SUPPORTING INFORMATION Hydrogen-treated hierarchical titanium oxide nanostructures for photoelectrochemical water splitting Luca Mascarettia, Simona Ferrullib, Piero Mazzolinia,b, Carlo S. Casaria,b, Valeria Russoa, Roberto Matarresec, Isabella Novac, Giancarlo Terraneob,d, Ning Liue, Patrik Schmukie,f, Andrea Li Bassia,b,* a
Micro- and Nanostructured Materials Laboratory, Department of Energy, Politecnico di Milano, via
Ponzio 34/3, 20133, Milano, Italy. b
Center for Nanoscience and Technology – IIT@Polimi, via Giovanni Pascoli 70/3, 20133, Milano,
Italy. c
Laboratory of Catalysis and Catalytic Processes, Department of Energy, Politecnico di Milano, via
La Masa 34, 20156, Milano, Italy. d
Laboratory of Nanostructured Fluorinated Materials (NFMLab), Department of Chemistry, Materials, and Chemical Engineering “Giulio Natta”, Politecnico di Milano, via L. Mancinelli 7, 20131 Milano, Italy. e
Department of Materials Science WW4-LKO, University of Erlangen-Nuremberg, Martenstrasse
7, 91058, Erlangen, Germany. f
Department of Chemistry, King Abdulaziz University, Jeddah, Saudi Arabia.
*
[email protected]
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1. Additional data for O2-TiO2 films
Figure S1: SEM images of O2-TiO2 samples. A) As-deposited sample; B) Air annealed sample; C) Ar/H2 annealed sample; D) Air+Ar/H2 annealed sample.
Figure S2: A) Raman spectra of annealed O2-TiO2 samples (red: Air; blue: Air+Ar/H2; black: Ar/H2). Spectra are separated in two panels with arbitrary intensity units because the peak at 144 cm-1 is largely more intense than all the other peaks. B) Photoluminescence spectra (acquired at room temperature with excitation wavelength of 514.5 nm) of annealed O2-TiO2 samples (same colors as A).
Figure S3: Optical analysis of annealed O2-TiO2 samples; red line: Air; black line: Ar/H2; blue line: Air+Ar/H2. A) Transmittance curves; B) absorbance curves.
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2. Additional data for Ar/H2-TiO2 films
Figure S4: SEM images of Ar/H2-TiO2 samples. A) As-deposited sample; B) Air annealed sample; C) Ar/H2 annealed sample; D) Air+Ar/H2 annealed sample.
Figure S5: A) Raman spectra of annealed Ar/H2-TiO2 samples (red: Air; blue: Air+Ar/H2; black: Ar/H2). Spectra are separated in two panels with arbitrary intensity units because the peak at 144 cm-1 is largely more intense than all the other peaks. B) Photoluminescence spectra (acquired at room temperature with excitation wavelength of 514.5 nm) of annealed Ar/H2-TiO2 samples (same colors as A).
Figure S6: Optical analysis of annealed Ar/H2-TiO2 samples; red line: Air; black line: Ar/H2; blue line: Air+Ar/H2. A) Transmittance curves; B) absorbance curves.
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3. Additional data for Ar/O2-TiO2 samples
Figure S7: Additional optical properties of annealed Ar/O2-TiO2 samples (red: Air; black: Ar/H2; blue: Air+Ar/H2). A) Haze factor curves; B) Tauc plots.
4. Ar/H2-TiO2 samples deposited at 10 Pa A further set of Ar/H2-TiO2 samples were deposited at 10 Pa, instead of 5 Pa, since the former samples showed a more compact morphology (as discussed in the text); accordingly, a hierarchical morphology was obtained (as in Fig. S8). This deposition, also, was meant to show if the low photoresponse of Ar/H2-TiO2 samples would have been improved by adjusting the deposition conditions. However, as shown by Fig. S10, the photoresponse remains lower than the O2- and, mostly, Ar/O2-TiO2 samples; this observation supports the argument that deposition with Ar/H2 mixture induces an excessive amount of defects in the material, compromising its photoresponse.
Figure S8: SEM images of Ar/H2-TiO2 samples deposited at 10 Pa. A) As-deposited sample; B) Air annealed sample; C) Ar/H2 annealed sample; D) Air+Ar/H2 annealed sample.
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Figure S9: A) Raman spectra of annealed 10 Pa-Ar/H2-TiO2 samples (red: Air; blue: Air+Ar/H2; black: Ar/H2). Spectra are separated in two panels with arbitrary intensity units because the peak at 144 cm -1 is largely more intense than all the other peaks. B) Photoluminescence spectra (acquired at room temperature with excitation wavelength of 514.5 nm) of annealed 10 Pa-Ar/H2-TiO2 samples (same colors as A).
Figure S10: Photoelectrochemical behavior of annealed Ar/H2-TiO2 photoanodes deposited at 10 Pa (red: Air; black: Ar/H2; blue: Air+Ar/H2).
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