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 Differing semiconductors have varying conductive band potentials Conductive Band Valence Band hνhν

Usable band gap of 1.9 eV 2 H 2 O (l)  O 2 (g) + 4 H + (aq) +4 e E 0 = eV 2 H e -  H 2( g ) E 0 = 0.0 eV Conductive Band higher than Hydrogen -.9 V 1 V hνhν 1.9V Why Cu 2 O?

Cu 2 O Stability Cu 2 O known to be unstable by photo degradation when illuminated in H 2 O Cu 2 O + H 2 O + 2e -  2 Cu + OH ev Nanocrystalline Cu 2 O does not degrade Stability unexplained

Cu 2 O film production Electrochemical deposition pH Deposition time Sol-gel Commercially available Cu 2 O CuCl 2 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 ‘Cu 2 O: Electrodeposition and Characterization’ P.E. de Jongh, Chem. Mater (1999) ‘Photoelectrochemistry of Electrodeposited Cu 2 O’, P.E. de Jongh JES, 147(2) (2000).

Electrochemical Deposition

Cu 2 O Standard Highly oriented crystal structure

Electrochemical Deposition

Light Current Dark Current Effective Photocurrent

Sol-gel(Cu 2 O) Cu 2 O suspended in H 2 O w/ acetyl acetone and triton X Annealed for 1 360˚C to ITO glass Adapted from ‘Testing of Dye Sensitized TiO2 Solar Cells I & II’ G.P. Smestad SEM&SC (1994).

Sol-gel(Cu 2 O) Cu 2 O Standard Positive ID of Cu 2 O Random orientation

Sol-gel(Cu 2 O)

Light Current Effective Photocurrent Dark Current

Sol-gel (Nanocubes) Chemical reduction CuCl NaOH  Cu(OH) NaCl 4 Cu(OH) 2 + N 2 H 4  Cu 2 O + 6 H 2 O + N 2

Sol-gel (Nanocubes) Nanocubes annealed in same manner as bulk Cu 2 O Method adapted from ‘Room temperature synthesis of Cu 2 O nanocubes and nanoboxes’ Z. Wang SSC (2004)

XRD of Nanocubes Cu 2 O CuO Cu 2 OCuO

Sol-gel (Nanocubes)

Nanocubes

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

Redox Potentials of Relevant Rxns E (V vs. SCE) VB CB Cu 2 O - Cu 2 O + H 2 O + 2e - ↔ 2Cu + 2OH - - 2CuO + H 2 O + 2e- ↔ Cu 2 O + 2OH - - O 2 + 2H 2 O +2e - ↔ 2OH - + H 2 O 2 - O 2 + 2H 2 O +4e - ↔ 4OH - - 2H + + 2e - ↔ H 2

Mechanism of CuO Solar Cell Ox Red h+h+ VB CBe-e- e-e- e-e- Pt CuO redox couple in solution VB CB EfEf Ph(CN) 2 PhNO 2 PhN 2 AQ BQ AQ = anthroquinone BQ = benzoquinone

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