Anion-Induced Size Selection of Î²-Mo2

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Anion Induced Size Selection of #-Mo2C Supported on NitrogenDoped Carbon Nanotubes for Electrocatalytic Hydrogen Evolution Min Ji, Siqi Niu, Yunchen Du, Bo Song, and Ping Xu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b02194 • Publication Date (Web): 09 Aug 2018 Downloaded from http://pubs.acs.org on August 10, 2018

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ACS Sustainable Chemistry & Engineering

Anion Induced Size Selection of β-Mo2C Supported on Nitrogen-Doped Carbon Nanotubes for Electrocatalytic Hydrogen Evolution Min Ji,†,⁋ Siqi Niu†,⁋ Yunchen Du, † Bo Song*,‡ and Ping Xu*,† †

MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and

Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, No. 92 West Dazhi Street, Nangang District, Harbin 150001, China ‡

Academy of Fundamental and Interdisciplinary Sciences, Department of Physics, Harbin

Institute of Technology, No. 92 West Dazhi Street, Nangang District, Harbin 150001, China ⁋

These two authors contributed equally.

AUTHOR INFORMATION Corresponding Author *Email: [email protected] (P.X.); [email protected] (B.S.)

KEYWORDS: β-Mo2C, carbon nanotubes, electrocatalysis, hydrogen evolution reaction, polyaniline, size selection

ACS Paragon Plus Environment

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ABSTRACT: Molybdenum carbide materials are considered to be promising hydrogen evolution reaction (HER) electrocatalysts due to their similar electronic structures and catalytic activities to Pt-based catalysts. Here, we report a facile synthesis of β-Mo2C nanoparticles supported on nitrogen-doped carbon nanotubes (Mo2C/N-C) through a one-step carbonization of Mo-containing anion doped polyaniline nanotubes. It has been revealed that the size of the obtained Mo2C nanoparticles can be effectively tuned by applying different Mo-containing anions. With MoO42- from Na2MoO4, the as-prepared Mo2C/N-C(S) with ultrasmall (2-3 nm) Mo2C nanoparticles shows excellent electrocatalytic HER activity in acidic media, with an overpotential of 189 mV vs reversible hydrogen electrode (RHE) at a geometric current density of -10 mA cm-2 and a Tafel slope of 58 mV dec-1. This study opens up a new avenue for the sizecontrollable synthesis of transition metal carbide nanoparticles loaded on carbon supports for energy conversion applications.


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Introduction Hydrogen is regarded as a promising energy carrier with zero carbon emission. As a most economical and sustainable route for hydrogen production in large scale, water splitting by electrolysis has attracted extensive attention, where highly effective electrocatalysts are crucial to reduce the overpotential and enhance the reaction kinetics.13

To date, noble metal (e.g. Pt) and related compounds remain the most efficient

electrocatalysts for the hydrogen evolution reaction (HER), which, however, is greatly limited by their scarcity and high cost.4 Recently, various earth-abundant non-noble-metal materials

(transition

metal

sulfides,5-9

selenides,10-13

nitrides,14-15

phosphides,16

phosphosulfides,17-19 and carbides20-27) have been explored as promising alternatives. Among them, transition metal carbides, with remarkable catalytic activity and stability, have demonstrated their potentials as active HER electrocatalysts. Molybdenum

carbide

(Mo2C)

materials

are

identified

as

promising

HER

electrocatalysts owing to their highly similar electronic structures and catalytic activities to Pt-based catalysts.28-33 Particularly, β-phase molybdenum carbide (β-Mo2C) has been widely studied as a superior HER electrocatalysts.29 Recently, controllable synthesis of ultrasamll Mo2C nanoparticles have been proposed to further enhance the HER activity, and Mo2C nanoparticles with sizes smaller than 3 nm coated on graphene shells exhibit superior HER performance in acid media.34 Mo2C⁋based electrocatalyst supported on biomass-derived sulfur and nitrogen co-doped carbon has shown promising HER activity.35 Mo2C nanoparticles that are about 10 nm in size embedded in black carbon also shows highly efficient electrocatalysis for Hydrogen Evolution.36 In addition, the bottleneck of electron transport of Mo2C materials can be effectively solved by


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introducing other elements such as nitrogen or phosphorus.30, 37-40 However, size control of the Mo2C component in the Mo2C/carbon hybrid system is still challenging in order to achieve enhanced electrocatalytic performances. Herein, we demonstrate a facile preparation of β-Mo2C nanoparticles supported on nitrogen-doped carbon nanotubes (Mo2C/N-C) through a one-step carbonization of the Mo-containing anion doped polyaniline (PANI) nanotubes (Scheme 1). An unexpected anion induced size selection of the Mo2C nanoparticles is revealed, which greatly influences the electrocatalytic HER activity of the resultant Mo2C/N-C materials. In particular, Mo2C/N-C with ultrasmall (2-3 nm) Mo2C nanoparticles, obtained through the carbonization of MoO42--doped PANI, displays enhanced electrocatalytic HER activity in acidic media, with an overpotential of 189 mV vs reversible hydrogen electrode (RHE) to achieve a geometric current density of -10 mA cm-2 and a Tafel slope of 58 mV dec-1. We believe this study can provide a new and facile avenue for the size-controllable synthesis of transition metal carbide materials for energy conversion and storage applications. Experimental Section Reagents. Methyl orange (MO), Iron chloride hexahydrate (FeCl3·6H2O), ammonium persulfate (NH4S2O8, APS) were purchased from Sinopharm Chemical Reagent Co., Ltd. Molybdate tetrahydrate (NH4)6Mo7O24·4H2O, sodium molybdate (Na2MoO4·2H2O), and aniline monomers were purchased from Aladdin. All the regents were used without further purification. Synthesis of Mo-containing anion doped PANI nanotubes and Mo2C/N-C nanotubes. Mocontaining anion-doped PANI nanotubes were prepared through a self-degraded template method


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according to previous studies.41-43 In brief, 3 mmol of FeCl3·6H2O and 0.2 mmol of methyl orange were dissolved in 30 mL deionized water under magnetic stirring. Then, 3 mmol of aniline and 10 ml of 0.4 M H2SO4 were added. Later, 0.143 mmol of (NH4)6Mo7O24·4H2O was introduced into the above solution, and then 3 mmol of APS in 5 ml H2O was dropwise added to the reaction mixture to initialize the polymerization. After 24 h, the precipitate was collected by centrifugation and repeatedly washing with deionized water and ethanol to get the Mo-containing anion-doped PANI nanotubes. Subsequently, the Mo-containing anion-doped PANI nanotubes were calcined at 800 oC for 4 h at a heating rate of 5 oC min-1 in Ar flow to obtain the Mo2C/NC(A) nanotubes. In comparison, we replace (NH4)6Mo7O24·4H2O with Na2MoO4·2H2O to get the Mo2C/N-C(S) with the same method. Characterization. Scanning electron microscopy (SEM, FEI Quanta 200F) and transmission electron microscopy (TEM, Tecnai F20) images were used to analyze the size and morphology. Raman spectra were recorded on a Renishaw in Via confocal micro-Raman spectroscopy system using a TE air-cooled 576×400 CCD array at a laser wavelength of 532 nm. X-ray photoelectron spectra (XPS) were recorded on an ESCALAB MKII using Al Kα as the excitation source. The X-ray diffraction (XRD) patterns were collected on a Ragaku/Max-3A X-ray diffractometer with Cu Kα radiation (λ = 1.54178 Å) and the operation voltage and current were maintained at 40 mV and 40 mA. Nitrogen adsorption/desorption isotherms were measured on a QUADRASORB SIKR/MP (Quantachrome, USA) after heating the materials under vacuum at 120 °C. Electrochemical measurements. Electrochemical measurements were operated on CHI 660E electrochemical workstation in three-electrode systems in 0.5 M H2SO4 aqueous solution. A graphite rod (Alfa Aesar, 99.9995%) and an Ag/AgCl (in 3 M KCl solution)


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electrode were used as counter and reference electrodes, respectively. To prepare the ink, 2 mg catalyst was ultrasonically dispersed in a 0.4 mL water-ethanol solution (v/v 1:1) containing 5 µL Nafion solution. Then, 7.5 µL of the ink was dropcasted onto the glassy carbon electrode (0.19625 cm-2) serving as the working electrode, with a calculated catalyst loading of 0.19 ± 0.01 mg cm-2. Cyclic voltammogram (CV) and linear sweep voltammetry (LSV) were carried out between -0.7 and 0.2 V vs Ag/AgCl at a scan rate of 5 mV s-1. The electrochemical impedance spectroscopy (EIS) was carried out within the frequency range from 100 kHz to 0.01 Hz. CVs at various scan rates (20, 40, 60, 80, 100, 120, 140, 160, 180 and 200 mV s-1) were collected to estimate the double-layer capacitance. Electrochemically active surface area (ECSA) of the catalyst can be calculated according to: ECSA = Cdl/Cs, where Cdl is the double layer capacitance of the catalyst, and Cs is the capacitance of the glass carbon electrode (Cs = 0.040 mF cm-2).34 To keep the accuracy of measurement results, the resistance determined from EIS experiments was used to correct the polarization curves and subsequent Tafel analysis for the iR losses. All potentials were referenced to a reversible hydrogen electrode (RHE). Results and Discussion The synthesis strategy for Mo2C/N-C nanotubes is displayed in Scheme 1 (See Experimental section for more details). During the synthesis of PANI nanotubes through the self-degraded template method,41 Mo-containing anion is introduced and can be doped into the PANI chain, similar to our previous acid doping route of conjugated polymers.44 A subsequent carbonization process of the Mo-containing anion doped PANI nanotubes simultaneously coverts the Mo-containing anion into Mo2C and the PANI nanotubes into N-doped carbon nanotubes, resulting in the formation of Mo2C/N-C nanotubes. Here, it is


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interesting to find that the size of the final Mo2C nanoparticles is dependent on the number of Mo atoms in the Mo-containing anions (MoO42- or Mo7O246-), which consequently affects the electrocatalytic HER activity of the as-synthesizd Mo2C/N-C materials.

Scheme 1. Schematic illustration of the preparation of Mo2C/N-C materials through a one-step carbonization of the Mo-containing anion-doped polyaniline (PANI) nanotubes. Figure 1 shows the Raman spectra of the PANI, Mo-containing anion-doped PANI nanotubes, and Mo-containing anion precursors. Mo-PANI(A) and Mo-PANI(S) refer to the PANI nanotubes prepared in the presence of (NH4)6Mo7O24·4H2O and Na2MoO4·2H2O, respectively. It can be seen that besides the Raman features of PANI, Raman band due to the Mo7O246- or MoO42- can be clearly found in the Mo-PANI(A) or Mo-PANI(S), an indication that our strategy is feasible for the doping of PANI nanotubes with Mocontaining anions. This is also a good foundation for fabrication of Mo2C materials that can tightly bind with PANI-derived carbon materials for electrochemical water splitting.


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Figure 1. Raman spectra of the PANI, Mo-containing anion-doped PANI nanotubes, and Mo-containing anion precursors.

Figure 2. TEM and HRTEM images of Mo2C/N-C(A) (a, b) and Mo2C/N-C(S) (c, d). Scanning transmission electron microscopy (STEM) image (e) and elemental mapping of C (f), Mo (g), and N (h) of a single Mo2C/N-C(S) nanotube


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SEM and TEM images show that both Mo-containing anion doped PANI precursors prepared in the presence of MoO42- or Mo7O246- are of nanotube structures that are 100200 nm in diameter and several microns in length (Figure S1 and S2 in Supporting Information). The nanotube structures can be well maintained in the following hightemperature carbonization process, and the diameter is more or less reduced due to the reforming of the carbon frameworks (Figure 2 and Figure S3 in Supporting Information). Notably, the size of the produced Mo2C nanoparticles is distinct according to the adopted Mo-containing anions. With Mo7O246-, the obtained Mo2C@N-C(A) nanotubes are about 50-100 nm in diameter, and the surface is stacked with nanocrystals that are about 30 nm in size (Figure 2a). A closer look from high resolution TEM (HRTEM) image displays obvious lattice fringes of 0.23 nm (Figure 2b), corresponding to the (101) plane of βMo2C.21, 45 In comparison, usage of MoO42- results in the 100-150 nm Mo2C@N-C(S) nanotubes that are loaded with ultrasmall Mo2C nanoparticles (2-3 nm) (Figure 2c). A same lattice fringe of 0.23 nm from HRTEM image tells that these ultrasmall Mo2C nanoparticles are also in β-Mo2C phase (Figure 2d). This anion induced size selection of Mo2C nanoparticles may be rationalized by the fact that Mo-rich anion (Mo7O246-) doped at a single site on the PANI chain can typically lead to Mo2C with larger size during the carbothermic reduction of Mo-containing anions. Although a few reports mentioned that ultrasmall Mo2C nanoparticles could be obtained from various Mo-containing anions,46-48 it should be pointed out that in our synthesis route for Mo2C@N-C(S) and Mo2C@NC(A), the only difference is the used Mo-containing anions. Scanning transmission electron microscopy (STEM) image of a single Mo2C/N-C(S) nanotube (Figure 2e) and the corresponding elemental mappings (Figure 2f-h) show the homogeneous distribution


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of C, N, and Mo elements, confirming the formation of Mo2C nanoparticles uniformly supported on N-doped carbon nanotubes. In order to further study the structure and composition of the as-prepared Mo2C@N-C(A) and Mo2C@N-C(S) materials, XRD, Raman, and XPS analyses were conducted. The diffraction peaks in the XRD patterns (Figure 3a) of Mo2C@N-C(A) and Mo2C@N-C(S) at 34.5, 37.8, 39.4, 52.2, 61.5, 69.5, 74.6 and 75.5o can be well indexed to the (100), (002), (101), (102), (110), (103), (200), (112) and (201) planes of β-Mo2C (JCPDS 35-0787).1, 49-52 In the Raman spectra of both Mo2C/N-C materials (Figure 3b), one can only see D (1355 cm-1) and G (1574 cm-1) bands from carbon materials.53-54 However, it should be pointed out that after long-term laser irradiation, Raman features due to MoO3 clearly emerge with the carbon materials, with peaks at 810 (terminal Mo-O stretching) and 993cm-1 (bridge Mo-O-Mo stretching).55-57 This reveals that Mo2C materials are not highly stable under laser excitation in the air condition. The intensity ratio of the D band to G band (ID/IG) can be used to investigate the degree of graphitization or defect density in carbon materials, and a higher ID/IG value indicates more disordered structure in graphitic carbon or improved graphitization degree of amorphous carbon.41 Here, calculated ID/IG values for Mo2C/N-C(S) and Mo2C/N-C(A) samples from the integral areas of the D and G bands are 0.85 and 0.91, respectively, suggesting that carbon in Mo2C/N-C(A) should have a relatively higher graphitization degree and thus a higher electrical conductivity.


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Figure 3. XRD patterns (a) and Raman spectra (b) of the Mo2C@N-C(A) and Mo2C@NC(S) materials, and Mo 3d (c) and C 1s (d) XPS spectra of the Mo2C@N-C(S). The survey XPS spectra (Figure S4 in Supporting Information) reveal the existence of only Mo, C, N and O elements for both samples. Taking Mo2C@N-C(S) for example, the Mo 3d XPS spectrum (Figure 3c) can be deconvoluted into three doublets ascribed to Mo2+ 3d (228.6, 231.6 eV), Mo4+ (229.7, 232.9eV), and Mo6+ (232.6, 235.6 eV), corresponding to the main Mo2C and slight surface-oxidized MoOx species, as the surface of Mo2C can be easily contaminated with molybdenum oxides when exposed to air (as evidened in the Raman study), while MoOx species are inactive for HER.45, 57-60 Highresolution C 1s XPS spectrum shows two main peaks at 284.5 and 285.6 eV that can be attributed to C-C/C=C, and C-N in N-doped carbon materials (Figure 3d).30,

61-62

Pyridinic-N, pyrrolic-N, graphtic-N, as well as Mo-N species are found in the high-


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resolution N 1s XPS spectrum (Figure S5 in Supporting Information), an indication of N doping in the carbon matrix as well as Mo2C.48 XPS results of Mo2C@N-C(A) are basically identical to those of Mo2C@N-C(S) (Figure S6 in Supporting Information). Aforementioned analyses convincingly reveal that the as-prepared Mo2C/N-C(S) and Mo2C/N-C(A) materials are composed of β-Mo2C nanocrystallites anchored on nitrogendoped carbon nanotubes. We also measured the N2 adsorption-desorption isotherms for both samples (Figure S7 in Supporting Information). Mo2C/N-C(S) has a distinctly higher Brunauer-Emmett-Teller (BET) surface area (27.5 m2 g-1) than Mo2C/N-C(A) (6.9 m2 g1

), mainly due to the difference in size of the Mo2C nanoparticles as their pore size

features are very similar.


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Figure 4. Electrochemical performances of the Mo2C@N-C(A) and Mo2C@N-C(S) materials toward HER in 0.5 M H2SO4. (a) Polarization curves, (b) Tafel plots derived from the polarization curves, (c) Plots showing the extraction of the Cdl, and (d) Nyquist plots measured over the frequency range of 100 kHz to 0.01 Hz (inset shows the equivalent circuit). (e) LSV curves of Mo2C@N-C(S) before and after 1000 CV cycles in 0.5 M H2SO4. (f) Long-term chronoamperometric curve of Mo2C@N-C(S) in 0.5 M H2SO4 under an overpotential of 210 mV. The catalyst loading was controlled at 0.19 ± 0.01 mg cm-2. To assess the electrocatalytic performance of Mo2C/N-C(A) and Mo2C/N-C(S) towards HER, electrochemical measurements were carried out with a rotating disk electrode (RDE) configuration in 0.5 M H2SO4. As well known, the catalyst loading will also influence the


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number of active sites, and thus a controlled catalyst loading of 0.19± 0.01 mg cm-2 was applied in our measurements. The polarization curves after iR correction indicate that Mo2C/N-C(S) needs a smaller overpotential (189 mV vs RHE) than Mo2C/N-C(A) (215 mV vs RHE) to achieve a geometric catalytic current density of -10 mA cm-2 (Figure 4a). From an extrapolation of the linear range of overpotential (η) vs. log j (Figure 4b), Tafel slopes of 58 and 89 mV dec-1 (after iR correction) are obtained for Mo2C/N-C(S) and Mo2C/N-C(A), respectively. The low Tafel slope and overpotential observed for the Mo2C/N-C(S) are comparable to most previously reported Mo2C-based electrocatalysts (Table S1 in Supporting Inforamtion). Here, the limited conductivity of the carbon nanotubes obtained from a medium carbonization temperature (800 o

C) might greatly influence the apparent electrocatalytic activity of the as-prepared catalysts.

Although Raman study indicates a higher conductivity of the carbon in Mo2C/N-C(A), its inferior electrocatalytic activity to Mo2C/N-C(S) clealry reveals that the size of Mo2C plays a decisive role in the HER process. To further understand the HER performance from Mo2C/NC(S) and Mo2C/N-C(A), the double-layer capacitance (Cdl),

an indicator of the effective

electrochemically active surface area (ECSA), was measured from the cyclic voltammogrametry measurement (Figure S8 in Supporting Inforamtion). Cdl values were extracted from capacitive current as a function of scan rate (Figure 4c), which are 9.75 and 5.05 mF cm-2 for Mo2C/N-C(S) and Mo2C/N-C(A), respectively, indicating that Mo2C/N-C(A) with ultrasmall Mo2C nanoparticles exposes more catalytically active sites during the HER process. The ECSAnormalized current density was applied to compare the intrinsic activity of the electrocatalysts, where the Mo2C/N-C(S) sample provides a higher ECSA-normalized current density of -0.092 mA cm-2 at an overpotential of 210 mV vs RHE, suggesting its better intrinsic activity toward the HER process (Figure S9 in Supporting Information).


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In order to better understand the electrode kinetics during the HER process, electrochemical impedance spectroscopy (EIS) was also employed.50 The semi-circles in both Nyquist plots (Figure 4d) were fitted by a Randles equivalent circuit (inset in Figure 4d) to obtain the charge transfer resistance (Rct). Rct values of 15.6 and 32.4 Ω were obtained for Mo2C/N-C(S) and Mo2C/N-C(A), respectively, an indication that the ultrasmall Mo2C nanoparticles supported on N-doped carbon nanotubes can greatly facilitate the charge transfer process. Above results clearly reveal that the Mo2C/N-C(S) sample has better overall HER catalysis performance. The long-term cycling stability is another important parameter for the as-prepared electrocatalysts. Polarization curves of Mo2C/N-C(S) reveal no clear degradation even after 1,000 cycles (Figure 4e), and the long-term chronoamperometric curve under an overpotential of 210 mV vs RHE also indicates a steady current density without obvious degradation after an operation time of 25 h (Figure 4f). Besides, a systematic morpholgy, composition, and crystallinity study further shows that the as-prepared Mo2C/N-C(S) materials are stable after long-term HER tests (Figure S10 and S11 in Supporting Inforamtion). Although Mo2C/N-C(A) sample is also relatively stable during the HER study (Figure S12 and S13 in Supporting Inforamtion), the catalytic activity is always a little inferior to that of the Mo2C/N-C(S) sample.


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Figure 5. Electrochemical performances of the Mo2C@N-C(A) and Mo2C@N-C(S) materials toward HER in 1 M KOH (a, b) and in phosphate buffer (pH = 6.94) (c, d).

The electrocatalytic HER activity of the Mo2C/N-C(A) and Mo2C/N-C(S) materials in alkine media (1 M KOH) and neutral solution (phosphate buffer) was also investigated, and it is found that the HER performence in alkaline solution is much better than that in neutral media but lower than that in acid media. As shown in Figure 5, Mo2C/N-C(S) and Mo2C/N-C(A) require overpotentials of 271 and 328 mV vs RHE to obtain a geometric catalytic current density of -10 mA cm-2 in 1 M KOH solution, with the corresponding Tafel slopes of 90 and 114 mV dec-1, respectively. However, it is difficult for both samples to achieve a geometric catalytic current density of -10 mA cm-2 in neutral solution (phosphate buffer), indicating such Mo2C-based electrocatalysts are not feasible for electrochemical water splitting in neutral media. Generally, Mo2C/N-C(S) presents lower overpotentials and Tafel slopes in both alkaline and neutral conditions, suggesting


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more efficient kinetics for hydrogen evolution.5 Furthermore, we also investigated the Mo2C/N-C(S) samples prepared at different carbonization temperatures (600-900 oC). It is found that though the morphology does not change obviously (Figure S14 in Supporting Inforamtion), while a relatively low temperature of 600 oC cannot guarantee the production of highly crystalline Mo2C, and a higher temperature of 900 oC will lead to the formation of Mo besides Mo2C (Figure S15 in Supporting Inforamtion). A comparative study of the electrochemical performance suggests that a mild carbon temperature of 800 oC is optimal for the construction of Mo2C/N-C(S) with higher electrocatalytic HER activity (Figure S16 in Supporting Inforamtion). Conclusions In conclusion, Mo2C/N-C nanocomposites consisting of Mo2C nanoparticles that are uniformly anchoredon N-doped carbon nanotubes have been successfully prepared through a one-step carbonization of the Mo-containing anion doped polyaniline (PANI) nanotubes. An anion induced size selection of Mo2C nanoparticles is revealed, where Morich anion (with multiple Mo atoms) typically lead to Mo2C with larger size during the carbothermic reduction process. The as-prepared Mo2C/N-C(S) with ultrasmall (2-3 nm) Mo2C nanoparticles from MoO42--doped PANI shows excellent electrocatalytic HER activity in acidic condition that is comparable to most Mo2C-based materials, requiring a low overpotential of 189 mV vs RHE to achieve a geometric current density of -10 mA cm-2 and a Tafel slope of 56 mV dec-1. This study provides a new pathway for the size selection of transition metal carbide materials and a novel route for the synthesis of transition metal carbide loaded on carbon supports for electrocatalytic applications.


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ASSOCIATED CONTENT Supporting Information. The following files are available free of charge. Experimental details and additional characterizations (PDF) AUTHOR INFORMATION Notes The authors declare no competing financial interests. ACKNOWLEDGMENT We thank the financial support from the National Natural Science Foundation of China (21471039, 21571043, 21671047), Fundamental Research Funds for the Central Universities (PIRS of HIT A201502 and HIT. BRETIII. 201223), China Postdoctoral Science Foundation (2014M560253), Postdoctoral Scientific Research Fund of Heilongjiang Province (LBHQ14062, LBH-Z14076), and Natural Science Foundation of Heilongjiang Province (B2015001). REFERENCES (1) Jia, J.; Zhou, W.; Wei, Z.; Xiong, T.; Li, G.; Zhao, L.; Zhang, X.; Liu, H.; Zhou, J.; Chen, S. Molybdenum Carbide on Hierarchical Porous Carbon Synthesized from Cu-MoO2 as Efficient Electrocatalysts for Electrochemical Hydrogen Generation. Nano Energy 2017, 41, 749-757. (2) Wan, C.; Regmi, Y. N.; Leonard, B. M. Multiple Phases of Molybdenum Carbide as Electrocatalysts for the Hydrogen Evolution Reaction. Angew. Chem. Int. Ed. 2014, 53 (25), 6407-6410. (3) Liu, Y.; Ding, J.; Sun, J.; Zhang, J.; Bi, J.; Liu, K.; Kong, F.; Xiao, H.; Sun, Y.; Chen, J. Molybdenum Carbide as an Efficient Catalyst for Low-Temperature Hydrogenation of Dimethyl Oxalate. Chem. Commun. 2016, 52 (28), 5030-5032. (4) Song, B.; Li, K.; Yin, Y.; Wu, T.; Dang, L. N.; Caban-Acevedo, M.; Han, J. C.; Gao, T. L.; Wang, X. J.; Zhang, Z. H.; Schmidt, J. R.; Xu, P.; Jin, S. Tuning Mixed Nickel Iron Phosphosulfide Nanosheet Electrocatalysts for Enhanced Hydrogen and Oxygen Evolution. ACS Catal. 2017, 7 (12), 8549-8557.


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(5) Yin, Y.; Han, J.; Zhang, Y.; Zhang, X.; Xu, P.; Yuan, Q.; Samad, L.; Wang, X.; Wang, Y.; Zhang, Z.; Zhang, P.; Cao, X.; Song, B.; Jin, S. Contributions of Phase, Sulfur Vacancies, and Edges to the Hydrogen Evolution Reaction Catalytic Activity of Porous Molybdenum Disulfide Nanosheets. J. Am. Chem. Soc. 2016, 138 (25), 7965-7972. (6) Liu, T.; Liu, D.; Qu, F.; Wang, D.; Zhang, L.; Ge, R.; Hao, S.; Ma, Y.; Du, G.; Asiri, A. M.; Chen, L.; Sun, X. Enhanced Electrocatalysis for Energy-Efficient Hydrogen Production over CoP Catalyst with Nonelectroactive Zn as a Promoter. Adv. Energ. Mater. 2017, 7 (15), 1700020. (7) Yang, Y.; Zhang, K.; Lin, H.; Li, X.; Chan, H. C.; Yang, L.; Gao, Q. MoS2–Ni3S-2 Heteronanorods as Efficient and Stable Bifunctional Electrocatalysts for Overall Water Splitting. ACS Catal. 2017, 7 (4), 2357-2366. (8) Wu, Y.; Liu, Y.; Li, G.-D.; Zou, X.; Lian, X.; Wang, D.; Sun, L.; Asefa, T.; Zou, X. Efficient Electrocatalysis of Overall Water Splitting by Ultrasmall NixCo3−xS4 Coupled Ni3S2 Nanosheet Arrays. Nano Energy 2017, 35, 161-170. (9) Yu, X. Y.; Feng, Y.; Jeon, Y.; Guan, B.; Lou, X. W.; Paik, U. Formation of Ni-Co-MoS2 Nanoboxes with Enhanced Electrocatalytic Activity for Hydrogen Evolution. Adv. Mater. 2016, 28 (40), 9006-9011. (10) Deng, S.; Zhong, Y.; Zeng, Y.; Wang, Y.; Yao, Z.; Yang, F.; Lin, S.; Wang, X.; Lu, X.; Xia, X.; Tu, J. Directional Construction of Vertical Nitrogen-Doped 1T-2H MoSe2 /Graphene Shell/Core Nanoflake Arrays for Efficient Hydrogen Evolution Reaction. Adv. Mater. 2017, 29 (21), 1700748. (11) Swesi, A. T.; Masud, J.; Nath, M. Nickel Selenide as a High-Efficiency Catalyst for Oxygen Evolution Reaction. Energ. Environ. Sci. 2016, 9 (5), 1771-1782. (12) Tang, C.; Cheng, N.; Pu, Z.; Xing, W.; Sun, X. NiSe Nanowire Film Supported on Nickel Foam: An Efficient and Stable 3D Bifunctional Electrode for Full Water Splitting. Angew. Chem. Int. Ed. 2015, 54 (32), 9351-9355. (13) Yin, Y.; Zhang, Y. M.; Gao, T. L.; Yao, T.; Zhang, X. H.; Han, J. C.; Wang, X. J.; Zhang, Z. H.; Xu, P.; Zhang, P.; Cao, X. Z.; Song, B.; Jin, S. Synergistic Phase and Disorder Engineering in 1T-MoSe2 Nanosheets for Enhanced Hydrogen-Evolution Reaction. Adv. Mater. 2017, 29 (28), 1700311. (14) Lau, V. W.; Moudrakovski, I.; Botari, T.; Weinberger, S.; Mesch, M. B.; Duppel, V.; Senker, J.; Blum, V.; Lotsch, B. V. Rational Design of Carbon Nitride Photocatalysts by Identification of Cyanamide Defects as Catalytically Relevant Sites. Nat. Commun. 2016, 7, 12165. (15) Ma, L.; Ting, L. R. L.; Molinari, V.; Giordano, C.; Yeo, B. S. Efficient Hydrogen Evolution Reaction Catalyzed by Molybdenum Carbide and Molybdenum Nitride Nanocatalysts Synthesized via the Urea Glass Route. J. Mater. Chem. A 2015, 3 (16), 8361-8368. (16) Yan, H.; Tian, C.; Wang, L.; Wu, A.; Meng, M.; Zhao, L.; Fu, H. Phosphorus-Modified Tungsten Nitride/Reduced Graphene Oxide as a High-Performance, Non-Noble-Metal Electrocatalyst for the Hydrogen Evolution Reaction. Angew. Chem. Int. Ed. 2015, 54 (21), 6325-6329. (17) Wu, T.; Stone, M. L.; Shearer, M. J.; Stolt, M. J.; Guzei, I. A.; Hamers, R. J.; Lu, R.; Deng, K.; Jin, S.; Schmidt, J. R. Crystallographic Facet Dependence of the Hydrogen Evolution Reaction on CoPS: Theory and Experiments. ACS Catal. 2018, 8 (2), 1143-1152.


19


Page 20 of 24

(18) Caban-Acevedo, M.; Stone, M. L.; Schmidt, J. R.; Thomas, J. G.; Ding, Q.; Chang, H. C.; Tsai, M. L.; He, J. H.; Jin, S. Efficient Hydrogen Evolution Catalysis Using Ternary Pyrite-Type Cobalt Phosphosulphide. Nat. Mater. 2015, 14 (12), 1245-1251. (19) Li, K.; Rakov, D.; Zhang, W.; Xu, P. Improving the Intrinsic Electrocatalytic Hydrogen Evolution Activity of Few-Layer NiPS3 by Cobalt Doping. Chem. Commun. 2017, 53 (58), 81998202. (20) Gong, Q.; Wang, Y.; Hu, Q.; Zhou, J.; Feng, R.; Duchesne, P. N.; Zhang, P.; Chen, F.; Han, N.; Li, Y.; Jin, C.; Li, Y.; Lee, S. T. Ultrasmall and Phase-Pure W2C Nanoparticles for Efficient Electrocatalytic and Photoelectrochemical Hydrogen Evolution. Nat. Commun. 2016, 7, 13216. (21) Liao, L.; Wang, S.; Xiao, J.; Bian, X.; Zhang, Y.; Scanlon, M. D.; Hu, X.; Tang, Y.; Liu, B.; Girault, H. H. A Nanoporous Molybdenum Carbide Nanowire as an Electrocatalyst for Hydrogen Evolution Reaction. Energ. Environ. Sci. 2014, 7 (1), 387-392. (22) Liu, Y.; Yu, G.; Li, G. D.; Sun, Y.; Asefa, T.; Chen, W.; Zou, X. Coupling Mo2C with Nitrogen-Rich Nanocarbon Leads to Efficient Hydrogen-Evolution Electrocatalytic Sites. Angew. Chem. Int. Ed. 2015, 54 (37), 10752-10757. (23) Han, N.; Yang, K. R.; Lu, Z.; Li, Y.; Xu, W.; Gao, T.; Cai, Z.; Zhang, Y.; Batista, V. S.; Liu, W.; Sun, X. Nitrogen-Doped Tungsten Carbide Nanoarray as an Efficient Bifunctional Electrocatalyst for Water Splitting in Acid. Nat. Commun. 2018, 9 (1), 924. (24) Ma, F. X.; Wu, H. B.; Xia, B. Y.; Xu, C. Y.; Lou, X. W. Hierarchical beta-Mo2C Nanotubes Organized by Ultrathin Nanosheets as a Highly Efficient Electrocatalyst for Hydrogen Production. Angew Chem Int Ed 2015, 54 (51), 15395-15399. (25) Zhang, K.; Zhao, Y.; Fu, D.; Chen, Y. Molybdenum Carbide Nanocrystal Embedded Ndoped Carbon Nanotubes as Electrocatalysts for Hydrogen Generation. J. Mater. Chem. A 2015, 3 (11), 5783-5788. (26) Alhajri, N. S.; Anjum, D. H.; Takanabe, K. Molybdenum Carbide–Carbon Nanocomposites Synthesized from a Reactive Template for Electrochemical Hydrogen Evolution. J. Mater. Chem. A 2014, 2 (27), 10548-10556. (27) Huo, L. L.; Liu, B. C.; Gao, Z. Q.; Zhang, J. 0D/2D Heterojunctions of Molybdenum Carbide-Tungsten Carbide Quantum Dots/N-doped Graphene Nanosheets as Superior and Durable Electrocatalysts for Hydrogen Evolution Reaction. J. Mater. Chem. A 2017, 5 (35), 18494-18501. (28) Zhu, J. H.; Yao, Y.; Chen, Z.; Zhang, A. J.; Zhou, M. Y.; Guo, J.; Wu, W. D.; Chen, X. D.; Li, Y. G.; Wu, Z. X. Controllable Synthesis of Ordered Mesoporous Mo2C@Graphitic Carbon Core-Shell Nanowire Arrays for Efficient Electrocatalytic Hydrogen Evolution. ACS Appl. Mater. Interfaces 2018, 10 (22), 18761-18770. (29) Vrubel, H.; Hu, X. Molybdenum Boride and Carbide Catalyze Hydrogen Evolution in Both Acidic and Basic Solutions. Angew. Chem. Int. Ed. 2012, 51 (51), 12703-12706. (30) Xiao, P.; Ge, X.; Wang, H.; Liu, Z.; Fisher, A.; Wang, X. Novel Molybdenum CarbideTungsten Carbide Composite Nanowires and Their Electrochemical Activation for Efficient and Stable Hydrogen Evolution. Adv. Funct. Mater. 2015, 25 (10), 1520-1526. (31) Huang, Y.; Gong, Q. F.; Song, X. N.; Feng, K.; Nie, K. Q.; Zhao, F. P.; Wang, Y. Y.; Zeng, M.; Zhong, J.; Li, Y. G. Mo2C Nanoparticles Dispersed on Hierarchical Carbon Microflowers for Efficient Electrocatalytic Hydrogen Evolution. ACS nano 2016, 10 (12), 11337-11343. (32) Wu, H. B.; Xia, B. Y.; Yu, L.; Yu, X. Y.; Lou, X. W. Porous Molybdenum Carbide Nanooctahedrons Synthesized via Confined Carburization in Metal-Organic Frameworks for Efficient Hydrogen Production. Nat. Commun. 2015, 6, 6512.


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Page 21 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(33) Lv, C. C.; Huang, Z. P.; Yang, Q. P.; Wei, G. F.; Chen, Z. F.; Humphrey, M. G.; Zhang, C. Ultrafast Synthesis of Molybdenum Carbide Nanoparticles for Efficient Hydrogen Generation. J. Mater. Chem. A 2017, 5 (43), 22805-22812. (34) McCrory, C. C. L.; Jung, S.; Ferrer, I. M.; Chatman, S. M.; Peters, J. C.; Jaramillo, T. F. Benchmarking Hydrogen Evolving Reaction and Oxygen Evolving Reaction Electrocatalysts for Solar Water Splitting Devices. J. Am. Chem. Soc. 2015, 137 (13), 4347-4357. (35) An, K. L.; Xu, X. X.; Liu, X. X. Mo2C-Based Electrocatalyst with Biomass-Derived Sulfur and Nitrogen Co-Doped Carbon as a Matrix for Hydrogen Evolution and Organic Pollutant Removal. ACS Sustain. Chem. Eng. 2018, 6 (1), 1446-1455. (36) Wang, D. Z.; Wang, J. C.; Luo, X. N.; Wu, Z. Z.; Ye, L. In Situ Preparation of Mo2C Nanoparticles Embedded in Ketjenblack Carbon as Highly Efficient Electrocatalysts for Hydrogen Evolution. ACS Sustain. Chem. Eng. 2018, 6 (1), 983-990. (37) Anjum, M. A. R.; Lee, J. S. Sulfur and Nitrogen Dual-Doped Molybdenum Phosphide Nanocrystallites as an Active and Stable Hydrogen Evolution Reaction Electrocatalyst in Acidic and Alkaline Media. ACS Catal. 2017, 7 (4), 3030-3038. (38) Chen, W.; Pei, J.; He, C. T.; Wan, J.; Ren, H.; Zhu, Y.; Wang, Y.; Dong, J.; Tian, S.; Cheong, W. C.; Lu, S.; Zheng, L.; Zheng, X.; Yan, W.; Zhuang, Z.; Chen, C.; Peng, Q.; Wang, D.; Li, Y. Rational Design of Single Molybdenum Atoms Anchored on N-Doped Carbon for Effective Hydrogen Evolution Reaction. Angew. Chem. Int. Ed. 2017, 56 (50), 16086-16090. (39) Jing, S.; Zhang, L.; Luo, L.; Lu, J.; Yin, S.; Shen, P. K.; Tsiakaras, P. N-Doped Porous Molybdenum Carbide Nanobelts as Efficient Catalysts for Hydrogen Evolution Reaction. Appl. Catal. B-Environ. 2018, 224, 533-540. (40) Chen, Y. Y.; Zhang, Y.; Jiang, W. J.; Zhang, X.; Dai, Z.; Wan, L. J.; Hu, J. S. Pomegranatelike N,P-Doped Mo2C@C Nanospheres as Highly Active Electrocatalysts for Alkaline Hydrogen Evolution. ACS nano 2016, 10 (9), 8851-8860. (41) He, Y. Z.; Xu, P.; Zhang, B.; Du, Y. C.; Song, B.; Han, X. J.; Peng, H. S. Ultrasmall MnO Nanoparticles Supported on Nitrogen-Doped Carbon Nanotubes as Efficient Anode Materials for Sodium Ion Batteries. ACS Appl. Mater. Interfaces 2017, 9 (44), 38401-38408. (42) Yang, X.; Zhu, Z.; Dai, T.; Lu, Y. Facile Fabrication of Functional Polypyrrole Nanotubes via a Reactive Self-Degraded Template. Macromol. Rapid Commun. 2005, 26 (21), 1736-1740. (43) Mi, H.; Zhang, X.; Yang, S.; Ye, X.; Luo, J. Polyaniline nanofibers as the electrode material for supercapacitors. Mater. Chem. Phys. 2008, 112 (1), 127-131. (44) Xu, P.; Han, X. J.; Zhang, B.; Du, Y. C.; Wang, H. L. Multifunctional Polymer-Metal Nanocomposites via Direct Chemical Reduction by Conjugated Polymers. Chem. Soc. Rev. 2014, 43 (5), 1349-1360. (45) Kim, H. J.; Yang, S.; Kim, H.; Moon, J. Y.; Park, K.; Park, Y. J.; Kwon, J. Y. Enhanced Electrical and Optical Properties of Single-Layered MoS2 by Incorporation of Aluminum. Nano Res. 2018, 11 (2), 731-740. (46) Shi, Z. P.; Nie, K. Q.; Shao, Z. J.; Gao, B. X.; Lin, H. L.; Zhang, H. B.; Liu, B. L.; Wang, Y. X.; Zhang, Y. H.; Sun, X. H.; Cao, X. M.; Hu, P.; Gao, Q. S.; Tang, Y. PhosphorusMo2C@Carbon Nanowires toward Efficient Electrochemical Hydrogen Evolution: Composition, Structural and Electronic Regulation. Energ. Environ. Sci. 2017, 10 (5), 1262-1271. (47) Chi, J. Q.; Gao, W. K.; Lin, J. H.; Dong, B.; Qin, J. F.; Liu, Z. Z.; Liu, B.; Chai, Y. M.; Liu, C. G. Porous core-shell N-doped Mo2C@C nanospheres derived from inorganic-organic hybrid precursors for highly efficient hydrogen evolution. J. Catal. 2018, 360, 9-19.


21


Page 22 of 24

(48) Ji, L. L.; Wang, J. Y.; Teng, X.; Dong, H.; He, X. M.; Chen, Z. F. N,P-Doped Molybdenum Carbide Nanofibers for Efficient Hydrogen Production. ACS Appl. Mater. Interfaces 2018, 10 (17), 14632-14640. (49) Kim, S. K.; Yoon, D.; Lee, S.-C.; Kim, J. Mo2C/Graphene Nanocomposite As a Hydrodeoxygenation Catalyst for the Production of Diesel Range Hydrocarbons. ACS Catal. 2015, 5 (6), 3292-3303. (50) Wang, S.; Wang, J.; Zhu, M.; Bao, X.; Xiao, B.; Su, D.; Li, H.; Wang, Y. MolybdenumCarbide-Modified Nitrogen-Doped Carbon Vesicle Encapsulating Nickel Nanoparticles: A Highly Efficient, Low-Cost Catalyst for Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2015, 137 (50), 15753-15739. (51) Liao, L.; Wang, S.; Xiao, J.; Bian, X.; Zhang, Y.; Scanlon, M. D.; Hu, X.; Tang, Y.; Liu, B.; Girault, H. H. A nanoporous molybdenum carbide nanowire as an electrocatalyst for hydrogen evolution reaction. Energy Environ. Sci. 2014, 7 (1), 387-392. (52) Chen, W. F.; Wang, C. H.; Sasaki, K.; Marinkovic, N.; Xu, W.; Muckerman, J. T.; Zhu, Y.; Adzic, R. R. Highly Active and Durable Nanostructured Molybdenum Carbide Electrocatalysts for Hydrogen Production. Energ. Environ. Sci. 2013, 6 (3), 943-951. (53) Wang, H.; Sun, C.; Cao, Y.; Zhu, J.; Chen, Y.; Guo, J.; Zhao, J.; Sun, Y.; Zou, G. Molybdenum Carbide Nanoparticles Embedded in Nitrogen-Doped Porous Carbon Nanofibers as a Dual Catalyst for Hydrogen Evolution and Oxygen Reduction Reactions. Carbon 2017, 114, 628-634. (54) Tang, C.; Wang, W.; Sun, A.; Qi, C.; Zhang, D.; Wu, Z.; Wang, D. Sulfur-Decorated Molybdenum Carbide Catalysts for Enhanced Hydrogen Evolution. ACS Catal. 2015, 5 (11), 6956-6963. (55) Silveira, J. V.; Vieira, L. L.; Filho, J. M.; Sampaio, A. J. C.; Alves, O. L.; Souza Filho, A. G. Temperature-Dependent Raman Spectroscopy Study in MoO3 Nanoribbons. J. Raman Spectro. 2012, 43 (10), 1407-1412. (56) Kang, J. S.; Kim, J.; Lee, M. J.; Son, Y. J.; Chung, D. Y.; Park, S.; Jeong, J.; Yoo, J. M.; Shin, H.; Choe, H.; Park, H. S.; Sung, Y. E. Electrochemically Synthesized Nanoporous Molybdenum Carbide as a Durable Electrocatalyst for Hydrogen Evolution Reaction. Adv. Sci. 2018, 5 (1), 1700601. (57) Li, J. S.; Wang, Y.; Liu, C. H.; Li, S. L.; Wang, Y. G.; Dong, L. Z.; Dai, Z. H.; Li, Y. F.; Lan, Y. Q. Coupled Molybdenum Carbide and Reduced Graphene Oxide Electrocatalysts for Efficient Hydrogen Evolution. Nat. Commun. 2016, 7, 11204. (58) Lu, C.; Tranca, D.; Zhang, J.; Rodri Guez Hernandez, F. N.; Su, Y.; Zhuang, X.; Zhang, F.; Seifert, G.; Feng, X. Molybdenum Carbide-Embedded Nitrogen-Doped Porous Carbon Nanosheets as Electrocatalysts for Water Splitting in Alkaline Media. ACS Nano 2017, 11 (4), 3933-3942. (59) Zhao, Y.; Kamiya, K.; Hashimoto, K.; Nakanishi, S. In situ CO2-Emission Assisted Synthesis of Molybdenum Carbonitride Nanomaterial as Hydrogen Evolution Electrocatalyst. J. Am. Chem. Soc. 2015, 137 (1), 110-113. (60) Wan, C.; Regmi, Y. N.; Leonard, B. M. Multiple Phases of Molybdenum Carbide as Electrocatalysts for the Hydrogen Evolution Reaction. Angew. Chem. Int. Ed.2014, 53 (25), 6407-10. (61) Li, B.; Dai, F.; Xiao, Q.; Yang, L.; Shen, J.; Zhang, C.; Cai, M. Nitrogen-Doped Activated Carbon for a High Energy Hybrid Supercapacitor. Energ. Environ. Sci. 2016, 9 (1), 102-106.


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(62) Vitale, G.; Guzmán, H.; Frauwallner, M. L.; Scott, C. E.; Pereira-Almao, P. Synthesis of Nanocrystalline Molybdenum Carbide Materials and Their Characterization. Catal. Today 2015, 250, 123-133.


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TOC GRAPHICS

Ultrasmall Mo2C nanoparticles supported on nitrogen-doped carbon nanotubes through a onestep carbonization of Mo-containing anion doped polyaniline nanotubes show excellent electrocatalytic hydrogen evolution activity


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Anion-Induced Size Selection of Î²-Mo2

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