Phase-Controlled 1T Transition-Metal Dichalcogenide-Based Multidimensional Hybrid Nanostructures

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLE1 Nov 2021Phase-Controlled 1T Transition-Metal Dichalcogenide-Based Multidimensional Hybrid Nanostructures Hou-Ming Xu†, Chao Gu†, Xiao-Long Zhang†, Lei Shi, Qiang Gao, Shaojin Hu, Shi-Kui Han, Xiao Zheng, Min-Rui Gao and Shu-Hong Yu Hou-Ming Xu† Key Laboratory of Advanced Catalytic Materials and Reaction Engineering, School of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009 †H.-M. Xu, C. Gu, and X.-L. Zhang contributed equally to this work.Google Scholar More articles by this author , Chao Gu† Hefei National Laboratory for Physical Sciences at the Microscale, Division of Nanomaterials and Chemistry, Department of Chemistry, CAS Centre for Excellence in Nanoscience, Hefei Science Centre of CAS, Hefei Comprehensive National Science Centre, Institute of Energy, University of Science and Technology of China, Hefei 230026 †H.-M. Xu, C. Gu, and X.-L. Zhang contributed equally to this work.Google Scholar More articles by this author , Xiao-Long Zhang† Hefei National Laboratory for Physical Sciences at the Microscale, Division of Nanomaterials and Chemistry, Department of Chemistry, CAS Centre for Excellence in Nanoscience, Hefei Science Centre of CAS, Hefei Comprehensive National Science Centre, Institute of Energy, University of Science and Technology of China, Hefei 230026 †H.-M. Xu, C. Gu, and X.-L. Zhang contributed equally to this work.Google Scholar More articles by this author , Lei Shi Hefei National Laboratory for Physical Sciences at the Microscale, Division of Nanomaterials and Chemistry, Department of Chemistry, CAS Centre for Excellence in Nanoscience, Hefei Science Centre of CAS, Hefei Comprehensive National Science Centre, Institute of Energy, University of Science and Technology of China, Hefei 230026 Google Scholar More articles by this author , Qiang Gao Hefei National Laboratory for Physical Sciences at the Microscale, Division of Nanomaterials and Chemistry, Department of Chemistry, CAS Centre for Excellence in Nanoscience, Hefei Science Centre of CAS, Hefei Comprehensive National Science Centre, Institute of Energy, University of Science and Technology of China, Hefei 230026 Google Scholar More articles by this author , Shaojin Hu Hefei National Laboratory for Physical Sciences at the Microscale, Division of Theoretical and Computational Sciences, CAS Centre for Excellence and Synergetic Innovation Centre in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026 Google Scholar More articles by this author , Shi-Kui Han *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory of Advanced Catalytic Materials and Reaction Engineering, School of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009 Google Scholar More articles by this author , Xiao Zheng Hefei National Laboratory for Physical Sciences at the Microscale, Division of Theoretical and Computational Sciences, CAS Centre for Excellence and Synergetic Innovation Centre in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026 Google Scholar More articles by this author , Min-Rui Gao *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Hefei National Laboratory for Physical Sciences at the Microscale, Division of Nanomaterials and Chemistry, Department of Chemistry, CAS Centre for Excellence in Nanoscience, Hefei Science Centre of CAS, Hefei Comprehensive National Science Centre, Institute of Energy, University of Science and Technology of China, Hefei 230026 Google Scholar More articles by this author and Shu-Hong Yu *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Hefei National Laboratory for Physical Sciences at the Microscale, Division of Nanomaterials and Chemistry, Department of Chemistry, CAS Centre for Excellence in Nanoscience, Hefei Science Centre of CAS, Hefei Comprehensive National Science Centre, Institute of Energy, University of Science and Technology of China, Hefei 230026 Google Scholar More articles by this author https://doi.org/10.31635/ccschem.021.202000578 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Metallic-phase transition-metal dichalcogenides (TMDCs) exhibit unusual physicochemical properties compared with their semiconducting counterparts. However, they are thermodynamically unstable to access and it is even more challenging to construct their metastable-phase heterostructures. Herein, we demonstrate a general solution protocol for phase-controlled synthesis of distorted octahedral 1T WS2-based (1T structure denotes an octahedral coordination for W atom) multidimensional hybrid nanostructures from two-dimensional (2D), one-dimensional (1D), and zero-dimensional (0D) templates. This is realized by tuning the reactivity of tungsten precursor and the interaction between crystal surface and ligands. As a conceptual study on crystal phase- and dimensionality-dependent applications, we find that the three-dimensional (3D) hierarchical architectures achieved, comprising 1T WS2 and 2D Ni3S4, are very active and stable for catalyzing hydrogen evolution. Our results open up a new way to rationally design phase-controlled nanostructures with increased complexity and more elaborate functionalities. Download figure Download PowerPoint Introduction Crystal phase engineering of inorganic materials plays a key role in extending the spectrum of reachable materials and exploring their uncovered physicochemical properties.1–5 In particular, group-VI transition-metal dichalcogenides (TMDCs; the transition metals are Mo and W, and the chalcogens are S, Se, and Te) have been extensively studied due to their unique metallic octahedral or distorted octahedral 1T phases (1T structure denotes an octahedral coordination for W atom).6,7 These 1T TMDCs have been reported to exhibit superior performance for catalytic hydrogen evolution reaction (HER) compared with their corresponding semiconducting prismatic 2H phases (2H structure denotes a prismatic coordination for W atom), owing to the dramatically reduced charge-transfer resistance and increased active sites of the basal plane.8,9 Previous synthetic approaches mainly focused on solid-state procedures10 or chemical vapor deposition (CVD) growth,11 whereas the direct wet-chemical protocols are quite rare.12–14 The wet-chemical synthesis methods hold promise for scale-up production and provide a versatile ground for chemical functionalization and hybridization with other materials, but the subtle chemistry and reactivity in solution-phase synthesis (e.g., precursor, surfactant, and temperature) are difficult to control.15,16 Until now, it remains a big challenge to synthesize 1T TMDCs-based nanostructures with high-purity crystal phases and well-controlled sizes and morphologies. Precise control over thre composition, spatial distribution of each domain, and interfaces between different components in hybrid nanostructures (HNs) has become the research focus recently, which facilitates advances in synthesis and assembly methodologies, as well as fundamental insights into the structure–property–function relationships.17–21 However, a systematic design of proper synthetic conditions for fabricating HNs with controlled physical parameters remains challenging. For instance, integrating materials of different dimensionalities (e.g., one-dimensional [1D]/two-dimensional [2D],22,23 2D/1D,24 and 2D/2D25 HNs) can generate high surface area and new electron states, but little progress has been made up till now, considering the limitation of materials choice with appropriate compatibility and the difficulty in combination of different growth modes. Moreover, it is even more challenging to construct the metastable-phase heterostructures because of their thermodynamically unstable nature, especially for 1T TMDCs, which easily undergo phase transition to more stable 2H phases under external disturbance.26 Thus, a general synthetic approach with delicate control over crystal phase and dimensionality in HNs is highly desirable, which will provide a controllable platform for exploring novel, optimized, or enhanced properties. Herein, we report a general solution protocol for phase-controlled synthesis of distorted octahedral 1T WS2-based multidimensional HNs from 2D, 1D, and zero-dimensional (0D) Ni3S4 templates (denoted as 1T WS2-2D/1D/0D Ni3S4 HNs), which is realized by tuning the reactivity of the tungsten precursor and the interaction between crystal surface and ligands. By changing the reaction temperature, the corresponding prismatic 2H WS2-based HNs (denoted as 2H WS2-2D/1D/0D Ni3S4 HNs) can also be achieved. This unique toolbox for the synthesis and formation process of monodispersed, uniform, and phase-controlled multidimensional 1T WS2-2D/1D/0D Ni3S4 HNs is demonstrated in Figure 1. As a proof-of-concept application, the crystal phase- and dimensionality-dependent electrocatalysis is demonstrated by evaluating their HER performances. Remarkably, the 1T WS2-2D Ni3S4 HNs exhibit a low overpotential of 109 mV at 10 mA cm−2, and show no evidence of deactivation after long-term operation. Our studies offer new perspectives for designing advanced materials based on crystal phase and dimensionality engineering strategies. Figure 1 | Schematic illustration of the general solution protocol for phase-controlled synthesis of 1T WS2-based multidimensional HNs from 2D, 1D, and 0D Ni3S4 templates. Download figure Download PowerPoint Experimental Methods Materials synthesis Ammonium tetrathiotungstate [(NH4)2WS4] was purchased from Alfa Aesar (Haverhill, MA). 1,2-Hexadecanediol (HDD, 98%) was purchased from Aladdin (Shanghai, China). Nickel(II) acetylacetonate [Ni(acac)2] (95%), oleylamine (OAm, 70%), oleic acid (OA, 90%), 1-octadecene (ODE, 90%), and 1-dodecanethiol (DDT, 98%) were purchased from Sigma-Aldrich (St. Louis, MO). NiCl2·6H2O, acetic acid, hexane, and ethanol were purchased from Sinopharm Chemical Reagent (Shanghai, China). All chemicals were used as received without further purification. In a typical procedure, 35 mg (NH4)2WS4 was added into 10 mL OAm in a 25 mL three-neck flask and heated to 120 °C for 20 min under vacuum. Then the flask was purged with N2, and 25 mg Ni(acac)2 dissolved in 5 mL hot OAm was injected. Then the solution was maintained at 150 °C for 30 min (formation of 2D Ni3S4) and slowly heated to 210 °C for 60 min. The mixture was cooled to room temperature. Finally, the obtained product was collected by centrifugation (8000 rpm, 3 min) and washed several times with hexane and ethanol for further characterization. As for 2H WS2-2D Ni3S4 HNs, the reaction temperature was increased to 310 °C. The 1D Ni3S4 and 0D Ni3S4 were synthesized according to reported methods.27 In a typical procedure for 1T WS2-1D/0D Ni3S4 HNs, 35 mg (NH4)2WS4 and 10 mg as-synthesized 1D/0D Ni3S4 were added into 10 mL OAm in a 25 mL three-neck flask and heated to 120 °C for 20 min under vacuum. Then the solution was slowly heated to 280 °C for 30 min under N2 atmosphere. Finally, the mixture was cooled to room temperature. As for 2H WS2-1D/0D Ni3S4 HNs, the reaction temperature was increased to 340 °C. The 1T and 2H WS2 were synthesized by modification of reported methods.28 In a typical procedure for 1T WS2, 35 mg (NH4)2WS4 was added into 10 mL OAm in a 25 mL three-neck flask and heated to 120 °C for 20 min under vacuum. Then the solution was slowly heated to 280 °C for 30 min under N2 atmosphere. Finally, the mixture was cooled to room temperature. As for 2H WS2, the reaction temperature was increased to 340 °C. Characterizations Powder X-ray diffraction (PXRD) was performed on a SmartLab 9kW (Rigaku, Tokyo, Japan)X-ray diffractometer equipped with graphite monochromaticized Cu Kα radiation (λ = 1.54056 Å). Transmission electron microscopy (TEM) images were employed on HT-7700 (Hitachi, Tokyo, Japan) with an acceleration voltage of 100 kV. High-resolution TEM (HRTEM) images and high-angle annular dark-field scanning TEM (HAADF-STEM) images were carried out on JEM-ARM 200F (JEOL, Tokyo, Japan). STEM energy-dispersive X-ray spectroscopy (STEM-EDS) analysis were conducted on Talos F200X (FEI, Hillsboro, OR). X-ray photoelectron spectra (XPS) were recorded on an ESCALab 250Xi (Thermo Scientific, Waltham, MA) X-ray photoelectron spectrometer using Al Kα radiation exciting source. Raman scattering spectra were recorded with a LabRAM HR Evolution (HORIBA Jobin Yvon, Paris, France) spectrometer using the 532 nm line. Fourier transform infrared (FT-IR) spectra were measured on a Nicolet 6700 (Thermo Nicolet, Wisconsin) FT-IR spectrometer. Optical absorption spectra were measured at room temperature using a DUV-3700 UV–vis–near-infrared (NIR) spectrometer (Shimadzu, Kyoto, Japan). Electrocatalytic measurements Electrochemical measurements were performed at room temperature using a rotating disk working electrode made of glassy carbon (GC) (PINE, 5 mm diameter, 0.196 cm2) connected to a Multipotentiostat (IMPex, ZAHNER-Elektrik, Germany). Graphite rod and Ag/AgCl (3.5 M KCl) were used as counter and reference electrodes, respectively. All reported potentials were converted to the reversible hydrogen electrode (RHE) through RHE calibration in 1 M KOH, E(RHE) = E(Ag/AgCl) + 1.03 V. The preparation method of the working electrodes containing various catalysts can be found as follows. In short, 5 mg of catalyst powder was dispersed in 1 mL of ethanol with 20 μL of Nafion solution (5 wt %; Sigma-Aldrich). Then the mixture was ultrasonicated for ∼30 min to generate a homogeneous ink. Next, 8 µL of the dispersion was transferred onto the GC disk. Finally, the as-prepared catalyst film was dried at room temperature. For comparison, a bare GC electrode that had been polished and cleaned was also dried for electrochemical measurement. Before electrochemical measurements, the electrolyte (1 M KOH) was bubbled with pure Ar for at least 30 min. The polarization curves were obtained by sweeping the potential from −0.8 to 0.2 V versus RHE at room temperature and 1600 rpm with a sweep rate of 5 mV s−1. All polarization curves arising from the solution resistance were iR-corrected. The electrochemical impedance spectroscopy (EIS) measurement was performed in the same configuration at 250 mV overpotential over a frequency range from 100 kHz to 100 mHz at the amplitude of the sinusoidal voltage of 5 mV. Cyclic voltammograms performed at different sweep rates used to estimate the double-layer capacitance (Cdl) were recorded in the potential region of 0.1–0.2 V versus RHE at room temperature. For the stability evaluation, electrode potential was cycled from −0.3 to 0.2 V versus RHE with a sweep rate of 100 mV s−1. At the end of the cycling experiment, the polarization curve was obtained with a sweep rate of 5 mV s−1. Chronoamperometry data were collected on various catalyst-coated carbon fiber papers (1 cm2, catalyst loading: 1 mg) at 250 mV overpotential. The polarization curves were replotted as η (η) versus log current (log j) to get Tafel plots. By fitting the linear portion of the Tafel plots to the Tafel equation (η = b log (j) + a), the Tafel slope (b) can be obtained. Density functional theory calculations We performed the density functional theory (DFT) calculations using the Vienna ab initio simulation package (VASP)29,30 program with the projector augmented wave (PAW)31,32 method. The Perdew–Burke–Ernzerhof (PBE)33 generalized gradient approximation (GGA) exchange–correlation functional was used throughout. A 500 eV plane-wave kinetic energy cutoff was chosen, and a 4 × 2 × 1 Monhorst–Pack k-point sampling was adopted for the structure relaxation. The convergence criterion for the electronic self-consistent iteration was set to be 10–4 eV. A residual force threshold of 0.02 eV Å−1 was set for geometry optimizations. The calculations were conducted on (0 0 1) surface of 1T and 2H WS2, and (0 1 1) surface of Ni3S4 slab models. A vacuum layer 15 Å thick was used to ensure the separation between slabs. The key reaction steps in alkaline HER: (1) H 2 O + e − + * → * H + OH − (Volmer step) (2) 2 * H → H 2 (Tafel step) (3) * H + H 2 O + e − → * + O H − + H 2 (Heyrovsky step) Here, * denotes the corresponding surface models. The free energy for steps (1) and (3) should be the same at the equilibrium potential of HER. Under this assumption, one can avoid computation of the exact free energy of OH− in solutions by using computational hydrogen electrodes.34 Herein, four main stages are considered: initial state, activated water adsorption, H* intermediates formation, and H2 desorption.35 The free energies are calculated as: G 0 = G ( * ) + G ( H 2 O ) G 1 = G ( * H − OH ) G 2 = G ( * H ) + G ( OH − ) G 3 = G ( * ) + 1 / 2 G ( H 2 ) + G ( OH − ) And G 0 = G 3 The Gibbs free energy changes are calculated as follows: Δ G 1 = G 1 − G 0 Δ G 2 = G 2 − G 1 Δ G 3 = G 3 − G 2 The free energy was calculated using the equation: G = E + E ZPE − T S Here, E, EZPE, T, and S are the total energy from DFT calculations, zero-point energy (ZPE), temperature (298 K), and the entropy, respectively. ZPE values are calculated from the frequency calculations. The entropic contributions from H2 and H2O molecules are taken from Chemical Rubber Company Press (CRC) Handbook. Results and Discussion Preparation and structural analyses of 1T WS2-2D Ni3S4 HNs We achieved the vertical growth of distorted octahedral 1T WS2 nanosheets on 2D Ni3S4 nanoplates (denoted as 1T WS2-2D Ni3S4 HNs) through successive thermolysis of Ni(acac)2 and (NH4)2WS4 metal precursors in OAm solution at 210 °C for 1 h. Simply increasing the reaction temperature to 310 °C leads to the formation of corresponding prismatic 2H WS2-based counterparts (denoted as 2H WS2-2D Ni3S4 HNs) (see Experimental Methods for details). This is caused by the different reactivity of the precursor and the interaction between crystal surface and ligands: a lower temperature benefits the deactivation of (NH4)2WS4, giving rise to the metastable 1T phase.12 Moreover, 1T-WS2 consists of negatively charged WS2− surfaces that stabilized by positively charged oleylammonium ligands, hence a lower temperature could strengthen their coordination effect, and consequently the stability.36 The low- and high-magnified transmission electron microscopy (TEM) images (Figures 2a and 2b) show uniform 2D/2D hierarchical architectures with the branch length of ∼40 nm, as well as the plate length and thickness of ∼60 and ∼8 nm respectively, inherited well from the original templates ( Supporting Information Figure S1). High-resolution TEM (HRTEM) images (Figures 2c and 2d) taken from the white solid squares (1 and 2 in Figure 2b) confirm the structural relationship of the interfaces between two distinct components, indicating the formation of crystalline polydymite Ni3S4 with resolved lattice fringes of (111) and (113) planes on lateral and basal sides, respectively. This analysis agrees with the X-ray diffraction (XRD) patterns ( Supporting Information Figure S2), in which cubic Ni3S4 with spinel structure (JCPDS no. 43-1469) can be observed.37 However, diffraction peaks from WS2 are relatively weak, probably owing to its ultrathin nature (white dotted lines and dotted circles in Figures 2c and 2d). Note that the main peak in the 32° region was observed to shift toward lower angles by ∼1.2°, indicating the formation of the unusual distorted octahedral 1T phase,13 which agrees with the XRD results of the as-synthesized 1T and 2H WS2 nanosheets ( Supporting Information Figure S3). HR-HAADF-STEM images (Figures 2e and 2f) exhibit typical 1T WS2 on Ni3S4 template in achieved 1T WS2-2D Ni3S4 HNs according to their zigzag chains of W atoms. By contrast, the 2H WS2-2D Ni3S4 HNs show typical 2H WS2 with hexagonal packing crystal structures. Moreover, the corresponding intensity profile analysis (Figure 2g) along the white solid rectangles (3 and 4 in Figures 2e and 2f) reveals the spatial location of W and S atoms, further confirming the formation of 1T and 2H phases.38 These results also match well with the HR-HAADF-STEM analysis of the as-synthesized 1T and 2H WS2 nanosheets ( Supporting Information Figure S4). STEM-EDS elemental mapping images (Figure 2h) of a typical 1T WS2-2D Ni3S4 HN show W-rich branches and Ni-rich plates with S enrichment in the whole structure. By comparison, the 2H WS2-2D Ni3S4 HNs show almost the same size, morphology, crystal phases of Ni3S4, and the distribution of Ni, S, and W elements ( Supporting Information Figure S5). Together, these results support that we have succeeded in phase-controllable synthesizing the new, uniform, and high-purity 1T/2H WS2-2D Ni3S4 HNs. Figure 2 | (a) Low- and (b) high-magnified TEM images of 1T WS2-2D Ni3S4 HNs. (c) Side and (d) top view HRTEM images of the white solid squares 1 and 2 in (b). (e and f) HR-HAADF-STEM images of interfaces between WS2 and Ni3S4 of 1T/2H WS2-2D Ni3S4 HNs, respectively. Inset: crystal models of 1T/2H WS2. Color scheme: W, blue; S yellow. (g) Corresponding intensity profile along the white solid rectangles 3 and 4 in (e and f), respectively. (h) STEM-EDS elemental mapping images of a typical 1T WS2-2D Ni3S4 HN, showing the distribution of Ni (green), S (yellow), and W (red). Download figure Download PowerPoint Preparation and structural analyses of 1T WS2-1D/0D Ni3S4 HNs We also achieved the growth of 1T WS2 nanosheets on 1D Ni3S4 nanorods and 0D Ni3S4 nanoparticles (denoted as 1T WS2-1D/0D Ni3S4 HNs) by gradual thermolysis of (NH4)2WS4 in OAm solution comprising the presynthesized 1D or 0D Ni3S4 templates ( Supporting Information Figures S6 and S7) at 280 °C for 30 min. Similarly, increasing the reaction temperature to 340 °C leads to the formation of corresponding 2H WS2-based counterparts (denoted as 2H WS2-1D/0D Ni3S4 HNs) (see Experimental Methods for details). TEM ( Supporting Information Figure S8) and HAADF-STEM images (Figures 3a and 3b) of 1T WS2-1D/0D Ni3S4 HNs show that the length and diameter of the nanorods were ∼40 and ∼10 nm, respectively, and the average length of the nanoparticles was ∼15 nm. HRTEM images demonstrate good crystallinity of a typical polydymite Ni3S4 nanorod and nanoparticle, with resolved lattice fringes of (113) and (022) planes, respectively. The white dotted circles suggest the ultrathin 1T WS2 interfaced with the Ni3S4 component (insets in Figures 3a and 3b). XRD patterns further confirm the diffraction peaks are indexed to the same cubic spinel-structured Ni3S4 (JCPDS no. 43-1469). But the almost negligible diffraction peaks from WS2 in the 32° region result from its low degree of crystallinity ( Supporting Information Figure S9). HR-HAADF-STEM images (Figures 3c and 3d) of 1T WS2-1D/0D Ni3S4 HNs exhibit 1T WS2 on both 1D and 0D Ni3S4 templates with zigzag-chained W atom arrangement, whereas 2H WS2-1D/0D Ni3S4 HNs display obvious 2H WS2 with uniform crystal structures of hexagonal packing ( Supporting Information Figure S10). Furthermore, the corresponding intensity profile analysis (Figure 3e) along the white solid rectangles (1 and 2 in Figures 3c and 3d) demonstrates the spatial location of W and S atoms, confirming the formation of 1T and 2H phases. STEM-EDS elemental mapping images (Figures 3f and 3g) of 1T WS2-1D/0D Ni3S4 HNs show W-rich layers and Ni-rich rods/particles with S enrichment in the whole structure. By comparison, the 2H WS2-1D/0D Ni3S4 HNs also show almost the same size, morphology, crystal phases of Ni3S4, and distribution of Ni, S, and W elements ( Supporting Information Figures S11–S13). Figure 3 | (a and b) HAADF-STEM images of 1T WS2-1D/0D Ni3S4 HNs, respectively. Inset: HRTEM images of typical 1T WS2-1D/0D Ni3S4 HNs, respectively. White dotted circles suggest the interfaces between 1T WS2 and Ni3S4. (c and d) HR-HAADF-STEM images of 1T WS2-1D/0D Ni3S4 HNs, respectively. Inset: crystal models of 1T WS2. Color scheme: W, blue; S, yellow. (e) Corresponding intensity profile along the white solid rectangles 1 and 2 in (c and d), respectively. (f and g) STEM-EDS elemental mapping images of typical 1T WS2-1D/0D Ni3S4 HNs, showing the distribution of Ni (green), S (yellow), and W (red). Download figure Download PowerPoint Formation mechanism To gain an insight into the formation mechanism of the 1T WS2-2D Ni3S4 HNs, a series of control experiments were performed. The ratio of precursors greatly affects their final morphologies ( Supporting Information Figures S14 and S15). The nucleation and growth of 1T WS2 are controlled through reaction temperature and time. The reaction between 150 and 180 °C quickly enables the Ni precursors to be confined in the soft organic–inorganic intermediates of OAm and tungsten precursors, giving rise to uniform 2D platforms for subsequent growth.39 Increasing reaction temperature to 210 °C leads to the formation and vertical growth of high-density starting nuclei into sheet-like structures via consumption of the tungsten precursors on preformed templates, which yields uniform three-dimensional (3D) hierarchical architectures composed of 2D 1T WS2 nanosheets and 2D Ni3S4 nanoplates ( Supporting Information Figure S16), similar to the previous reported 1T MoS2-2D NiS2 structures.40 As for 1T WS2-1D Ni3S4 HNs, the reaction between 220 and 250 °C indicates no sign for the formation of ultrathin sheet-like structures on surfaces of preformed templates. After the reaction temperature is increased to 280 °C, the formation and growth of starting nuclei into sheet-like structures were observed, which yielded uniform ultrathin curled layers composed of 2D 1T WS2 nanosheets and 1D Ni3S4 nanorods ( Supporting Information Figure S17). Crystal structures and characterization of 1T/2H WS2-2D Ni3S4 HNs Figure 4a illustrates the side (up) and top (bottom) views of the atomic crystal structures of 1T/2H WS2-Ni3S4 slab models, where the symmetry differences between the distorted octahedral coordinated 1T WS2 and the prismatic coordinated 2H WS2 (red dotted circles) can be clearly observed. We used XPS to study the chemical states of the 1T/2H WS2-2D Ni3S4 HNs. As shown in Figure 4b, W 4f peaks of 1T WS2-2D Ni3S4 HNs were located at 32 eV (4f7/2) and 34.1 eV (4f5/2), which both show a shift of ∼0.9 eV to lower binding energy compared with the 2H WS2-2D Ni3S4 HNs. This binding energy shift could be originated from the change in the metal coordination and the slightly increased W–S bond length. Meanwhile, the minor fractions of the 2H phase (32.7 and 34.8 eV) and traces of oxidized tungsten (35.6 and 37.8 eV) exist. We attributed this to the H2O generated from the condensation of OAm reacting with (NH4)2WS4, which might oxidize 1T WS2 or even damage the metastable 1T phase structure. Figure 4c shows that S 2p peaks of 1T WS2-2D Ni3S4 HNs were located at 161.4 (2p3/2) and 162.6 eV (2p1/2), which both show a shift of ∼1 eV to lower binding energy compared with the 2H WS2-2D Ni3S4 HNs. These W 4f and S 2p results are consistent with the XPS analysis for pure 1T and 2H WS2 ( Supporting Information Figure S18). Moreover, the binding energy of Ni 2p peaks (Figure 4d) for 1T WS2-2D Ni3S4 HNs markedly increases by ∼0.7 eV versus the 2H WS2-2D Ni3S4 HNs. This chemical shift observed for Ni 2p peaks is remarkable, which is probably due to strong charge transfer from Ni3S4 to 1T WS2 at the nanoscale interfaces.41 Figure 4 | (a) Side and top view atomic crystal structures of typical 1T/2H WS2-Ni3S4 slab models. Inset: Red dotted circles suggest the coordination environment of single W atom in 1T/2H WS2 structures, respectively. (b) W 4f, (c) S 2p, and (d) Ni 2p XPS spectra of 1T WS2-2D Ni3S4 (top) and 2H WS2-2D Ni3S4 (bottom) HNs. Doublets of (b and c) corresponding to 1T WS2 are given in blue, 2H WS2 in green, and oxidized tungsten in pink. Doublets of (d) corresponding to Ni2+ of 1T WS2-2D Ni3S4 HNs are given in blue, Ni2+ of 2H WS2-2D Ni3S4 HNs in green; dark cyan and purple doublets are assigned to Ni3+ and concomitant shakeup satellites. (e) Raman and (f) UV–vis absorption spectra of 1T/2H WS2-2D Ni3S4 HNs, respectively. Download figure Download PowerPoint Raman spectrum of 1T WS2-2D Ni3S4 HNs shows a clearly distinct set of vibration m