Supporting Information

Transcription

1 Supporting Information A TiO 2 /FeMnP Core/Shell Nanorod Array Photoanode for Efficient Photoelectrochemical Oxygen Evolution Desmond E. Schipper,, Zhenhuan Zhao,,, Andrew P. Leitner, Lixin Xie, Ω Fan Qin, Md Kamrul Alam, Shuo Chen, Ω Dezhi Wang, Ω Zhifeng Ren, Ω Zhiming Wang, Jiming Bao,*,, and Kenton H. Whitmire, * Department of Chemistry, MS60, Rice University, 6100 Main Street, Houston, Texas 77005, United States whitmir@rice.edu, jbao@central.uh.edu Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu , China Department of Electrical and Computer Engineering, University of Houston, Houston, Texas 77204, United States Ω Department of Physics & Texas Center for Superconductivity at the University of Houston, University of Houston, Houston, Texas 77204, United States These authors contributed equally.

2 Figure S1. The home-made MOCVD apparatus employed in this work. Figure S2. SEM image of bare TiO 2 nanorod array on FTO substrate.

3 Figure S3. XRD of TiO 2 /FeMnP core/shell nanorod array on FTO substrate. For comparison, the spectra of bare TiO 2 nanorod array on FTO and bare FTO are also illustrated. Figure S4. XRD of FeMnP on FTO substrate.

4 Table S1. Comparison of OER activity of single phase catalysts. Catalysts Electrolytes Substrate Overpotential at 10 ma cm -2 Tafel slope (mv dec -1 ) Ref. Amorphous FeOOH films 1 M NaCO 3 FTO 550 mv N/A Mn 3 O 4 film 1 M KOH FTO 570 mv N/A a-mno 2 β-mno 2 film MnO polypods 1 M KOH 1.0 M NaOH 0.1 M KOH Pyrolytic graphite 490 mv 77.5 FTO 500 mv 90 Pyrolytic graphite 580 mv 149 CoSe 2 nanobelt 0.1 M KOH GCE 484 mv 66 Nitrogen doped graphite 0.1 M KOH GCE 380 mv N/A β-ni(oh) 2 plates 0.1 M KOH GCE 440 mv 246 Mesoporous Co 3 O M KOH Gold disk 525 mv N/A Co 3 O 4 nanowire 0.1 M KOH Cu foil 400 mv 123 N, P codoped graphene 0.1 M KOH GCE 390 mv N/A NiO x, CoPi, NiCeO x 1 M NaOH GCE >400 mv N/A CoCo LDH 1 M KOH GCE 388 mv 57 CoP nanorods Ni 2 P nanoparticles/nano wires NiCoP nanoparticles Nanoporous (Co 0.52 Fe 0.48 ) 2 P CoMnP nanoparticles FeMnP nanoplates 1 M KOH Nickel foam 1 M KOH GCE 290 mv mv/330 mv 59/47 1 M KOH Ti foil 340 mv 86 1 M KOH Co/Fe alloy 270 mv M KOH GCE 330 mv M KOH FTO 300 mv This work

5 Figure S5. Nyquist plot of FeMnP/FTO electrode at overpotential of 300 mv in 1.0 M KOH. The insert refers to the corresponding equivalent circuit consisting of the equivalent series resistance (R s ) from the leads, solution resistance and wires, charge transfer resistance (R t ) and the double-layer capacitance (C t ).

6 Figure S6. Measurements of the electrochemically active surface area (ECSA). (a) and (b) the CV scans of FTO and FeMnP/FTO at different scan rates in 1.0 M KOH in the non-faradaic potential range. (c) and (d) the corresponding current density difference between the anodic current and the cathodic current at V vs RHE as a function of scan rate for the FTO and FeMnP/FTO electrodes, respectively. The slope of the linear part is the electrochemical double-layer capacitance, which has a positive linear relationship with the ECSA.

7 Figure S7. (a) Time dependence of catalytic current density of FeMnP/FTO electrode in 1.0 M KOH at overpotential of 300 mv. (b) Faradaic efficiency: experimentally produced O 2 versus theoretically calculated amount of O 2. Figure S8. (a) UV-VIS spectra of TiO 2 nanorod array on FTO glass showing the light absorption edge of 400 nm. (b) The corresponding Tauc plot of TiO 2 giving the band gap of 3.0 ev.

8 Figure S9. Transmittance of TiO 2 and TiO 2 /FeMnP.

9 Table S2. Comparison of photoanodes under simulated light irradiation (100 mw cm -2 ) Photoanodes Electrolytes Current density at 1.23 V vs RHE (ma cm -2 ) Photo to electrical conversion efficiency Ref. NiFe-LDH/rGO/TiO 2 nanorod 0.5 M Na 2 SO CoPi/TiO 2 nanowire 0.1 M KPi % at 0.13 V vs SCE 0.17% at 0.7V vs RHE CoPi/C 3 N 4 /TiO M Na 2 SO N/A GO/TiO 2 nanorod 1 M KOH 0.8 N/A N, Ta incorporated TiO 2 nanorod TiO 2 disorder surface layer/tio 2 nanorod 1 M KOH 0.52 N/A 0.5 M Na 2 SO N/A TiO 2 /BaTiO 3 core/shell nanowire 0.5 M phosphate buffer MnO x /TiO 2 nanotube 0.5 M Na 2 SO Carbon nitride/tio 2 nanotube 0.1 M Na 2 SO N/A 0.56% at 0.05 V vs Ag AgCl 0.63% at 0.1 V vs Ag AgCl Ti doped Fe 2 O 3 /Ni(OH) 2 /IrO 1 M NaOH % at 1.0 V vs RHE 28 TiO 2 /FeMnP core/shell nanorod 1 M NaOH % at 0.95 V vs RHE This work

10 Figure S10. Sputtering assisted XPS analysis of the chemical state of TiO 2 /FeMnP core/shell nanorod after stability test. Figure S11. Nyquist plots of the TiO 2 and TiO 2 /FeMnP core/shell nanorod photoanodes at 1.23 V vs RHE under light irradiation. The curves can also be modeled using the same equivalent circuit in Figure S5. The much smaller radius of the semi-circle indicated the significantly decreased charge transfer resistance.

11 Figure S12. Work function of FeMnP/FTO and bare FTO. CPD refers to the contact potential difference between the gold probe and the sample. Figure S13. SEM image at different magnifications of TiO 2 /FeMnP core/shell nanorod array after stability test.

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