Synthesis and Properties of 2D Carbon—Graphdiyne

Article Cite This: Acc. Chem. Res. 2017, 50, 2470-2478

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Synthesis and Properties of 2D CarbonGraphdiyne Zhiyu Jia,† Yongjun Li,†,‡ Zicheng Zuo,† Huibiao Liu,*,†,‡ Changshui Huang,§ and Yuliang Li*,†,‡ †

Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Organic Solids, Institute of Chemistry, CAS Research/Education Center for Excellence in Molecular Sciences, Chinese Academy of Sciences, Beijing 100190, P. R. China ‡ School of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China § Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, No. 189 Songling Road, Qingdao 266101, P. R. China CONSPECTUS: Graphdiyne (GDY) is a flat material comprising sp2- and sphybridized carbon atoms with high degrees of π conjugation that features uniformly distributed pores. It is interesting not only from a structural point of view but also from the perspective of its electronic, chemical, mechanical, and magnetic properties. We have developed an in situ homocoupling reaction of hexaethynylbenzene on Cu foil for the fabrication of large-area ordered films of graphdiyne. These films are uniform and composed of graphdiyne multilayers. The conductivity of graphdiyne films, calculated at 2.52 × 10−4 S m−1, is comparable to that of Si, suggesting excellent semiconducting properties. Through morphologycontrolled syntheses, we have prepared several well-defined graphdiyne structures (e.g., nanotubes, nanowires, and nanowalls) having distinct properties. The graphdiyne nanotube arrays and graphdiyne nanowalls exhibited excellent field emission performance, higher than that of some other semiconductors such as graphite and carbon nanotubes. These structures have several promising applications, for example, as energy storage materials and as anode materials in batteries. The unique atomic arrangement and electronic structure of graphdiyne also inspired us to use it to develop highly efficient catalysts; indeed, its low reduction potential and highly conjugated electronic structure allow graphdiyne to be used as a reducing agent and stabilizer for the electroless deposition of highly dispersed and surfactant-free Pd clusters. GDY-based three-dimensional (3D) nanoarchitectures featuring well-defined porous network structures can function as highly active cathodes for H2 evolution. Heteroatom-doped GDY structures are excellent metal-free electrocatalysts for the oxygen reduction reaction (ORR). Its excellent electrocatalytic activity and inexpensive, convenient, and scalable preparation make GDY a promising candidate for practical and efficient energy applications; indeed, we have explored the application of GDY as a highly efficient lithium storage material and have elucidated the method through which lithium storage occurs in multilayer GDY. Lithium-ion batteries featuring GDY-based electrodes display excellent electrochemical performance, including high specific capacity, outstanding rate performance, and long cycle life. We have also explored the application of GDY in energy conversion and found that it exhibits excellent conductivity. In this Account, we summarize the relationships between the functions of graphdiyne and its well-defined nanostructures. Our results suggest that GDY is a novel 2D carbon material possessing many attractive properties. It can be designed into new nanostructures and materials across a range of compositions, sizes, shapes, and functionalities and can be applied in the fields of electronics, optics, energy, and optoelectronics.

1. INTRODUCTION Full-carbon materials have developed rapidly in the past two decades at the frontier of synthetic organic chemistry. Many researchers are now paying attention to carbon allotropes having unusual structures and electronic and optical properties,1−3 such as two-dimensional (2D) arrays of planar hexagonal units (C 6) of sp2 -hybridized carbon atoms, graphene,4−6 which stirred the development of carbon materials. Complementary to the naturally existing carbon allotropes, novel carbon allotropes comprising sp2- and sphybridized carbon atoms can display more versatility and flexibility.7−9 Diederich and co-workers synthesized various practical (and impractical) structures for 2D and 3D all-carbon networks that differ from those of graphite and diamond.1,10 Cyclo[n]carbons (cyclo-Cn) are n-membered monocyclic rings © 2017 American Chemical Society

of sp-hybridized carbon atoms that display unique electronic structures, resulting from two perpendicular systems of conjugated π orbitals, one in-plane and one out-of-plane.11 Highly strained cyclo-C12 is a potential monomeric precursor to the network named graphyne (GY). Baughman and Eckhardt12 had predicted that GY would have a crystalline-state formation energy much lower than that of any other carbon phase and that it would be a large-band-gap semiconductor (Eg = 1.2 eV) rather than a metal or semimetal. Controlled oligotrimerization of cyclo-C18 or oxidative polymerization of hexaethynylbenzene could lead to the phenylbutadiyne network named graphdiyne (GDY). Haley et al.13 proposed the first preparation of GDY, Received: April 25, 2017 Published: September 15, 2017 2470

DOI: 10.1021/acs.accounts.7b00205 Acc. Chem. Res. 2017, 50, 2470−2478

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Accounts of Chemical Research

Figure 1. (a) Schematic representation of the synthesis of nanoscale GDY films. Adapted with permission from ref 31. Copyright 2015 Elsevier. (b) Photograph and scanning electron microscopy (SEM) image of a large-area GDY film. Adapted with permission from ref 21. Copyright 2015 Springer Nature. (c) Atomic force microscopy (AFM) image and corresponding I−V curve of a GDY film. Adapted with permission from ref 20. Copyright 2010 Royal Society of Chemistry.

Figure 2. (a) SEM image of GDY nanofilms. Adapted with permission from ref 21. Copyright 2015 Springer Nature. (b, c) SEM images of GDY nanowires. Adapted with permission from ref 23. Copyright 2012 Royal Society of Chemistry. (d) SEM image of GDY nanowalls. Adapted from ref 24. Copyright 2015 American Chemical Society. (e) TEM image of GDY nanosheets produced at a liquid−liquid interface and (inset) corresponding SAED pattern and (f) AFM topographic image of GDY nanosheets produced at a gas−liquid interface. Adapted from ref 26. Copyright 2017 American Chemical Society.

the most stable one of the diacetylene-containing sp- and sp2carbon materials.14 The networks of GY and GDY can be considered as the C6 hexagons in graphene interconnected by acetylene linkages, which have a special atomic arrangement and electronic structure.15,16 These flat (sp2- and sp-hybridized) carbon networks have high degrees of π conjugation, uniformly distributed pores, and tunable electronic properties, and they should have tunable or even enhanced performance compared with graphene. They have several potential applications, for example, as energy storage materials, as anode materials in batteries, and in the biology field,17−19 each of which we have already realized experimentally. In this Account, we discuss the properties of large-area ordered films of GDY fabricated from hexaethylbenzene; the preparation of GDY in various morphologies (e.g., nanotubes, nanowires, and nanowalls); and the applications in catalysis, Li storage, solar cells, hole-transporting materials, and fieldemission devices. For the purposes of this Account, our focus

is primarily on the fabrication of large-area single-/oligolayer GDY films and their applications in several fields. We hope not only to highlight the increasing amount of research on nanostructured GDY but also to provide insight into how GDY can be used for the preparation of highly functionalized materials.

2. SELF-ASSEMBLED AGGREGATE NANOSTRUCTURES OF GRAPHDIYNE Although great efforts had been exerted in the preparation of several monomeric and oligomeric structures for the construction of GDY, the fabrication of a novel, stable GDY form of carbon remained elusive for many years. In 2010, GDY was synthesized on a large scale through homocoupling of hexaethynylbenzene on the surface of copper foil in the presence of pyridine (Figure 1).20 The copper serves as both the catalyst and substrate during this process. The flexible films obtained had a thickness of approximately 1 μm and were 2471

DOI: 10.1021/acs.accounts.7b00205 Acc. Chem. Res. 2017, 50, 2470−2478

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Accounts of Chemical Research

Figure 3. (a) Band structures of GDY at the LDA and GW levels. Adapted with permission from ref 27. Copyright 2011 American Physical Society. (b, c) Band structures of (b) bilayer and (c) trilayer graphdiyne. Adapted with permission from ref 28. Copyright 2012 Royal Society of Chemistry. (d) Band structure and density of states (DOS) of a single GDY sheet obtained from DFT calculations; the Brillouin zone is also displayed. Adapted from ref 29. Copyright 2011 American Chemical Society.

Moreover, the gas−liquid interfacial synthesis produced fewlayer graphdiyne of higher quality.26

composed of GDY multilayers. Selected-area electron diffraction (SAED) and X-ray diffraction (XRD) patterns confirmed the high crystallinity of these structures. The current−voltage (I−V) curve of a GDY film exhibited typical Ohmic behavior; it was linear with a slope of 2.53 × 10−3, and the conductivity was calculated as 2.52 × 10−4 S m−1, which is comparable to that of silicon, demonstrating that GDY is an excellent semiconductor. This finding gave us the impetus to examine the functionalization of GDY. GDY films of various thicknesses were synthesized on ZnO nanorod arrays by using a combination of reduction and a self-catalyzed vapor−liquid−solid (VLS) growth process.21 The GDY films exhibited field-effect mobilities as high as 100 cm2 V−1 s−1 (Figure 2a). The preparation of GDY with various well-defined structures and distinct properties has led to significant developments in the applications of these new carbon allotropes. Since the first synthesis of a GDY film, several explorations have been made into other GDY morphologies, including nanotubes,22 nanowires,23 and nanowalls.24 Graphdiyne nanotubes (GDYNTs) had a smooth surface with a diameter of 200 nm and a wall thickness of 40 nm. After annealing, the GDYNT arrays exhibited excellent field emission performance, higher than that of some other semiconductors (e.g., graphite, carbon nanotubes). Graphdiyne nanowires (GDYNWs) having very high quality, defect-free surfaces were constructed through VLS growth upon ZnO nanorod arrays on a silicon slice as a substrate (Figure 2b,c).23 These GDYNWs were excellent semiconductors, with a conductivity of 1.9 × 103 S m−1 and a mobility of 7.1 × 102 cm2 V−1 s−1. Graphdiyne nanowalls synthesized on various substrates also exhibited excellent and stable field-emission (Figure 2d) and photoelectrochemical water-splitting properties.24,25 The original synthesis of graphdiyne involved hazardous solvents and harsh reaction conditions, but the Nishihara group developed a bottom-up method for the synthesis of crystalline graphdiyne nanosheets at a gas−liquid or liquid−liquid interface (Figure 2e,f) that made the preparation of the material more eco-friendly.

3. THEORETICAL CALCULATIONS ON GRAPHDIYNE There have been many theoretical studies about the graphyne family. Here we focus on the electronic band structure of GDY, which is related to the photoelectronic properties. Firstprinciples calculations have indicated that GDY allotropes have a natural band gap, in contrast to the zero band gap of graphene. The existence of a direct band gap facilitates the application of GDY in photoelectronic devices. The electronic properties can be tuned by varying the number of layers of GDY. The local density approximation (LDA) and the GW approximation (GW) were employed to calculate the band structure of a GDY monolayer (Figure 3a).27 Band gaps of 0.44 and 1.10 eV were obtained at the LDA and GW levels, respectively. The optical absorption spectrum simulated by Bethe−Salpeter equation (BSE) matches well with the experimental data: three excitonic peaks (at 0.75, 1.00, and 1.82 eV) obtained by BSE correspond to three experimentally measured peaks (at 0.56, 0.89, and 1.79 eV). Moreover, the Young’s modulus of GDY (ca. 412 GPa) is as large as that of silicon carbide (ca. 450 GPa) and approximately 40% of that of graphene or diamond (ca. 1100 GPa). The structure and electronic properties of bilayer and trilayer graphdiyne were investigated by the first systematic ab initio study.28 Direct band gaps of 0.35 and 0.14 eV were obtained for bilayer graphdiyne stacked in the most and second most stable arrangements, respectively, while band gaps of 0.18−0.33 eV were predicted for trilayer graphdiyne stacked in stable styles (Figure 3 b,c) . Thus, GDY is an excellent candidate with tunable electronic properties for use in nanoscale semiconductors and optoelectronic devices. Density functional theory (DFT) and the Boltzmann transport equation with the relaxation time approximation were used to calculate the electronic structure and the charge mobility of graphdiyne sheets and nanoribbons scattered by 2472

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Figure 4. (a) Photograph of the assembly of a full LIB and its applied discharge for lighting an LED bulb, (b) galvanostatic charge/discharge profile of a GDY-1 electrode, and (c) rate performance of the GDY-1 electrode. Adapted with permission from ref 31. Copyright 2015 Elsevier. (d) Schematic representation of a GDY LIC, (e) galvanostatic charge/discharge voltage profiles of the GDY LIC, and (f) Ragone plots for GDY/AC LICs and previously reported graphite and graphene LICs. Adapted with permission from ref 36. Copyright 2016 Elsevier.

longitudinal acoustic phonons (Figure 3d).29 The GDY sheet is a semiconductor having a band gap of 0.46 eV. GDY nanoribbons (GDYNRs) are predicted to be semiconductors, with the smallest band gap (D2) being approximately 0.8 eV, a useful feature for employing GDYNRs as semiconducting channels in field-effect transistors. The room-temperature electron and hole mobilities of a single GDY sheet were predicted to be 2 × 105 and 2 × 104 cm2 V−1 s−1, respectively. The electron mobility of GDYNRs was calculated to be around 104 cm2 V−1 s−1 at room temperature, which was evidently bigger than the hole mobility. Meanwhile, the electronic and structural properties of a GDYNT and a single-layer graphdiyne sheet were also studied. The theoretical results suggest that GDYNT exhibits a carrier mobility larger than that of a carbon nanotube (CNT).30

Furthermore, the capacitances of GDY samples must be improved if they are to be used in applications with high power requirements. Many efforts have been made to enhance the energy density and specific capacity of carbon-based LIBs. Nitrogen doping is one of the most effective ways of adjusting the structures of carbon-based electrode materials, endowing them with new properties and applications. We have found that N doping of GDY improves the Li intercalation properties relative to those of pristine GDY.34 Assembled batteries based on N-GDY electrodes have displayed superior cycle stability, with a reversible capacity of 510 mA h g−1 obtained after 1000 cycles at a current density of 2 A g−1 (418 mA h g−1 achieved for GDY). These results are similar to those obtained using graphene and CNTs. The cycle life of batteries based on NGDY electrodes reached as long as 1000 cycles, similar to the behavior observed with GDY-based electrodes. The electrochemical properties of graphdiyne nanostrucutres had been investigated for supercapacitor applications.35 Compositing a bulk GDY anode and an activated carbon (AC) cathode to construct a hybrid lithium-ion capacitor (LIC) is another method to increase the energy density without sacrificing the power density or cycle life (Figure 4d−f).36 This capacitor delivered an initial specific energy as high as 112.2 W h kg−1 at a power density of 400.1 W kg−1, with 94.7% retention after 1000 cycles. Interestingly, it even displayed an energy density of 95.1 W h kg−1 at a power density of 1000.4 W kg−1, a value higher than those of graphite and graphene. Thus, GDY has great potential for application in next-generation batteries. The sodium storage of GDY powders was also investigated. The assembled sodium-ion batteries exhibited reversible moderate specific capacity, long cycle life, and excellent rate performance, and a specific capacity of 261 mA h g−1 can be obtained after 300 cycles at a current density of 50 mA g−1.37

4. ENERGY STORAGE MATERIALS APPLICATIONS OF GRAPHDIYNE Several carbon-based materials have been investigated for applications as next-generation lithium storage materials, including fullerenes, CNTs, and graphene. The carbon atoms in these structures are all sp2-hybridized, the same as those in graphite. The unique structure of GDY, with its numerous large triangle-like pores, endows it with many Li storage sites and facilitates the rapid transport of electrons and ions.31−33 Highcapacity Li storage in the form of LiC3 (744 mA h g−1) had been predicted by many theoretical studies. The unique atomic arrangement and electronic structure of GDY enable Li atoms to diffuse readily upon a GDY layer with moderate energy barriers ranging from 0.18 to 0.84 eV. We examined GDY as a high-efficiency lithium storage material.31 Lithium-ion batteries (LIBs) having a GDY-based electrode exhibit excellent electrochemical performance, with high specific capacity, outstanding rate performance, and long cycle life (Figure 4a− c). The specific capacity of these GDY samples increased continuously during the first 200 cycles and remained stable during the next 200 cycles. After 1000 cycles at a high current density of 2 A g−1, reversible capacities up to 420 mA h g−1 were obtained for the GDY-1 electrode.

5. ENERGY CONVERSION MATERIALS APPLICATION OF GRAPHDIYNE As a novel highly π-conjugated carbon material, GDY has capability for charge transport and semiconductivity. Thus, the effect of GDY as a dopant in the poly(3-hexylthiophene) 2473

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Figure 5. (a) Schematic representation of a perovskite solar cell featuring a P3HT hole-transporting material modified with GDY and (b) J−V characteristics and (c) IPCE spectra of perovskite solar cells containing various HTM layers. Adapted with permission from ref 38. Copyright 2015 Wiley. (d) Schematic representation of a GDY-based inverted-structure perovskite solar cell, (e) J−V characteristics of PCBM- and PCBM:GDYbased perovskite solar cells, and (f) conductive AFM image of an ITO/PCBM:GDY film. Adapted from ref 39. Copyright 2015 American Chemical Society.

Figure 6. (a) Schematic illustration of PbS CQD solar cells with a GDY anode buffer layer and (b) J−V characteristics measured under simulated AM 1.5 G irradiation. Adapted with permission from ref 40. Copyright 2016 Wiley. (c) Schematic illustration of fabricated PDs based on a ZnO film, GDY/ZnO bilayer film, GDY:ZnO film, and GDY:ZnO/ZnO bilayer film, (d) I−V curves of the fabricated PDs measured in the dark and light, and (e) comparison of rise and decay times of the fabricated PDs. Adapted with permission from ref 42. Copyright 2016 Wiley.

differences in the IPCE spectra were mainly attributed to the presence of GDY in the HTM layer. The well-dispersed GDY powder shows strong absorption over the whole visible range, particularly in the short-wavelength region. An overlay effect could provide the enhancement of absorption in the shortwavelength region rather than in the long-wavelength region. That is, the scattering of GDY aggregates contributes to the lower transmittance, especially in the wavelength range of 520− 760 nm. Doping GDY into the [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) film of organic/inorganic perovskite solar cells would increase the electrical conductivity, electron mobility,

(P3HT) hole-transporting material (HTM) layer of a perovskite solar cell was examined.38 The photovoltaic performance of the perovskite solar cell incorporating P3HT was characterized by a short-circuit current density (Jsc) of 18.3 mA cm−2, an open-circuit potential (Voc) of 932 mV, and a fill factor (FF) of 0.676, yielding a power conversion efficiency (PCE) of 11.53%; for the P3HT/GDY-based device, these values were 21.7 mA cm−2, 941 mV, 0.713, and 14.58%, respectively (Figure 5a−c). The incident photon-to-current conversion efficiency (IPCE) of the P3HT/GDY-based device was enhanced significantly in the long-wavelength range (530− 750 nm). Compared with the P3HT-based device, the 2474

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Figure 7. (a) Schematic representation of the formation of Pd/GDYO, (b) time-dependent UV−vis absorption spectra recorded during the catalytic reduction of 4-NP with the Pd/GDYO nanocomposite, and (c) plots of ln(Ct/C0) with respect to the reaction time for the reductions of 4-NP catalyzed by four different catalysts. Adapted from ref 43. Copyright 2015 Americal Chemical Society. (d) Schematic representation of the photodegradation of dyes in the presence of TiO2−GDY and TiO2−GR composites, (e) HRTEM images of a TiO2(001)−GDY composite, and (f) photocatalytic degradation of MB over TiO2(001) and over TiO2(001)−GDY and TiO2(001)−GR composites. Adapted from ref 45. Copyright 2013 American Chemical Society.

and charge extraction.39 GDY was doped into the PCBM layer of a perovskite solar cell having an inverted structure [indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate/CH3NH3PbI3−xClx/PCBM:GDY/C60/Al] to improve the electron transport (Figure 5d−f). The device using PCBM:GDY as the electron transport layer provided a Jsc of 23.4 mA cm−2, a Voc of 0.969 V, and an FF of 0.654, yielding a PCE of 14.8%. The average PCE of the PCBM:GDY-based devices (13.9%) was remarkably higher (28% enhancement) than that of the device incorporating pure PCBM (10.8%). SEM measurements revealed that the PCBM:GDY-based devices featured better coverage on the rough perovskite layer in terms of superior interfacial contact and lower degrees of charge recombination. Graphdiyne has a rigid carbon network and a natural band gap, which results in a large specific area and high hole mobility. The integration of GDY NPs with other nanomaterials could open up new device concepts and enhanced device performance. Accordingly, the effect of GDY as an anode buffer layer in colloidal quantum dot (CQD) solar cells was examined (Figure 6a,b).40 The device exhibits a PCE of 10.64%, with a Jsc of 22.83 mA cm−2, Voc of 0.654 V, and FF of 72.14%. Impedance spectroscopy (IS) and transient photovoltage (TPV) measurements indicated that GDY contributed to the increased carrier lifetime and decreased carrier recombination within the device due to the improved contact between the PbS-EDT layer and the Au anode. Remarkably, the device exhibited excellent longterm stability. In addition, a nanocomposite of GDY nanosheets and Pt nanoparticles (PtNP−GDYNS) was also prepared for use in dye-sensitized solar cells (DSSCs).41 Because of their special “p−n junction”-like structures, the PCEs of the DSSCs were significantly enhanced. GDY:ZnO nanocomposites were also obtained through self-assembly of GDY NPs onto the surfaces of n-propylamine (PrA)-modified ZnO NPs, which were used to fabricate UV photodetectors (PDs).42 The

performance of the devices was enhanced relative to that of a conventional reference device, with a high responsivity of 1260 A W−1 and short rise and decay times of 6.1 and 2.1 s, respectively (Figure 6c−e).

6. CATALYTIC MATERIALS APPLICATION OF GRAPHDIYNE For economic and environmental reasons, highly efficient and stable metal catalysts are particularly interesting in chemistry and materials science. The unique atomic arrangement and electronic structure of GDY inspired us to investigate its use in the development of highly efficient catalysts. We have found that GDY can be used for the electroless deposition of Pd nanoparticles (NPs) through a direct redox reaction between GDY and PdCl42− (Figure 7a−c).43 Furthermore, Pd/graphdiyne oxide (Pd/GDYO) nanocomposites synthesized from GDYO and PdCl42− exhibited high catalytic performance in the NaBH4-mediated reduction of 4-nitrophenol (4-NP). The rate constant for the reduction of 4-NP catalyzed by Pd/GDYO was 0.322 min−1; in comparison, the corresponding values for Pd/ GO, Pd/MWNT, and a commercial Pd/C catalyst were 0.029, 0.008, and 0.058 min−1, respectively. These results suggest that the smaller size of the Pd clusters and larger π-conjugated structure of the GDYO were mainly responsible for the more efficient catalysis of 4-NP reduction. These initial findings suggest a promising role for GDY species in the development of active metal catalysts in practical applications. The calculated intrinsic charge mobility of a graphdiyne sheet is up to 105 cm2 V−1 s−1 at room temperature. This high change mobility suggests that GDY should have excellent electron transport properties, which may be utilized in composites to improve the photocatalytic performance of P25 TiO2. The activity of the P25−GDY photocatalyst was much higher than those of bare P25, P25−CNT, and P25−GR structures. 2475

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Figure 8. (a) Fabrication process for the Cu@GDY NA/CF, (b) SEM images of Cu(OH)2, Cu, and Cu@GDY NA/CFs, and (c) HER polarization curves of as-prepared catalysts at a sweep rate of 5 mV s−1. Adapted with permission from ref 47. Copyright 2016 Elsevier. (d) TEM and HRTEM images of CoNC/GDY and (inset) sketch map of CoNC/GDY, and (e, f) HER polarization curves of (e) CoNC/GDY in 1 M KOH and (f) CoNC/GDY and commercial Pt/C (10 wt %) before and after 36 000 and 8000 CV scans. Adapted from ref 48. Copyright 2016 American Chemical Society.

curve. In contrast, the commercial Pt/C (10 wt %) underwent an obvious loss of activity in the low-current-density range after only 8000 cycles. Thus, the durability of the CoNC/GDY structure would be much greater than that of Pt/C during longterm electrochemical HER processing in alkaline electrolytes. We also employed GDY as a hole transfer layer in the photocathode for H2 production in neutral water.49 The assembled photocathode exhibited a photocurrent of approximately −70 μA cm−2 in 0.1 M Na2SO4 (pH 6.8) at an applied potential of 0 V vs normal hydrogen electrode (NHE) and simultaneously provided a rate of H2 production of 27 000 μmol h−1 g−1 cm−2 at −0.20 V vs NHE. Faradic efficiencies of up to 95% were obtained, with an average value of 90 ± 5%. The pore size of GDY sheets can be further tuned by replacing the carbon atoms in the linear atomic chains with heteroatoms for the purpose of enhancing the electrocatalytic activity. For example, N doping of graphdiyne was used to tune the catalytic activity for the oxygen reduction reaction (ORR).50 The electrocatalytic activity of the N 550-GDY/GC electrode (GC = glassy carbon) was much greater than those of the GDY/GC electrode and other N-doped GDY/GC electrodes. Moreover, N 550-GDY had better stability and increased tolerance to the crossover effect relative to Pt/C catalysts in this medium. Theoretical calculations revealed that N doping leads to high degrees of positive charge on the carbon atoms adjacent to the N atoms, thereby facilitating the ORR. Interestingly, N/F-codoped graphdiyne (NFGDY) displayed high selectivity for the four-electron ORR pathway.51 Compared with commercial Pt/C, NFGDY exhibited excellent electrocatalytic activity in half-cell and full-cell (primary Zn−air battery) tests. Meanwhile, it has better stability as well as a higher tolerance to methanol crossover and CO poisoning effects.

Moreover, the photocatalytic activity of P25−GDY could be adjusted by changing the content of GDY in the composite. This approach may open up new pathways for using TiO2−C nanocomposites as high-performance photocatalysts.44 We used first-principles DFT to calculate the chemical structures and electronic properties of TiO2−GDY and TiO2−GR composites featuring different TiO2 facets.45 The rate constant for the photocatalytic degradation of methylene blue (MB) using the TiO2(001)−GDY composite was 1.63 times that using pure TiO2(001) and 1.27 times that using the TiO2(001)−GR composite. Thus, GDY appears to be a competitive material for photocatalysis and photovoltaics (Figure 7d−f). Meanwhile, a novel graphdiyne−ZnO nanohybrid was prepared by the hydrothermal method and showed superior photocatalytic properties compared with the bare ZnO nanoparticles, as evidenced by the absorption spectra and total organic carbon analyses.46 The porous structure of GDY also makes it a good electrocatalyst for the hydrogen evolution reaction (HER) because of the capability of rapid transport of electrons and ions. We used a facile self-catalyzed growth method to synthesize a novel 3D nanocomposite electrocatalyst featuring GDY as the shell and Cu nanowire arrays (NA) as the core on copper foam (CF) (Figure 8a−c).47 The Cu@GDY NA/CF electrocatalyst exhibited an onset overpotential of 275 mV vs reversible hydrogen electrode (RHE)a value lower than those of pure GDY and Cu NA/CF and almost equal to that of a commercial Pt/C catalyst (20 wt %). Moreover, this system showed excellent durability during long-term electrochemical processing. Furthermore, we prepared GDY-supported Co NPs wrapped in N-doped carbon layers.48 The CoNC/GDY structure had a remarkably high HER activity, with an onset potential (170 mV) lower than those of Co/GDY (260 mV), NC/GDY (300 mV), and pristine GDY (700 mV) (Figure 8d− f). Notably, the current density of the CoNC/GDY structure was higher than that of Pt/C (10 wt %) when the applied potential exceeded 406 mV, suggesting that its catalytic activity was also higher. The polarization curve of the CoNC/GDY structure recorded after continuous cyclic voltammetry (CV) scanning for 36 000 cycles was almost identical to its initial

7. CONCLUSION AND PERSPECTIVES This Account has covered progress in the synthesis, selfassembly, and functionalization of GDY with well-defined assembled structures. GDY, with its high degree of π conjugation, uniformly distributed pores, and tunable electronic properties, has been examined theoretically and experimentally 2476

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ACKNOWLEDGMENTS We thank all of the members of the Yuliang Li laboratory. Our studies have been supported by the National Natural Science Foundation of China (21790050 and 21790051), the National Key Research and Development Project of China (2016YFA0200104), and the Key Program of the Chinese Academy of Sciences (QYZDY-SSW-SLH015).

for its structural, mechanical, and electronic properties. The construction of well-defined nanostructures of GDY with distinct properties has contributed to the basic study and development of novel functional systems from this new type of carbon allotrope. We have reviewed several new methods for the chemical synthesis of different GDY morphologies. GDYbased 3D nanoarchitectures featuring well-defined porous network structures can function as highly active cathodes for H2 evolution. Heteroatom-doped GDY structures are excellent metal-free electrocatalysts for the ORR. LIBs featuring GDYbased electrodes also display excellent electrochemical performance. Although a series of functional systems derived from GDY had been successfully applied in the fields of energy and catalysis, many challenges still need to be explored. Further research should help us understand the fundamental processes behind the behavior of GDY and strengthen its applications. The chemical and physical properties of GDY can be improved by controlled growth of different aggregates and by derivatization. These aggregate materials produced will exhibit strong potential for applications in several fields, such as optics, electronics, energy, and catalysis.

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REFERENCES

(1) Diederich, F.; Rubin, Y. Synthetic approaches toward molecular and polymeric carbon allotropes. Angew. Chem., Int. Ed. Engl. 1992, 31, 1101−1123. (2) Marsden, J. A.; Miller, J. J.; Haley, M. M. Let the Best Ring Win: Selective Macrocycle Formation through Pd-Catalyzed or CuMediated Alkyne Homocoupling. Angew. Chem., Int. Ed. 2004, 43, 1694−1697. (3) Diederich, F.; Kivala, M. All-Carbon Scaffolds by Rational Design. Adv. Mater. 2010, 22, 803−812. (4) Geim, A. K.; Novoselov, K. S. The rise of graphene. Nat. Mater. 2007, 6, 183−191. (5) Nair, R. R.; Blake, P.; Grigorenko, A. N.; Novoselov, K. S.; Booth, T. J.; Stauber, T.; Peres, N. M. R.; Geim, A. K. Fine Structure Constant Defines Visual Transparency of Graphene. Science 2008, 320, 1308. (6) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric Field Effect in Atomically Thin Carbon Films. Science 2004, 306, 666−669. (7) Haley, M. M. Synthesis and properties of annulenic subunits of graphyne and graphdiyne nanoarchitectures. Pure Appl. Chem. 2008, 80, 519−532. (8) Diederich, F.; Kivala, M. All-carbon scaffolds by rational design. Adv. Mater. 2010, 22, 803−812. (9) Rivera-Fuentes, P.; Diederich, F. Allenes in molecular materials. Angew. Chem., Int. Ed. 2012, 51, 2818−2828. (10) Diederich, F. Carbon scaffolding: Building acetylenic all-carbon and carbon-rich compounds. Nature 1994, 369, 199−207. (11) Diederich, F.; Rubin, Y.; Knobler, C. B.; Whetten, R. L.; Schriver, K. E.; Houk, K. N.; Li, Y. All-carbon molecules: Evidence for the generation of cyclo 18 carbon from a stable organic precursor. Science 1989, 245, 1088−1090. (12) Baughman, R. H.; Eckhardt, H.; Kertesz, M. Structure−property predictions for new planar forms of carbon: Layered phases containing sp2 and sp atoms. J. Chem. Phys. 1987, 87, 6687−6699. (13) Haley, M. M.; Brand, S. C.; Pak, J. J. Carbon networks based on dehydrobenzoannulenes: Synthesis of graphdiyne substructures. Angew. Chem., Int. Ed. Engl. 1997, 36, 836−838. (14) Vollhardt, K. P. C. Cobalt-mediated [2 + 2+2]-cycloadditions-A maturing synthetic strategy. Angew. Chem., Int. Ed. Engl. 1984, 23, 539−556. (15) Cranford, S. W.; Brommer, D. B.; Buehler, M. J. Extended graphynes: simple scaling laws for stiffness, strength and fracture. Nanoscale 2012, 4, 7797−7809. (16) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Katsnelson, M. I.; Grigorieva, I. V.; Dubonos, S. V.; Firsov, A. A. Twodimensional gas of massless Dirac fermions in graphene. Nature 2005, 438, 197−200. (17) Gao, X.; Zhou, J.; Du, R.; Xie, Z.; Deng, S.; Liu, R.; Liu, Z.; Zhang, J. Robust superhydrophobic foam: A graphdiyne-based hierarchical architecture for oil/water separation. Adv. Mater. 2016, 28, 168−173. (18) Wang, C.; Yu, P.; Guo, S.; Mao, L.; Liu, H.; Li, Y. Graphdiyne oxide as a platform for fluorescence sensing. Chem. Commun. 2016, 52, 5629−5632. (19) Li, S.; Chen, Y.; Liu, H.; Wang, Y.; Liu, L.; Lv, F.; Li, Y.; Wang, S. Graphdiyne Materials as Nanotransducer for in Vivo Photoacoustic Imaging and Photothermal Therapy of Tumor. Chem. Mater. 2017, 29, 6087−6094. (20) Li, G.; Li, Y.; Liu, H.; Guo, Y.; Li, Y.; Zhu, D. Architecture of graphdiyne nanoscale films. Chem. Commun. 2010, 46, 3256−3258.

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Yongjun Li: 0000-0003-1359-1260 Changshui Huang: 0000-0001-5169-0855 Yuliang Li: 0000-0001-5279-0399 Notes

The authors declare no competing financial interest. Biographies Dr. Zhiyu Jia received his Ph.D. degree in 2014 at Universitat Autònoma de Barcelona. He is now a postdoctoral researcher in Prof. Yuliang Li’s group at the Institute of Chemistry, Chinese Academy of Sciences (ICCAS), working on the synthesis of carbon materials. Prof. Yongjun Li received his Ph.D. degree in 2006 from ICCAS. He is currently a Professor in Professor Yuliang Li’s group at ICCAS, designing and synthesizing functional organic molecules. Dr. Zicheng Zuo received his Ph.D. degree in 2011 from ICCAS. He is currently an Assistant Professor in Professor Yuliang Li’s group at ICCAS, working on the application of carbon-based nanomaterials to develop novel model energy storage devices. Prof. Huibiao Liu received his Ph.D. degree in 2001 from Nanjing University. He is currently a Professor at ICCAS, studying inorganic/ organic hybrid nanomaterials and nanoscale and nanostructured materials. Prof. Changshui Huang received his Ph.D. degree in 2008 from ICCAS. He is currently an Professor at the Qingdao Institute of Bioenergy and Bioprocess Technology, working on the application of carbon-based nanomaterials to develop novel model energy storage devices and related key materials. Prof. Yuliang Li has worked at ICCAS since 1975. His research interests lie in the field of the growth of low-dimensional and 2D carbon nanostructures, covalently and non-covalently assembled molecular materials, and supramolecular chemistry. 2477

DOI: 10.1021/acs.accounts.7b00205 Acc. Chem. Res. 2017, 50, 2470−2478

Article

Accounts of Chemical Research (21) Qian, X.; Liu, H.; Huang, C.; Chen, S.; Zhang, L.; Li, Y.; Wang, J.; Li, Y. Self-catalyzed growth of large-area nanofilms of twodimensional carbon. Sci. Rep. 2015, 5, 7756. (22) Li, G.; Li, Y.; Qian, X.; Liu, H.; Lin, H.; Chen, N.; Li, Y. Construction of tubular molecule aggregations of graphdiyne for highly efficient field emission. J. Phys. Chem. C 2011, 115, 2611−2615. (23) Qian, X.; Ning, Z.; Li, Y.; Liu, H.; Ouyang, C.; Chen, Q.; Li, Y. Construction of graphdiyne nanowires with high-conductivity and mobility. Dalton Trans. 2012, 41, 730−733. (24) Zhou, J.; Gao, X.; Liu, R.; Xie, Z.; Yang, J.; Zhang, S.; Zhang, G.; Liu, H.; Li, Y.; Zhang, J.; Liu, Z. Synthesis of graphdiyne nanowalls using acetylenic coupling reaction. J. Am. Chem. Soc. 2015, 137, 7596− 7599. (25) Gao, X.; Li, J.; Du, R.; Zhou, J.; Huang, M.-Y.; Liu, R.; Li, J.; Xie, Z.; Wu, L.-Z.; Liu, Z.; Zhang, J. Direct synthesis of graphdiyne nanowalls on arbitrary substrates and its application for photoelectrochemical water splitting cell. Adv. Mater. 2017, 29, 1605308. (26) Matsuoka, R.; Sakamoto, R.; Hoshiko, K.; Sasaki, S.; Masunaga, H.; Nagashio, K.; Nishihara, H. Crystalline Graphdiyne Nanosheets Producted at a Gas/Liquid or Liquid/Liquid Interface. J. Am. Chem. Soc. 2017, 139, 3145−3152. (27) Luo, G. F.; Qian, X. M.; Liu, H. B.; Qin, R.; Zhou, J.; Li, L. Z.; Gao, Z. X.; Wang, E. G.; Mei, W. N.; Lu, J.; Li, Y. L.; Nagase, S. Quasiparticle energies and excitonic effects of the two-dimensional carbon allotrope graphdiyne: Theory and experiment. Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 84, 075439. (28) Zheng, Q.; Luo, G.; Liu, Q.; Quhe, R.; Zheng, J.; Tang, K.; Gao, Z.; Nagase, S.; Lu, J. Structural and electronic properties of bilayer and trilayer graphdiyne. Nanoscale 2012, 4, 3990−3996. (29) Long, M.; Tang, L.; Wang, D.; Li, Y.; Shuai, Z. Electronic structure and carrier mobility in graphdiyne sheet and nanoribbons: Theoretical predictions. ACS Nano 2011, 5, 2593−2600. (30) Jalili, S.; Houshmand, F.; Schofield, J. Study of carrier mobility of tubular and planar graphdiyne. Appl. Phys. A: Mater. Sci. Process. 2015, 119, 571−579. (31) Huang, C.; Zhang, S.; Liu, H.; Li, Y.; Cui, G.; Li, Y. Graphdiyne for high capacity and long-life lithium storage. Nano Energy 2015, 11, 481−489. (32) Zhang, S.; Liu, H.; Huang, C.; Cui, G.; Li, Y. Bulk graphdiyne powder applied for highly efficient lithium storage. Chem. Commun. 2015, 51, 1834−1837. (33) Jang, B.; Koo, J.; Park, M.; Lee, H.; Nam, J.; Kwon, Y.; Lee, H. Graphdiyne as a high-capacity lithium ion battery anode material. Appl. Phys. Lett. 2013, 103, 263904. (34) Zhang, S.; Du, H.; He, J.; Huang, C.; Liu, H.; Cui, G.; Li, Y. Nitrogen-doped graphdiyne applied for lithium-ion storage. ACS Appl. Mater. Interfaces 2016, 8, 8467−8473. (35) Krishnamoorthy, K.; Thangavel, S.; Veetil, J. C.; Raju, N.; Venugopal, G.; Kim, S. J. Graphdiyne nanostructures as a new electrode material for electrochemical supercapacitors. Int. J. Hydrogen Energy 2016, 41, 1672−1678. (36) Du, H.; Yang, H.; Huang, C.; He, J.; Liu, H.; Li, Y. Graphdiyne applied for lithium-ion capacitors displaying high power and energy densities. Nano Energy 2016, 22, 615−622. (37) Zhang, S.; He, J.; Zheng, J.; Huang, C.; Lv, Q.; Wang, K.; Wang, N.; Lan, Z. Porous graphdiyne applied for sodium ion storage. J. Mater. Chem. A 2017, 5, 2045. (38) Xiao, J.; Shi, J.; Liu, H.; Xu, Y.; Lv, S.; Luo, Y.; Li, D.; Meng, Q.; Li, Y. Efficient CH3NH3PbI3 perovskite solar cells based on graphdiyne (GDY)-modified P3HT hole-transporting material. Adv. Energy Mater. 2015, 5, 1401943. (39) Kuang, C.; Tang, G.; Jiu, T.; Yang, H.; Liu, H.; Li, B.; Luo, W.; Li, X.; Zhang, W.; Lu, F.; Fang, J.; Li, Y. Highly efficient electron transport obtained by doping PCBM with graphdiyne in planarheterojunction perovskite solar cells. Nano Lett. 2015, 15, 2756−2762. (40) Jin, Z.; Yuan, M.; Li, H.; Yang, H.; Zhou, Q.; Liu, H.; Lan, X.; Liu, M.; Wang, J.; Sargent, E. H.; Li, Y. Graphdiyne: An efficient hole transporter for stable high-performance colloidal quantum dot solar cells. Adv. Funct. Mater. 2016, 26, 5284−5289.

(41) Ren, H.; Shao, H.; Zhang, L.; Guo, D.; Jin, Q.; Yu, R.; Wang, L.; Li, Y.; Wang, Y.; Zhao, H.; Wang, D. A new graphdiyne nanosheet/Pt nanoparticle-based counter electrode material with enhanced catalytic activity for dye-sensitized solar cells. Adv. Energy Mater. 2015, 5, 1500296. (42) Jin, Z.; Zhou, Q.; Chen, Y.; Mao, P.; Li, H.; Liu, H.; Wang, J.; Li, Y. Graphdiyne:ZnO nanocomposites for high-performance UV photodetectors. Adv. Mater. 2016, 28, 3697−3702. (43) Qi, H.; Yu, P.; Wang, Y.; Han, G.; Liu, H.; Yi, Y.; Li, Y.; Mao, L. Graphdiyne oxides as excellent substrate for electroless deposition of Pd Clusters with high catalytic activity. J. Am. Chem. Soc. 2015, 137, 5260−5263. (44) Wang, S.; Yi, L.; Halpert, J. E.; Lai, X.; Liu, Y.; Cao, H.; Yu, R.; Wang, D.; Li, Y. A novel and highly efficient photocatalyst based on P25-graphdiyne nanocomposite. Small 2012, 8, 265−271. (45) Yang, N.; Liu, Y.; Wen, H.; Tang, Z.; Zhao, H.; Li, Y.; Wang, D. Photocatalytic properties of graphdiyne and graphene modified TiO2: From theory to experiment. ACS Nano 2013, 7, 1504−1512. (46) Thangavel, S.; Krishnamoorthy, K.; Krishnaswamy, V.; Raju, N.; Kim, S. J.; Venugopal, G. J. Phys. Chem. C 2015, 119, 22057−22065. (47) Xue, Y.; Guo, Y.; Yi, Y.; Li, Y.; Liu, H.; Li, D.; Yang, W.; Li, Y. Self-catalyzed growth of Cu@graphdiyne core-shell nanowires array for high efficient hydrogen evolution cathode. Nano Energy 2016, 30, 858−866. (48) Xue, Y.; Li, J.; Xue, Z.; Li, Y.; Liu, H.; Li, D.; Yang, W.; Li, Y. Extraordinarily Durable Graphdiyne-Supported Electrocatalyst with High Activity for Hydrogen Production at All Values of pH. ACS Appl. Mater. Interfaces 2016, 8, 31083−31091. (49) Li, J.; Gao, X.; Liu, B.; Feng, Q.; Li, X.; Huang, M.; Liu, Z.; Zhang, J.; Tung, C.; Wu, L. Graphdiyne: A metal-free material as hole transfer layer to fabricate quantum dot-sensitized photocathodes for hydrogen production. J. Am. Chem. Soc. 2016, 138, 3954−3957. (50) Liu, R.; Liu, H.; Li, Y.; Yi, Y.; Shang, X.; Zhang, S.; Yu, X.; Zhang, S.; Cao, H.; Zhang, G. Nitrogen-doped graphdiyne as a metalfree catalyst for high-performance oxygen reduction reactions. Nanoscale 2014, 6, 11336−11343. (51) Zhang, S.; Cai, Y.; He, H.; Zhang, Y.; Liu, R.; Cao, H.; Wang, M.; Liu, J.; Zhang, G.; Li, Y.; Liu, H.; Li, B. Heteroatom doped graphdiyne as efficient metal-free electrocatalyst for oxygen reduction reaction in alkaline medium. J. Mater. Chem. A 2016, 4, 4738−4744.

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