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216 th ECS Meeting: October 8, 2009

Comparison of Inexpensive Photoanode Materials for Hydrogen Production Using Solar Energy. N.Cook, R. Gallen S. Dennison , K. Hellgardt, G.H. Kelsall, Department of Chemical Engineering Imperial College London, SW7 2AZ, UK s.dennison@imperial.ac.uk. 216 th ECS Meeting: October 8, 2009.

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216 th ECS Meeting: October 8, 2009

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  1. Comparison of Inexpensive Photoanode Materials for Hydrogen Production Using Solar Energy N.Cook, R. Gallen S. Dennison, K. Hellgardt, G.H. Kelsall, Department of Chemical EngineeringImperial College London, SW7 2AZ, UK s.dennison@imperial.ac.uk 216th ECS Meeting: October 8, 2009

  2. 14 TW Energy Gap by 2050! 1

  3. H2 as sustainable energy carrier? 2 adapted and modified from J.A.Turner, Science 285, 687(1999)

  4. Plugging the energy gap (14TW) Combined area of black dots would provide total world energy demand 3

  5. Solar Hydrogen at Imperial • £4.2M EPSRC sponsored project (5 years) • Chemical Engineering, Chemistry, Biology, Earth Science and Engineering • Approx. 20-25 researchers at any one time • 2 strands: Biophotolysis and Photoelectrochemistry • Chemical Engineering to develop devices and reactors and technology for scale-up and scale out 4

  6. Application • Targets: • Biophotolytic H2: £5.00/kg; • Photoelectrolytic H2: £2.50/kg • Fuel Cell Operation • Distributed Market 5

  7. Candidate Materials • TiO2: Eg ~ 3.0-3.2 eV (410-385 nm) • Fe2O3: Eg ~ 2.2 eV (>565 nm) • WO3: Eg ~ 2.6 eV (475 nm) 6

  8. Stability of Fe2O3 7

  9. Stability of TiO2 8

  10. Stability of WO3 9

  11. Photoelectrolysis – Materials Evaluation • Photocurrent Spectroscopy • Photo-electrochemical activity of photo-anodes based on transition metal oxides (Fe, W, Ti) • Fe-based system needs bias but otherwise promising (& cheap) 10

  12. WO3: further investigations • From H2WO4: • Electrodeposition: potential cycling -0.4 - +0.8 V vs. SCE 1 • “Doctor blading”: using stabilised H2WO4 sol 2 • Both annealed: 15 min at 550°C 1 Santato et al., J Amer Chem Soc, 2001, 123, 10639 2 Kulesza and Faulkner, J Electroanal Chem, 1988, 248, 305 11

  13. Measured band-edge potentials of WO3 12

  14. Ir/IrO2 Electrodeposition • Ir: • From “IrCl3,aq” : E0 = +0.86 V vs NHE 1 • Convert to IrO2 by electrochemical oxidation 2 • IrO2: • From [IrCl6]3-/oxalate @ pH 10.5/galvanostatic deposition 3 1 Munoz and Lewerenz, J Electrochem Soc, 2009, 156, D184 2 Elzanowska et al. Electrochim Acta, 2008, 53, 2706 3 Marzouk, Anal Chem, 2003, 75, 1258 13

  15. Ir Electrodeposition – Cycle 1 Vitreous carbon electrode: 10 mM IrCl3/0.5 M KCl Sweep rate: 0.01 Vs-1 Ir nucleation 14

  16. Ir Electrodeposition – Selected Cycles Vitreous Carbon electrode 10 mM IrCl3/0.5 M KCl Sweep rate: 0.01 Vs-1 15

  17. IrO2 Electrodeposition H2IrCl6 + (COOH)2 (pH 10.5, K2CO3) Sweep rate: 0.01Vs-1 16

  18. Effect of IrO2 on WO3 Photoresponse 1M H2SO4 Sweep rate: 0.01 Vs-1 17

  19. Mott-Schottky analysis following IrO2-coating 1M H2SO4 Modulation frequency: 10 kHz 18

  20. Conclusions • The electrodeposition of Ir and IrO2 is interesting! • Deposition of Ir & IrO2 onto WO3 results in loss of photoelectrochemical O2 evolution activity. • This is due to: a) deposition of excessive quantities of Ir/IrO2 b) irreversible damage of the WO3 (MS data). 19

  21. Design and Development of a Photoelectrochemical Reactor • Key criteria: • Optimising illumination of photoelectrode • Optimising fluid and current distributions • Product separation • Minimising bubble formation • Materials (of construction) selection 20

  22. Photoelectrolytic Reactor Design 21

  23. Photoelectrolytic Reactor Design 22

  24. Photoelectrolytic Reactor Design 23

  25. Photoelectrolytic Reactor Design 24

  26. Photoelectrolytic Reactor Design 25

  27. Photoelectrolytic Reactor Performance 26

  28. Photoelectrolytic Reactor: conclusions • Main contributing factors to response: • Photoanode material quality • Cathode gauze too coarse • Large illumination losses (mirror, etc.) 27

  29. Future Work • Materials fabrication: WO3 and Fe2O3 • Photoelectrochemical reactor: • Photoanode material quality • Reduce shading by cathode • Hydrogen measurement and collection • Fully develop reactor model 28

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