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1 Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A. This journal is The Royal Society of Chemistry 2016 Electronic Supplementary Information (ESI) Synthesis of 1T-MoSe 2 ultrathin with an expanded interlayer spacing of 1.17 nm for efficient hydrogen evolution reaction Miao Jiang, a1 Junjun Zhang, bc1 Meihui Wu, a Wenjing Jian, a Hongtao Xue, b Tsz-Wai Ng, b Chun-Sing Lee* b and Jun Xu* a a School of Electronic Science & Applied Physics, Hefei University of Technology, Hefei, , People s Republic of China b Center of Super-Diamond and Advanced Films (COSDAF), and Department of Physics and Materials Sciences, City University of Hong Kong, Hong Kong SAR, People s Republic of China c Department of Materials Science and Engineering, South University of Science and Technology of China, Shenzhen, , People s Republic of China 1 The authors contributed equally. *Corresponding authors: apjunxu@hfut.edu.cn (J. Xu), apcslee@cityu.edu.hk (C.-S. Lee) 1

2 Experimental Synthesis 0.4 mmol of MoCl 5 and 0.8 mmol of SeO 2 powders were added into 25 ml of octylamine in a Teflon-lined autoclave (50 ml). After the solution was stirred for several minutes, the autoclave was sealed and kept in an oven at 180 C for 6-12 h, and then cooled down to room temperature. The product was collected by centrifugation and washed with absolute ethanol and distilled water several times, and vacuum-dried. 2H-MoSe 2 was prepared by annealing the as-prepared sample at C in an Ar/H 2 (5% H 2 ) flow. Characterization Structures, morphologies and compositions of the samples were characterized with X-ray diffraction (XRD) (Rigaku D/MAX2500V, Cu K radiation), scanning electron microscopy (SEM) (Philips XL30 FEG), transmission electron microscopy (TEM) (Philips CM 20 FEG or JEOL JEM-2100F, 200 kv), Raman spectroscopy (Lab RAM HR, 532 nm excitation), X-ray photoelectron spectroscopy (XPS) (VG ESCALAB 220i-XL, Al K ), and thermogravimetric (TG) analysis (Mettler Toledo TGA-DSC-1). Electrochemical Measurements Electrochemical measurement was performed in a standard three-electrode configuration on an electrochemical workstation (CHI 660E). The threeelectrode configuration contains a glassy-carbon electrode with the MoSe 2 2

3 electrocatalysts as the working electrode, a saturated calomel electrode (SCE) as the reference electrode, and a Pt foil as the counter electrode. Typically, 10 mg of the MoSe 2 electrocatalysts was added in a mixture of 1600 L of DI water, 400 L of ethanol, 160 L of Nafion solution (5 wt%). The mixture was vigorously sonicated for about 30 min to form a homogeneous ink solution. 5 L of the ink was loaded onto a glassy-carbon electrode with a diameter of 3 mm, and dried at room temperature. The loading density of the catalysts is about 0.32 mg cm 2. A 0.5 M H 2 SO 4 solution was used as electrolyte and degassed by bubbling pure N 2 for 30 min. Linear sweep voltammetry was carried out at an scan rate of 5 mv s 1 for the polarization curves. All of the potentials were carefully calibrated to a reversible hydrogen electrode (RHE). 3

4 Fig. S1 HRTEM image of the as-prepared MoSe 2 flower-like assemblies in the internal area, showing that the contain about 3-7 monolayers. 4

5 100 Weight Retention (%) (ii) (i) Temperature ( C) Fig. S2 TG analysis curves of (i) the as-prepared MoSe 2 sample and (ii) the MoSe 2 sample annealed at 300 C. The larger weight loss in curve (i) is resulted from evaporation of octylamine molecules. 5

6 Fig. S3 EDX spectrum of the as-prepared MoSe 2 sample. 6

7 Fig. S4 HRTEM image of the MoSe 2 sample after annealing at 300 C. 7

8 Fig. S5 (a) Cycling voltammetry (CV) curves of the as-prepared 1T-MoSe 2 electrocatalyst at scan rates from 20 to 100 mv s 1 in the region of V vs. RHE, (b) CV curves of the annealed 2H-MoSe 2 electrocatalyst at scan rates from 20 to 100 mv s 1 1, (c) The differences in current density variation ( J= (Ja J c) ) at V vs. RHE plotted against scan rate fitted to a linear regression for estimation of C dl. 8

9 Fig. S6 (a) Polarization curves of the as-prepared 1T-MoSe 2 electrocatalyst, revealing that negligible degradation of HER activity after 3000 CV cycles. (b) Controlled potential electrolysis result of the as-prepared 1T-MoSe 2 sample at V (vs RHE). 9

10 Table S1 Recent advance of HER perormance of MoSe 2 -based catalysts. No Samples Interlayer-expanded 1T-MoSe 2 Exfoliated 1T- MoSe 2 MoSe 2 film with vertically aligned layers Hierarchical ultrathin MoSe 2-x Onset potential (V vs. RHE) Tafel slope (mv per decade) Overpotential at 10 ma cm 2 (V vs. RHE) References This work ~ ~ NA ~ MoSe 2 ~ MoSe 2 porous microspheres Monolayered MoSe 2 S-doped MoSe 2 Pure MoSe 2 S-doped MoSe 2 x S-doped MoSe 2 x nanotubes MoSe 2 nanocaterpillars MoSe 2 /rgo hybrid nanostructures Pure MoSe 2 nanoflowers MoSe 2 /graphene hybrid Pure MoSe 2 Vertical aligned MoSe 2 on carbon fiber paper Epitaxial MoSe 2 NiSe nanohybrids Pure MoSe 2 Few-layer MoSe 2 grown on SnO 2 nanotubes ~0.125 ~ ~ ~0.22 ~ ~0.21 ~ ~0.23 ~ ~ ~ ~ ~ ~0.28 ~ ~ Chem. Commun., 2015, 51, Nano Lett., 2013, 13, Nanoscale, 2014, 6, ACS Catal., 2015, 5, Nano Res., 2015, 8, Nanoscale, 2015, 7, J. Mater. Chem. A, 2014, 2, Inorg. Chem. Front., 2015, 2, J. Mater. Chem. A, 2015, 3, J. Mater. Chem. A, 2014, 2, Nano Lett., 2013, 13, Chem. Mater. 2016, 28, J. Mater. Chem. A, 2015, 3,