Electrochemicalenergy storage devices are becoming increasingly important in modern societyfor efficient energy storage. The use of these devices is mainly dependent onthe electrode materials. As a newly discovered carbon allotrope, graphdiyne(GDY) is a two-dimensional full-carbon material. Its wide interlayer distance(0.365 nm), large specific surface area, special three-dimensional porousstructure (18-C hexagon pores), and high conductivity make it a potentialelectrode material in energy storage devices. In this paper, based on thefacile synthesis method and the unique porous structure of GDY, theapplications of GDY in energy storage devices have been discussed in detailfrom the aspects of both theoretical predictions and recent experimentaldevelopments. The Li/Na migration and storage in mono-layered and bulk GDYindicate that GDY-based batteries have excellent theoretical Li/Na storagecapacity. The maximal Li storage capacity in mono-layered GDY is LiC₃(744 mAh∙g^-1). The experimental Li storage capacity of GDY issimilar to theoretical predictions. The experimental Li storage capacity of athick GDY film is close to that of mono-layered GDY' (744 mAh∙g^-1).A thin GDY film with double-side storage model has two-times the Li storagecapacity (1480 mAh∙g^-1) of mono-layered GDY. Powder GDY has lower Listorage capacity than GDY film. The maximal Na storage capacity in GDYcorresponds to NaC_5.14 (316 mAh∙g^-1), and mono-layeredGDY possesses higher theoretical Na storage capacity (NaC_2.57). Theexperimental Na storage capacity (261 mAh∙g^-1) is similar to itstheoretical value. Besides, GDY as electrode material, applied in metal-sulfurbatteries, presents excellent electrochemical performance (in Li-S battery: 0.1C, 949.2 mAh∙g^-1; in Mg-S battery: 50 mA∙g^-1, 458.9 mAh∙g^-1).This ingenious design presents a new way for the preparation of carbon-loadedsulfur. GDY electrode material is also successfully used in supercapacitors, including the traditional supercapacitor, Li-ion capacitors, and Na-ioncapacitors. The traditional supercapacitor with GDY as the electrode material showsgood double layer capacitance and pseudo-capacitance. Both Li-ion capacitor(100.3 W∙kg^-1, 110.7 Wh∙kg^-1) and Na-ion capacitor (300W∙kg^-1, 182.3 Wh∙kg^-1) possess high power and energydensities. Moreover, the effects of synthesis of GDY nanostructure, heattreatment of GDY, and atom-doping in GDY on the performance of electrochemicalenergy storage will be introduced and discussed. The results indicate that GDYhas great potential for application in different energy storage devices as anefficient electrode material.

Graphdiyne(GDY) is a new booming carbon material with a highly π-conjugatedstructure that consists of sp-and sp²-hybridizedcarbon atoms. Due to the diverse compositions of the carbon atoms, GDYs can bedivided into several forms based on their structure and periodicity. Until2010, γ-GDY has been successfully synthesized and becomes a new member of thecarbon family. Many researchers have subsequently devoted their attention tothe study of GDY. Compared to the traditional carbon materials, GDY exhibits aunique carbon network and electronic structure, thereby attracting considerableattention in a variety of fields. With the development of its syntheticchemistry, many types of GDY with different structures have been synthesizedand characterized. The characterization of their micromorphology is crucial forstudying the synthesis procedure and understanding the properties of GDYmaterials. At present, the developed method can characterize GDY morphology, crystal structure, and thechemical bonds of the carbon atoms. Specifically, the morphology and thicknessof GDY can be evaluated by scanning electron microscopy, transmission electronmicroscopy, and atomic force microscopy. The crystal structure can beinvestigated using X-ray diffraction and high-resolution transmission electronmicroscopy. The chemical bonding of the carbon atoms can be analyzed by Ramanspectroscopy, X-ray photoelectron spectroscopy, Fourier transforminfrared (FT-IR) spectroscopy, C-13 nuclear magnetic resonance (¹³C NMR), UV-visible (UV-Vis) absorption spectroscopy, etc. However, methods for therapid and nondestructive characterization of the highly crystalline graphdiyneare still absent, restricting the study of the intrinsic properties of GDY. Dueto the unique electronic and porous structure of GDY, it has been the focus ofextensive investigations in the field of catalysis. As a result of itsfavorable electronic structure and good capability for transferringphotoexcited electrons and holes, GDY can enhance light absorption andfacilitate the separation of photoexcited charge carriers in semiconductors andthereby significantly promote their photocatalytic performance. In addition, GDY can be modified using foreign elements, providing an ideal platform toprepare a highly active catalyst for the hydrogen evolution reaction, oxygenevolution reaction, oxygen reduction reaction, etc. Furthermore, GDY can besynthesized on arbitrary substrates in a three-dimensional nanosheet arraystructure, which can provide a large number of channels for the transfer ofelectrons and a large contact area with the reactant, which is beneficial inelectrocatalytic reactions. This review focused on the recent developments incharacterization methods as well as the photo and electrocatalysis applicationsof GDY, and elaborated the opportunities and challenges for the investigationof GDY in the future.

Graphdiyne(GDY) is a novel carbon allotrope containing sp-and sp²-hybridized carbon atoms.Because of GDY's special structure, theoretical studies have predicted Li storage as dense as 744 mAh∙g⁻¹ in the form of LiC₃, representing twice the specific capacity of graphite.Previous studies have reported that GDY film, bulk GDY, N-doped graphdiyne, and similar materials exhibit high specific capacity, excellent rate performance, and long cycle life when used as anode materials in lithium ion batteries(LIBs).The flat(sp²-and sp-hybridized) carbon networks endow GDY with extensive π-conjunction and uniformly distributed pores, which allow π–π interactions between GDY and organic conjugated molecules to construct a GDY/organic conjugated molecule hybrid material for high-performance anodes with in LIBs.Anode materials with higher specific capacity, better rate performance, and longer cycle life still present an important challenge in LIBs.Nitrogen doping of GDY is one of the effective ways to improve the performance of LIBs.Nitrogen doping of GDY has been achieved by annealing at high temperature in an ammonia atmosphere.The resulting material shows enhanced electrochemical properties due to the creation of numerous heteroatomic defects and active sites.Herein, we have developed a new method based on supramolecular chemistry for preparing N-doped GDY(graphdiyne/porphine) with π–π interactions between graphdiyne and organic conjugated molecules.As opposed to previously reported graphdiyne films, the as-prepared graphdiyne/porphine film can be used as an anode for LIBs without any binders or conducting agents.The resulting anode delivers a high capacity of 1000 mAh∙g⁻¹ and exhibits excellent performance and cycle stability, suggesting that the high rate capability and long cycle life are due to the large amount of active sites provided by porphine for lithium storage.Galvanostatic measurements were performed for 5 cycles each, and retentions of 915.4, 778.9, 675.9, 553.6, and 375.2 mAh∙g⁻¹ were obtained at current densities of 100, 200, 500, 1000, and 2000 mA∙g⁻¹, respectively.When the current density was reset to 50 mA∙g⁻¹, the capacity reached 900 mA∙g⁻¹, indicating excellent structural stability during the high-rate measurements.Excellent cyclic stability with a retention of 1000 mAh∙g⁻¹ at 50 mA∙g⁻¹ after 50 cycles was obtained for LIB applications, which results from the unique hierarchical porosity due to the presence of butadiyne linkages.The unique hierarchical structure of the GDY/porphine film was not destroyed after 50 charge/discharge cycles at 50 mA∙g⁻¹, which suggested high structural stability.The competitive lithium storage values provide promising potential for the development of high-performance LIBs.This strategy opens an avenue for designing N-doped graphdiyne with tunable electronic properties under mild conditions.

Graphyne is a rapidly rising star material of carbon allotropes containing only sp and sp² hybridized carbon atoms forming extended two-dimensional layers. In particular, graphdiyne is an important member of graphyne family. With unique nanotopological pores, two-dimensional layered conjugated frameworks, and excellent semiconducting and optical properties, graphdiyne has displayed distinct superiorities in the fields of energy storage, electrocatalysis, photocatalysis, nonlinear optics, electronics, gas separation, etc. Therefore, the synthesis of high-quality graphdiyne is highly required to fulfill its potentially extraordinary applications. Furthermore, the development of a standardized and systematic set of characterization procedures is an urgent need, and would be based on intrinsic samples. However, there are still obvious barriers to synthesizing this new-born carbon allotrope that can be mainly considered as follows. The selection and stability of monomers is essential for synthesis. The synthesis process in solution also suffers from an annoying problem of the relatively free rotation possible about the alkyne-aryl single bonds, which leads to the coexistence and rapid equilibration of coplanar and twisted structures. Furthermore, the limited reaction conversion and side reactions also lead to a confusion of configuration.

In this review, we primarily focus on the state-of-the-art progress of the synthetic strategies for graphdiyne. First, we give a brief introduction about the structure of graphyne and graphdiyne. We subsequently discuss in detail the recent developments in synthetic methods that can mainly be divided into three aspects: total organic synthesis, on-surface covalent reaction, and polymerization in a solution phase. In particular, much progress in solution polymerization has been achieved since in-situ polymerization on Cu surface was reported in 2010. Liquid/liquid interface, gas/liquid interface, and surface template were also employed for confined reaction, and contribute significantly to the synthesis of a graphdiyne film. Through such strategies, graphdiyne with a well-defined structure and diverse morphologies could be achieved successfully. Finally, the opportunities and challenges for the synthesis of graphdiyne are prospected. A more rational design is desired in terms of monomer modification and reaction regulation.

ZnO is an ideal material for ultraviolet (UV) detection due to its wide direct-bandgap, high exciton binding energy, and high internal photoconductive gain.However, ZnO UV detectors have the disadvantages of slow response speed and low detectivity.Graphdiyne (GD) is a novel carbonaceous allotrope, and possesses excellent electronic performance in air.In this study, the metal-semiconductor-metal (MSM) structured lateral ZnO UV detectors were prepared, and GD was employed to modify the ZnO surface.The effects of GD deposited 1–3 times (viz.1T, 2T, and 3T GD) on the performance of ZnO ultraviolet detector were carefully investigated.The results show that the dark current of the bare ZnO detector is 24 μA under a bias of 10 V, while that of the graphdiyne-modified detector is ~0.34 μA (about two orders of magnitude reduction).The dark current remains almost the same for the 1T, 2T and 3T GD films.The photocurrents of 1–3T GD-modified detectors were 0.21, 0.32, 0.27 mA, respectively.The device modified with 2T GD displays the highest photocurrent, which is significantly enhanced in comparison to the unmodified device (0.08 mA) under a 365-nm UV radiation of 100 μW·cm⁻².Meanwhile, the responsivity and detectivity are improved remarkably.Under a bias of 10 V, the 2T-GD-modified detector displays high responsivity of 1759 A·W⁻¹ and detectivity of 4.23×10¹⁵ Jones.The detectivity is thus far the highest for ZnO UV detectors prepared by the sol-gel method.The improved performance of the GD-modified detector is attributed to the p-n junction formed between the GD and the ZnO film.At dark, the p-n junction is formed between the ZnO film and the GD, which greatly decreases the dark current of the detector.Under UV illumination, photogenerated holes accumulate in the GD, reducing electron-hole recombination; thus, the photocurrent is significantly increased.Furthermore, desorption and absorption of oxygen on the ZnO surface are much reduced due to the GD attached on the ZnO surface, thus improving the response speed of the detector.However, the intensive distribution of GD slightly hinders the UV absorption of ZnO thin films, reducing the responsivity of the detector.Careful optimization shows that the use of 2T GD gives the best output, and the corresponding ZnO UV detector exhibits very good performance.Overall, this study demonstrates that using GD can effectively improve the performance of ZnO UV detector.

Graphdiyne features sp and sp² hybridized carbon atoms. The direct natural band gap and Dirac cone structure for graphdiyne are believed to originated from inhomogeneous π-bonding of differently hybridized carbon atoms and overlap of carbon 2p_z orbitals. The special electronic structures and pore structures of graphdiyne are responsible for its potential and important applications in the fields of information technology, electronics, energy, catalysis, and optoelectronics. Recent basic and applied research studies of graphdiyne have led to important results; as a result, graphdiyne has become a new research field for carbon materials. The high activity of acetylenic units in graphdiyne provides a good platform for chemical modification and doping. Several approaches have been developed to modify the band gap of graphdiyne, including invoking strain, BN-doping, preparing nanoribbons, and hydrogenation, leading to a new graphdiyne (GDY) or graphyne (GY) derivatives. In this review, we summarize the recent progress in nonmetallic heteroatom doping, especially by nitrogen, boron, or oxygen; by modifying metal atoms for tuning electronic/spintronic properties, enhancing water splitting performance, and applying dye-sensitized solar cells and catalysts; and by surface functionalization of graphdiyne via hydrogenation, hydroxylation, and halogenation to adjust the band gap. Hence, it can be surmised that the electronic structures of graphdiynes can be tuned for specific applications. These results suggest that graphdiynes can be more advantageous than grapheme for tailoring energy band gaps for application in nanoelectronics. We also discuss the influence of doping and functionalization on the electronic properties of graphdiyne and their effects on the synergistic enhancement of photoelectrocatalytic performance. We hope that the deep and wide application of these new materials in many fields such as energy transfer and storage, catalyst, electronics, gas separation, and spintronics will draw much attention and become a widely focused research direction.

In recent years, the successful preparation of single-layer graphene, MoS₂, and other two-dimensional materials has started a new era of two-dimensional materials.The potential applications of two-dimensional materials in emerging electronics have drawn widespread attention.Two-dimensional carbon materials, with their unique properties, have become the research hotspot of condensed matter physics, nanoelectronics, and biological medicine.The remarkable success in preparing graphene provides additional possibilities for developing sensitive biodevices and medicine systems.However, graphene is gapless and thus is unsuitable for building nanoelectronic devices or biosensors due to the too low on/off current ratio.More than 20 years ago, graphyne and its family (viz.graphdiyne, graphyne-3, etc.), as hypothetical C allotropes, were theoretically predicted to be semiconductors with a layered structure.Recently, graphdiyne was successfully synthesized on the surface of copper via a cross-coupling reaction using hexaethynylbenzene.Graphdiyne, as a new two-dimensional carbon material with semiconductor properties and a unique porous structure, is more advantageous than graphene for nanoelectronic and biosensing applications.As the first discovered semiconducting two-dimensional carbon material, with independent intellectual property rights in China, graphdiyne has great research significance.Compared with graphene, graphdiyne has a unique structure with larger pores composed of high π-conjugated acetylenic bonds, which may facilitate strong adsorption to biomolecules.Therefore, further research is needed to reveal how the physical properties of graphdiyne can be modulated effectively to meet the requirements of practical applications.The interaction between biological molecules and materials is an important subject of research in condensed matter physics and materials science.Detailed understanding of the interactions between graphdiyne and small molecules may facilitate the development of advanced biological applications such as biosensors for the detection of biomolecules and living cells, drug delivery systems, and cell imaging technologies.In sensitive analysis, the ultimate goal is to achieve reliable detection of trace amounts of molecules.In this work, first-principles calculations were employed to investigate the electronic structure of graphdiyne nanoribbons and the adsorption of graphdiyne to small molecules.To improve the chemical response of graphdiyne to single molecules, we considered modifying graphdiyne by doping 3d transition metal atoms.We chose Sc and Ti, which have the largest adsorption energies on graphdiyne, and studied the room-temperature stabilities of Sc-and Ti-doped graphdiyne and the possibility of using Sc-and Ti-doped graphdiyne as materials for molecular sensing.Finally, we investigated the interaction between graphdiyne and amino acid molecules and discovered that the dispersion force plays a large role in the interaction.The influence of amino acids on the electronic transport properties of graphdiyne was also studied, and the potential applications of graphdiyne to biosensors were investigated.

The electronic structures, deformation potential, electron-phonon couplings (EPCs), and intrinsic charge transport of layered systems — the sp +sp² hybridized carbon allotropes, graphynes (GYs) and graphdiynes (GDYs), as well as sp² + sp³ hybridized structure with buckling, such as stanine — have been investigated theoretically. Computational studies showed that, similar to graphene, some GYs can possess Dirac cones (such as α-, β-, and 6, 6, 12-GYs), and that the electronic properties of GYs and GDYs can be tuned by cutting into nanoribbons with different widths and edge morphologies. Focusing on the features of Dirac cones, band structure engineering can provide a clue for tuning electronic transport in 2D carbon-based materials. Based on the Boltzmann transport equation and the deformation potential approximation (DPA), the charge carrier mobilities in GYs and GDYs were predicted to be as high as 10⁴–10⁵ cm²·V^-1·s^-1 at room temperature. Interestingly, due to lower EPC strength and longer relaxation time, the charge carrier mobility in 6, 6, 12-GY with double Dirac cones structure was found to be even larger than that of graphene at room temperature. The unique electronic properties and high mobilities of GYs and GDYs make them highly promising candidates for applications in next generation nanoelectronics. Additionally, through the full evaluation of the EPC by density functional perturbation theory (DFPT) and Wannier interpolation, the EPCs with different phonon branches and wave-vectors as well as charge carrier mobilities for graphene, GYs and stanene have been discussed. This showed that the longitudinal acoustic (LA) phonon scattering in the long wavelength limit is the main scattering mechanism for GYs and graphene, and thus the DPA is applicable. Due to stronger LA phonon scattering, the electron mobilities (∼10⁴ cm²·V^-1·s^-1) of α-GYs and γ-GYs were predicted to be one order of magnitude smaller than that of graphene at room temperature by full evaluation of the EPC. However, the DPA would fail if there was buckling in the honeycomb structure and the planar symmetry was broken (absence of σ_h), such as in stanene, where the inter-valley scatterings from the out-of-plane acoustic (ZA) and transverse acoustic (TA) phonons dominate the carrier transport process and limit the electron mobilities to be (2–3) × 10³ cm²·V^-1·s^-1 at room temperature. In addition to our calculations, others have also found that the main scattering mechanisms in layered systems with buckling, such as silicene and germanene, are ZA and TA phonons. Thus, these results give us new insights into the role of EPCs and the limitation of the DPA for carrier transport in layered systems. They also indicate that the carrier mobilities of systems without σ_h-symmetry can be improved by suppressing the out-of-plane vibrations, for example by clamping by a substrate.

Since the successful synthesis of graphdiyne, graphynes have emerged as an active field in carbon materials research.Hydrogen-substituted graphyne, structurally similar to graphynes, is a kind of two-dimensional (2D) carbon-rich material composed of sp²-hybridized carbon and hydrogen from phenyl groups and sp-hybridized carbon from ethynyl linkages.The large pore size in the molecular structure of hydrogen-substituted graphyne aids the diffusion of ions and molecules.In this work, hydrogen-substituted graphyne was synthesized by a facile mechanochemical route.Calcium carbide (CaC₂) was employed as the precursor of sp-hybridized carbon and 1, 3, 5 tribromobenzene (PhBr₃) as that of sp²-hybridized carbon and hydrogen.Hydrogen-substituted graphyne was directly obtained via the cross-coupling reaction performed by ball milling under vacuum and the impurities were removed by dilute nitric acid and benzene.Mechanochemistry is a mature technology for the simple and high-yield synthesis of nanostructured materials.The composition of the as-prepared hydrogen-substituted graphyne was confirmed by Raman and ¹H solid-state nuclear magnetic spectroscopies.Energy-dispersive X-ray (EDX) spectrum and X-ray diffraction (XRD) patterns indicated that the purity and crystallinity of the prepared samples are high, which was further confirmed by the corresponding selected area electron diffraction (SAED) patterns.Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images illustrated that samples had nanosheet structure with a layer-to-layer distance of 0.35 nm.However, owing to the lack of a substrate, the nanosheets reunite to form irregular microparticles, as shown in the scanning electron microscopy (SEM) images.Twin structure was found in the as-prepared samples, which might be relevant to the mechanochemical process.The samples were used to prepare electrodes for the photoelectrochemical and electrochemical catalytic analysis.The open circuit potential under chopped irradiation of the electrode showed that the as-prepared hydrogen-substituted graphyne was a p-type semiconductor.The band gap was calculated to be 2.30 eV by UV-Vis diffused reflectance (UV-Vis DRS) spectroscopy.The electrocatalytic properties of the sample were determined using a three-electrode cell in a neutral solution (Na₂SO₄, 0.5 mol·L⁻¹).The onset overpotential for hydrogen evolution was −0.17 V; however, the Tafel slope was too large (1088.4 mV·dec⁻¹), which restricted application in electrocatalytic hydrogen evolution.On the other hand, the overpotential for oxygen evolution reaction was only 0.04 V and the Tafel slope was 70.0 mV·dec⁻¹, making applications in electrocatalytic oxygen evolution and photocatalysis possible.This strategy opens a new avenue for preparing graphyne with good electrochemical properties using readily available precursors under mild conditions.

As a new member of the carbon allotrope family, graphdiynes (GDs)consist of both sp-and sp²-hybridized carbon atoms, possessing unique π-conjugated carbon skeletons and expanded 18C-hexagonalpores in two dimensions. In contrast with the zero band gap graphene (GR), GDis a semiconductor with a direct band gap of 1.22 eV calculated according tothe density functional theory (DFT) using the HSE06 method; this makes it apotential semiconductor material that can supplant silicon in the integratedcircuit industry. Moreover, owing to the presence of diacetylenic linkagesbetween its hexagonal carbon rings, GD shows electron-deficient properties, which lead to its electron-accepting tendency. Graphdiynes exhibit unusualsemiconducting properties with excellent charge mobilities and electrontransport properties that are associated with its distinct topological andelectronic structures. Graphdiynes play the role of not only electron-acceptorsthat efficiently collect the electrons from other materials but also electron-donorsthat inject electrons into other systems, thus exhibiting excellentelectron-transfer enhancement characteristics. The unique electron-transferenhancement property of GDs inspired us to summarize the interactions betweenGDs and other materials including metal oxides, metal nano-particles, andorganic molecules. In this review paper, we first introduce the TiO₂/GDnanocomposite, because the linking of GDs and titania nanoparticles (P25) throughthe Ti—O—Cbond sets an important precedent for exploring the electron-transfer behaviors involvingGDs and the metal oxide. These results indicate that the GDs can act asacceptors of the photogenerated electrons in the TiO₂/GD system, effectively suppressing charge recombination and resulting in excellent photocatalyticproperties. Nevertheless, the GDs in CdSe quantum dots (QDs)/GD composites areable to collect photogenerated holes from the QDs and perform as promising hole-transfermaterials in the photoelectrochemical cell for water splitting. As a result, the interactions between GDs and various metal compounds should be explored todeeply understand the electron-transfer properties of GDs. Furthermore, GDs canbe also used as electron donors to reduce PdCl₄^2- toPd nanoparticles that can subsequently be used for the electroless depositionof highly dispersed Pd nanoparticles. Based on electrostatic potential surfaceanalysis over the Pt₂/GD, GDs can attract the electron cloud fromthe Pt nanoparticles and produce a positive polarization of the metal atomsurface. However, due to its large π-conjugated system, GD can alsocollect and transfer electrons from the electrode under a bias voltage, making ita new type of electrocatalyst material, especially for single-atom catalysts.The interactions between GDs and metal particles/clusters/atoms have attracted thebroad attention of the rapidly developing field of single-atom catalysis.Finally, research on the interactions between GDs and organic molecules, especially biomolecules, is still in its infancy and requires development. In summary, we overview the recent research progress on GD and its enhanced ability forelectron transfer in this review paper, including metal oxides/GD, metalnano-particles/GD, polymers/GD, and organic molecules/GD, from bothexperimental and theoretical perspectives, and emphasize the interactions andelectron-transfer enhancement properties. It is expected that this review canpromote the development and applications of GD chemistry.