Unraveling
the charge-carrier dynamics at electrocatalyst/electrode
interfaces is critical for the development of efficient photoelectrochemical
(PEC) water oxidation. Unlike the majority of photoanodes investigated
for PEC water oxidation, the integration of electrocatalysts with
CuWO4 electrodes generally results in comparable or worse
performance compared to the bare electrode. This is despite the fact
that the surface state recombination limits the water oxidation efficiency
with CuWO4 electrodes, and an electrocatalyst ought to
bypass this reaction and improve performance. Here, we present results
that deepen the understanding of the energetics and electron-transfer
processes at the CuWO4/electrocatalyst interface, which
controls the performance of such systems. Ni0.75Fe0.25O
y
(denoted as Ni75) was chosen
as a model electrocatalyst, and through dual-working electrode experiments,
we have been able to provide significant insight into the role of
the electrocatalyst on the charge-transfer process at the CuWO4/Ni75 interface. We have shown a lack of performance improvement
for CuWO4/Ni75 relative to the bare electrode to water
oxidation. We attribute this surprising result to water oxidation
on the CuWO4 surface kinetically outcompeting hole transfer
to the Ni75 electrocatalyst interface.