Copper (II) oxide
(CuO) nanostructures were prepared on fluorine-doped
tin oxide (FTO) using a three-step heat treatment process in a sol–gel
dip-coating method. The precursor used for the dip-coating process
was prepared using copper acetate, propan-2-ol, diethanolamine, and
polyethylene glycol 400. Dip-coated films in layers of 2, 4, 6, 8,
and 10 were prepared by drying each layer at 110 and 250 °C for
10 and 5 min, respectively, followed by calcination at 550 °C
for 1 h. The films were applied toward photocatalytic hydrogen evolution
from water. The X-ray diffraction (XRD) pattern of the films confirmed
the tenorite phase of pure CuO. Raman spectroscopy revealed the 1A
g
and 2B
g
phonon modes of CuO, confirming the high
purity of the films produced. The CuO films absorb significant photons
in the visible spectrum due to their low optical band gap of 1.25–1.33
eV. The highest photocurrent of −2.0 mA/cm
2
at 0.45
V vs reversible hydrogen electrode (RHE) was recorded for CuO films
consisting of six layers under 1 sun illumination. A more porous surface,
low charge transfer resistance, and high double-layer capacitance
at the CuO/electrolyte interface observed for the films consisting
of six layers contributed to the high photocurrent density attained
by the films. CuO films consisting of six layers prepared using the
conventional two-step heat treatment process for comparative purposes
yielded 65.0% less photocurrent at 0.45 V vs RHE compared to similar
films fabricated via the three-step heating method. The photocurrent
response of the CuO nanostructures prepared using the three-step heat
treatment process is promising and can be employed for making CuO
for photovoltaic and optoelectronic applications.
Using x-ray spectroscopy to analyze a photoelectrochemical cell during water oxidation and hydrogen formation sheds light on the physics and chemistry of photoelectrodes.
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