filled with argon, or de-aerated aqueous solutions. 1. Department of Chemistry, Imperial College London, Exhibition Road, London, SW7 2AZ, United Kingdom.
Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2010
Electronic Supporting Information
Dynamics of photogenerated holes in nanocrystalline !-Fe2O3 electrodes for water oxidation probed by transient absorption spectroscopy Stephanie Pendlebury,1 Monica Barroso,a* Alexander J. Cowan,a Kevin Sivula,2 Junwang Tang,3 Michael Grätzel,b David Klug,a and James R. Durranta*
Undoped APCVD !-Fe2O3 films Undoped !-Fe2O3 (hematite) films were prepared by atmospheric pressure chemical vapour deposition, as described and characterised previously,1 without an SiO2 layer between the FTO-glass substrate and Fe2O3. Photoelectrochemistry A three-electrode air-tight borosilicate glass cell with Ag/AgCl reference electrode (saturated KCl), Pt gauze counter electrode and de-aerated 0.1M NaOH electrolyte was used for PEC measurements.
The applied potential was controlled using a Ministat 251 potentiostat
(Thompson Electrochemical); films were illuminated through the FTO-glass substrate (SE) by a 150 W ozone-free Xe lamp in a home-made housing with no filters (illumination intensity was approximately 1 Sun). The dark- and photo-current were measured before each TAS experiment; the photocurrent is comparable to that reported recently for undoped hematite APCVD films.1 The aim of these measurements was not to achieve maximum photocurrent, but rather to ensure that the cell was working as expected and to qualitatively establish the effect of methanol on the photocurrent. Transient absorption spectroscopy without applied bias - !s-ms timescale Band gap excitation was achieved using a PTI GL-3300 nitrogen laser (337 nm, 2 Hz, 0.190.22 mJ cm-2 pulse-1), while the 580 nm probe light was supplied by a 100 W tungsten lamp with monochromators before and after the Fe2O3 film, as described in detail elsewhere.2 Films were illuminated through the FTO glass substrate (SE), in a sealed quartz cuvette filled with argon, or de-aerated aqueous solutions. !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !
Department of Chemistry, Imperial College London, Exhibition Road, London, SW7 2AZ, United Kingdom." "Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland." $ "Department of Chemical Engineering, University College London, Torrington Place, London, WC1E 7JE, United Kingdom." #
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Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2010
Photoelectrochemistry and transient absorption spectroscopy with applied bias - !s-s timescale The same three-electrode set-up was used for the !s-s transient absorption measurements with applied bias as for the PEC measurements. The third harmonic of a Nd:YAG laser (Continuum Surelite I-10, 355 nm, ~0.2 mJ cm-2 after absorption by glass cell, 0.33-1.40 Hz, 6 ns pulse width) and monochromated 75 W Xe lamp (Hamamatsu Photonics) were employed as the excitation and probe light sources, respectively, as described in detail elsewhere.3 There is no change in the TA decay dynamics of !-Fe2O3 at -0.1 V vs Ag/AgCl (similar to open-circuit condition) when methanol (a hole-scavenger) is added to the electrolyte (c.a. 0.2 mM methanol), as shown in Figure S1. This behaviour is in contrast to that observed at +0.4 V (see Figure S2 and main text).
Figure S1 Transient absorption decays of hematite (excited at 355 nm and probed at 580 nm) at -0.1 V vs Ag/AgCl (probed at 580nm), in 0.1 M NaOH with (red) and without (black) methanol.
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Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2010
Figure S2 Transient absorption decays of hematite (excited at 355 nm and probed at 580 nm) in 0.1M NaOH at open circuit (~ -0.25 V vs Ag/AgCl, green curve), under negative applied bias of -0.1 V vs Ag/AgCl (blue) and under positive applied bias of +0.4V vs Ag/AgCl (black); at of +0.4V vs Ag/AgCl in the presence of methanol (red).
References 1. 2. 3.
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I. Cesar, K. Sivula, A. Kay, R. Zboril and M. Graetzel, J. Phys. Chem. C, 2009, 113, 772-782. J. Tang, J. R. Durrant and D. R. Klug, J. Am. Chem. Soc., 2008, 130, 13885-13891. A. J. Cowan, J. Tang, W. Leng, J. R. Durrant and D. R. Klug, J. Phys. Chem. C, 2010, 114, 4208-4214.
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