posted on 2022-01-31, 18:45authored byYutong Liu, Rodney D. L. Smith
A high
degree of variability in behavior and performance of hematite
as photoanodes for the oxygen evolution reaction signifies a need
to improve our understanding of the interplay between defects and
photoelectrochemical performance. We approach this problem by applying
structure–property analysis to a series of hematite samples
synthesized under either O2 or N2 environments
such that they exhibit highly variable performance for photoelectrocatalytic
oxygen evolution. X-ray absorption fine-structure spectroscopy and
Raman spectroscopy provide parameters describing the structure of
samples across the series. Systematic comparisons of these parameters
to those describing photoelectrochemical performance reveal different
defects in samples prepared under N2 or O2.
Distinct correlations between both the iron oxidation state and charge
carrier density with photoelectrocatalytic performance lead to assignment
of the primary defects as oxygen vacancies (N2) and iron
vacancies (O2). Differences in the structural distortions
caused by these defects are seen in correlations between short-range
structural parameters and photoelectrochemical behavior. These distortions
are readily observed by Raman spectroscopy, suggesting that it may
be possible to calibrate the width, energy, and intensity of peaks
in Raman spectra to enable direct analysis of defects in hematite
photoanodes.