition
with a scan rate of 10 mV s −1 . (d) The corresponding IPCE spectra for A-hematite and N-hematite col-
lected at potentials of 1.23 and 1.5 V versus RHE. Source : Reproduced with permission from Ling et al.
[46]. (See color insert.)
charge transport in the hematite. Moreover, IPCE studies also showed
enhanced photoactivity in the entire wavelength region that is consistent with
the bandgap of hematite.
Previous studies have primarily focused on binary metal oxides for PEC
water splitting. However, one of the fundamental constrains of these binary
metal oxides is that their valence bands are typically composed of O2p char-
acter, which lie far more positive than the water oxidation potential. As
a result, some energy will be wasted during water oxidation and limit the
solar conversion efficiency. Recently, ternary metal oxides have attracted
renew attentions on PEC water splitting, as their electronic bands are formed
by atomic orbitals from more than one element and the modulation of the
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