Supporting Information 1T-Phase MoS 2 Nanosheets on Nanorod Arrays: 3D Photoanode with Extraordinary Catalytic Performance Yuxi Pi, Zhen Li, Danyun Xu, Jiapeng Liu, Yang Li, Fengbao Zhang, Guoliang Zhang, Wenchao Peng,* and Xiaobin Fan* State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Collaborative Innovation Center of Chemical Science and Engineering, Tianjin University, No. 135, Yaguan Road, Jinnan District, Tianjin 300354, China *E-mail: xiaobinfan@tju.edu.cn *E-mail: wenchao.peng@tju.edu.cn Total pages: 15 Total number of Figures: 13 S1
Current density (ma/cm 2 ) (a) Current density (ma/cm 2 ) 3.2 2.4 1.6 0.8 /1T-MoS 2 (0.1mg) /1T-MoS 2 (0.2mg) /1T-MoS 2 (0.05mg) /1T-MoS 2 (0.5mg) /1T-MoS 2 (0.01mg) Off On 0.0 0 40 80 120 160 Time (s) (b) 2.0 1.6 1.2 0.8 0.4 0.0 /2H-MoS 2 (0.1 mg) /2H-MoS 2 (0.05 mg) /2H-MoS 2 (0.01 mg) /2H-MoS 2 (0.2 mg) /2H-MoS 2 (0.5 mg) Off On 0 40 80 120 160 Time (s) Figure S1. Transient current densities with light On/Off every 20 s at an external bias of 0.8 V measured from (a) NAs/1T-MoS 2 and (b) NAs/2H-MoS 2 composite with different loading of MoS 2 in the dark and under AM 1.5 G illumination (100 mw/cm 2 ). S2
Figure S2. Selected SEM image of NAs/1T-MoS 2 composite (a) and the corresponding elemental mapping images of Ti (b), O (c), Mo (d) and S (e); (f) EDX spectrum results from NAs/1T-MoS 2 composite (a). S3
Figure S3. (a) Selected SEM image of NAs/1T-MoS 2 composite in a large scale; Corresponding elemental mapping images of (b) Ti, (c) O, (d) Mo and (e) S; (f) EDX spectrum results from NAs/1T-MoS 2 composite (a). S4
Figure S4. Typical TEM and HRTEM images of the 1T-MoS 2 nanosheets (a), (b) and 2H-MoS 2 nanosheets (c), (d). Note that the blown-up image and corresponding FFT pattern shows the individual Mo (red dot) atoms of the 1T-MoS 2 nanosheets (inset in b), whereas individual Mo (red dot) and S (green dot) atoms and their honeycomb arrangement were confirmed of 2H-MoS 2 nanosheets (inset in d). S5
Absorbance 1.5 1.2 C 1T-MoS 2 2H-MoS 2 0.9 0.6 B A 0.3 0.0 400 600 800 1000 Wavelength (nm) Figure S5. Absorption spectra of pure 1T- and 2H-MoS 2 nanosheets in aqueous solution. 1T-MoS 2 nanosheets show featureless absorption from the UV to NIR region, while the 2H-MoS 2 nanosheets show characteristic A, B and C excitonic features. Specifically, the A and B excitonic peaks arising from the K point of the Brillouin zone can be observed between 600 nm and 700 nm, and the C-exciton appears at around 420 nm. 1-2 S6
Intensity 1T-MoS 2 A 1g 2H-MoS 2 J 1 J 2 E 1g J E 1 3 2g E 2 1u A 1g E 1 2g E 2 1u 100 200 300 400 500 600 700 800 Raman shift (cm -1 ) Figure S6. Raman spectra of pure 2H- and 1T-MoS 2 nanosheets. S7
Intensity Intensity Intensity Intensity (a) 1T-MoS 2 Mo 3d 5/2 (b) /1T-MoS 2 Mo 3d 5/2 2H Mo 3d 3/2 1T 2H Mo 3d 3/2 1T S 2S S 2S 234 232 230 228 226 224 234 232 230 228 226 224 Binding Energy (ev) Binding Energy (ev) (c) 2H-MoS2 (d) /2H-MoS 2 Mo 3d 5/2 Mo 3d 5/2 Mo 3d 3/2 2H Mo 3d 3/2 2H S 2S S 2S 234 232 230 228 226 224 234 232 230 228 226 224 Binding Energy (ev) Binding Energy (ev) Figure S7. XPS spectra of Mo 3d, S 2s for (a) 1T-MoS 2 nanosheets, (b) NAs/1T-MoS 2 composite, (c) 2H-MoS 2 nanosheets, and (d) NAs/2H-MoS 2 composite. S8
Intensity Intensity (a) 2p 3/2 Ti 2p 2p 1/2 NAs/1T-MoS 2 (b) O 1s NAs/1T-MoS 2 NAs/2H-MoS 2 TiO2 NAs/2H-MoS2 NAs NAs 464.0 458.3 468 464 460 456 452 540 538 536 534 532 530 528 526 Binding Energy (ev) Binding Energy (ev) Figure S8. XPS spectra of (a) Ti 2p, (b) O 1s for NAs, NAs/2H-MoS 2, and NAs/1T-MoS 2 composites. As shown in Figure S8, the binding energies of Ti 2p 3/2 and Ti 2p 1/2 for NAs are 458.3 and 464.0 ev respectively, which are ascribed to the Ti 4+ oxidation state. 3-4 After loading MoS 2 nanosheets onto NAs, the binding energies of Ti 2p 3/2 and Ti 2p 1/2 for NAs/MoS 2 composites shift to higher energies due to the existence of Ti 3+ states. 5 To be specific, the values shifted in NAs/1T-MoS 2 composite is larger than NAs/2H-MoS 2 composite, which coincides with the fact that the higher electronic interaction between NAs and 1T-MoS 2 nanosheets. 4, 6 From Figure S8b, O 1s can be seen and it will be useful in identifying the core levels. As for NAs, the O 1s peaks at 529.5 ev attributed to the Ti O Ti bond, 531.7 ev attributed to adsorbed water. 3, 6 Interesting, the phenomenon of peak shift also appear in NAs/MoS 2 composites, which is similar to the peak shift of Ti 2p. S9
IPCE (%) 25 20 15 NAs NAs/2H-MoS 2 NAs/1T-MoS 2 10 5 0 380 400 420 440 460 480 500 520 540 Wavelength (nm) Figure S9. IPCE spectra of NAs, NAs/2H-MoS 2 and NAs/1T-MoS 2 photoanodes at the incident wavelength range from 380 to 550 nm at a potential of 0.8 V vs. Ag/AgCl. The incident-photon-to-current-conversion efficiency (IPCE) was calculated from the current density recorded at different wavelengths using following formula IPCE (%)= 1240 J ph (ma cm -2 ) λ (nm) P light (mw cm -2 ) 100 where J ph is the photocurrent density, λ is the incident wavelength and P light is the incident irradiance. As shown in Figure S9, IPCE of both the two composites show improved performance compared to the NAs. Their IPCE values are more than 2 times of that of the NAs, in both visible and UV region. We believe that the broadened absorption should contribute to the improved IPCE. For example, the valence band edge potentials of 2H-MoS 2 is measured to be 1.54 V vs. NHE in ph 7 solution (Figure 8), which is sufficient to drive water oxidation reaction (E(H 2 O/O 2 )= 0.81 V thermodynamically. S10
Current density ( A/cm 2 ) 60 45 30 15 0 NAs NAs/2H-MoS 2 NAs/1T-MoS 2 0.6 0.8 1.0 1.2 Potential (V) vs. Ag/AgCl Figure S10. Photocurrent density versus applied potential of NAs, NAs/2H-MoS 2, and NAs/1T-MoS 2 composites in the dark. S11
Figure S11. SEM images of (a) NAs/1T-MoS 2 and (b) NAs/2H-MoS 2 composites after electrochemical measurements. S12
(a) TiO2 NAs/2H-MoS2 0.4 1.2 1.0 0.8 0.3 (c) 2.6 j (ma/cm2) 1.4 j (ma/cm2) 0.5 j (ma/cm2) (b) TiO2 NAs TiO2 NAs/1T-MoS2 2.4 2.2 2.0 1.8 1.6 0.6 0 2 4 6 8 10 12 Time (h) 0 2 4 6 8 Time (h) 10 12 0 2 4 6 8 10 12 Time (h) Figure S12. Photoanode stability at 0.8 V versus Ag/AgCl for TiO2 NAs, TiO2 NAs/2H-MoS2 and TiO2 NAs/1T-MoS2 photoanodes under constant AM 1.5 G illumination (100 mw/cm2). S13
(a) 1/C 2 10 9 (F -2 cm 4 ) (c) 1/C 2 10 9 (F -2 cm 4 ) 6.0 5.0 4.0 3.0 2.0 1.0 0.0 2.5 2.0 1.5 1.0 0.5 0.0 100 HZ 80 HZ 60 HZ FTO -0.31 V -0.4-0.2 0.0 0.2 0.4 Potential (V vs. NHE) 100 HZ 80 HZ 60 HZ 2H-MoS 2 0.13 V 0.0 0.2 0.4 0.6 0.8 Potential (V vs. NHE) (b) 1/C 2 10 10 (F -2 cm 4 ) (d) 1/C 2 10 9 (F -2 cm 4 ) 4.0 3.0 2.0 1.0 0.0 8.0 6.0 4.0 2.0 0.0 100 HZ 80 HZ 60 HZ NAs -0.21 V -0.4-0.2 0.0 0.2 0.4 Potential (V vs. NHE) 100 HZ 80 HZ 60 HZ 1T-MoS 2 0.16 V 0.0 0.2 0.4 0.6 0.8 Potential (V vs. NHE) Figure S13. Mott Schottky plots of (a) bare FTO substrate, (b) NAs, (c) 2H-MoS 2 nanosheets, and (d) 1T-MoS 2 nanosheets in 0.5 M Na 2 SO 4, ph=7. S14
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