α‑Fe<sub>2</sub>O<sub>3</sub>/NiOOH:
An Effective Heterostructure for Photoelectrochemical Water Oxidation
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Abstract
The
study of the semiconductor/electrocatalyst interface in electrodes
for photoelectrochemical water splitting is of paramount importance
to obtain enhanced solar-to-fuel efficiency. Here, we take into consideration
the multiple effects that a thin layer of photodeposited amorphous
Ni-oxyhydroxide (NiOOH) induces on hematite (α-Fe<sub>2</sub>O<sub>3</sub>) photoanodes. The reduction of overpotential produced
a photocurrent onset potential advance of 150 mV and an increase of
photocurrent of about 50% at 1.23 V vs RHE. To give an interpretation
to these phenomena, we carried out deep electrochemical investigations
by cyclic voltammetry and electrochemical impedance spectroscopy.
The effective charge injection into the electrolyte due to the reduction
of the charge transfer resistance at the electrode/electrolyte interface
was observed and increased along with the amount of deposited NiOOH.
The benefits of NiOOH deposition are ascribable to its ability to
scavenge holes from hematite surface traps. This effect is mitigated
at a potential higher than 1.25 V, since a fraction of photogenerated
holes is consumed into the Ni redox cycle