Carbon-Encapsulated Copper Sulfide Leading to Enhanced

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Cite This: ACS Appl. Mater. Interfaces 2019, 11, 22457−22463

Carbon-Encapsulated Copper Sulfide Leading to Enhanced Thermoelectric Properties Xinqi Chen,†,‡,# Hui Zhang,†,# Yuye Zhao,† Wei-Di Liu,§ Wei Dai,‡ Tian Wu,‡ Xiaofang Lu,† Cao Wu,† Wei Luo,† Yuchi Fan,† Lianjun Wang,*,† Wan Jiang,*,† Zhi-Gang Chen,§,∥ and Jianping Yang*,†

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†

State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, P.R. China ‡ School of Physics and Mechanical & Electrical Engineering, Hubei University of Education, Wuhan 430205, P.R. China § Materials Engineering, The University of Queensland, Brisbane, Queensland 4072, Australia ∥ Centre for Future Materials, University of Southern Queensland, Springfield, Queensland 4300, Australia S Supporting Information *

ABSTRACT: Copper sulfide has been regarded as a promising thermoelectric material with relatively high thermoelectric performance and abundant resource. Large-scale synthesis and low-cost production of high-performance thermoelectric materials are keys to widespread application of thermoelectric technology. Here, Cu2−xS particles encapsulated in a thin carbon shell are fabricated by a scalable wet chemical method (19.7 g/batch). The synthesized particles go through the crystal-phase transition from orthorhombic to tetragonal during high-temperature annealing and sintering. After the phase transition, electrical conductivity of this composite (Cu2−xS@C) increases by approximately 50% compared to that of the pure Cu2−xS sample, and can be attibuted to an increase in carrier concentration. Phonon scattering interface formation and superionic phase of Cu2−xS@C results in very low lattice thermal conductivity of 0.22 W m−1 K−1, and maximum thermoelectric figure of merit (ZT) of 1.04 at 773 K, which is excellent for thermoelectric performance in pure-phase copper sulfide produced via chemical synthesis. This discovery sets the stage for the use of facile wet chemical synthesis methods for large-scale transition-metal chalcogenide thermoelectric material production. KEYWORDS: copper sulfide, thermoelectric properties, wet chemical method, carbon encapsulation, semiconductor

1. INTRODUCTION Thermoelectric technology that is capable of directly and reversibly converting heat into electricity continues to attract the attention of research and industrial sectors.1,2 Current research focuses largely on thermoelectric device efficiency improvement through the optimization of thermoelectric material properties.3,4 The dimensionless thermoelectric figure of merit (ZT) (eq 1) is the key metric used to evaluate the performance of thermoelectric materials: ZT = S2σT/κ

Stoichiometric copper sulfide (Cu2S) has three polymorphic phases: orthorhombic below ∼373 K, hexagonal between ∼373 and ∼700 K, and cubic above ∼700 K. The naturally found copper sulfides have a nonstoichiometric composition of Cu2−xS (0 < x < 1), which becomes apparent during thermal cycling as the presence of multiple mixed phases and broadening of phase transition temperature intervals.17,18 The ideal concept of “phonon-liquid electron-crystal” (PLEC)19 is mimicked by the extraordinarily low thermal conductivity (κ) and high thermoelectric performance (ZT) in the superionic phase of Cu2−xS.20,21 Additionally, composition tuning is an effective strategy to enhance the thermoelectric performance of Cu2−xS.8,22 For example, Na-doped Cu9S5 bulk sample exhibits a significantly reduced thermal conductivity and reaches a ZT value of 1.1 at 773 K.23 Further to the doping of the transitionmetal sites, introduction of carbon nanotubes (CNTs) or graphene into the copper chalcogenide thermoelectric material bulk has achieved significant enhancement of ZT.24−27 Threedimensional graphene heterointerface into the Cu2−xS matrix

(1)

where S is Seebeck coefficient, σ is electrical conductivity, κ is thermal conductivity, and T is absolute temperature.5,6 Traditional thermoelectric materials such as bismuth telluride and lead chalcogenides perform well only in narrow working temperature regions.7−9 Considering the scarceness of tellurium and the toxicity of lead, attention from the scientific community had shifted to Te- and Pb-free thermoelectric compounds.10 Among them, metal chalcogenides, copper chalcogenides, in particular, stand out as the most costeffective and eco-friendly thermoelectric materials with high conversion efficiency.11−16 © 2019 American Chemical Society

Received: April 9, 2019 Accepted: June 3, 2019 Published: June 3, 2019 22457

DOI: 10.1021/acsami.9b06212 ACS Appl. Mater. Interfaces 2019, 11, 22457−22463

Research Article

ACS Applied Materials & Interfaces

Figure 1. Schematic illustration of the carbon-encapsulated copper sulfide (Cu2−xS@C) composite synthesis process. washed with distilled water and ethanol several times, and dried at 60 °C in a convection oven. 2.3. Synthesis of Cu2−xS@C. The Cu2−xS particles were dispersed into glucose in ethanol solution (the ratio of C in Cu2−xS@glucose is 0.25, 0.50, and 0.75 wt %) using ultrasonic agitation for 10 min followed by stirring for 2 h. Then the mixture was placed on a hot plate at 60 °C with stirring until full solvent evaporation. Last, the Cu2−xS@glucose mixture was annealed under Ar/H2 atmosphere at 700 °C (10 °C/min) for 2 h to obtain the Cu2−xS@C. 2.4. Characterization. X-ray diffraction (XRD) patterns of all samples were collected using a Rigaku D/Max-2550 PC diffractometer (Tokyo, Japan) equipped with Cu Kα radiation (λ = 1.5406 Å). X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy (Via-Reflex) were used to characterize the chemical composition and crystal structure of the samples. Scanning electron microscopy (SEM) images of all the samples were collected using an Hitachi S4800 (Japan) microscope. Transmission electron microscopy (TEM) images were collected on a JEOL JEM-2100F microscope. 2.5. Thermoelectric Measurements. The Cu2−xS@C powders were loaded into a graphite die with a diameter of 12 mm and sintered into a pellet at 420 °C under 70 MPa for 5 min by the spark plasma sintering (SPS) technique. The resultant pellet was cut into pieces and polished into cuboids (∼2 mm × 3 mm × 10 mm) for electrical property measurements. The electrical conductivity and the Seebeck coefficient were measured simultaneously under a helium atmosphere from room temperature to 500 °C using ZEM-3 tool (ULVAC-RIKO, Japan). For thermal property measurement, the pellet was cut and polished into a disk shape with a diameter of 10 mm and a thickness of 1 mm. The thermal diffusivity was measured by a Netzsch LFA427 (Germany). The thermal conductivity (κ) was calculated using eq 2

has shown the highest reported ZT value of 1.56 at 873 K in the sample with 0.75 wt % graphene.25 The most commonly used synthesis pathways for thermoelectric materials are melting-casting, mechanical alloying, and powder metallurgy methods, which are to some extent energyconsuming and time-consuming.28 A variety of other routes, including colloidal synthesis method, solvothermal and hydrothermal methods, and template-directed synthesis methods, have been developed for the fabrication of copper sulfides in the pure phase form;15,29−31 nevertheless, these approaches are not able to produce large-scale quantities for practical thermoelectric applications. A room-temperature wet chemical method is a promising approach toward a scalable fabrication of transition-metal compounds in solvents.32 However, the chemical method needs to improve the repeatability of thermoelectric properties after sintering, which is the reason that chemical methods are not widely used in the industry at present. Thus, it is still imperative to explore fast and low-cost strategies of copper sulfide thermoelectric material fabrication that are scalable but do not compromise material performance. In this work, Cu2−xS particles are fabricated using an optimized wet chemical method in large batches at room temperature, which is more facile and less costly compared to other chemical synthesis methods. Cu2−xS particles are then encapsulated with carbon shells to produce thermoelectric composites. The electrical conductivity of the thermoelectric composites improves with the incorporation of carbon.33−35 Additionally, the formation of new interface layers in the composite improves energy filtering and phonon scattering. It has been demonstrated that carbon-encapsulated Cu2−xS (Cu2−xS@C) samples have a 50% improvement of the electrical conductivity and power factor. Furthermore, the lattice thermal conductivity of Cu2−xS@C samples below 0.5 W m−1 K−1 is introduced by a phase transition from orthorhombic to tetragonal. Overall, a ZT value of 1.04 has been achieved at 773 K in the 0.25 wt % Cu2−xS@C sample, which proves the strong practical application potential of such composites.

κ = DC pρ0

(2)

where D is the thermal diffusivity, Cp is the heat capacity, and ρ0 is the density of the sample, which was calculated using the geometrical dimensions of the specimen and its mass by eq 3 ρ0 = M1/(M1 − M 2)ρH

(3)

where M1 and M2 are the mass of the sample in the air and in the distilled water, respectively, and ρH is the density of the distilled water (ρH = 1.0 g/cm3). The mass was weighed several times and averaged. Relative densities of all samples are ∼90%. The densities of all samples are closely consistent with each other. Thus, the thermoelectric performance of these samples should be comparable with each other. The heat capacity was determined using a NETZSCH DSC 204F1 Phoenix. Lattice thermal conductivity κL is calculated by eq 4

2. EXPERIMENTAL SECTION 2.1. Chemicals. Copper powder, sulfur powder, sodium hydroxide, and anhydrous ethanol were purchased from Sinopharm Chemical Reagent Co., Ltd. 2-Mercaptoethanol and hydrazine solution (35 wt %) were obtained from Sigma-Aldrich. All chemical reagents were used as received. 2.2. Synthesis of Cu2−xS. In a typical synthesis, copper powder (15.252 g), sulfur powder (7.696 g), 50.4 mL of 2-mercaptoethanol, 4 mL of sodium hydroxide (7 M), and 400 mL of anhydrous ethanol were loaded into a 500 mL flask. After the mixture was allowed to react for 24 h, the resulting black precipitates were separated from the solution. These precipitates were dispersed in 200 mL of hydrazine solution and stirred for 20 min. Then the precipitates were filtered,

κL = κ − κe

(4)

where κ is the total thermal conductivity and κe is the electronic thermal conductivity.36 κe is calculated by eq 5 κe = L0σT

(5)

where L0 is the Lorenz number, σ is the electrical conductivity, and T is the absolute temperature. L0 is taken as 2.0 × 10−8 (V2 K−2).36 The carrier concentration nH = 1/eRH and carrier mobility μH = RH/ρ at room temperature were determined using the Hall measurement system (Lake Shore 8400). The uncertainties of S, σ, D, and Cp 22458

DOI: 10.1021/acsami.9b06212 ACS Appl. Mater. Interfaces 2019, 11, 22457−22463

Research Article

ACS Applied Materials & Interfaces

Figure 2. (a) XRD patterns of Cu2−xS@glucose and annealed Cu2−xS@C composites with varying glucose content Z (Z = 0%, 0.25%, 0.50%, and 0.75%). (b) HRTEM image of an annealed Cu2−xS sample. (c) HRTEM image of Cu2−xS sample before annealing. The insets are the FFT patterns of the respective HRTEM images. (d) Structure diagrams of orthorhombic and tetragonal Cu2S unit cells.

Figure 3. (a) TEM image and (b) HRTEM image of 0.25 wt % Cu2−xS@C sample. The inset in (a) is the SAED pattern typical for Cu2−xS@C samples. The inset in (b) is a FFT patterns of the HRTEM image. (c−e) EDX elemental mapping of Cu, S, and C for typical Cu2−xS@C sample. XPS spectra of 0.25 wt % Cu2−xS@C sample: (f) survey spectrum; (g) Cu 2p spectrum; and (h) S 2p spectrum. measurements were taken as 5%, and uncertainties of S2σ and ZT were subsequently estimated as 10% and 12%.

After 700 °C annealing, all peaks of the Cu2−xS@C samples match the standard peaks of tetragonal Cu1.81S (JCPDS 41959). It is noteworthy that there is a crystal-phase transition from orthorhombic to tetragonal during the high-temperature annealing. A high-resolution transmission electron microscope (HRTEM) imaging technique was employed to confirm the phase transition of Cu2−xS during the annealing. The lattice fringes of annealed Cu2−xS with a spacing of 0.302 nm match well with those of the (115) planes of tetragonal phase (Figure 2b), while the unannealed Cu2−xS displays a spacing of 0.238 nm in lattice fringe of orthorhombic phase (Figure 2c). The fast Fourier transforms (FFT) patterns demonstrate two different crystal structures as well. Structure diagrams of orthorhombic and tetragonal Cu2S unit cells are shown in

3. RESULTS AND DISCUSSION 3.1. Identification of Phase Transition and Carbon Existence in Cu2−xS. Procedures for the fabrication of carbon-encapsulated Cu2−xS structures are illustrated in Figure 1. The X-ray diffraction (XRD) patterns of Cu2−xS@C samples are shown in Figure 2a. The XRD peaks of the Cu2−xS samples with and without glucose match well with standard peaks of orthorhombic Cu2S (JCPDS 2-1294), which is consistent with the orthorhombic phase of stoichiometric Cu2S below about 373 K. The addition of glucose in the Cu2−xS samples has no visible diffraction peaks because of its amorphous structure. 22459

DOI: 10.1021/acsami.9b06212 ACS Appl. Mater. Interfaces 2019, 11, 22457−22463

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ACS Applied Materials & Interfaces

Figure 4. Thermoelectric properties of Z wt % Cu2−xS@C samples (Z = 0, 0.25, 0.50, 0.75) in the temperature range between 300 and 773 K: (a) Electrical conductivity (σ), (b) Seebeck coefficient (S), (c) power factor (S2σ), (d) thermal conductivity (κ), (e) derived lattice thermal conductivity (κL), and (f) figure-of-merit (ZT).

peak from S2− is loaded at 163.6 eV. The ratio of Cu/S in Cu2−xS was calculated to be 1.82. The trace of carbon is further confirmed by Raman results (Figure S5). The disorder-induced D band and the graphite G band centered at 1353 and 1591 cm−1 are detected in the 0.25 wt % Cu2−xS@C sample. 3.2. Exploration of the Carbon Encapsulation Influence on Thermoelectric Properties of Cu2−xS. The high-temperature thermoelectric properties of Cu2−xS@C samples are illustrated in Figure 4. The electrical conductivities of carbon-encapsulated samples are higher than that of the pure Cu2−xS sample from room temperature to 773 K (Figure 4a). The electrical conductivity of Cu2−xS@C sample reaches 2.0 × 104 S m−1, which is 2 times higher than that of the pure Cu2−xS sample at 773 K. Because of their high electrical conductivities, the Seebeck coefficient of Cu2−xS@C samples is lower than that of the pure Cu2−xS sample (Figure 4b). Following the same trend as with the electrical conductivity, the highest power factor (PF = S2σ) of 70 μW m−1 K−2 in Cu2−xS@C sample has been calculated at 773 K (Figure 4c). In the entire experimental temperature range, the values of the total thermal conductivity (κ) of Cu2−xS@C samples are slightly increased, except for the 0.25 wt % Cu2−xS@C sample. This particular sample exhibits κ of 0.48 W m−1 K−1 which is lower than κ of pure Cu2−xS sample at 773 K (Figure 4d). The prominent reduction in lattice thermal conductivity (κL) of the 0.25 wt % Cu2−xS@C sample results in a substantially decreased κ (Figure 4e). The calculated ZT values of all Cu2−xS@C samples are plotted in Figure 4f in which a maximum ZT = 1.04 is achieved in the 0.25 wt % Cu2−xS@C sample at 773 K, which is higher compared to the peak ZT of 0.9 for the pure Cu2−xS sample at the same temperature. To explain the higher electrical conductivity and lower lattice thermal conductivity of Cu2−xS@C samples, the unique carbon encapsulation and tetragonal structure were considered. First, compared to the sample without carbon encapsulation,

Figure 2d. The phase transition is also confirmed by the prominent peak at 373 K in the heat capacity (Cp) of Cu2−xS@ C as measured (Figure S1 in Supporting Information). The stable tetragonal phase in Cu2−xS@C samples was retained after the spark plasma sintering (SPS). The XRD patterns indicate that there is no further phase transition and only the intensity changes for the diffraction peak in the pellet samples after SPS and thermoelectric measurement (Figure S2). Although the transformation from glucose to carbon is difficult to detect in the XRD patterns and the SEM images (Figures S3 and S4), the existence of carbon can be characterized by TEM, XPS, and Raman spectroscopy. With use of the 0.25 wt % Cu2−xS@C sample as an example, the TEM image indicates that the sample was assembled by small particles with irregular shapes encapsulated into a carbon shell, which is consistent with the polycrystalline diffraction patterns (Figure 3a). In Figure 3b, the TEM image clearly displays a boundary between the lattice fringes and an amorphous layer. The lattice fringes with a spacing of 0.32 nm match well with those of the (245) planes of orthorhombic Cu2S. The FFT pattern also confirms its crystal structures. An amorphous layer is recognized as carbon, which is determined by the energydispersive X-ray (EDX) elemental mapping image (Figure 3e). Apart from carbon, the elements of Cu and S throughout the whole sample have homogeneous distribution (Figure 3c,d). The same 0.25 wt % Cu2−xS@C sample was characterized by XPS as well, and Figure 3f−h shows the binding energies of elements in the sample after calibration with the binding energy of O 1s at 532 eV. In general, the binding energy of C 1s is used as a calibration position. When the sample contains carbon, the binding energy of O 1s can be calibrated to avoid errors. The spectra of Cu 2p orbit in Figure 3g presented two peaks corresponding to Cu 2p1/2 and Cu 2p3/2. The binding energy of Cu 2p3/2 can be fitted into two peaks located at 932.9 eV (Cu+, 80.87%) and 934.4 eV (Cu2+, 19.13%). The S 2p 22460

DOI: 10.1021/acsami.9b06212 ACS Appl. Mater. Interfaces 2019, 11, 22457−22463

Research Article

ACS Applied Materials & Interfaces electrical conductivity (σ) for Cu2−xS@C composites exhibit a healthy increase (Figure 4a) because of the increase in carrier concentration. This is mainly attributed to the high charge carrier mobilities of carbon. The carrier concentration (nH) and carrier mobility (μH) of samples measured at room temperature are shown in Figure 5a. The results illustrate that

Second, the special structure of carbon encapsulation shows properties which are not a simple average result of its constituants, as demonstrated here with the significantly reduced thermal conductivity in the Cu2−xS@C sample (Figure 4e). When the added carbon content is 0.25 wt %, κL is reduced to 0.2−0.3 W m−1 K−1 at 500−773 K, which is surprisingly low considering the minimum theoretical κL in Cu2−xS (0.35 W m−1 K−1). The reduction of κL in the Cu2−xS@C composites may be partially rationalized by the fact that the formation of new interface layers in composites have energy filtering and result in strong phonon scattering. Furthermore, the low thermal conductivity of Cu2−xS results from the liquid-like ionic motion of the cubic structure at high temperature.20 A stoichiometric Cu2S has cubic phase above 700 K, while the nonstoichiometric Cu2−xS has some intermediate phases during the temperature increasing process.17 It is important to note that the tetragonal structure is a pseudocubic structure of the symmetrical cubic supercell, which is composed of two cubic structure units in the cdirection (Figure 5c, left side).14,39 Even in the repeated lattice unit, four cubic lattice units and two tetragonal lattice units are the same (Figure 5c, right side). In fact, the reversible tetragonal-cubic phase transition can take place over a small temperature range (less than 1 K) at high temperature.40 In the cubic structure as reported, the sulfur atoms maintain a rigid sublattice; the copper ions are distributed throughout many possible positions, which is indicative of the high degree of disorder and the low threshold for ion motion that is characteristic of liquid-like behavior. The tetrahedral bond could exhibit high mobility in the lattice structure as well as cubical bond.41 The XRD patterns confirm that there was no phase transition in the 0.25 wt % Cu2−xS@C sample after sintering and measurement at high temperature, except for changes in the exposed crystal surface (Figure 5d). Thus, the carbon encapsulation and stable tetragonal structure contribute to the lower lattice thermal conductivity of Cu2−xS@C samples and their enhanced thermoelectric performance. On the basis of the temperature-dependent ZT data, our Cu2−xS@C composites match or outperform other reported copper sulfides and their composites fabricated by other typically used techniques at the same working temperature range. Figure 6 compares the crystal structure and ZT values of our Cu2−xS@C samples to those of the reported copper sulfide and its composites in the 500−800 K temperature range.20,23,25,41−48 The 0.25 wt % Cu2−xS@C composite stands out with the best thermoelectric performance. It is fabricated using a wet chemical method and exhibits a relatively high thermoelectric performance when compared to samples made by melting and ball-milling methods within the same temperature range. This facile wet chemical method for copper sulfides interprets more efforts to necessitate reduction in cost of synthesis in the energy materials.

Figure 5. (a) Temperature dependence of Hall carrier concentration (orange curve) and carrier mobility (blue curve) at room temperature. (b) ZT as a function of Hall carrier concentration at 773 K. Symbols and solid curves are predicted from the single parabolic band model. (c) Crystal structures of cubic and tetragonal Cu2S cell in different angles of view, respectively. (d) XRD patterns of the 0.25 wt % Cu2−xS@C pellet after sintering and thermoelectric measurements.

carbon addition enhances nH rather than μH for Cu2−xS@C composites. The higher nH of Cu2−xS@C samples further leads to increased σ according to eqs 6 and 7. ρ = 1/μne

(6)

S = (k /e)[r − ln(n/N0)]

(7)

where ρ, μ, n, e, S, k, r, and N0 are the electrical resistivity, carrier mobility, carrier concentration, charge of the electron, Seebeck coefficient, Boltzmann’s constant, scattering factor, and Avogadro constant, respectively.28 The rise of nH results in more carrier scattering; thus, the μH appears to slightly decline (the blue curve in Figure 5a).25 In addition, we modeled the electronic properties of samples using a single parabolic band model, which assumes a single type of carrier.37 The model at the highest measured temperature (773 K) was applied to avoid possible phase transition around 700 K in Cu2−xS.20 The nH and μH at 773 K were estimated based on measured nH and σ. The predicted curves of ZT as a function of Hall carrier concentration are shown in Figure 5b. According to Figure 5b and our estimates of the optimum Hall carrier concentrations, the Cu2−xS@C sample has Hall carrier concentration closer to its respective optimum than does the pure Cu2−xS sample, which is why the particular 0.25 wt % Cu2−xS@C sample measured has greater ZT values than those reported for the pure Cu2−xS sample.38

4. CONCLUSIONS In conclusion, carbon-encapsulated Cu2−xS particles (Z wt % Cu2−xS@C, Z = 0, 0.25, 0.50, 0.75) are fabricated by a scalable wet chemical method at room temperature with low cost of production. The powders were sintered by SPS technology and the thermoelectric performance was evaluated from 300 to 773 K. The presence of carbon shell improves ZT values through optimized carrier concentration and increased the electrical conductivity. The low lattice thermal conductivity below 0.4 W m−1 K−1 is attributed to the unique tetragonal structure formed 22461

DOI: 10.1021/acsami.9b06212 ACS Appl. Mater. Interfaces 2019, 11, 22457−22463

Research Article

ACS Applied Materials & Interfaces

the Central Universities. J.P.Y. is grateful for financial support from the Shanghai Pujiang Program (17PJ1400100); the Shanghai Committee of Science and Technology, China (17ZR1401000, 18JC1411200, and 16JC1401800); the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning; State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University. The authors also thank Dr. Tomas Katkus for critical reading of the manuscript.

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Figure 6. Crystal structures and ZT values for the 0.25 wt % Cu2−xS@ C and other reported copper sulfide composite high-temperature data.

after the phase transition and new interface formation in Cu2−xS@C composites. The highest ZT value of 1.04 was achieved at 773 K for the 0.25 wt % Cu2−xS@C sample, which is comparable to the reported Cu2−xS and its composite ZT value at the same temperature. This work demonstrated an easy and straightforward way to prepare carbon-encapsulated Cu2−xS for thermoelectric energy conversion applications.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.9b06212. Temperature dependence of the heat capacity of pellets after SPS; XRD patterns of pellets after SPS; Raman spectra of samples; SEM images of samples (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (L.W.). *E-mail: [email protected] (W.J.). *E-mail: [email protected] (J.Y.). ORCID

Yuchi Fan: 0000-0001-7713-6748 Lianjun Wang: 0000-0003-3709-9801 Zhi-Gang Chen: 0000-0002-9309-7993 Jianping Yang: 0000-0003-1495-270X Author Contributions #

X.Q.C. and H.Z. contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This project was funded by the National Natural Science Foundation of China (51702091, 51702046, 51772050, 51822202, and 51432004); the Innovation Program of Shanghai Municipal Education Commission (2017-01-07-0003-E00025). X.Q.C. gratefully acknowledges the support from the Natural Science Foundation of Hubei Province, China (2017CFB192), China Postdoctoral Science Foundation (2017M621320), and the Fundamental Research Funds for 22462

DOI: 10.1021/acsami.9b06212 ACS Appl. Mater. Interfaces 2019, 11, 22457−22463

Research Article

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DOI: 10.1021/acsami.9b06212 ACS Appl. Mater. Interfaces 2019, 11, 22457−22463