SUPPORTING INFORMATION

Transcription

1 SUPPORTING INFORMATION SrTaO2N Nanowire Photoanode Modified with a Ferrihydrite Hole- Storage Layer for Photoelectrochemical Water Oxidation Martin Davi, Felix Schrader, Tanja Scholz, Zili Ma, Anna Rokicinska, Richard Dronskowski, Piotr Kustrowski, and Adam Slabon*, Institute of Inorganic Chemistry, RWTH Aachen, Landoltweg 1, D Aachen, Germany Faculty of Chemistry, Jagiellonian University, Gronostajowa 2, Krakow, Poland *adam.slabon@ac.rwth-aachen.de Table of Content A. Synthetic procedure for preparation of SrTaO2N photoanodes based on microcrystalline powder. B. Figures Figure S1. SEM image of SrTaO2N nanowires before ferrihydrite modification. Figure S2. SEM cross section of SrTaO2N nanowire on tantalum substrate. Figure S3. TEM SAED pattern of SrTaO2N/Fh nanowires with assigned reflection peaks. Figure S4. Absorption coefficient of SrTaO2N nanowires. Figure S5. Cyclic voltammetry of SrTaO2N/Fh nanowire photoanode. Figure S6. LSV of various SrTaO2N/Fh nanowire photoanodes as a function of deposition time for ferrihydrite coating. Figure S7. SEM image 1 of FTO/SrTaO2N/Fh photoanode. Figure S8. SEM image 2 of FTO/SrTaO2N/Fh photoanode. Figure S9. LSV of FTO/SrTaO2N/Fh photoanode, Ta/SrTaO2N/Fh nanowire photoanode and bare electrode Fh. Figure S10. CA of Fh photoanode and FTO/SrTaO2N/Fh photoanodes with and without a hole scavenger in the form of Na2SO3. Figure S11. LSV of nanowire photoanode and ball-milled (nanoparticle) FTO/SrTaO2N/Fh. Figure S12. CA of Ta/SrTaO2N/Fh and unprotected Ta/SrTaO2N nanowire photoanodes. Figure S13. CA of SrTaO2N/Fh nanowire photoanode at 1.23 V vs. RHE for 2h. Figure S14. TEM EDX line scan on a nanowire after PEC water oxidation. Figure S15. IPCE at 1.23 V vs. RHE of FTO/SrTaO2N/Fh and Ta/SrTaO2N/Fh nanowire photoanodes. S-1

2 A. Synthetic procedure for preparation of SrTaO 2N photoanodes based on microcrystalline powder. Preparation of FTO/SrTaO 2N photoanode g (8.00 mmol) of SrCO3 powder (99.9 wt.-%, Alfa Aesar) was mixed with 1.77 g (4.00 mmol) of Ta2O5 powder (99.99 wt.-%, Sigma). The mixture was placed in an alumina crucible and heated at 923 K for 8 h under ambient atmosphere. 100 mg of the white product was placed in another alumina crucible and nitridated at 1273 K for 8 h under a constant flow of NH3 (15 ml min 1 ) and H2 (5 ml min 1 ). The resulting orange powder was immobilized on a FTO glass substrate by EPD. First, two FTO glass slides were cleaned in 1 M nitric acid and washed with deionized water and ethanol. 6 mg of iodine and 20 mg of SrTaO2N were dispersed in 20 ml of acetone by ultrasound. The two FTO glass slides were electrically wired and placed inside the solution within a distance of 5 mm. A potential of 20 V was applied for 5 min to coat the FTO substrate with an oxynitride layer. This procedure gave the best PEC performance of the resulting electrodes. The FTO glass was removed from the solution, washed with deionized water and ethanol, and dried under ambient atmosphere. The FTO/SrTaO2N electrode was illuminated from the back side, i.e. the nonconductive side of the FTO glass. B. Figures. Figure S1. SEM image of SrTaO2N nanowires before ferrihydrite modification. Figure S2. SEM cross section of SrTaO2N nanowire on tantalum substrate. S-2

3 Figure S3. TEM SAED pattern of SrTaO2N/Fh nanowires with assigned reflection peaks. Since the sample is not single-crystalline but polycrystalline, the intensities of corresponding reflection peaks are strongly depended on the angle. Figure S4. Absorption coefficient of SrTaO2N nanowires. S-3

4 Figure S5. Cyclic voltammetry of SrTaO2N/Fh nanowire photoanode. Figure S6. LSV of various SrTaO2N/Fh nanowire photoanodes as a function of deposition time for ferrihydrite coating. Figure S7. SEM image 1 of FTO/SrTaO2N/Fh photoanode. S-4

5 Figure S8. SEM image 2 of FTO/SrTaO2N/Fh photoanode. Figure S9. LSV of FTO/SrTaO2N/Fh photoanode, Ta/SrTaO2N/Fh nanowire photoanode and bare electrode Fh. Measurements were performed in 0.1 M NaOH electrolyte (ph 13) under interrupted AM 1.5 G illumination (100 mw cm 2 ) at a scanrate of 10 mv s 1. Figure S10. CA of Fh photoanode and FTO/SrTaO2N/Fh photoanodes with and without a hole scavenger in the form of Na2SO3. Measurements were performed in 0.1 M NaOH electrolyte (ph 13) under interrupted AM 1.5 G illumination (100 mw cm 2 ).. S-5

6 Figure S11. LSV of nanowire photoanode and ball-milled (nanoparticle) FTO/SrTaO2N/Fh at a scan rate of 10 mv s 1. Measurements were performed in 0.1 M NaOH electrolyte (ph 13) under interrupted AM 1.5 G illumination (100 mw cm). The ball-milled displayed a brighter color and the photocurrent was neglible. Figure S12. CA of Ta/SrTaO2N/Fh and unprotected Ta/SrTaO2N nanowire photoanodes. Measurements were performed in 0.1 M NaOH electrolyte (ph 13) under AM 1.5 G illumination (100 mw cm 2 ). S-6

7 Figure S13. CA of SrTaO2N/Fh nanowire photoanode at 1.23 V vs. RHE for 2h. Illumination was interrupted twice to see whether a photocurrent is still present. The electrode was previously exposed to all PEC and electrochemical experiments reported in this work. Figure S14..TEM EDX line scan on a SrTaO2N nanowire after 2h CA at 1.23 V vs RHE. The grey line shows the direction of the scan. Figure S15. IPCE at 1.23 V vs. RHE of FTO/SrTaO2N/Fh and Ta/SrTaO2N/Fh nanowire photoanodes S-7