Incorporation of Mo and W into Nanostructured BiVO 4 Films to Improve Photoelectrochemical Water Oxidation Performance

Transcription

1 Power Density ( W cm -2 ) Supporting Information Incorporation of Mo and W into Nanostructured BiVO 4 Films to Improve Photoelectrochemical Water Oxidation Performance Sean P. Berglund, Alexander J.E. Rettie, Son Hoang, and C. Buddie Mullins* Departments of Chemical Engineering and Chemistry and Biochemistry, Center for Electrochemistry, Texas Materials Institute, and Center for Nano- and Molecular Science University of Texas at Austin 1 University Station C0400 Austin, TX (U.S.) *address correspondance to: mullins@che.utexas.edu Wavelength (nm) Figure S1. Typical power density spectrum for light that was incident on the film during IPCE measurements. The power was measured using a UV enhanced silicon photo-detector. 1

2 Current Density (ma cm -2 ) x10-6 Torr O 2 no background gas Potential (V vs. RHE) Figure S2. Chopped (dark and white light) LSV scans for BiVO 4 films deposited in vacuum with no background gas and with 5x10-6 Torr of O 2. After deposition both films were annealed in air at 500 o C in for 2 hours. Measurements were conducted in mixture of 0.1 M Na 2 SO 4 and 0.1 M phosphate buffer solution (ph 6.8) with a scan rate of 25 V s -1. Figure S3. SEM images of films with a Bi:V:Mo:W atomic ratio of 50:50:0:0 deposited at =55 o in vacuum with no background gas and with 5x10-6 Torr of O 2. The films have not been annealed. 2

3 (c) (d) (e) (f) Figure S4. SEM images of films with Bi:V:Mo:W atomic ratios of 46:46:6:2 deposited in vacuum at different deposition angles ( ) taken before and after annealing in air at 500 o C for 2 hours: =0 o, before annealing =0 o, after annealing (c) =55 o, before annealing (d) =55 o, after annealing (e) =75 o, before annealing (f) =75 o, after annealing. 3

4 Photocurrent Density (ma cm -2 ) % Mo, 2% W 5% Mo 2.5% W pure BiVO Age Since Annealing (days) Figure S5. Trends showing improvement in photocurrent density with age since annealing for BiVO 4 films with varying atomic percentages of Mo and W (relative to the total Bi, V, Mo, and W). The photocurrent density values were taken from LSV scans (value at 1.6 V vs. RHE) in 0.1 M Na 2 SO 4 and 0.1 M phosphate buffer solution (ph 6.8) with a scan rate of 25 V s -1. Between measurements the films were simply left in plastic container in the laboratory at normal atmospheric conditions. 4

5 C -2 (F -2 ) C -2 (F -2 ) 1.0x x Hz 1000 Hz 5.0x x x x Applied Potential (V vs. RHE) 500 Hz 1000 Hz 1.5x x x Applied Potential (V vs. RHE) Figure S6. Mott-Schottky plot for pure BiVO 4 and 6% Mo, 2% W BiVO 4 films conducted in 0.1 M Na 2 SO 4 and 0.1 M 5

6 Count Rate (arb) Count Rate (arb) Count Rate (arb) Count Rate (arb) phosphate buffer solution (ph 6.8). 1 day post anneal 41 days post anneal 1 day post anneal 41 days post anneal Bi 4f 5/2 Bi 4f 7/2 O 1s V 2p 3/2 V 2p 1/ Binding Energy (ev) Binding Energy (ev) (c) 1 day post anneal 41 days post anneal 1 day post anneal 41 days post anneal Bi 5d 7/2 Mo 3d 3/2 Mo 3d 5/2 (d) Bi 5d 3/2 W 4f 7/2 Mo 4f 5/ Binding Energy (ev) Binding Energy (ev) Figure S7. XPS spectra for a single 6% Mo, 2% W BiVO 4 film taken 1 day and 41 days after annealing. 6

7 Current Density (ma cm -2 ) % Mo, 2% W (frontside) 6% Mo, 2% W (backside) 6% Mo, 2% W, brushed surface (frontside) 6% Mo, 2% W, brushed surface (backside) Potential (V vs. RHE) Figure S8. Chopped (dark and white light) LSV scans for a 6% Mo, 2% W BiVO 4 film before brushing the film surface (frontside and backside illumination) and after brushing the film surface and rinsing it with de-mineralized water to remove irregular surface structures (frontside and backside illumination). Measurements were conducted in mixture of 0.1 M Na 2 SO 4 and 0.1 M phosphate buffer solution (ph 6.8) with a scan rate of 25 V s -1. Figure S9. Top view SEM images of a 6% Mo, 2% W BiVO 4 film before brushing the film surface and after brushing the film surface and rinsing it with de-mineralized water. 7

8 Absorbance % Mo, 2% W 6% Mo, 2% W, brushed surface Wavelength (nm) Figure S10. UV-Vis absorbance spectrum for a 6% Mo, 2% W BiVO 4 film taken before and after brushing the film surface and rinsing it with de-mineralized water. The measurements were taken using a Cary 5000 spectrophotometer in transmission mode so any diffusely scattered light contributed to the measured absorbance. 8