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Cu 2 O and CuO Nanocrystalline Photoelectrochemical Systems

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

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Cu 2 O and CuO Nanocrystalline Photoelectrochemical Systems

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  1. Cu2O and CuO Nanocrystalline Photoelectrochemical Systems Thomas Polson

  2. 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 hν Valence Band

  3. Why Cu2O? • 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 hν 1.9V 1 V

  4. 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

  5. Cu2O film production • Electrochemical deposition • pH • Deposition time • Sol-gel • Commercially available Cu2O • CuCl2 • Nanocubes

  6. Electrochemical Deposition Reference Counter Working ITO Coated Glass Cupric Lactate Solution 45g CuSO4 75 mL 85% Lactic acid 225mL 5M NaOH Pt SCE (sat’d KCl)

  7. 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).

  8. Electrochemical Deposition

  9. Electrochemical Deposition 111 222 Cu2O Standard • Highly oriented crystal structure

  10. Electrochemical Deposition

  11. Electrochemical Deposition Light Current Effective Photocurrent Dark Current

  12. 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).

  13. Sol-gel(Cu2O) Cu2O Standard • Positive ID of Cu2O • Random orientation

  14. Sol-gel(Cu2O)

  15. Sol-gel(Cu2O) Light Current Effective Photocurrent Dark Current

  16. Sol-gel (Nanocubes) • Chemical reduction CuCl2 + 2 NaOH  Cu(OH)2 + 2 NaCl 4 Cu(OH)2 + N2H4  Cu2O + 6 H2O + N2

  17. Sol-gel (Nanocubes) • Nanocubes annealed in same manner as bulkCu2O • Method adapted from • ‘Room temperature synthesis of Cu2O nanocubes and nanoboxes’ Z. Wang SSC 130 585-589 (2004)

  18. XRD of Nanocubes Cu2O CuO CuO Cu2O CuO

  19. Sol-gel (Nanocubes)

  20. Nanocubes

  21. Sol-gel (Nanocubes) Light Current Effective Photocurrent Dark Current

  22. Redox Potentials of Relevant Rxns CB E (V vs. SCE) -1.0 - 2H+ + 2e- ↔ H2 -.5 - Cu2O + H2O + 2e-↔ 2Cu + 2OH- - 2CuO + H2O + 2e- ↔ Cu2O + 2OH- 0 - O2 + 2H2O +2e- ↔ 2OH- + H2O2 +.5 VB - O2 + 2H2O +4e- ↔ 4OH- Cu2O

  23. Mechanism of CuO Solar Cell CB -1.74 Ph(CN)2 -1.72 CB e- PhNO2 -1.33 e- -1.20 PhN2 Ox Red Pt AQ -0.95 e- CuO BQ -0.52 h+ VB AQ = anthroquinone BQ = benzoquinone redox couple in solution 0.00 Ef +0.16 +0.26 VB

  24. Redox Couple Photocurrent

  25. Redox Couple Photocurrent

  26. Future of the Project • Deposit Pt on electrodeposited nanocrystalline sheets • Couple with n-type semiconductor • Produce hydrogen

  27. Thank you Cornell Center for Materials Research Ithaca Chemistry Department Jacy Spado Meagan Daniels Akiko Fillinger

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