Competitive Photo-Oxidation
of Water and Hole Scavengers
on Hematite Photoanodes: Photoelectrochemical and Operando Raman Spectroelectrochemistry
Study
posted on 2022-12-22, 12:37authored byVivek Ramakrishnan, Anton Tsyganok, Elena Davydova, Mariela J. Pavan, Avner Rothschild, Iris Visoly-Fisher
Hematite
(α-Fe2O3) is one of the most
studied photoanode materials due to its stability in alkaline electrolytes
and visible light absorption. However, its reported performance lags
significantly behind its theoretical limit. Toward determining routes
for efficient photo-oxidation on hematite, we investigated the role
of hole-trapping surface states as reaction intermediates using sacrificial
reductant reagents as hole scavengers, H2O2 and
FeCN. Photoelectrochemical characterization at low scavenger concentrations
and intermediate potentials, as opposed to previous studies at high
scavenger concentrations, has shown the reaction mechanism to include
competitive photo-oxidation between water molecules and the hole scavengers,
similar for both H2O2 and FeCN. Using operando
Raman spectroelectrochemistry, we show similar transient features
for both scavengers, interpreted as scavenger adsorption to a two-site
reaction intermediate participating in the photogenerated hole transfer
of water photo-oxidation, hence the competition. These findings strengthen
the significance of hole-trapping surface states for water photo-oxidation
on hematite and the previously suggested two-site reaction pathway
for efficient hole transfer in this reaction. A better understanding
of the mechanisms of photoelectrochemical water splitting can assist
in improving the efficiency of solar hydrogen production.