Supporting Information

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1 Supporting Information Wiley-VCH Weinheim, Germany Hierarchical Nanosheet-Based MoS 2 Nanotubes Fabricated by an Anion-Exchange Reaction of MoO 3 Amine Hybrid Nanowires** Sifei Zhuo, You Xu, Weiwei Zhao, Jin Zhang, and Bin Zhang* anie_ _sm_miscellaneous_information.pdf

2 1. Experimental Section: 1.1 Chemicals: All chemicals are analytical grade and used as received without further purification. MoS 2 bulks was of analytic grade and purchased from Aladdin Industrial Corporation. 1.2 Synthesis of MoO 3 -EDA inorganic-organic hybrid nanowires: The MoO 3 -EDA inorganic-organic hybrid nanowires were synthesized using the reported method (Q. Gao, S. Wang, H. Fang, J. Weng, Y. Zhang, J. Mao, Y. Tang, J. Mater. Chem. 2012, 22, 4709.). XRD pattern shows that the samples are Mo 3 O 10 (C 2 H 10 N 2 ) (ethylenediamine trimolybdate). In our manuscript, the hybrid sheets are named as MoO 3 -EDA here. 1.3 Transformation of MoO 3 -EDA inorganic-organic hybrid nanowires into hierarchical nanosheet-based MoS 2 nanotubes: In a typical chemical transformation procedure, 0.1 g of the MoO 3 -EDA hybrid nanowires was added to 15 ml of aqueous solution containing L-cysteine (0.2836g) to form a dispersion aqueous solution under constant strong stirring. The dispersion was transferred into a 25 ml Teflon-lined autoclave. The sealed vessel was then maintained at 200 ºC for 14 h. The black samples were collected and washed several times with water and ethanol respectively, and then dried at 60 for one day. 1.4 Photoelectrochemical Measurements: Photoelectrochemical measurements were carried out in a standard three-compartment cell consisting of a working electrode, a Pt gauze counter electrode, and a saturated calomel reference electrode (SCE) performed using an electrochemical workstation (CHI 660D, CH Instruments, Austin, TX) under visible light illumination (λ > 420 nm) in the presence of 10 vol % lactic as electrolyte and scarifying agent. An indium-tin oxide glass (ITO) decorated with catalyst samples were used as the working electrode. For a typical procedure for fabricating the working electrode, 4 mg of MoS 2 catalysts were dispersed in ml of water containing Nafion solution (40 μl, 5 wt%), then the mixture was ultrasonicated to generate a homogeneous ink. Then 160 μl of the catalyst ink (containing mg of catalyst) was spreaded on an ITO glass (loading amount: ~ 0.12 mg/cm 2 ). The electrochemical impedance spectroscopy (EIS) measurements were carried out at open circuit potential (0.228 V) from 1000 khz Hz under visible light (λ > 420 nm) irradiation with the same conditions as photoelectrochemical measurement. 1.5 Electrochemical Measurements: Electrochemical measurements were carried out in a S1

3 typical three-electrode cell consisting of a working electrode, a Pt wire counter electrode, and a saturated calomel reference electrode (SCE) performed using an electrochemical workstation (CHI 660D, CH Instruments, Austin, TX) in the presence of 0.5M H 2 SO 4 as electrolyte. A glassy carbon electrode decorated with catalyst samples were used as the working electrode. For a typical procedure for fabricating the working electrode, 4 mg of MoS 2 catalysts and 80 μl of 5 wt% Nafion solution were dispersed in 1 ml of 4:1 v/v water/ethanol by sonication to form a homogeneous ink. Then 5 μl of the catalyst ink (containing 20 μg of catalyst) was loaded onto a glassy carbon electrode of 3 mm in diameter (loading amount: ~ mg/cm 2 ). Linear sweep voltammetry was conducted in 0.5 M H 2 SO 4 with scan rate of 2 mvs 1. The electrochemical impedance spectroscopy (EIS) measurements were carried out in the same configuration at η = 0.2 V from 1000 khz Hz with an AC voltage of 5 mv. 1.6 Characterization: The scanning electron microscopy (SEM) images and Energy-dispersive X-ray spectroscopic (EDX) analysis were taken with a Hitachi S-4800 scanning electron microscope (SEM, 5 kv) equipped with the Thermo Scientific energy-dispersion X-ray fluorescence analyzer. Transmission electron microscopy (TEM), higher-magnification transmission electron microscopy (HRTEM) and Electron energy loss spectroscopy (EELS) elemental distribution images were obtained with FEI Tecnai G 2 F20 system equipped with GIF 863 Tridiem (Gatan). Specimens for TEM and HRTEM measurements were prepared via dropcasting a droplet of ethanol suspension onto a copper grid, coated with a thin layer of amorphous porous carbon film, and allowed to dry in air. The X-ray diffraction patterns (XRD) of the products were recorded with Bruker D8 Focus Diffraction System using a Cu Kα source (λ= nm). The pore size distributions of the synthesized materials were determined by nitrogen physisorption using Quadrasorb SII Quantachrome Instrument. Pore size distributions were calculated using the Barrett-Joyner-Halenda method from the desorption branch. FTIR spectra were recorded on a MAGNA-IR 750 (Nicolet Instrument Co) FTIR spectrometer. UV-vis diffuse reflectance spectra (UV-vis DRS) were recorded on a Lambda 750 UV-vis-NIR spectrometer (Perkin-Elmer) equipped with an integrating sphere. The UV-vis DRS of solid samples were collected in nm against BaSO 4 reflectance standard. S2

4 Figure S1. FTIR spectra of the MoO 3 -EDA inorganic-organic nanowires and the as-prepared hierarchical nanosheet-based MoS 2 inorganic nanotubes. These spectra suggest that the hybrid precursors can be successfully transformed into inorganic materials. Figure S2. SEM image (a) and TEM image (b) of the hierarchical nanosheet-based MoS 2 nanotubes synthesized by the anion-exchange reaction of the inorganic-organic MoO 3 -EDA hybrid nanowires with S 2- under hydrothermal conditions. S3

5 Figure S3. Nitrogen adsorption/desorption isotherms (left figure) and pore size distribution (right figure) of the hierarchical nanosheet-based MoS 2 nanotubes. The pore size distributions calculated with the Barrett-Joyner-Halenda method from the nitrogen desorption isotherm suggests that the nanosheet-based hierarchical MoS 2 nanotubes hold macropores of around 200 nm and mesopores of about 30 nm. The former is associated with the tubular structure, and the later is attributed to the porous aggregates of nanosheets on the tubular walls. Figure S4. STEM elemental mapping of the hierarchical nanosheet-based MoS 2 nanotubes. The inset of (a) is the STEM image in accord with the STEM elemental mapping. S4

6 Figure S5. a,b) SEM images of MoO 3 nanowires synthesized by using the reported method (C. Zhang, H. B. Wu, Z. Guo, X. W. Lou, Electrochem. Commun. 2012, 20, 7-10.), c,d) SEM images of MoS 2 particles composed of nanosheets when treating MoO 3 inorganic nanowires with L-cysteine and other conditions of the reaction are identical to the hierarchical nanosheet-based MoS 2 nanotube case S5

7 Figure S6. SEM images of the hierarchical nanosheet-based MoS 2 nanotubes (HNN-MoS 2 ) when thiourea (a) and thioacetamide (b) were used to replace L-cysteine as sulphur source and other conditions remain unchanged, respectively,. Figure S7. SEM images of the commercial MoS 2. S6

8 Figure S8. a) Current-voltage characteristics in a three-compartment cell with the hierarchical nanosheet-based MoS 2 nanotubes (HNN-MoS 2 ) used as the working electrode, a Pt gauze counter electrode and a reference electrode (SCE) under visible light illumination (λ > 420 nm). This figure shows the photocurrent increases as the applied potential is scanned toward more positive which is beneficial to the separation and transport of charge carriers for enhanced photocurrent generation (T. Hasobe, H. Murata, P. V. Kamat, J. Phys. Chem. C 2007, 111, ). b) Photocurrent-time curve of HNN-MoS 2 electrode at a bias potential of 0.6 V vs SCE under visible light illumination (λ > 420 nm). Figure S9. Electrochemical impedance spectroscopy of hierarchical nanosheet-based MoS 2 nanotubes (HNN MoS 2 ) at an open circuit potential (0.228 V) from 1000 khz to 0.1 Hz under visible light (λ > 420 nm) irradiation with the three-electrode system. As displayed in Figure S8, the plot is composed of a semicircle in high-to-medium frequency region which should be attributed to the charge transfer process at the electrode/electrolyte interface, and a straight line in low frequency which should be ascribed to the diffusion process of charges inside the electrode. S7

9 Figure S10. a) Polarization curves for HER of bare glassy carbon electrode(1), and glassy carbon electrode modified by commercial MoS 2, (C-MoS 2 ) catalysts (2), the as-prepared hierarchical nanosheet-based MoS 2 nanotubes (HNN-MoS 2 ) catalysts(3) and Pt/C catalysts (20 wt% Pt, Johnson Matthey) (4). It indicates that our HNN-MoS 2 catalysts showed a small overpotential (η) about of V for the HER, beyond which the cathodic current rose rapidly under more negative potentials. In sharp contrast, C-MoS 2 exhibited little HER activity. b) Electrochemical impedance spectroscopy of C-MoS 2 (2) and HNN-MoS 2 (3) catalysts. The significantly decreased diameter for HNN-MoS 2 demonstrated the improved HER kinetics compared to C- MoS 2. S8