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