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 78712 (U.S.) *address correspondance to: mullins@che.utexas.edu 180 160 140 120 100 80 60 40 20 0 350 400 450 500 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
Current Density (ma cm -2 ) 0.1-0.1 5x10-6 Torr O 2 no background gas -0.2 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 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
(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
Photocurrent Density (ma cm -2 ) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 6% Mo, 2% W 5% Mo 2.5% W pure BiVO 4 0 10 20 30 40 50 60 70 80 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
C -2 (F -2 ) C -2 (F -2 ) 1.0x10 11 7.5x10 10 500 Hz 1000 Hz 5.0x10 10 2.5x10 10 2.5x10 10 2.0x10 10 0.1 0.2 0.3 0.4 Applied Potential (V vs. RHE) 500 Hz 1000 Hz 1.5x10 10 1.0x10 10 5.0x10 9 0.1 0.2 0.3 0.4 0.5 0.6 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
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 1/2 168 166 164 162 160 158 156 Binding Energy (ev) 535 530 525 520 515 510 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 5/2 240 235 230 225 Binding Energy (ev) 40 35 30 25 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
Current Density (ma cm -2 ) -0.5-1.0-1.5-2.0 6% Mo, 2% W (frontside) 6% Mo, 2% W (backside) 6% Mo, 2% W, brushed surface (frontside) 6% Mo, 2% W, brushed surface (backside) -2.5 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 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
Absorbance 3.0 2.5 6% Mo, 2% W 6% Mo, 2% W, brushed surface 2.0 1.5 1.0 0.5 400 450 500 550 600 650 700 750 800 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