Vertically Grown MoS2 Nanoplates on VN with an Enlarged Surface

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Vertically Grown MoS Nanoplates on VN with an Enlarged Surface Area as an Efficient and Stable Electrocatalyst for HER Kai Meng, Shuxian Wen, Lujing Liu, Zhijun Jia, Yi Wang, Zhigang Shao, and Tao Qi ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.9b00201 • Publication Date (Web): 15 Mar 2019 Downloaded from http://pubs.acs.org on March 18, 2019

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ACS Applied Energy Materials

Vertically Grown MoS2 Nanoplates on VN with an Enlarged Surface Area as an Efficient and Stable Electrocatalyst for HER Kai Meng1,2, Shuxian Wen3, Lujing Liu1, Zhijun Jia1, Yi Wang1,*, Zhigang Shao4, Tao Qi1,* 1National

Engineering Laboratory for Hydrometallurgical Cleaner Production

Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China 2University

of Chinese Academy of Sciences, Beijing 100049, China

3Guangdong 4Dalian

Experimental High School, Guangzhou 510375, China

Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023,

China

ABSTRACT Layered MoS2 has attracted increasing interests as a promising low-cost alternative to Pt-based electrocatalysts for hydrogen evolution reaction (HER). As is known to all, insufficient active sites and poor conductivity of MoS2 impede the improvement of its catalytic efficiency. In this work, the vanadium nitride (VN) with an enlarged specific surface area (VN(CTAB), CTAB refers to hexadecyl trimethyl ammonium bromide) was prepared as a substrate and MoS2 nanoplates were vertically grown on the obtained VN(CTAB) for the first time. The synthesized MoS2-VN(CTAB) as an electrocatalyst for HER performs a low onset overpotential (85 mV) and small Tafel slope (53.31 mVdec-1), as well as superior stability. Besides the benefits from higher conductivity (106 Sm-1) and greater stability of VN(CTAB) beyond the traditional carbon-based substrates, the expanded interlayer spacing (1.00 nm) and extra defects, along with the lower valence states of Mo and S due to the stronger electron interaction between VN(CTAB) and MoS2 1

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also effectively contribute to the excellent catalytic performance of MoS2-VN(CTAB). This study shows a new method to design efficient and stable HER electrocatalysts by means of non-carbon substrates. KEYWORDS：Molybdenum disulfide; Vanadium nitride; Enlarged specific surface area; Hydrogen evolution reaction; Electron interaction

INTRODUCTION Hydrogen, an environmental-benign energy resource with high gravimetric energy density, is considered as the most potential alternative to fossil fuel.1-4 Water splitting is a simple and effective method for hydrogen production. However, the kinetics of HER (one of the half-reactions of water splitting) is desired to be improved for commercial application.5,

6

Till date, although Pt-based materials perform the best electrocatalytic

activity for HER, their high cost and scarcity hinder the extensive use.7-9 Therefore, development of non-noble metal electrocatalysts with an affordable price and abundant raw material remains a long-term challenge. MoS2 as one of transition metal dichalcogenides, has been demonstrated to possess high electrocatalytic activity for HER in recent years.10-12 By theoretical and experimental research, it is proved that the active sites of HER derive from sulfur edge of MoS2 plates instead of catalytically inert basal planes.13, 14 Therefore, many strategies were devoted to increase the density of active edge sites for the HER performance enhancement of MoS2, like vertically grown MoS2 layers,15, structure20,

21

and quantum dot.22,

23

16

nanoplates,17,

18

nanoflower,19 amorphous

On the other hand, the main crystalline forms of

MoS2 include metallic 1T and semiconducting 2H phase. 1T-MoS2 shows higher electrical conductivity and better HER electrocatalytic activity.24-26 Unfortunately, due to the instability of 1T-MoS2, a large part of effort has been focused on the build of nanostructures and improvement of conductivity of 2H-MoS2.27-29 Recent research 2


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demonstrates that the growth of vertical MoS2 nanoplates on conductive substrates can expose more edge active sites and achieve efficient charge transfer from electrode to the electrocatalysts.30 Carbon-based materials are commonly applied as support materials of MoS2 for HER in virtue of their relatively large surface area, special structure, as well as high conductivity.31 For instance, reduced graphene oxide (rGO),28,

32, 33

carbon

nanotubes (CNTs),34-35 amorphous carbon36 and carbon cloth37, 38 have been studied for supporting catalysts. However, carbon-based materials are liable to suffer from corrosion, causing the decrease in pore size and porosity of carbon-based supports, and leading to negative influence on HER performance.39, 40 Recently, transition metal nitrides (TMNs) are drawing tremendous attention in electrochemical application, due to their high conductivity and chemical stability.41,

42

VN, as one of TMNs, possesses the merits of

anticorrosion and superior electrical conductivity (106 Sm-1), as well as remarkable stability in acidic and basic media.43,

44

It has already been used as a good substrate

material in various areas of electrochemistry, such as supercapacitors,45 oxygen evolution reaction (OER),46 and fuel cells.47 In our previous studies, VN was employed as the substrate and promotor of electrocatalysts for OER and methanol electrooxidation, respectively.43,

46

It has been proved that VN improves the activity and stability of

electrocatalysts markedly. However, with the best of our knowledge, there was not any report about VN as support materials for HER catalysts. Furthermore, the VN prepared by common methods (VN nanoparticles, VNNPs) only possesses a small specific surface area (SSA) less than 60 m2g-1, which originates from the aggregation of VN precursors in calcination process. Apparently, the small SSA of VN is unfavorable to the exposure of catalytic active sites as well as the synergy between catalysts and substrates, limiting its practical application in electrocatalysis.42, 48 From the above, it is of great significance to enlarge the SSA of VN substrate for supporting MoS2 and to investigate its electrocatalytic performance for HER. In this study, the MoS2 nanoplates grown on the 3



VN with an enlarged SSA (VN(CTAB)) was synthesized by a soft template method and following hydrothermal method. In virtue of the advantages of VN(CTAB), the resultant MoS2-VN(CTAB) performs superior HER activity and improved stability as compared to unsupported MoS2 and MoS2 loaded on VNNPs (MoS2-VNNPs).

EXPERIMENTAL SECTION Scheme 1. Schematic of the synthesis process of MoS2-VN(CTAB).

Syntheses of VN(CTAB) and VNNPs The VN(CTAB) was prepared by a facile reaction in aqueous solution followed by calcination in ammonia atmosphere (Scheme 1). Typically, 1.45 g CTAB as soft templates was added into 100 mL absolute ethanol with continuously stirring until it was dissolved. Then, 100 mL deionized water (DW) was mixed into above solution. 2.34 g ammonium metavanadate (NH4VO3) was added into the solution little by little. Next, the solution was dried at 40 ℃ under stirring. The obtained product was calcinated at 300 ℃ for 1 h in the air and sequentially calcinated at 600 ℃ for 6 h in ammonia with the heating rate of 2 ℃/min in order to get VN(CTAB). For comparison, VNNPs were prepared by direct calcination of purchased vanadium pentoxide (V2O5) under the same conditions. Syntheses of MoS2-VN(CTAB) and MoS2-VNNPs The MoS2-VN(CTAB) was prepared through a simple hydrothermal method (Scheme 1). In brief, 2.5 mmol sodium molybdate dihydrate (Na2MoO42H2O), 5 mmol 4


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thioacetamide (CH3CSNH2), 200 mg VN(CTAB) and 0.1 mmol CTAB were dissolved in 120 mL DW. After vigorously stirring for 30 min, the suspension was transferred into 200 mL Teflon-lined autoclave and hydrothermally treated at 180 ℃ for 30 h, and subsequently naturally cooled down to room temperature. Then, the hydrothermal products were filtered and washed several times with DW and absolute ethanol. Finally, the as-synthesized sample was dried at 60 ℃. MoS2-VNNPs was prepared by the same route except that the VN(CTAB) was replaced by VNNPs. To investigate the effect of the proportion

between

MoS2

and

VN(CTAB),

the

MoS2-VN(CTAB)-62%,

MoS2-VN(CTAB)-35% and MoS2-VN(CTAB)-29% (the percentages represent the molar contents of MoS2) were synthesized by the same route except changing the mass of VN(CTAB) to 100, 300 and 400 mg, respectively. For comparison, the commercial MoS2 and 20%Pt/C were purchased from Aladdin Industrial Corporation. Materials characterization X-ray diffraction (XRD, Smart Lab (9 kW), Cu Kα) was used to analyze the composition and structure of catalysts. Field emission scanning electron microscopy (FE-SEM,

SU8020),

transmission

electron

microscopy

(TEM,

JEM-2100F),

high-resolution transmission electron microscopy (HRTEM, JEM-2100F), scanning transmission electron microscopy (STEM, JEM-2100F) and energy dispersive X-ray spectroscopy (EDS, JEM-2100F) were performed for the morphology of materials and the information of element dispersion. X-ray photoelectron spectroscopy (XPS, ESCALAB 250Xi) was tested for the chemical-state analysis of sample surface. Nitrogen sorption measurements (Micromeritics ASAP 2020 Analyzer) were conducted for the calculation of SSA of catalysts and pore size distribution using Brunauer−Emmett−Teller (BET) and Barrett–Joyner–Halenda (BJH) methods, respectively. Electrochemical measurement The electrochemical measurement was performed by a three-electrode cell using an 5



electrochemical workstation (CHI760D, Chenhua, Shanghai) and the electrolyte was N2-saturated 0.5 M H2SO4. A Pt foil and saturated calomel electrode (SCE) were used as counter and reference electrode, respectively. The electrocatalyst ink was prepared by ultrasonically dispersing 5 mg of catalysts in 1 mL ethanol. The working electrode was prepared by dropping 5 μL of electrocatalyst ink onto glassy carbon electrode and using 2 μL of 0.5% Nafion to fix catalysts after the ink was dried. All potentials were calibrated to the reversible hydrogen electrode E (vs RHE) = E (vs SCE) + 0.0592 pH + 0.242 V = E (vs SCE) + 0.242 V (PH=0). Linear sweep voltammetry (LSV) was tested from 0 to -0.6 V at 5 mVs-1 after the activation process under the same conditions except for a scan rate of 0.5 Vs-1. The cyclic voltammograms (CVs) were measured from -0.15 to -0.03 V at different scan rates (from 20 to 180 mVs-1, interval is 20 mVs-1) for obtaining the electrical double-layer capacitances (Cdl). Electrochemical impedance spectra (EIS) were conducted at -0.11 V from 100 kHz to 0.01 Hz with ac perturbation amplitude of 5 mV. The durability was investigated by chronoamperometry for 30 h and LSV after 1000 cycles of CVs at a scan rate of 50 mVs-1.

RESULTS AND DISCUSSION The XRD patterns of VNNPs and VN(CTAB) in Figure S1 are well consistent with the standard XRD pattern of VN (#35-0768). The SEM images of VN(CTAB) and VNNPs are displayed in Figure S2. It is seen that VN(CTAB) are porous granules which consists of numerous VN nanoparticles with diameters of dozens of nanometers, while VNNPs are composed of closely agglomerated particles with different diameters. Figure S3 shows the results of nitrogen sorption measurements. As substrates, the SSAs of VNNPs and VN(CTAB) are 30.12 and 122.78 m2g-1, respectively. The SSAs of MoS2, MoS2-VNNPs and MoS2-VN(CTAB) were also tested, which are 1.53, 3.93 and 27.98 6


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m2g-1, respectively. Moreover, from the insets of Figure S3, the pore sizes are mainly above 2 nm in all samples, which are ascribed to mesoporous and macroporous structures. It is noteworthy that VN(CTAB) possesses more and narrower mesoporous structure. It is inferred that in the synthetic process of VN(CTAB), as a soft template, CTAB plays a significant role in the formation of uniform pores structure and prevents the aggregation of the precursor.49 In contrast, VN particles aggregate closely in VNNPs and have much smaller spacing among them. Therefore, VN(CTAB) possesses about quadruple larger SSA than VNNPs, which significantly enhances the SSA of MoS2-VN(CTAB) and favors the abundance of S edge sites for HER.

Figure 1. (a) XRD patterns of MoS2-VN(CTAB), MoS2-VNNPs and MoS2, (b-d) SEM images of MoS2-VN(CTAB), MoS2-VNNPs and MoS2, respectively. The chemical composition and structure of the three MoS2 samples were 7



characterized by XRD and SEM. In Figure 1a, the diffraction peaks at around 32.3°, 33.4°, 35.6° and 57.6° can be well matched with (100), (101), (102) and (110) planes of 2H-MoS2 (JCPDF #37-1492) while other peaks at around 37.9°, 44.2°, 64.0°, 77.1° and 81.0° are indexed to (111), (200), (220), (311) and (222) planes of VN (JCPDF #35-0768). It is worthy to note that the diffraction peak at around 14.3° (related to (002) lattice plane of MoS2) in MoS2-VN(CTAB) and MoS2-VNNPs disappears nearly compared with the pattern of MoS2 and is replaced by two new diffraction peaks at 8.9° and 17.3°. Based on Bragg's Law, the d spacing of the two new peaks is 10.1 and 5.1 Å, respectively. The diploid relationship between the d spacing indicates the formation of expanded lamellar structures.50,

51

The interlayer spacing of MoS2-VN(CTAB) and

MoS2-VNNPs is enlarged by 3.9 Å in contrast to that of MoS2 (6.2 Å). SEM images in Figure 1b-c reveal the growth of MoS2 nanoplates on VN(CTAB) and VNNPs. As compared with MoS2 image in Figure 1d, more MoS2 edges are obviously exposed in MoS2-VN(CTAB) and MoS2-VNNPs, which can offer more S sites for HER. Besides, comparing Figure 1b with 1c, the partial agglomerations of VNNPs and MoS2 can be seen in MoS2-VNNPs. In contrast, MoS2-VN(CTAB) possesses a larger number of slimmer and curled MoS2 nanoplates with uniform distribution. Additionally, the EDS mapping images (Figure S4) further verify that MoS2 nanoplates successfully grow on VN(CTAB) and VNNPs. TEM shows the refined nanostructure of MoS2-VN(CTAB). In Figure 2a, the layered MoS2 nanoplates grown on VN can be seen. The HRTEM images are observed for the further structure features. In Figure 2b, the lattice fringes with 0.21 nm interlayer spacing are attributed to the (200) lattice plane of VN(CTAB), which are consistent with the XRD result in Figure 1a. The interlayer spacing of MoS2 nanoplates in MoS2-VN(CTAB) is measured to be about 1.00 nm, corresponding to the XRD pattern of MoS2-VN(CTAB). It is remarkable that this value is much larger than the theoretical 8


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distance of 0.62 nm in MoS2.52,

53

This structural feature is beneficial to the greater

exposure of S edge sites and thereby may improve the HER activity. Besides the enlarged interlayer spacing, a few defects such as cracks and amorphousness are detected in Figure

Figure 2. (a) TEM image, (b-d) HRTEM images and (e) STEM-EDS mapping images of MoS2-VN(CTAB). 2d (marked with red and black cycles, respectively). These changes derive from the modulation effect of VN towards MoS2 and the arisen defects can act as new catalytical sites for HER.50, 54 In addition, the TEM images of MoS2-VNNPs and commercial MoS2 are presented as contrasts in Figure S5. It can be seen that VNNPs gather together 9



partially and the distribution of MoS2 nanoplates is nonuniform (Figure S5a). In Figure S5b, the commercial MoS2 nanosheets stack along the vertical plane of MoS2. From the above, the synthesized MoS2-VN(CTAB) possesses the preferable nanostructure, which benefits the exposure of active sites and close contact between VN and MoS2 nanoplates. Additionally, the STEM and corresponding EDS mapping images of MoS2-VN(CTAB) are shown in Figure 2e. These images indicate the homogeneous distribution of Mo, V, S and N, which overlap well with each other.

Figure 3. (a) XPS survey spectrum of MoS2-VN(CTAB), high-resolution XPS spectra of (b) Mo 3d and (c) S 2p for MoS2-VN(CTAB) and MoS2. XPS spectra were collected to reveal the surface element valence states and electron interaction in catalysts. As shown in Figure 3a, the catalyst consists of Mo, S, V and N. The atomic ratio of S/Mo is 1.80, 2.14 and 2.18 for MoS2, MoS2-VNNPs and MoS2-VN(CTAB), respectively. It suggests that there are more unsaturated S which can act as active sites on MoS2 in MoS2-VNNPs and MoS2-VN(CTAB) than those in commercial MoS2. As a result, the uncoordinated S atoms can give rise to new defects as active sites, which is in agreement with TEM images. The high-resolution Mo 3d XPS spectra for MoS2-VN(CTAB) and MoS2 are shown in Figure 3b. For MoS2, two strong peaks of 3d5/2 at 229.3 eV and 3d3/2 at 232.4 eV are attributed to Mo4+.55, 56 Besides, a weak peak of Mo6+ at 235.7 eV is also detected. In contrast, the MoS2-VN(CTAB) has 10


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the about 0.9 eV and 0.8 eV negative shifts in the 3d5/2 and 3d3/2 peaks, respectively. It suggests the existence of Mo with a lower valence state in MoS2-VN(CTAB). This is ascribed to the interaction between VN and MoS2. According to Li et al. and Xiao et al.’s work,57, 58 N element can induce the hybridization among N 2p, Mo 3d and S 2p orbitals at Fermi level, which is beneficial to the electron transfer from N to MoS2. In addition, by DFT calculation, it was reported that the doping of V is capable of decreasing the barrier of charge transfer from V to MoS2 and consequently leads to the lower oxidation state of Mo in MoS2.59 The binding energy of S 2p in MoS2-VN(CTAB) is also found to have obvious negative shifts in comparison with S 2p XPS spectrum in MoS2 (Figure 3c), which manifests the lower valence states of S in MoS2-VN(CTAB). Besides, the V 2p XPS spectra for VNNPs and VN(CTAB) are collected in Figure S6 for comparison with those for MoS2-VNNPs and MoS2-VN(CTAB), respectively. The V 2p1/2 and 2p3/2 peaks exhibit evident positive shifts after MoS2 grew on VNNPs and VN(CTAB). This result further verifies the property of providing electrons of VN substrate and resulting MoS2 with rich electrons. According to the mechanism for HER, the protons near the electrode require to gain an electron and band to the MoS2 surface as H adatom. It has been reported that the enhanced charge density on MoS2 can decrease the Gibbs free energy of hydrogen adsorption and improve the conductivity of MoS2 on the other hand, which is favor of charge transfer in HER.60 Therefore, the reduction of valence states of Mo and S in MoS2 can effectively improve the activity for HER.57, 59 Additionally, by comparing the high-resolution Mo 3d and S 2p XPS spectra for MoS2-VN(CTAB) and MoS2-VNNPs (Figure S7), it is found that the extra negative shifts can be observed for MoS2-VN(CTAB). The negative shifts indicate the stronger electron modulation effects between MoS2 and VN(CTAB) deriving from the higher SSA of VN(CTAB), which offers closer and more contact between VN(CTAB) and MoS2.43 LSV was adopted in 0.5 M H2SO4 to evaluate the electrocatalytic activity of 11



MoS2-VN(CTAB), MoS2-VNNPs, commercial MoS2 and VN(CTAB) for HER, and the LSV curve of 20%Pt/C was also tested as a contrast. According to Figure 4a, VN exhibits almost no cathodic current in the test potential range. It means that VN has almost no

Figure 4. (a) LSV curves of MoS2, MoS2-VNNPs, MoS2-VN(CTAB), VN(CTAB) and 20%Pt/C, (b) Tafel plots of MoS2-VN(CTAB), MoS2-VNNPs, MoS2 and 20%Pt/C, (c) EIS of MoS2-VN(CTAB), MoS2-VNNPs and MoS2, (d) LSV curves before and after 1000 cycles of CVs for MoS2-VN(CTAB). catalytic activity for HER. However, MoS2-VN(CTAB) delivers superior HER activity compared with MoS2 and MoS2-VNNPs. It shows a low onset overpotential about 85 mV and the overpotential of 180 mV at the cathodic current density of 10 mAcm-2. The Tafel slopes of MoS2, MoS2-VNNPs, MoS2-VN(CTAB) and 20%Pt/C are calculated to elucidate the underlying mechanism (Figure 4b), and the corresponding values are 77.31, 12


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65.99, 53.31 and 35.73 mVdec-1, respectively. This result demonstrates that MoS2-VN(CTAB) has faster reaction kinetics and the Volmer-Heyrovsky mechanism indicates the rate-determining step.61, 62 Besides, in order to select an appropriate ratio of MoS2

and

VN(CTAB),

the

performance

of

MoS2-VN(CTAB)-62%,

MoS2-VN(CTAB)-35% and MoS2-VN(CTAB)-29% was measured for comparison. In Figure S8, the MoS2-VN(CTAB), which contains 45% of MoS2, owns the least overpotential to meet the same current density as well as the lowest Tafel slope in contrast to MoS2-VN(CTAB)-62%, MoS2-VN(CTAB)-35% and MoS2-VN(CTAB)-29%. That is to say, the 45% for MoS2 and 55% for VN(CTAB) are optimum ratio in these four ratios of catalysts. Furthermore, the catalytic performance of MoS2-VN(CTAB) and MoS2-VNNPs is compared with that of other reported state-of-the-art MoS2-based electrocatalysts in Table S1. It can be seen that MoS2-VN(CTAB) and MoS2-VNNPs have lower onset overpotentials and Tafel slopes than most of reported materials. Especially, the onset overpotential (85 mV) of MoS2-VN(CTAB) is almost lower than those of all of MoS2-based electrocatalysts except for NPNi-MoS2/RGO (85 mV) and IE-MoS2 on GO/rGO (75 mV), while the latter two catalysts have higher Tafel slopes. EIS were tested for taking a close look at internal electrochemical properties of catalysts. The charge transfer resistances (Rct) of the three electrocatalysts are obtained by the simulation of equivalent circuits in Figure 4c. It is clear that the Rct decreases from MoS2 (2155 Ω) and MoS2-VNNPs (1280 Ω) to MoS2-VN(CTAB) (467 Ω), which implies that the MoS2-VNNPs and MoS2-VN(CTAB) have a faster electron transfer between the catalyst and electrolyte. This is attributed to the high conductivity of VN and the enhanced charge density on MoS2 in the samples containing VN according to XPS analyses, which accelerate the electrochemical reaction. Moreover, the MoS2-VN(CTAB) exhibits the lower Rct than MoS2-VNNPs, which results from the stronger electron interaction between VN(CTAB) and MoS2 corresponding to extra shifts of Mo 3d and S 13



2p for MoS2-VN(CTAB) in Figure S7. This lower Rct reflects the faster charge transfer rate and higher HER activity in MoS2-VN(CTAB).58, 59 The number of active sites on catalysts was evaluated through Cdl. The CVs at different scan rates and the linear relationships between current density and scan rate are shown in Figure S9. According to the fitting results, the Cdl of MoS2, MoS2-VNNPs and MoS2-VN(CTAB) are 8.01, 11.05 and 26.63 mFcm-2, respectively. The Cdl of MoS2-VN(CTAB) is about 3.3 times higher than that of MoS2, which means that there are more active sites in the MoS2-VN(CTAB). This is ascribed to the vertical growth of MoS2 on VN(CTAB), expanded interlayer spacing of MoS2 nanoplates and the extra defects confirmed by TEM, XRD and XPS. Long-cycle durability of catalysts is deemed to be another significant indicator for practical application. As shown in Figure 4d, for MoS2-VN(CTAB), the negligible deterioration of current density at the same overpotential can be observed after 1000 cycles of CVs. Besides, the microscopic structure and morphology of MoS2-VN(CTAB) after 1000 cycles of CVs were characterized by XRD and SEM, which are shown in Figure S10. It is seen that the characteristic peaks of MoS2-VN(CTAB) are well preserved and the morphology has almost no changes in contrast to the MoS2-VN(CTAB) before the CV cycles. Apart from that, chronoamperometry curves of MoS2-VN(CTAB) were measured at -0.14 V in 0.5 M H2SO4 for 30 h to test long-term durability (Figure S11). For comparison, MoS2-VNNPs and MoS2 were also tested at appropriate potential. It can be seen that MoS2-VN(CTAB) and MoS2-VNNPs perform the stabilized HER current density of 2.10 mAcm-2 and 1.43 mAcm-2 after 30h, which respectively remains 81.39% and 75.26% of original values. However, MoS2 suffers from large attenuation and only maintains 65.5% current density at -0.25 V after 30 h. These consequences prove the high durability of MoS2-VN(CTAB) in acidic media.

14


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CONCLUSIONS In this work, VN with an enlarged SSA (VN(CTAB)) was successfully prepared by a soft template method. Then, MoS2 nanoplates were vertically grown on VN(CTAB) via a facile hydrothermal reaction for the first time. The MoS2-VN(CTAB) manifests much superior electrocatalytic activity and stability for HER than MoS2-VNNPs and commercial MoS2. As a substrate, VN(CTAB) plays a crucial role in the promotion for electrocatalytic performance of MoS2 catalysts. On one hand, the interlayer spacing among MoS2 nanoplates is enlarged and more structural defects are generated due to the special structure and morphology of VN(CTAB), which effectively increase the number of active sites in catalysts. On the other hand, highly conductive VN and the lower valence states of Mo and S owing to the stronger electron interaction between VN(CTAB) and MoS2 accelerate the charge transfer in the process of electrochemical reaction. These factors contribute to the excellent electrocatalytic performance of MoS2-VN(CTAB). This work proves that the VN with an enlarged SSA is able to be an efficient non-carbon substrate of electrocatalysts for HER.

ASSOCIATED CONTENT Supporting Information available: Additional experimental data of morphological, N2 adsorption/desorption, XRD, XPS, electrochemical characterizations, and comparison of the catalytic performance.

AUTHOR INFORMATION Corresponding Author *E-mail

Addresses: Y. Wang, [email protected]; T. Qi, [email protected]

ORCID K. Meng: 0000-0003-1145-0616 15



Y. Wang: 0000-0002-5919-4626 Notes The authors declare no competing financial interests.

ACKNOWLEDGMENTS The authors are grateful for the financial support by Key Research Program of Frontier Sciences of Chinese Academy of Sciences (Grant No. QYZDJ-SSW-JSC021), Chinese National Programs for High Technology Research and Development (2014AA06A513), as well as by the 973 Program (Grant No. 2015CB251303).

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Vertically Grown MoS2 Nanoplates on VN with an Enlarged Surface

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