Vertically Aligned OxygenatedâCoS2âMoS2 ... - ACS Publications

Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE

Vertically Aligned Oxygenated–CoS2–MoS2 Heteronanosheet Architecture from Polyoxometalate for Efficient and Stable Overall Water Splitting Jungang Hou, Bo Zhang, Zhuwei Li, Shuyan Cao, Yiqing Sun, Yunzhen Wu, Zhanming Gao, and Licheng Sun ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b00668 • Publication Date (Web): 16 Apr 2018 Downloaded from http://pubs.acs.org on April 16, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 38 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

ACS Catalysis

Vertically Aligned Oxygenated–CoS2–MoS2 Heteronanosheet Architecture from Polyoxometalate for Efficient and Stable Overall Water Splitting Jungang Hou,*† Bo Zhang,† Zhuwei Li,† Shuyan Cao,† Yiqing Sun,† Yunzhen Wu,† Zhanming Gao,† Licheng Sun*†‡ †

State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on

Molecular Devices, Institute of Energy Science and Technology, Dalian University of Technology (DUT), Dalian 116024, China ‡

Department of Chemistry, KTH Royal Institute of Technology, 10044 Stockholm, Sweden

ABSTRACT: To achieve efficient conversion of renewable energy sources through water splitting, low-cost, earth-abundant and robust electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are required. Herein, vertically aligned oxygenated–CoS2–MoS2 (O–CoMoS) heteronanosheets grown on flexible carbon fiber cloth as bifunctional

electrocatalysts

have

been

produced

by

use

of

Anderson–type

(NH4)4[Co(II)Mo6O24H6]·6H2O polyoxometalate as bimetal precursors. In comparison to different O–FeMoS, O–NiMoS and MoS2 nanosheets arrays, the O–CoMoS heteronanosheet array exhibited low overpotentials of 97 and 272 mV to reach a current density of 10 mA cm−2 in

ACS Paragon Plus Environment

1

ACS Catalysis 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

Page 2 of 38

alkaline solution for HER and OER, respectively. Assembled as an electrolyzer for overall water splitting, the O–CoMoS heteronanosheets as both the anode and the cathode delivers a current density of 10 mA cm−2 at a quite low cell voltage of 1.6 V. This O–CoMoS architecture is highly advantageous for the disordered structure, the exposure of active heterointerfaces, the “highway” of charge transport on two-dimensional conductive channels, and the abundant active catalytic sites from the synergistic effect of the heterostructures, accomplishing the dramatically enhanced performance for OER, HER, and overall water splitting. This work represents a feasible strategy to explore efficient and stable bifunctional bimetal-sulfides electrocatalysts for renewable energy applications.

KEYWORDS: Oxygenated–CoS2–MoS2, Polyoxometalates, Heteronanosheets, Electrocatalysts, Overall water splitting

INTRODUCTION

With increasing demands in energy, renewable energy sources have been explored through electrochemical water splitting as a promising approach to resolve the environmental crisis and energy concerns.1-3 Presently, noble metals (e.g., Pt) and noble metal oxides (e.g., RuO2, IrO2) the state-of-the-art electrocatalysts have been applied to implement highly electrochemical performance overall water splitting for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively.4-17 Owing to high cost, low abundance, and poor stability, it is


2

Page 3 of 38 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

ACS Catalysis

essential to search low-cost, earth-abundant catalysts as alternatives to Pt and RuO2/IrO2.5,6 For instances, various transition metal sulfides,18,19 nitrides,20 carbides,21 phosphides,22-24 selenides,2527

borides and the hybrids have been applied for the HER,28-30 accomplishing metal oxides,

hydroxides, phosphates and nanocomposites for the OER.31-35 To simply the electrochemical system and accelerate the commercialization of water splitting, efficient bifunctional electrocatalysts, such as metal oxides, sulfides, nitrides, phosphides and the composites, have attracted considerable attention to catalyze both OER and HER in alkaline media.36-43 Notwithstanding significant progress, it is still highly desirable to develop alternative bifunctional electrocatalysts. Among kinds of materials, transition metal sulfides have presented inherent advantages over other materials.44-46 In comparison, most of oxides materials have not been active for both OER and HER due to low conductivity or inappropriate crystal structure.47,48 To date, some sulfides catalysts have been reported to simultaneously catalyze OER and HER in alkaline electrolyte solutions.43,46 What is the most significant is, the metal sulfides electrocatalysts, such as MoS 2, Ni2S3, CoS2, WS2, have been extensively illustrated superior HER performance due to the exposed edge surfaces and good electrical conductivity.44,46,49,50 For examples, Ni-Mo-S/C electrode for HER in neutral electrolyte presented a current density of 10 mA cm −2 at a small overpotential of 200 mV.51 The graphene oxide/MoS2 composite catalyst owing to the abundant exposed edges showed superior catalytic performance.52 Moreover, the MoS2/CoSe2 catalyst with a small Tafel slope of 36 mV per decade and onset potential of mere 11 mV, showed robust HER


3

ACS Catalysis 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

Page 4 of 38

catalytic activities in acidic media.53 Compared to the HER, it is difficult to accomplish the OER for the metal sulfides due to the thermodynamical and kinetical limitation. Nevertheless, oxygen incorporated amorphous cobalt sulfide (CoS4.6O0.6) porous nanocubes achieved a current density of 10 mA cm−2 at 1.52 V. RHE for oxygen evolution reaction.54 Nitrogen-doped CoS2 catalysts for OER reached the current density of 10 mA cm−2 at a small overpotential.55 Despite the significant progress, there are few metal sulfides electrocatalysts capable to catalyze both HER and OER in the alkaline electrolyte.56-58 Thus, it is of significant importance to produce electrochemically active transition bimetal sulfides as bifunctional electrocatalysts. With regard to bifunctional catalysts, there are few reports about non-noble-metal-based electrocatalysts for HER and OER. What deserves to be mentioned the most is transition bimetal sulfides as bifunctional catalysts. For examples, CoS-doped β-Co(OH)2@MoS2+x hybrid catalyst grown on nickel foam presented high performance overall water splitting.56 A cobalt sulfide/molybdenum disulfide as hybrid system showed great enhancement in both HER and OER performance.57 MoS2/Ni3S2 heterostructures as bifunctional electrocatalysts delivered the current density of 10 mA cm–2 at the low cell voltage.59,60 However, those sulfides still presented the limited OER electrocatalytic activities. What the most important thing is that it is hard to control the precise component of transition bimetal sulfides according to the ideal stoichiometric ratio. To address these limitations, it is of great interest to construct the oxygenated–sulfides heteronanosheets as integrated electrocatalysts towards overall water splitting.


4

Page 5 of 38 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

ACS Catalysis

Herein, the vertically aligned oxygenated–heteronanosheets architecture (O–CoMoS, O– FeMoS, O–NiMoS) grown on conductive and flexible carbon fiber cloth have been systematically investigated through a proof-of-concept hydrothermal strategy by use of Anderson–type (NH4)4[M(II)Mo6O24H6]·6H2O polyoxometalates (M= Co, Ni and Fe) polyoxometalate as bimetal precursors. In comparison of O–FeMoS, O–NiMoS and MoS2, asprepared O–CoMoS heteronanosheet array presented low overpotentials of 97 and 272 mV to achieve a current density of 10 mA cm−2 in alkaline electrolyte for HER and OER, respectively. Furthermore, assembled in a two-electrode system of the O–CoMoS electrocatalyst, an overpotential of only 1.6 V was required for overall water splitting at a current density of 10 mA cm−2 for 10 h. This work has addressed the limitations of OER activities and the precise regulation of the component for the transition bimetal sulfides. Hence, balancing the benefits among the large surface area, the exposure of active heterointerfaces, the “highway” of charge transport on two-dimensional conductive channels, and the abundant active catalytic sites from the synergistic effect of the heterostructures anchored on conductive and flexible carbon fiber cloth, is the most promising but challenging task for developing efficient electrocatalysts.

EXPERIMENTAL SECTION Fabrication of bimetal sulfides heteronanosheets array: Firstly, cobaltous sulfate (6 mmol) with H2O2 solution was dissolved into (NH4)6Mo7O24·4H2O (10 mmol) solution in H2O. The asprepared solution was followed by recrystallization from the above boiling solution, achieving


5

ACS Catalysis 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

Page 6 of 38

green crystals of Anderson–type (NH4)4[Co(II)Mo6O24H6]·6H2O polyoxometalate as the bimetal precursor. In comparison, the bimetal precursors of as-prepared (NH4)4[M(II)Mo6O24H6]·6H2O (M=Ni, Fe) polyoxometalates without use of H2O2 have also been synthesized by use of nickel sulfate and ferric sulfate. Secondly, the polyoxometalates (0.1 mmol) and thiourea (2 mmol) were added into 40 mL water. The obtained solution and carbon fiber cloth (1 × 3 cm2) were placed into a 50 mL Teflon-lined stainless steel autoclave for hydrothermal reaction at 200 oC for 24 h. After washing and drying, the bimetal sulfides (O–CoMoS, O–NiMoS, O–FeMoS) heteronanosheets arrays grown on flexible carbon fiber cloth by use of tunable polyoxometalates precursors were achieved under the thermal treatment at 400 oC in Ar atmosphere. In comparison, Pt/C (20wt% Pt) and IrO2 catalysts were purchased from Sigma-Aldrich. Structural Characterization: XRD patterns of the products were tested with X-ray diffractometer (Japan Rigaku Rotaflex) by Cu Kα radiation (λ=1.5418 nm, 40 kV, 40 mA) at room temperature. SEM images of the products were captured by a field-emission scanning electron microscope (SEM, FEI Nova Nano SEM 450). TEM images of the products were performed on transmission electron microscopy (TEM, FEI TF30). The FTIR and Raman spectra were recorded on VERTEX 80V FT–IR spectrometer and Thermo Fisher DXR Raman spectrometer. The chemical states of the sample were determined by X-ray photoelectron spectroscopy (XPS) in a Thermo VG ESCALAB250 surface analysis system. Electron paramagnetic resonance (EPR) spectra were obtained using a JEOL JES-FA200 EPR


6

Page 7 of 38 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

ACS Catalysis

spectrometer. The surface area and the pore size distribution of the product were measured by a Brunauer–Emmett–Teller method and a Barrett–Joyner–Halenda route (TriStar 3000-BET/BJH). Electrochemical Measurements: All the electrochemical performance tests in 1 M KOH electrolyte media were performed by a CHI660D electrochemical workstation, using Ag/AgCl electrode, a graphite rod and as-prepared bimetal sulfides electrodes as the reference electrodes, the counter electrode and the working electrode, respectively. All polarization curves at 2 mV s−1 were corrected for 90% iR–compensation. The mass loading of CoMoS nanosheets anchored on carbon fiber cloth was ~1 mg cm-2. The EIS tests were measured by AC impedance spectroscopy at the frequency ranges 106 to 1 Hz. According to the Nernst equation (ERHE = EAg/AgCl + 0.059pH + 0.197), where ERHE was the potential vs. a reversible hydrogen potential, EAg/AgCl was the potential vs. Ag/AgCl electrode, and pH was the pH value of electrolyte.

RESULTS AND DISCUSSION To achieve single-phase bimetal precursor, the mixtures of the sulfate and ammonium heptamolybdate were firstly dissolved in aqueous solution by a boiling route, then the precursors were obtained through a recrystallization approach by use of above-mentioned solution. As illustrated in Figure 1, our attempt was to synthesize the different oxygenated–sulfides heteronanosheets architecture grown on conductive and flexible carbon fiber cloth by use of Anderson–type (NH4)4[M(II)Mo6O24H6]·6H2O polyoxometalates as bimetal precursors. Most importantly, as-prepared vertically aligned oxygenated–CoS2–MoS2 architecture assembled an


7

ACS Catalysis 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

Page 8 of 38

alkaline electrolyzer for both HER and OER (Figure 1b), achieved robust bifunctional electrode materials for overall water splitting.

Figure 1. Schematic illustrations of (a) the synthesis of as-prepared oxygenated-bimetal-sulfides heteronanosheets

arrays

grown

on

carbon

fiber

cloth

by use

of

Anderson–type

(NH4)4[M(II)Mo6O24H6]·6H2O polyoxometalates and (b) overall water splitting by use of O– CoMoS heteronanosheets array as anode and cathode in alkaline solution.


8

Page 9 of 38 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

ACS Catalysis

Based on the boiling and recrystallization strategies, X–ray diffraction (XRD) pattern of the 6molybdocobaltate precursor (Figure 2) can be indexed to tetraammonium hexahydrogen hexamolybdocobaltate (II) tetrahydrate ((NH4)4[Co(II)Mo6O24H6]·6H2O) with B–type Anderson structure heteropolyoxoanions [H6Co2-Mo6O24]4- polyanion, according to the previous reports about crystal analysis.61-63 The fourier transform infrared (FTIR) spectra of as-prepared (NH4)4[Co(II)Mo6O24H6]·6H2O was presented in Figure 2c. In details, the bands lied at 451, 587, 654, 895 and 946 cm-1 are ascribed to the characteristic peaks of Co–O and Mo–O in 6molybdocobaltate precursor.62 Moreover, the peaks located at 1400, 1636 and 3200~3600 cm-1 from the high regions of FTIR spectra can be arranged to O–H and N–H modes, indicating the presence of molecular water and NH4+ in the precursor.64 As shown in Figure 2d, the vibrational characteristic modes at 355, 557, 575, 894 and 943 cm-1 can be indexed to the main features of the Mo–O and Co–O–Mo bonds.65,66 Based on the analysis of XRD patterns, FTIR and Raman spectra, these results confirmed the formation of Anderson–type (NH4)4[Co(II)Mo6O24H6]·6H2O polyoxometalates. Furthermore, XRD patterns, FTIR and Raman spectra of as-prepared 6molybdonickelate and 6-molybdoferrate precursors have also been presented (Figure S2-S4), indicating that the synthesis of (NH4)4[M(II)Mo6O24H6]·6H2O (M= Ni and Fe) polyoxometalates. Thus, the bimetal precursors have been successfully produced by precise regulation of polyoxometalates components, demonstrating the promising candidates of the raw materials for the synthesis of transition bimetal sulfides.


9

ACS Catalysis 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

Page 10 of 38

(a)

Figure 2. (a) Schematic illustration of Anderson–type polyoxometalates, (b) XRD pattern, (c) FTIR spectra and (d) Raman spectra of (NH4)4[Co(II)Mo6O24H6]·6H2O precursor.

After the facile hydrothermal reaction by use of bimetal polyoxometalates, the typical Scanning electron microscope (SEM) images of the bimetal sulfides anchored on carbon fiber cloth have been presented. Figure 3 reveals that the O–CoMoS product consists of abundant edge exposing two-dimensional nanosheets which vertically aligned onto the surface of carbon fiber. In comparison, SEM images of the O–NiMoS and O–FeMoS products have been showed in


10

Page 11 of 38 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

ACS Catalysis

Figure S5, indicating the nanosheets-constructed architectures grown on carbon fiber. Under the same condition, it is hard to produce the perfect NiS and FeS2 products (Figure S6). As shown in Figure 3, transmission electron microscopy (TEM) images reveal that the O–CoMoS product is composed of crystalline MoS2 and CoS2 nanosheets. In details, the evident lattice fringe of 0.62 nm can be indexed to the (002) plane of MoS2 nanosheets, which are exposed with Mo and S edges. While the lattice fringe of 0.277 nm is assigned to (200) plane of CoS2. Interestingly, the discontinued fringes of these sulfides have been observed, indicating that the existence of disordered structure in the O–CoMoS. Thus, these results demonstrate the successful formation of MoS2 and CoS2 species for the O–CoMoS heteronanosheets with a moderate degree of disorder.65 In comparison, the O–NiMoS and O–FeMoS products from TEM images (Figure S7) are composed of NiS2–MoS2 and FeS2–MoS2, respectively. Furthermore, the elemental mappings by electron dispersive spectra (EDS) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), as shown in Figure S8/S9, indicate the homogenous distribution of Co, Mo, S and O, confirming the oxygen-incorporated CoMoS nanosheets. What deserves to be mentioned the most is, the measured Co-to-Mo, Ni-to-Mo and Fe-to-Mo ratios in O–CoMoS, O–NiMoS and O–FeMoS are approximate 1 : 6, which are in agreement with these relative polyoxometalates ratios. Thus, the successful regulation of the precise components of bimetal sulfides heteronanosheets is propitious to improve the electrocehmical water splitting performance.


11

ACS Catalysis 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

Page 12 of 38

Figure 3. (abc) SEM images, (de) TEM images and (f) element mappings for vertically aligned O–CoMoS heteronanosheets.


12

Page 13 of 38 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

ACS Catalysis

Figure 4. (a) XRD pattern, (b) FTIR spectra, (c) Raman spectra and (d) N2 adsorption-desorption isotherm with pore-size distribution of O–CoMoS heteronanosheets.

To confirm the crystal structures, XRD patterns, FTIR and Raman spectra of as-prepared bimetal sulfides have been presented in Figure 4. Several representative diffraction peaks of asprepared bimetal sulfides can be readily indexed to the planes of the CoS2 phase (JCPDS No. 653322) and MoS2 phase (JCPDS No. 65-1941), indicating the formation of the CoS2–MoS2 hybrid


13

ACS Catalysis 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

Page 14 of 38

in comparison of XRD pattern of single-phase MoS2 (Figure S10). Moreover, the the O–NiMoS and O–FeMoS products from XRD patterns consist of heterostructured NiS–MoS2 and FeS2– MoS2, respectively. All XRD patterns are in agreement with the analysis of TEM images for the bimetal sulfides. From FTIR spectra, the main peaks at 500~1000 cm−1 are assigned to the bending of Co–S/Mo–S and Co–O and the vibrational modes at 3436 and 1635 cm−1 are indexed to hydroxyl functionalities of adsorbed moisture on the O–CoMoS products.64,65 Moreover, the peaks lied at 380 cm−1 and 405 cm−1 can be identified as the E2g and A1g vibrational modes in O– CoMoS heterostructure from Raman spectra, while the peak located at 480 cm−1 can be assigned for the Co–O bond,66,67 thus proving the oxygen incorporation in the O–CoMoS heterostructure. Besides, Raman spectra of O–NiMoS and O–FeMoS have also compared (Figure S11), indicating the oxygen incorporation in the O–NiMoS and O–FeMoS heterostructures. According to the previous work,54 it is expected the O–NiMoS and O–FeMoS heteronanosheets as electrocatalysts could address the OER limitation and then enhance both OER and HER. Moreover, the N2 adsorption-desorption isotherms of O–CoMoS heteronanosheets have been performed in Figure 4, indicating the high Brunauer-Emmett-Teller surface area of 35.8 m2 g-1 and the Barret-Joyner-Halenda (BJH) pore size distribution s of 1~10 nm. These results benefit the generation of active electrochemical sites for the HER and the OER. Combined with XRD patterns, FTIR and Raman spectra as well as SEM/TEM images, these results have confirmed the formation of the bimetal sulfides nanosheets grown on carbon fiber cloth by use of Anderson– type polyoxometalates. Most importantly, this designed synthesis can possibly be extended to the


14

Page 15 of 38 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

ACS Catalysis

preparation of the traditional bimetal sulfides by use of different polyoxometalate materials through strong interfacial coupling effect.

Figure 5. High–resolution XPS spectra of (a) Co 2p, (b) Mo 3d, (c) S 2p and (d) O 1s of O– CoMoS nanosheets.

With regard to conduct the surface electronic states, X-ray photoelectron spectra (XPS) of asprepared O–CoMoS, O–NiMoS and O–FeMoS heteronanosheets have been measured in Figure 5


15

ACS Catalysis 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

Page 16 of 38

and Figure S12/S13. The two peaks located at 779.2 and 793.9 eV can be assigned to the Co–S bond while the peak at 781.2 eV is identified to the Co–O bond which is in agreement with the analysis from FTIR and Raman spectra, followed by two satellite peaks at 786.2 and 802.7 eV in the O–CoMoS nanosheets.68,69 The two peaks at 232.0 and 228.8 eV are attributed to the Mo4+ 3d3/2 and Mo4+ 3d5/2 for Mo–S species. However, the peak at 235.1 eV is indexed to Mo6+ 3d3/2. The two peaks at 161.8 and 162.8 eV can be indexed to S 2p3/2 and S 2p1/2, indicating the existence of terminal S2– in the CoS2 and MoS2 sites. Moreover, the O 1s core level spectra of O– CoMoS nanosheets was conducted to confirm the oxygen-containing groups on two-dimensional nanosheets surface. Especially, three peaks of O 1s spectra were located at 529.9, 531.2 and 532.0 eV, respectively. The O 1s peak at 529.9 eV can be indexed to the metal–O band, while the O 1s peaks at 531.2 and 532.6 eV are associated to the hydroxy group and adsorbed water, respectively.56 Moreover, the Ni 2p, Fe 2p, S 2p and O 1s spectra of as-prepared O–NiMoS and O–FeMoS nanosheets have been identified (Figure S12/S13),59 confirming the oxygenincorporated bimetal sulfides heterostructures. To further provide fingerprint information for a paramagnetic signal by electron paramagnetic resonance (EPR), a strong EPR signal of O– CoMoS heteronanosheets was observed while MoS2 nanosheets present a negligible EPR signal at a g value of 1.91−2.003 (Figure S14), which might be ascribed to the electrontrapped centers at S vacancies (Vs), promoting more active unsaturated sulfur atoms in more disordered structure.66 Thus, these results demonstrated the formation of the S vacancies confined in the oxygen-incorporated bimetal sulfides heterostructures.


16

Page 17 of 38 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

ACS Catalysis

Figure 6. (ab) HER polarization curves of metal sulfides nanosheets arrays, (c) Tafel slopes, (d) Nyquist plots, (e) double-layer capacitances for O–CoMoS, O–NiMoS and O–FeMoS arrays and (f) cycling stability at –0.2 V vs RHE of O–CoMoS array.


17

ACS Catalysis 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

Page 18 of 38

The electrocatalytic performance of metal sulfides nanosheets arrays in 1 M KOH electrolyte were probed by a three-electrode system. Graphite rod as stable counter electrode has been employed to set up three-electrode system for the electrochemical measurements, avoiding the influence of Pt deposition on the working electrode. For the HER, in comparison of MoS2, the O–CoMoS nanosheets array presented the enhanced HER activity (Figure 6ab), corresponding to an overpotential of 97 mV to reach a current density of 10 mA cm-2. However, the bare carbon fiber cloth showed negligible HER activity.51 Compared to the O–NiMoS (254 mV at 50 mA cm−2) and O–FeMoS (316 mV at 50 mA cm−2) arrays, the O–CoMoS array exhibited the best electrocatalytic activity with the overpotentials of 180, 206, 229 and 240 mV at the current densities of 50, 100, 200 and 300 mA cm−2, respectively, which is superior the values of the reported state-of-art HER electrocatalysts (Table S1). However, the commercial Pt/C catalyst exhibits the highest activity for HER (Figure S15). To understand the HER kinetics (Figure 6c), the Tafel slopes of as-prepared O–CoMoS, O–NiMoS and O–FeMoS arrays are 70, 80 and 123 mV dec−1, respectively, indicating the favorable HER reaction kinetics for the O–CoMoS array. Moreover, electrochemical impedance spectroscopy (EIS) analyses revealed that the charge transfer resistance of the O–CoMoS array is extremely lower than that of O–NiMoS and O– FeMoS arrays (Figure 6d), demonstrating the faster reaction kinetics and the higher electrical conductivity. In this case, the robust HER performance of O–CoMoS array could be ascribed to the vertically aligned oxygenated–CoS2–MoS2 heteronanosheet architecture. On one hand, the intimate integration of CoS2 and MoS2, maintains their properties of two different materials, even


18

Page 19 of 38 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

ACS Catalysis

brings the synergistic effect on the active catalytic heterointerface of oxygenated–CoS2–MoS2 array. On the other hand, two-dimensional nanosheets architecture builds the “highway” of charge transport on two-dimensional conductive channels, facilitating the faster electron transfer during HER process. Moreover, the S vacancies and the degree of disorder in the defective O– CoMoS array provide the abundant active edge sites and the enhancement of intrinsic conductivity for HER. Especially, the O–CoMoS array exhibits a high Faraday efficiency of 98.3% from the analysis between the detected hydrogen evolution and the theoretical value (Figure S16). Furthermore, the electrochemically active surface area (ECSA) in Figure 6e, was measured by the electrochemical double–layer capacitance (Cdl). Based on the ECSA evaluation with cyclic voltammograms (Figure S17), the Cdl values of the O–CoMoS, O–NiMoS and O–FeMoS arrays are 52.7, 27.3 and 11.1 mF cm–2, benifiting active catalytic sites on O–CoMoS heteronanosheets. Notably, the cycling stability of the O–CoMoS array was also tested for long-term operation (Figure 6f). After maintaining HER test for 10 h, there was no apparent change in the current density at –0.2 V vs. RHE. In details, the polarization curve after 1000 cycles was almost identical with the initial scan, demonstrating the outstanding stability of the O–CoMoS array. Although there is less reports upon OER by metal sulfides, we have also examined the OER activity of the bimetal sulfides nanosheets arrays under similar conditions. For the OER, compared to MoS2, as shown in Figure 7a, the O–CoMoS nanosheets array with the improved OER performance exhibited an overpotential of 272 mV to deliver a current density of 10 mA cm-2. Compared to the O–NiMoS and O–FeMoS, the O–CoMoS array presented the best OER


19

ACS Catalysis 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

Page 20 of 38

Figure 7 (ab) OER polarization curves, (c) Tafel slopes for different arrays and (d) time dependence of current density at 1.53 V vs RHE of O–CoMoS array.

performance (Figure 7b), corresponding to the overpotentials of 286, 301 and 310 mV at the current densities of 20, 50 and 100 mA cm−2, respectively. These data of O–CoMoS array is lower than those of the reported OER electrocatalysts (Table S2) and commercial IrO2 catalyst (Figure S18). To evaluate the OER kinetics (Figure 7c), the Tafel slopes of O–CoMoS, O–


20

Page 21 of 38 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

ACS Catalysis

NiMoS and O–FeMoS arrays are 45, 71 and 83 mV dec−1, respectively, indicating the robust intrinsic OER kinetics. Thus, the enhanced OER activity of the CoMoS array is ascribed to the two-dimensional nanosheet architecture, facilitating electron and mass transport and providing abundant catalytically active sites for OER.67-70 What deserves to be mentioned the most is the oxygen incorporation in CoMoS array promoted the formation of abundant Co active centers and the interfaces synergistical effect of the oxygenated–CoS2–MoS2 heteronanosheets. Notably, the durability of O–CoMoS array was also conducted in alkaline electrolyte (Figure 7d). What deserves to be mentioned the most is a high Faraday efficiency of 97.6%, confirming the capability of oxygenated–CoS2–MoS2 array as an OER electrode for oxygen evolution (Figure S19). After cycling test for 10 h, there was no obvious degradation in the current density at 1.53 V vs. RHE. However, single-phase MoS2 electrode loses most of its initial current density for OER activity (Figure 7d). Thus, these results indicate promise for long term practical applications of the O–CoMoS catalysts. To explore the real energy conversion, a two-electrode device by O–CoMoS heteronanosheets architectures as bifunctional electrocatalysts was fabricated for overall water splitting application in 1.0 M KOH solution. The O–CoMoS heteronanosheets electrode affords a water-splitting current density of 10 mA cm−2 at a low cell voltage of 1.6 V, which is lower than those of the reported state-of-art electrocatalysts (Table S3).71-75 Most importantly, there is a negligible change of the current density at 10 mA cm−2 during 10 h water electrolysis (Figure 8b). Moreover, XRD pattern and the surface morphology of the O–CoMoS electrode after the 10 h


21

ACS Catalysis 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

Page 22 of 38

test a low cell voltage of 1.6 V present almost no change (Figure S20/S21), confirming the high structural stability of the O–CoMoS array. Throughout the stability measurement of asassembled O–CoMoS||O–CoMoS cell, the apparent hydrogen and oxygen bubbles were observed from the two-electrode surfaces at 1.6 V (Movie S1), further confirming the superior durability of as-prepared oxygenated–CoS2–MoS2 heteronanosheets electrolyzer in alkaline media. Based on above-mentioned analysis, the superior electrocatalytic performance of oxygenated–CoS2– MoS2 heteronanosheets can be ascribed to the synergistic interaction among O, Co, Mo and S atoms. Firstly, two-dimensional oxygenated–bimetal-sulfides nanosheets have been grown on three-dimensional porous substrate as integrated architectures, facilitating electrolyte penetration and the release of the gas bubbles, enhancing the intimate contact between active sites and reactants, and building the “highway” of charge transport on two-dimensional conductive channels. Secondly, the disordered structure and S vacancies confined in two-dimensional oxygenated–bimetal-sulfides nanosheets heterojunction provides a large electrochemically active surface area, a great number of active sites, the exposure of active heterointerfaces as well as the enhancement of conductivity, thus accomplishing the dramatically enhanced performance for OER, HER, and overall water splitting.


22

Page 23 of 38 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

ACS Catalysis

Figure 8. (a) Overall water splitting performance and (b) time dependence of current densities under different constant potentials by use of O–CoMoS array as perspective anode and cathode for overall water splitting.

CONCLUSIONS In summary, the vertically aligned oxygenated–CoS2–MoS2 (CoMoS) heteronanosheets grown on conductive and flexible carbon fiber cloth have been produced by use of Anderson–type (NH4)4[Co(II)Mo6O24H6]·6H2O polyoxometalate as bimetal precursor. In comparison, asprepared O–CoMoS heteronanosheet array exhibited low overpotentials of 97 and 272 mV to reach a current density of 10 mA cm−2 in alkaline solution for HER and OER, respectively. Assembled as an electrolyzer for overall water splitting, the O–CoMoS heteronanosheets as both the anode and the cathode delivers a current density of 10 mA cm−2 at a quite low cell voltage of 1.6 V. More importantly, the improved electrocatalytic performance of O–CoMoS architecture


23

ACS Catalysis 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

Page 24 of 38

can mainly be attributed to the disordered structure, the exposure of active heterointerfaces, the “highway” of charge transport on two-dimensional conductive channels, and the abundant active catalytic sites from the synergistic effect of the heterostructures. This work represents a feasible strategy to design and explore effective hybrid materials as efficient electrocatalysts for promising renewable energy applications.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Schematic illustration; XRD patterns; FTIR spectra; Raman spectra; SEM images; TEM images; XPS spectra; HER and OER polarization curves; the yields of hydrogen and oxygen gasses; Cyclic voltammograms; comparison of electrocatalytic activities for various catalysts. AUTHOR INFORMATION Corresponding Author *E-mail for J.Hou.: [email protected] *E-mail for L.Sun.: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.


24

Page 25 of 38 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

ACS Catalysis

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by National Science Foundation of China (No. 51672034 and 51472027), National Basic Research Program of China (973 program, 2014CB239402), the Swedish Energy Agency, and the K&A Wallenberg Foundation.

REFERENCES (1) Chu, S.; Majumdar, A. Opportunities and Challenges for a Sustainable Energy Future. Nature 2012, 488, 294–303. (2) Jiao, Y.; Zheng, Y.; Jaroniec, M.; Qiao, S. Z. Design of Electrocatalysts for Oxygen- and Hydrogen-Involving Energy Conversion Reactions. Chem. Soc. Rev. 2015, 44, 2060–2086. (3) Morales-Guio, C. G.; Stern, L. A.; Hu, X. Nanostructured Hydrotreating Catalysts for Electrochemical Hydrogen Evolution. Chem. Soc. Rev. 2014, 43, 6555–6569. (4) Park, S.; Shao, Y.; Liu, J.; Wang Y. Oxygen Electrocatalysts for Water Electrolyzers and Reversible Fuel Cells: Status and Perspective. Energy Environ. Sci. 2012, 5, 9331–9344. (5) Stephens, I. E. L.; Chorkendorff, I. Minimizing the Use of Platinum in Hydrogen-Evolving Electrodes. Angew. Chem., Int. Ed. 2011, 50, 1476–1477.


25

ACS Catalysis 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

Page 26 of 38

(6) Hou, J.; Wu, Y.; Cao, S.; Sun, Y.; Sun, L. Active Sites Intercalated Ultrathin Carbon Sheath on Nanowire Arrays as Integrated Core–Shell Architecture: Highly Efficient and Durable Electrocatalysts for Overall Water Splitting. Small 2017, 13, 1702018. (7) Wu, D.; Wei, Y.; Ren, X.; Ji, X.; Liu, Y.; Guo, X.; Liu, Z.; Asiri, A.; Wei, Q.; Sun, X. Co(OH)2 Nanoparticle-Encapsulating Conductive Nanowires Array: Room-Temperature Electrochemical Preparation for High-Performance Water Oxidation Electrocatalysis. Adv. Mater. 2018, 30, 1705366. (8) Ren, X.; Ge, R.; Zhang, Y.; Liu, D.; Wu, D.; Sun, X.; Dua, B.; Wei, Q. Cobalt–Borate Nanowire Array as a High–Performance Catalyst for Oxygen Evolution Reaction in NearNeutral Media. J. Mater. Chem. A 2017, 5, 7291–7294. (9) Ren, X.; Wang, W.; Ge, R.; Hao, S.; Qu, F.; Du, G.; Asiri, A.; Wei, Q.; Chen, L.; Sun, X. An Amorphous FeMoS4 Nanorod Array toward Efficient Hydrogen Evolution Electrocatalysis under Neutral Conditions. Chem. Commun. 2017, 53, 9000–9003. (10) Ren, X.; Ji, X.; Wei, Y.; Wu, D.; Zhang, Y.; Ma, M.; Liu, Z.; Asiri, A.; Wei, Q.; Sun, X. In Situ Electrochemical Development of Copper Oxide Nanocatalysts within a TCNQ Nanowire Array: A Highly Conductive Electrocatalyst for The Oxygen Evolution Reaction. Chem. Commun. 2018, 54, 1425–1428. (11) Qian, M.; Cui, S.; Jiang, D.; Zhang, L.; Du, P. Highly Efficient and Stable Water Oxidation Electrocatalysis with a Very Low Overpotential Using FeNiP Substitutional Solid Solution Nanoplate Arrays. Adv. Mater. 2017, 29, 1704075.


26

Page 27 of 38 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

ACS Catalysis

(12) Jia, H.; Yao, Y.; Zhao, J.; Gao, Y.; Luo, Z.; Du, P. Novel Two-Dimensional Nickel Phthalocyanine–Based Metal-Organic Framework for Highly Efficient Water Oxidation Catalysis. J. Mater. Chem. A 2018, 6, 1188–1195. (13) Liu, X.; Zheng, H.; Sun, Z.; Han, A.; Du, P. Earth-Abundant Copper-Based Bifunctional Electrocatalyst for Both Catalytic Hydrogen Production and Water Oxidation. ACS Catal. 2015, 5, 1530–1538. (14) Zhang, X.; Wu, Y.; Sun. Y.; Ding, P.; Liu, Q.; Tang, L.; Guo, J. Hybrid of Fe4[Fe(CN)6]3 Nanocubes and MoS2 Nanosheets on Nitrogen–Doped Graphene Realizing Improved Electrochemical Hydrogen Production. Electrochimi. Acta 2018, 263, 140–146. (15) Zhang, X.; Zhang, Q.; Sun, Y.; Zhang, P.; Gao X.; Zhang, W.; Guo, J. MoS2–Graphene Hybrid Nanosheets Constructed 3D Architectures with Improved Electrochemical Performance for Lithium-Ion Batteries and Hydrogen Evolution. Electrochimi. Acta 2016, 189, 224–230. (16) Guo, J.; Zhang, X.; Sun, Y.; Tang, L.; Zhang, X. NiMoS3 Nanorods as pH-Tolerant Electrocatalyst for Efficient Hydrogen Evolution. ACS Sustainable Chem. Eng. 2017, 5, 9006– 9013. (17) Guo, J.; Zhang, X.; Sun, Y.; Tang, L.; Zhang, X. Self–Template Synthesis of Hierarchical CoMoS3 Nanotubes Constructed of Ultrathin Nanosheets for Robust Water Electrolysis. J. Mater. Chem. A 2017, 5, 11309–11315. (18) Huang, S. C.; Meng, Y. Y.; He, S. M.; Goswami, A.; Wu, Q. L.; Li, J. H.; Tong, S. F.; Asefa, T.; Wu, M. M. N–, O–, and S–Tridoped Carbon–Encapsulated Co9S8 Nanomaterials:


27

ACS Catalysis 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

Page 28 of 38

Efficient Bifunctional Electrocatalysts for Overall Water Splitting. Adv. Funct. Mater. 2017, 27, 1606585. (19) Tan, Y. W.; Liu, P.; Chen, L. Y.; Cong, W. T.; Ito, Y.; Han, J. H.; Guo, X. W.; Tang, Z.; Fujita, T.; Hirata, A.; Chen, M. W. Monolayer MoS2 Films Supported by 3D Nanoporous Metals for High–Efficiency Electrocatalytic Hydrogen Production. Adv. Mater. 2014, 26, 8023. (20) Jia, X.; Zhao, Y.; Chen, G.; Shang, L.; Shi, R.; Kang, X.; Waterhouse, G.; Wu, L.; Tung, C.; Zhang, T. Ni3FeN Nanoparticles Derived from Ultrathin NiFe–Layered Double Hydroxide Nanosheets: An Efficient Overall Water Splitting Electrocatalyst. Adv. Energy Mater. 2016, 6, 1502585. (21) Li, J.; Wang, Y.; Liu, C.; Li, S.; Wang, Y.; Dong, L.; Dai, Z.; Li, Y.; Lan, Y. Coupled Molybdenum Carbide and Reduced Graphene Oxide Electrocatalysts for Efficient Hydrogen Evolution. Nat. Commun. 2016, 7, 11204. (22) Jiang, P.; Liu, Q.; Liang, Y.; Tian, J.; Asiri, A.; Sun, X. A Cost-Effective 3D Hydrogen Evolution Cathode with Exceptionally High Catalytic Activity: FeP Nanowires Array as the Active Phase. Angew. Chem. Int. Ed. 2014, 53, 12855–12859. (23) Tian, J.; Liu, Q.; Asiri, A.; Sun, X. Self–Supported Nanoporous Cobalt Phosphide Nanowire Aarrays: An Efficient 3D Hydrogen–Evolving Cathode over the Wide Range of pH 0−14. J. Am. Chem. Soc. 2014, 136, 7587–7590.


28

Page 29 of 38 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

ACS Catalysis

(24) Hou, J.; Sun, Y.; Cao, S.; Wu, Y.; Chen, H.; Sun, L. Graphene Dots Embedded Phosphide Nanosheet–Assembled Tubular Arrays for Efficient and Stable Overall Water Splitting. ACS Appl. Mater. Interfaces 2017, 9, 24600–24607. (25) Fang, L.; Li, W.; Guan, Y.; Feng, Y.; Zhang, H.; Wang, S.; Wang, Y. Tuning Unique Peapod-Like Co(SxSe1–x)2 Nanoparticles for Efficient Overall Water Splitting. Adv. Funct. Mater. 2017, 27, 1701008. (26) Xu, R.; Wu, R.; Shi, Y.; Zhang, J.; Zhang, B. Ni3Se2 Nanoforest/Ni Foam as a Hydrophilic, Metallic, and Self–Supported Bifunctional Electrocatalyst for both H2 and O2 Generations. Nano Energy 2016, 24, 103–110. (27) Liu, B.; Zhao, Y.; Peng, H.; Zhang, Z.; Sit, C.; Yuen, M.; Zhang, T.; Lee, C.; Zhang, W. Nickel–Cobalt Diselenide 3D Mesoporous Nanosheet Networks Supported on Ni Foam: An All– pH Highly Efficient Integrated Electrocatalyst for Hydrogen Evolution. Adv. Mater. 2017, 29, 1606521. (28) Li, H.; Wen, P.; Li, Q.; Dun, C.; Xing, J.; Lu, C.; Adhikari, S.; Jiang, L.; Carroll, D.; Geyer, S. Earth–Abundant Iron Diboride (FeB2) Nanoparticles as Highly Active Bifunctional Electrocatalysts for Overall Water Splitting. Adv. Energy Mater. 2017, 7, 1700513 (29) Shifa, T.; Wang, F.; Liu, K.; Xu, K.; Wang, Z.; Zhan, X.; Jiang, C.; He, J. Engineering the Electronic Structure of Two–Dimensional WS2 Nanosheets Using Co Incorporation as CoxW1xS2

for Conspicuously Enhanced Hydrogen Generation. Small 2016, 12, 3802.


29

ACS Catalysis 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

Page 30 of 38

(30) Xue, Z.; Su, H.; Yu, Q.; Zhang, B.; Wang, H.; Li, X.; Chen, J. Janus Co/CoP Nanoparticles as Efficient Mott–Schottky Electrocatalysts for Overall Water Splitting in Wide pH Range. Adv. Energy Mater. 2017, 7, 1602355. (31) Lu, X.; Gu, L.; Wang, J.; Wu, J.; Liao, P.; Li, G. Bimetal–Organic Framework Derived CoFe2O4/C Porous Hybrid Nanorod Arrays as High–Performance Electrocatalysts for Oxygen Evolution Reaction. Adv. Mater. 2017, 29, 1604437. (32) Feng, J.; Ye, S.; Xu, H.; Tong, Y.; Li, G. Design and Synthesis of FeOOH/CeO2 Heterolayered Nanotubes for Oxygen Evolution Reaction. Adv. Mater. 2016, 28, 4698. (33) Liu, W.; Liu, H.; Dang, L.; Zhang, H.; Wu, X.; Yang, B.; Li, Z.; Zhang, X.; Lei, L.; Jin, S. Amorphous Cobalt–Iron Hydroxide Nanosheet Electrocatalyst for Efficient Electrochemical and Photo-Electrochemical Oxygen Evolution. Adv. Funct. Mater. 2017, 27, 1603904. (34) Jin, K.; Park, J.; Lee, J.; Yang, K.; Pradhan, G.; Sim, U.; Jeong, D.; Jang, H.; Park, S.; Kim, D.; Sung, N.; Kim, S.; Han, S.; Nam, K. Hydrated Manganese(II) Phosphate (Mn3(PO4)2·3H2O) as a Water Oxidation Catalyst. J. Am. Chem. Soc. 2014, 136, 7435–7443. (35) Feng, J.; Xu, H.; Dong, Y.; Ye, S.; Tong, Y.; Li, G. FeOOH/Co/FeOOH Hybrid Nanotube Arrays as High–Performance Electrocatalysts for the Oxygen Evolution Reaction. Angew. Chem. Int. Ed. 2016, 55, 3694–3698. (36) 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, 9351–9355.


30

Page 31 of 38 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

ACS Catalysis

(37) Ledendecker, M.; Calderyn, S.; Papp, C.; Steinrük, H.; Antonietti, M.; Shalom, M. The Synthesis of Nanostructured Ni5P4 Films and Their Use as a Non–Noble Bifunctional Electrocatalyst for Full Water Splitting. Angew. Chem. Int. Ed. 2015, 54, 12361–12365. (38) Wang, X.; Li, W.; Xiong, D.; Petrovykh, D.; Liu, L. Bifunctional Catalysts: Bifunctional Nickel Phosphide Nanocatalysts Supported on Carbon Fiber Paper for Highly Efficient and Stable Overall Water Splitting. Adv. Funct. Mater. 2016, 26, 4067. (39) Li, S.; Wang, Y.; Peng, S.; Zhang, L.; Al-Enizi, A.; Zhang, H.; Sun, X.; Zheng, G. Co–Ni Based Nanotubes/nanosheets as Efficient Water Splitting Electrocatalysts. Adv. Energy Mater. 2016, 6, 1501661. (40) Yu, J.; Li, Q.; Li, Y.; Xu, C.; Zhen, L.; Dravid, V.; Wu, J. Ternary Metal Phosphide with Triple-Layered Structure as a Low-Cost and Efficient Electrocatalyst for Bifunctional Water Splitting. Adv. Funct. Mater. 2016, 26, 7644. (41) Yang, Y.; Fei, H.; Ruan, G.; Tour, J. Porous Co–Based Thin Film as a Bifunctional Catalyst for Hydrogen Generation and Oxygen Generation. Adv. Mater. 2015, 27, 3175. (42) Hou, Y.; Lohe, M.; Zhang, J.; Liu, S.; Zhuang, X.; Feng, X. Vertically Oriented Cobalt Selenide/NiFe Layered–Double–Hydroxide Nanosheets Supported on Exfoliated Graphene Foil: An Efficient 3D Electrode for Overall Water Splitting. Energy Environ. Sci. 2016, 9, 478–483. (43) Kuang, M.; Han, P.; Wang, Q.; Li, J.; Zheng, G. CuCo Hybrid Oxides as Bifunctional Electrocatalyst for Efficient Water Splitting. Adv. Funct. Mater. 2016, 26, 8555.


31

ACS Catalysis 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

Page 32 of 38

(44) Sun, Y.; Alimohammadi, F.; Zhang, D.; Guo, G. Enabling Colloidal Synthesis of Edge– Oriented MoS2 with Expanded Interlayer Spacing for Enhanced HER Catalysis. Nano Lett. 2017, 17, 1963–1969. (45) Liu, Y.; Xiao, C.; Lyu, M.; Lin, Y.; Cai, W.; Huang, P.; Tong, W.; Zou, Y.; Xie, Y. Ultrathin Co3S4 Nanosheets that Synergistically Engineer Spin States and Exposed Polyhedra that Promote Water Oxidation under Neutral Conditions. Angew. Chem. Int. Ed. 2015, 54, 11231–11235. (46) Feng, L.; Yu, G.; Wu, Y.; Li, G.; Li, H.; Sun, Y.; Asefa, T.; Chen, W.; Zou, X. High–Index Faceted Ni3S2 Nanosheet Arrays as Highly Active and Ultrastable Electrocatalysts for Water Splitting. J. Am. Chem. Soc. 2015, 137, 14023–14026. (47) Zhao, Y.; Zhou, X.; Ding, Y.; Huang, J.; Zheng, M.; Ye, W. A Photocatalytic, Chemical and Electrocatalytic Water Oxidation Study on ACo2O4 (Ni, Cu, Zn) Samples through Doping Different Metal Ions. J. Catal. 2016, 338, 30–37. (48) Ma, T.; Dai, S.; Jaroniec, M.; Qiao, S. Metal-Organic Framework-Derived Hybrid Co3O4– Carbon Porous Nanowire Arrays as Reversible Oxygen Evolution Electrode. J. Am. Chem. Soc. 2014, 136, 13925–13931. (49) Zhang, J.; Xiao, W.; Xi, P.; Xi, S.; Du, Y.; Gao, D.; Ding, J. Activating and Optimizing Activity of CoS2 for Hydrogen Evolution Reaction through the Synergic Effect of N Dopants and S Vacancies. ACS Energy Lett. 2017, 2, 1022–1028.


32

Page 33 of 38 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

ACS Catalysis

(50) Duan, J.; Chen, S.; Chambers, B.; Andersson, G.; Qiao, S. Theree–Dimensional WS2 Nanolayers@Heteroatoms–Doped Graphene File as Hydrogen Evolution Catalyst Electrodes. Adv. Mater. 2015, 27, 4234. (51) Miao, J.; Xiao, F.; Yang, H.; Khoo, S.; Chen, J.; Fan, Z.; Hsu, Y.; Chen, H.; Zhang, H.; Liu, B. Hierarchical Ni–Mo–S Nanosheets on Carbon Fiber Cloth: A Flexible Electrode for Efficient Hydrogen Generation in Neutral Electrolyte. Sci. Adv. 2015, 1, e1500259. (52) Li, Y.; Wang, H.; Xie, L.; Liang, Y.; Hong, G.; Dai, H. MoS2 Nanoparticles Grown on Graphene: An Advanced Catalyst for the Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2011, 133, 7296–7299. (53) Gao, M.; Liang, J.; Zheng, Y.; Xu, Y.; Jiang, J.; Gao, Q.; Li, J.; Yu, S. An Efficient Molybdenum Disulfide/Cobalt Diselenide Hybrid Catalyst for Electrochemical Hydrogen Generation. Nat. Commun. 2015, 6, 5982. (54) Cai, P.; Huang, J.; Chen, J.; Wen, Z. Oxygen–Incorporated Amorphous Cobalt Sulfide Porous Nanocubes as High–Activity Electrocatalysts for the Oxygen Evolution Reaction in an Alkaline/Neutral Medium. Angew. Chem. Int. Ed. 2017, 56, 4858–4861. (55) Hao, J.; Yang, W.; Peng, Z.; Zhang, C.; Huang, Z.; Shi, W. A Nitrogen Doping Method for CoS2 Electrocatalysts with Enhanced Water Oxidation Performance. ACS Catal. 2017, 7, 4214– 4220.


33

ACS Catalysis 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

Page 34 of 38

(56) Yoon, T.; Kim, K. One–Step Synthesis of CoS–Doped β–Co(OH)2@Amorphous MoS2+x Hybrid Catalyst Grown on Nickel Foam for High–Performance Electrochemical Overall Water Splitting. Adv. Funct. Mater. 2016, 26, 7386. (57) Zhu, H.; Zhang, J.; Yanzhang, R.; Du, M.; Wang, Q.; Gao, G.; Wu, J.; Wu, G.; Zhang, M.; Liu, B.; Yao, J.; Zhang, X. When Cubic Cobalt Sulfide Meets Layered Molybdenum Disulfide: A Core–Shell System Toward Synergetic Electrocatalytic Water Splitting. Adv. Mater. 2015, 27, 4752. (58) Sivanantham, A.; Ganesan, P.; Shanmugam, S. Hierarchical NiCo2S4 Nanowire Arrays Supported on Ni Foam: An Efficient and Durable Bifunctional Electrocatalyst for Oxygen and Hydrogen Evolution Reactions. Adv. Funct. Mater. 2016, 26, 4661. (59) Zhang, J.; Wang, T.; Pohl, D.; Rellinghaus, B.; Dong, R.; Liu, S.; Zhuang, X.; Feng, X. Interface Engineering of MoS2/Ni3S2 Heterostructures for Highly Enhanced Electrochemical Overall−Water−Splitting Activity. Angew. Chem. Int. Ed. 2016, 55, 6702–6707. (60) Yang, Y.; Zhang, K.; Lin, H.; Li, X.; Chan, H.; Yang, L.; Gao, Q. MoS2−Ni3S2 Heteronanorods as Efficient and Stable Bifunctional Electrocatalysts for Overall Water Splitting. ACS Catal. 2017, 7, 2357–2366. (61) Lee, U.; Joo, H.; Kwon, J. Tetraammonium Hexahydrogen Hexamolybdonickelate(II) Tetrahydrate, (NH4)4[H6NiMo6O24]·4H2O. Acta Cryst. 2002, E58, i6–i8.


34

Page 35 of 38 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

ACS Catalysis

(62) Martin, C.; Lamonier, C.; Fournier, M.; Mentre, O.; Harle, V.; Guillaume, D.; Payen, E. Preparation and Characterization of 6−Molybdocobaltate and 6−Molybdoaluminate Cobalt Salts. Evidence of a New Heteropolymolybdate Structure. Inorg. Chem. 2004, 43, 4636–4644. (63) Cabelloa, C.; Botto, I.; Thomas, H. Anderson Type Heteropolyoxomolybdates in Catalysis: 1. (NH4)3[CoMo6O24H6]·7H2O/g−Al2O3 as Alternative of Co−Mo/g−Al2O3 Hydrotreating Catalysts. Appl. Catal. A Gen. 2000, 197, 79–86. (64) Botto, I.; Garcia, A.; Thomas, H. Spectroscopical Approach to Some Heteropolymolybdates with the Anderson Structure. J. Phys. Chem. Solids 1992, 53, 1075–1080. (65) Massey, A.; Gusain, R.; Kumari, S.; Khatri, O. Hierarchical Microspheres of MoS2 Nanosheets: Efficient and Regenerative Adsorbent for Removal of Water−Soluble Dyes. Ind. Eng. Chem. Res. 2016, 55, 7124–7131. (66) Xie, J.; Zhang, J.; Li, S.; Grote, F.; Zhang, X.; Zhang, H.; Wang, R.; Lei, Y.; Pan, B.; Xie, Y. Controllable Disorder Engineering in Oxygen−Incorporated MoS2 Ultrathin Nanosheets for Efficient Hydrogen Evolution. J. Am. Chem. Soc. 2013, 135, 17881–17888. (67) Tang, C.; Titirici, M.; Zhang, Q. A Review of Nanocarbons in Energy Electrocatalysis: Multifunctional Substrates and Highly Active Sites. J. Energy Chem. 2017, 26, 1077–1093. (68) Sun, X.; Huo, J.; Yang, Y.; Xu, L.; Wang, S. The Co3O4 Nanosheet Array as Support for MoS2 as Highly Efficient Electrocatalysts for Hydrogen Evolution Reaction. J. Energy Chem. 2017, 26, 1136–1139.


35

ACS Catalysis 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

Page 36 of 38

(69) He, Y.; Xu, J.; Wang, F.; Zhao, X.; Yin, G.; Mao, Q.; Huang, Y.; Zhang, Tao. In-Situ Carbonization Approach for the Binder-Free Ir-Dispersed Ordered Mesoporous Carbon Hydrogen Evolution Electrode. J. Energy Chem. 2017, 26, 1140–1146. (70) Zhou, Z.; Mahmood, N.; Zhang, Y.; Pan, L.; Wang, L.; Zhang, X.; Zou, J. CoP Nanoparticles Embedded in P and N Co-doped Carbon as Efficient Bifunctional Electrocatalyst for Water Splitting. J. Energy Chem. 2017, 26, 1223–1230. (71) Keng, P.; Kim, B.; Shim, I.; Sahoo, R.; Veneman, P.; Armstrong, N.; Yoo, H.; Pemberton, J.; Bull, M.; Griebel, J.; Ratcliff, E.; Nebesny, K.; Pyun, J. Colloidal Polymerization of Polymer−Coated Ferromagnetic Nanoparticles into Cobalt Oxide Nanowires. ACS Nano 2009, 3, 3143–3157. (72) Wang, H.; Tang, C.; Wang, B.; Li, B.; Zhang, Q. Bifunctional Transition Metal Hydroxysulfides: Room−Temperature Sulfurization and Their Applications in Zn−Air Batteries. Adv. Mater. 2017, 29, 1702327. (73) Hou, J.; Sun, Y.; Wu, Y.; Cao, S.; Sun, L. Promoting Active Sites in Core–Shell Nanowire Array as Mott–Schottky Electrocatalysts for Efficient and Stable Overall Water Splitting. Adv. Funct. Mater. 2018, 28, 1704447. (74) Yang, J.; Zhu, G.; Liu, Y.; Xia, J.; Ji, Z.; Shen, X.; Wu, S. Fe3O4–Decorated Co9S8 Nanoparticles In Situ Grown on Reduced Graphene Oxide: A New and Efficient Electrocatalyst for Oxygen Evolution Reaction. Adv. Funct. Mater. 2016, 26, 4712.


36

Page 37 of 38 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

ACS Catalysis

(75) Yin, J.; Li, Y.; Lv, F.; Lu, M.; Sun, K.; Wang, W.; Wang, L.; Cheng, F.; Li, Y.; Xi, P.; Guo, S. Oxygen Vacancies Dominated NiS2/CoS2 Interface Porous Nanowires for Portable Zn–Air Batteries Driven Water Splitting Devices. Adv. Mater. 2017, 29, 1704681.


37

ACS Catalysis 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

Page 38 of 38

TOC graphic

Vertically aligned oxygenated–CoS2–MoS2 heteronanosheets with oxygen-vacancies grown on carbon fiber cloth have been produced by Anderson–type (NH4)4[Co(Ⅱ)Mo6O24H6]·6H2O polyoxometalates. The oxygenated–CoS2–MoS2 arrays for overall water splitting deliver a current density of 10 mA cm−2 at 1.6 V due to regulation component, the exposure of active heterointerfaces, and the facilitated charge transport, accomplishing the enhanced electrocatalytic performance.


Vertically Aligned OxygenatedâCoS2âMoS2 ... - ACS Publications

Recommend Documents

Vertically Aligned OxygenatedâCoS2âMoS2 ... - ACS Publications