Electrodeposition and photoelectrochemistry of Cu2O in aqueous solutions

Article abstract of DOI:10.1524/zpch.1999.212.Part_2.187

Well-defined crystalline Cu₂O was electrodeposited on TFO from basic Cu(II)-lactate solutions. Experimental conditions, especially the temperature and pH of the deposition solution, had a strong influence on the deposition kinetics and the morphology of the formed layers. The photo-electrochemical properties of the Cu₂O were investigated. A composite material was made by electrodepositing the p-type Cu₂O inside a nanoporous n-type TiO₂ electrode. by Oldenbourg Wissenschaftsverlag, Muenchen.

Full text of DOI:10.1524/zpch.1999.212.Part_2.187

Zeitschrift für
©
Chemie,
Wissenschaftsverlag,
Bd. 212, S. 187-200
München
Physikalische
(1999)
by
Oldenbourg
and
Electrodeposition
Photoelectrochemistry
of
in
Solutions
Cu20
Aqueous
P. E.
de
D.
and J. J.
By
Jongh*,
Vanmaekelbergh
Kelly
Institute, Utrecht
PO
Box
3508
TA
Debye
The Netherlands
80000,
Utrecht,
University,
10, 1998;
December
(Received
August
accepted
10, 1998)
I
Cu201
Photo-electrochemistry
Electrodeposition
Well-defined
solutions.
was
on
TFO from basic
crystalline Cu20
electrodeposited
the
Cu(II)-lactate
conditions,
influence on
Experimental
and
and the
the Cu,0 were
of the
especially
the
temperature
pH
deposition
had
a
kinetics
solution,
of the
strong
The
deposition
morphology
formed
of
layers.
photo-electrochemical
A
properties
investigated.
material
was made
the
Cu,0
composite
inside
a
p-type
by electrodepositing
nanoporous
electrode.
Ti02
-type
Introduction
Cu,0 has direct
a
of 2.0-2.2
eV
which makes it
[1,
a
bandgap
2],
promis-
material for
the conversion
of solar
into electrical
or chemical
ing
energy
For
has
been
that
it
shown
to
than
small
energy.
Cu20
example
recently
particles
in
and
could
water
be used
as
a
Stable
water.
photocatalyst
more
split
hydrogen
evolution
took
for
1800 hours under
illumi-
oxygen
place
and
nation
in
environment
[3].
aqueous
usually
is
to
due
the
Cu20
It is
of Cu
vacancies.
elec-
conducting
p-type
p-type
presence
of the
can
be
one
trodeposition
tion.
few
semiconductors that
prepared
by
i.e.
reduction
of metal ions in
suitable
substrates
a
solu-
Au, Cu,
simple
by
been
ITO and stainless
electrolyte
has
on
several
Cu20
Pt,
deposited
including
steel
control
is
[4—8].
over
a
and
Electrodeposition
stoichiometry
cheap
the
and thickness
method,
of the de-
solu-
offering
A
drawback is the
limited
of
in
posited
Cu20
be
reduced
layers.
stability
aqueous
tions.
lumination
oxide
can
to
under il-
Single
crystalline
cuprous
copper
10].
[9,
is the
materials
a
to
inside
obtain
nano-
Interesting
possibility
electrodeposit
that it is
matrix.
Martin has shown
to
nanoscale
porous
possible
*
e-Mail:
author,
Corresponding
pjongh@fys.ruu.nl
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P. E. de
D.
and
J.
J.
188
Jongh,
Vanmaekelbergh
and
Kelly
semiconductors such
membranes
[11].
intimité
electrical
in
structures
or
as
ZnO
Ti02
porous
by growing
Also
contact
materials could
A1203
polycarbonate
composite
with
be
nents,
materials
between the
area
an
two
prepared,
compo-
and
internal interface
an
[12, 13].
and
extremely large
Composite
n-
of
semi-
suitable,
consisting
interpenetrated
p-type
a
conductors could
wide
of
range
interesting possible applications
present
as
such
electroluminescent devices
solid
of
and
solar cells.
state
In
this
the
on
Cu20
electrodeposition
conducting
as
paper
transparent
variables,
such
substrates is described. The influence of
tem-
morphology
of the oxide will be dis-
deposition
are
and
The
related
the
to
current
deposition
density
perature, pH
of the
layers.
photoelectrochemical properties
cussed.
it will be shown that it is
the
to
Cu20
Finally
possible
p-type
grow
an
in
electrode.
Ti02
-type
nanoporous
Experimental
were
on a
Cu20
substrate,
layers
electrodeposited
conducting
aqueous
transparent
basic
Cu2+
reduction of
from
solution
a
TFO,
Cu(II)lactate
[7].
by
Cu2+ is
almost
in alkaline
Cu(OH)2
unstable
insoluble
due
the formation of the
to
solutions,
aqueous
Therefore
like lactate-
a
a
[14].
complexing
agent
salt has
be added
stabilise the Cu2+.
45
to
lactic
acid
·
tartrate
was
or
to
Cu2S04 (Merck)
g
in
dissolved
75 ml 88%
the
(BDH)
forming
copperlactate
In
2
this
the coordination
Cu(CH3CHOHCOO)2
H20.
complex,
complex
of the
ion is
and it has four
from
two
atoms,
Cu(II)
planar,
square
oxygen
225 ml of a
each lactate
the
as
5
was
NaOH
stirred
NaOH
nearest
M
[15].
group,
neighbours
solution
added in small
was
The dark blue
the desired value
solution
using
portions.
and the
solution.
was
to
5 M
overnight
adjusted
pH
aqueous
Two
the
were
variables
important experimental
during
electrodeposition
the
and the of the
solution. The
pH
of the
pH
electrodeposition
temperature
7
no
solutions
from
13. Outside this
to
Cu20
deposition
ranged
pH
range
could be
The
of the
thermostatic
solution
varied
was
deposited.
deposition
temperature
°C
Cu20
°C
between 10
The
and 65
was
bath.
a
using
either
in
or
a
galvanostatically
potentiostatically
grown
PAR
an
273A
standard three electrode electrochemical
EG&G
a
using
set-up
electrode
A
and saturated calomel
area
counter
platinum
potentiostat.
large
electrode
used.
be
reference
limited
were
at
can
Cu20
(SCE)
only
electrodeposited
9
between
in
—0.15 and
a
potential
pH
approximately
range,
V
—0.60
from 0.05
SCE. The
densities
current
vs.
galvanostatic deposition
ranged
If the
current
mA/cm2.
3.0
the electrode-
to
was too
density
high,
oscillate.
and started
these
to
was
very
potential
negative
position
During
oscillations
but also Cu is formed
the densities
current
not
so
Cu20
[5],
only
chosen low
avoid oscillations.
to
were
enough
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and
of
in
189
Cu,0
Solutions
Electrodeposition
The
Photoelectrochemistry
Aqueous
characterised
were
Cu20
scanning
deposited
and
layers
by optical absorption
electron
XL30 FEG
a
microscopy using Philips
spectroscopy
electron
The thickness of the
determined
was
a
microscope.
layers
photoelectrochemical
using
AS500 surface
The
measurements
profiler.
Tallystep
done in the three electrode electrochemical
indifferent
were
an
using
set-up,
0.5
M
For the measurements under illumination
a
Na2S04.
;
electrolyte
W
with
450
Xenon
0.22m SPEX 1680
a
double-grating
lamp equipped
as
excitation
resolution of 10—15
monochromator
used
The
The
of the
mono-
was
an
source.
nm.
setting
chromator
a
splits
light intensity
output
gave
measured
Centronic
Si
of the
was
a
using
photodiode.
lamp
was
also
Ti02
in 1—2
thick
Cu20
Ti02 electrodes,
nm.
deposited
pm
P25)
nanoporous
of
with diameter of 20—30
a
consisting
particles
(Degussa
These
electrodes
TFO
were
prepared by dip-coating
conducting
nanoporous
from
160
and
were
for 2
hours at
substrates
a
Ti02
g/1
suspension
conditions
annealing
450 °C under air. The
on
similar
those for the
Ruther-
obtain infor-
was
to
deposition
In
bare TFO.
addition
the other
to
was
Cu20
ford
deposition
techniques
to
(RBS)
Backscattering Spectrometry
performed
in
mation about the distribution of the
the
electrode. RBS
Ti02
Cu20
done
2
beam and the
surface
tilted
25
at
resolution.
MeV He+
incident
a
was
using
sample
in order
obtain
the
beam
to
to
a
higher
degrees
depth
discussion
Results and
Electrodeposition
1
a
room
at
on
shows
9
TFO.
Thin
at
Cu20
Fig.
The
layer deposited
pH
temperature
consist of
found to
were
well-defined
deposited layers
crystals.
were
thicker
the
red. Determi-
of the elec-
were
to
layers
layers
bright yellow,
orange
nation of
thickness showed
the
that the
layer
efficiency
average
was
1.
faceted
almost
The
which
formed
were
nicely
trodeposition
crystals
that
limited
rather than diffusion limited.
behaviour
indicate
the
shows the
is
kinetically
growth
elec-
a
2
Fig.
potential-time
during galvanostatic
current
different
The
at
trodeposition
deposition
temperatures.
density
the
mA/cm2
of
—0.05
and the
solution
9. The
was
was
deposition
pH
shape
a
indicates
of the
mechanism.
curve
clearly
nucleation-growth
deposition
nuclei of
formed
at
the
Cu20
a
are
on
First,
Cu20
relatively negative potential,
nuclei
bare substrate. After the
the further
of the
are
formed,
less
becomes
growth
is easier and the
potential
negative.
of the
bath has
influence
clear
The
the
less
a
on
deposition
temperature
the
needed for
is
the
at
curve;
negative.
potential
higher
growth
temperatures
also
The
densities
in this limited
At
current
influence
could be used
higher
higher
temperatures
without oscillations
occurring.
indicates
strong
tempera-
deposition
activation
barrier for the
ture
a
region
process.
large
energy
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J. J.
D.
and
190
E. de
P.
Kelly
Vanmaekelbergh
Jongh,
9
at room
of
on TFO at
0.30 C/cnr
1. Electron
temperature,
thickness of
pH
Cu20
Fig.
deposited
micrograph
to
a
mA/cnr, total
current
0.03
corresponding
charge
density
0.74
pm.
0.02
0.10
0.08
0.04
0.06
0.00
Q
(C/cm2)
for different
2a. Potential-time behaviour
tempera-
deposition
galvanostatic
during
Fig.
9.
0.05
of the
tures
mA/cnr,
solution,
pH
room
below
and
at
visible
Another effect
the
was
especially
temperature;
is
increase in the
at
of
the
becomes
a
negative potential
steady
growth
layer
during
—0.6
9 around
it
too
seen.
If the
V,
negative,
pH
potential
is formed
but also Cu
oscillations
oscillate.
not
to
Cu20,
starts
During
only
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and
Solutions
191
of Cu,0 in
Electrodeposition
Photoelectrochemistry
Aqueous
Det
Acc.V
WD
1
µ )
Magn
Spot
Exp
t
10.0 kV 3.0 20000X SE 5.7
2
b. Electron
of
charge
10 °C.
at
current
Cu20
9,
pH
pH
Fig.
0.05
micrograph
deposition
deposited
C/cm2.
density
mA/cm2,
total
0.05
in
the
This limits the maximum thickness of
the
oxide
[4, 5].
layer
pure
layers
formed
less than
°C
At 65
at
to
room
a
to
layers
temperature
pm.
up
few
The
be formed.
a
can
pm
of the
formed
also
effected
formed.
while
was
morphology
crystals
strongly
by
At
at
the
at
were
higher
temperature;
larger crystals
temperatures,
of
were
than
could be
more
a
higher
crystals
temperatures
pm
grown,
10 °C
formed.
small
This is illustrated in
2
b and
only
particles
Figs.
c
which show
In
10
°C.
and 55
at
a
layers deposited
respectively
current
lead
to
a
more
galvanostatic
deposition higher
density
density
nega-
tive
If during
the
current
was
the
increased,
potential.
deposition
more
a
as
value ; however
the
to
the
as soon
current
potential changed
was
negative
the
back
into
also returned
value,
original
density
changed
potential
its
The
value.
of the
to
original
a
mor-
solution had
influence
the
on
strong
pH
deposition
At
were
7
of the formed
and
8
the
was
phology
layers.
pH
deposition efficiency
formed.
low and rounded
For
9
to 12 well-defined
particles
very
pH
of
faceted
formed. At
13 the
were
was
nicely
layers
crystals
were
pH
The nucleation
layer
spotty
formed.
and
isolated
was
large
crystals
process
the faster the
strong-
influenced
the
The
was
the
determined
and
nucleation
higher
ly
by
pH.
pH,
pro-
The nuclei
small
cess.
a
density
by passing
deposition
electron
area.
the
number of
was more
charge, taking
nuclei
than
with
micrographs
counting
average
surface
of
order
At
11 the
of nuclei formed
density
pH
per
an
than
shows
at
to
a
8,
layer
magnitude higher
small
pH
leading
morphology
3
11.
pH
a
at
relatively
crystals. Fig.
deposited
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P. E. de
and
J. J.
192
D.
Jongh,
Vanmaekelbergh
Kelly
2c.
Electron
fo
°C.
55
at
current
micrograph
Cu20
9,
pH
pH
density
Fig.
deposited
C/cm2.
0.05 mA/crrr, total
0.1
deposition charge
3. Electron
of
Current
11.
at
0.2 mA/cnr,
Fig.
micrograph
total
Cu20 deposited
pH
density
60
0.13 C/cm2.
°C,
temperature
deposition charge
Photoelectrochemical characterisation
cur-
The
rents.
TFO shows
cathodic
characteristics in
both
and anodic dark
the dark in 0.5
on
Cu20
as-deposited
M
4
shows the
a
Fig.
current-potential
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and
of
Solutions
193
Cu20 in
Electrodeposition
0.8
Photoelectrochemistry
Aqueous
-f
-0.40
-0.35
-0.30
-0.25
-0.20
V
vs
(V
SCE)
4.
Fig.
(b)
a
at
of 0.24
thick
the oxidation of
9. The anodic
Na2S04
rent
Cu20
cur-
µ
layer deposited
pH
to
Cu20
(1):
corresponds
+
—
+
+
2
2
h+
2
CuO
H+
H20
Cu20
(1)
is
The CuO
dissolves
After
and
back
to
on
slowly
scanning
negative
potentials,
reduced
the
has
Cu20
partly
again.
prolonged scanning
disappeared.
the
a
same
that
needed
as
was
to
Dissolving layer requires
nearly
charge
it. This
that dissolution
the
but the
of the
is
means
not
deposit
the
layers
interface.
taking
steady
place
state
near
at
A
small
substrate,
Cu20/electrolyte
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and
J. J.
E.
D.
P.
194
de
Vanmaekelbergh
Kelly
Jongh.
0.1
0.2
-0.4
-0.3
-0.2
-0.1
vs
0.0
V
SCE)
(V
4.
Fig.
(e)
in 0.5
on TFO
M
in
of 0.24
characteristics
4.
dark
0.7 cm- with
Na2S04
Cu20
and
Fig.
the
pm
illumination
450
Current-potential
Illuminated surface area
and under
(b)
(c).
(a)
chopped
10'7s cm2.
1.3X
This cathodic
as was
found of about 10
current
also found
dark
cathodic
is associated
for
current was
µ /cm2.
in the
with the reduction of
solution,
oxygen
with
it be reduced
Ar can
After
to
Cu20
the
[9].
purging
crystalline
single
1
less than
pA/cm2.
shows
Under
cathodic
under
rather stable
characteristics
a
illumination
Cu20
photo-
b
4
shows the
current.
chopped
current-potential
The
Fig.
cathodic
of the
with 450
for
transients
illumination
nm
efficiency
light.
quantum
Rather slow
is few
a
photo-
as-deposited layers
percent.
photocurrent
An
in
seen
be
can
are
as
anodic
dark
current
current
due
the inset.
observed
photo-
current
on
a
is
at
found
superimposed
large
potentials,
positive
of the
in
It
is shown
defined.
This
4c. The
to
dissolution
the
to
Cu20
Fig.
layer.
is difficult
is
of the
reversal of the
sharply
sign
photocurrent
the
is
the
anodic
the
at
same
as
Cu20
layer
potential
photocurrent
study
dissolving.
cathodic
reduction of
due
found for
the
is
was
to
The
oxide
partially
photocurrent
cuprous
Cu20 [9].
as
also
Cu
prolonged
metallic
to
2),
crystalline
single
(reaction
are
of
transformed into
illumination
the electrode
a
After
shiny
parts
layer;
copper
—
+
+
2e- 2Cu
+
2H'
(2)
H20
Cu20
10
a
after
tim-
Cu20,
partly
stabilises. Even
certain time the
after
However,
es more
photocurrent
reduce all the
is still
copper,
is
would be needed
with metallic
drawn than
it has
to
photocurrent
the
Cu20
although
layer,
spots
an
alternative
stable
re-
intact
and
a
Apparently
photocurrent.
producing
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195
and
of Cu,0 in
Solutions
Electrodeposition
Photoelectrochemistry
Aqueous
4.0
3.0
3.5
2.5
2.0
hv
(eV)
for 2.5
of the transmission
5. Photocurrent
vs.
in 0.5
M
the
Fig.
Cu20
quantum
efficiency
photon energy
µ
—0.4
vs. SCE. The inset shows
for
at
V
Na,S04
same
part
spectrum
electrode.
duction reaction is able
with the cathodic
to
effectively
decompo-
compete
reaction. This
reduction of dissolved
sition
be
the reduction
or
might
oxygen
of
water.
5
shows the
a
function of
as
a
Fig.
efficiency
photocurrent
pho-
was
quantum
for 0.69
thick electrode. The cathodic
V
ton
photocurrent
energy
measured
tion. For illumination
pm
a
of -0.4
SCE in indifferent
curve
solu-
at
vs.
potential
electrolyte
the
the
(a),
through
electrolyte,
photocurrent
increases with
a
energy;
quantum efficiency steadily
increasing photon
the
is absorbed
the
fraction of
near
interface,
larger
giving
light
efficient
Cu20/electrolyte
in
rise
the
For
carrier
to
Curve
5
more
(b)
charge
efficiency
separation.
Fig.
the sub-
for illumination
gives
photocurrent
through
quantum
lower than 2.7 eV
strate.
a
increase in
energies
slight
photon
efficiency
2.7 eV the ef-
of
energy
with
is observed. Above
a
energy
photon
photon
becomes
lower with
for illumination
in
clear
ficiency
gradually
increasing photon
energy,
the
the
are
contrast to
At these
efficiency
through
electrolyte.
electron hole
in the
bulk,
interface. The above results indicate
most
pairs
larger photon energies
generated
far
from the
Cu20/electrolyte
are
away
a
that electrons and holes
in limited
effectively
separated
only
region
car-
lifetime
the
interface. The
of the
near
Cu20/electrolyte
minority charge
riers
in de conduction
and hence the diffusion
seems
band)
Cu20.
(electrons
length
small in
be
The
the
shows
to
as-deposited
inset
trode. For
of the transmission
for the
spectrum
than 95% of the
elec-
same
part
above 2.7
more
non-reflect-
eV,
energies
photon
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and
P. E. de
D.
J. J.
196
Vanmaekelbergh
Kelly
Jongh,
6.
Fig.
ed
(a)
is absorbed
is due
this electrode. The
low
at
'absorption'
electrodes,
light
by
apparent
reflection
thicker
to
;
energies
especially
consisting
photon
of
reflect
crystals,
strongly.
larger
in
Ti02
Cu20
Cu20
nanoporous
also
in
was
a
of in-
network,
nanoporous
We tried
consisting
on
electrodeposited
to
terconnected 20—30
nm
Ti02
Cu20
particles.
deposit
single
under
and
both in the dark under cathodic
was
Ti02,
polarisation
crystalline
illumination. This
Cu could be formed. The
of
enable
the
not
possible, only
edge
the
a
to
conduction
of
of
is
the
the
band
Cu20.
at
too
Ti02
negative potential
On
under
illumination also
Ti02
Cu20
nanoporous
growth
only
formation of Cu occurred. However
could be
inside
Cu20
electrodeposited
In
the
electrode
from the substrate
TFO substrate.
the
this
on
a
case
a
Ti02
nanoporous
starts to
in
the
electrode.
6
a
through
thick
6b and show
Fig.
grow
pores
the surface of 1.5
a
is about 50—60%.
An
TiO, electrode. The
in the
shows
pm
nanoporous
po-
of
c
two
rosity
Fig.
growth
stages
of
0.04 and 0.4
is
5
Cu20.
Cu20
respectively
equivalent
to
deposited,
pm
fractions of
about
and 50%.
filling
respectively
corresponding
pore
from the TFO substrate
the
The
Cu20
electrode,
nanoporous
through
grows
certain
If
fractions
much
at
places.
filling
forming larger crystals
higher
50% the
started
electron
forms
the surface
on
than
were
to
used,
Cu20
larger crystals
as was seen
of
substantial
the
A
of the
which
Ti02,
microscopy.
by
part
be
could
reoxidised and dissolved
anodic
Cu20
polarisation,
upon
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and
Solutions
197
of Cu20 in
Photoelectrochemistry
Electrodeposition
Aqueous
Fig. 6.(c)
6.
in the
filling
pore
of
inside
a
1.5
pm
corre-
Cu20
Ti02 electrode,
Fig.
Stages
to
growth
nanoporous
5%
fractions of
0%
and
50%
(c).
(a),
(b)
respectively
sponding
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198
P. E.
de
and J. J.
D.
Jongh,
Vanmaekelbergh
Kelly
Ti
15(H
I
100-^
5(H
0
1.45
1.50
1.55
1.60
1.65
(MeV)
1.70
1.75
1.80
E
7. Rutherford
5% of
for
a
1.5
pm
electrodeposition.
thick TiO\
Fig.
Spectrum
with
Backscattering
the
electrode,
ap-
filled with
Cu,0
proximately
pores
by
that
meant
from
due
the
were not isolated.
Also
cathodic
the
isolated
was not
crystals
Ti02
the
the
measured.
both
as
substrate,
a
conducting
photocurrent
spectrum
could
to
and
an anodic
Cu20
due
the
to
photocurrent spectrum
Ti02
be
To
further
check
was
the
whether
Cu20
growing
homogeneously
Ti02/electrolyte
the
or
at the
performed.
Fig.
through
or
layer,
substrate/Ti02
preferentially
RBS
measurements were
A
The
interface,
measurement
onset
the elec-
on
trode shown
in
the
6b is
surface
spectrum
7.
shown
is
due
in
the
for
energy
detec-
Fig.
tion
The
at
of Cu
as is
onset
the
lower
Cu
at
Ti
of
indicated,
the
surface.
of the
starts
As
the
at
to
Cu
to
seems
the
Ti
part
before
energies,
a
of
signal
interfering,
corresponds
depth
approximately
be
150
nm.
can
seen the
be
to
Cu20
distance.
The
homo-
quite
deposited
this
over
of Cu
atoms
determined
with
was
geneously
density
This
a
that for
to
solid
Cu
respect
to
a
sample.
density
corresponded
in
pore
with
fraction
fraction
with
of about
which is
Cu20
from
filling
6%,
deposition
agreement
good
the
calculated
the
charge.
A
solid
state
device
was
of
constructed,
consisting
Cu20
interpenetrated
and
was
with
a TFO
both
sides.
First a
Ti02
on
contact
electrode
Ti02
nonporous
in
filled
with
Cu20
was
three-electrode
a
partly
by
set-
Some
the
electrodeposition
Then
this electrode
a
TFO.
up.
Cu20
Ti02.
on
pressed
against
layer
solution
in the
was
electrodeposition
put
porous
and
Galvanostatically
dissolved
was
from
the
Cu20
Ti02-side
Further
onto the
electrodeposited
Cu20
inside
the
matrix.
the
Ti02
was
layer
from
the
Cu20
deposited
solution
Cu(II)-
lactate
first
solution inside
with
Afterwards
the
and
from
was removed
pores.
by
then
remove
with
all
solution
ethanol
water,
to
under
vacuum. It
rinsing
drying
was
difficult
the
The
cells
very
were
pores.
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and
in
199
of Cu:0
Photoelectrochemistry
Solutions
Electrodeposition
Aqueous
characterised
cell
established. Also after
in the dark and under illumination. If
by cyclic voltammetry
a
was
between the
under
at
electrodes could be
no contact
two
air,
completely dry,
at
no
250 °C
electrical
contact
annealing
could be
established. After
annealing higher
short-circuiting
temperatures
found.
was
Conclusions
from alkaline
solutions
was
Cu20
Cu(II)lactate
Crystalline
electrodeposited
TFO substrates. The
kinetics
influenced
on
the
were
deposition
strongly
by
of
and the
the
solution. From
9
13
to
pH
deposition
were
pH
nicely
temperature
well defined
The nucleation
was
faceted,
strongly
crystals
grown.
different
process
11 the
at
to
a
dependent leading
pH
morphology,
pH
e.g.
leading
nuclei
much
than
much
was
at
to
a
8,
density
crystal
higher
pH
average
smaller
size. The
the
of the
solution had
deposition
average
temperature
a
influence
kinetics. The
on
profound
deposition
deposition potential,
in the
from 10
to
was
strongly
dependent
temperature
temperature
range
a
65
activation
for the
°C,
indicating
large
deposition
Larger
energy
process.
At and
could be
at
below
room tem-
grown
crystals
perature
limiting
Cu20
higher
temperatures.
a
increase in
was
found,
steady
negative potential during deposition
the thickness of the
that could be
layers
deposited.
oxidised
back
which
dissolved in
aque-
the CuO
could be
was
to
CuO,
anodically
On
slowly
ous
to
electrolyte.
scanning
negative potentials
It
reduced
showed cathodic
which
a
was
partly
again.
photo-current,
partly
due
the reduction of
Cu. The
that
became stable after
to
to
Cu20
photocurrent
alternative reduction reaction
an
illumination,
prolonged
indicating
could
with reduction of the
Photocurrent
Cu20.
took
effectively
compete
spectra
Cu20/
indicated that efficient
the
near
charge separation only
place
The
was
interface.
in
the order
quantum
photocurrent
efficiency
electrolyte
of a few
A
percent.
material
made
was
in
a
nano-
Cu20
Cu20
composite
by electrodepositing
to
matrix
TFO. It
was not
on
Ti02
possible
electrodeposit
porous
on
no
electrical
obtained between
contact was
Ti02.
directly
Unfortunately
Ti02.
the
and the
Cu20
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1.
2.
3.
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Solid State
Komoda,
359.
P. W.
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Kelly
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