cu 2 o and cuo nanocrystalline photoelectrochemical systems
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Cu 2 O and CuO Nanocrystalline Photoelectrochemical Systems. Thomas Polson. Why use a semiconductor?. Absorbed photons promote electrons to a higher energy state (conductive band) Electrons from conductive band used to split H 2 O - PowerPoint PPT PresentationTRANSCRIPT
Cu2O and CuO Nanocrystalline
Photoelectrochemical Systems
Thomas Polson
Why use a semiconductor?
Absorbed photons promote electrons to a higher energy state (conductive band)
Electrons from conductive band used to split H2O
Differing semiconductors have varying conductive band potentials
Conductive Band
Valence Band
hν
Usable band gap of 1.9 eV
2 H2O(l) O2 (g) + 4 H+(aq) +4 e
E0 = +1.23 eV
2 H+ + 2 e- H2(g)
E0 = 0.0 eV Conductive Band higher than
Hydrogen
-.9 V
1 V
hν1.9V
Why Cu2O?
Cu2O Stability
Cu2O known to be unstable by photo degradation when illuminated in H2O Cu2O + H2O + 2e- 2 Cu + OH- -.25ev
Nanocrystalline Cu2O does not degrade Stability unexplained
Cu2O film production
Electrochemical deposition pH Deposition time
Sol-gel Commercially available Cu2O CuCl2 Nanocubes
Electrochemical Deposition
Working
Counter
Reference
Cupric Lactate Solution
45g CuSO4
75 mL 85% Lactic acid
225mL 5M NaOH
ITO Coated Glass
SCE
(sat’d KCl)
Pt
Electrochemical Deposition
Vary time from 15 mins to 2 hrs Longer time thicker film
Vary pH from 8 to 12 pH ~10 most uniform film
Based on ‘Cu2O: Electrodeposition and Characterization’ P.E. de Jongh , Chem. Mater. 11 3512-
3517 (1999) ‘Photoelectrochemistry of Electrodeposited Cu2O’, P.E. de Jongh JES, 147(2) 484-489
(2000).
Electrochemical Deposition
Electrochemical Deposition
0
10000
20000
30000
40000
50000
60000
70000
80000
25 35 45 55 65 75 85
2θ
CP
S
Cu2O
Standard
111 222
• Highly oriented crystal structure
Electrochemical Deposition
Electrochemical Deposition
-2.00E-05
0.00E+00
2.00E-05
4.00E-05
6.00E-05
8.00E-05
1.00E-04
1.20E-04
1.40E-04
-0.2 -0.18 -0.16 -0.14 -0.12 -0.1 -0.08 -0.06 -0.04 -0.02 0
V (V vs SCE[sat'd KCl])
I (A
)
Light Current
Dark Current
Effective Photocurrent
Sol-gel(Cu2O)
Cu2O suspended in H2O w/ acetyl acetone and triton X
Annealed for 1 hr @ 360˚C to ITO glass Adapted from
‘Testing of Dye Sensitized TiO2 Solar Cells I & II’ G.P. Smestad SEM&SC 32 259-273 (1994).
Sol-gel(Cu2O)
01000
200030004000
500060007000
80009000
25 35 45 55 65 75
2θ
cps
Cu2O
Standard
• Positive ID of Cu2O• Random orientation
Sol-gel(Cu2O)
Sol-gel(Cu2O)
0.00E+00
5.00E-05
1.00E-04
1.50E-04
2.00E-04
2.50E-04
-0.2 -0.15 -0.1 -0.05 0
V vs SCE (sat'd KCl)
I (A
)
Light Current
Effective Photocurrent
Dark Current
Sol-gel (Nanocubes)
Chemical reduction
CuCl2 + 2 NaOH Cu(OH)2 + 2 NaCl
4 Cu(OH)2 + N2H4 Cu2O + 6 H2O + N2
Sol-gel (Nanocubes)
Nanocubes annealed in same manner as bulk Cu2O
Method adapted from ‘Room temperature synthesis of Cu2O nanocubes and nanoboxes’ Z. Wang
SSC 130 585-589 (2004)
XRD of Nanocubes
0200400600800
100012001400160018002000
25 30 35 40 45 50 55 60 65 70 75 802 theta
CP
S
Free Powder
Annealed
Cu2O
CuOCuO
Cu2O CuO
Sol-gel (Nanocubes)
Nanocubes
Sol-gel (Nanocubes)
0.00E+00
5.00E-05
1.00E-04
1.50E-04
2.00E-04
2.50E-04
3.00E-04
3.50E-04
4.00E-04
-0.2 -0.15 -0.1 -0.05 0
V vs SCE(sat'd KCl
I(A
)
Light Current
Dark Current
Effective Photocurrent
Redox Potentials of Relevant Rxns
E (V vs. SCE)
-1.0
-.5
0
+.5VB
CB
Cu2O
- Cu2O + H2O + 2e- ↔ 2Cu + 2OH-
- 2CuO + H2O + 2e- ↔ Cu2O + 2OH- - O2 + 2H2O +2e- ↔ 2OH- + H2O2
- O2 + 2H2O +4e- ↔ 4OH-
- 2H+ + 2e- ↔ H2
Mechanism of CuO Solar Cell
Ox
Red
h+
VB
CB e-
e-
e-
Pt
CuO
redox couple in solution
VB
CB
Ef
Ph(CN)2
PhNO2
PhN2
AQ
BQ
0.00+0.16+0.26
-0.52
-0.95
-1.20-1.33
-1.72
-1.74
AQ = anthroquinoneBQ = benzoquinone
Redox Couple Photocurrent
-4.00E-04
-2.00E-04
0.00E+00
2.00E-04
4.00E-04
6.00E-04
8.00E-04
1.00E-03
-1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4
V vs Ag/Ag+
I(A
)
Ph(CN)2 Dark
PhNO2 Dark
PhN2 Dark
BQ Dark
Ph(CN)2 Light
PhNO2 Light
PhN2 Light
BQ Light
-5.00E-05
0.00E+00
5.00E-05
1.00E-04
1.50E-04
2.00E-04
2.50E-04
3.00E-04
3.50E-04
-1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4
V vs Ag/Ag+
I(A
)
Ph(CN)2
PhNO2
PhN2
BQ
Redox Couple Photocurrent
Future of the Project
Deposit Pt on electrodeposited nanocrystalline sheets
Couple with n-type semiconductor Produce hydrogen
Thank you
Cornell Center for Materials Research
Ithaca Chemistry Department
Jacy Spado
Meagan Daniels
Akiko Fillinger