Synthesis and Applications of Graphdiyne-Based Metal-Free Catalysts

Recent Advances on Carbon-Based Metal-Free Electrocatalysts for Energy and Chemical Conversions

Over the last decade, carbon-based metal-free electrocatalysts (C-MFECs) have become important in electrocatalysis. This field is started thanks to the initial discovery that nitrogen atom doped carbon can function as a metal-free electrode in alkaline fuel cells. A wide variety of metal-free carbon nanomaterials, including 0D carbon dots, 1D carbon nanotubes, 2D graphene, and 3D porous carbons, has demonstrated high electrocatalytic performance across a variety of applications. These include clean energy generation and storage, green chemistry, and environmental remediation. The wide applicability of C-MFECs is facilitated by effective synthetic approaches, e.g., heteroatom doping, and physical/chemical modification. These methods enable the creation of catalysts with electrocatalytic properties useful for sustainable energy transformation and storage (e.g., fuel cells, Zn-air batteries, Li-O2 batteries, dye-sensitized solar cells), green chemical production (e.g., H2O2, NH3, and urea), and environmental remediation (e.g., wastewater treatment, and CO2 conversion). Furthermore, significant advances in the theoretical study of C-MFECs via advanced computational modeling and machine learning techniques have been achieved, revealing the charge transfer mechanism for rational design and development of highly efficient catalysts. This review offers a timely overview of recent progress in the development of C-MFECs, addressing material syntheses, theoretical advances, potential applications, challenges and future directions.

Structural identification of single boron-doped graphdiynes by computational XPS and NEXAFS spectroscopy

Boron-doped graphdiyne (B-GDY) material exhibits an excellent performance in electrocatalysis, ion transport, and energy storage. However, accurately identifying the structures of B-GDY in experiments remains a challenge, hindering further selection of suitable structures with the most ideal performance for various practical applications. In the present work, we employed density functional theory (DFT) to simulate the X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) spectra of pristine graphdiyne (GDY) and six representative single boron-doped graphdiynes at the B and C K-edges to establish the structure-spectroscopy relationship. A notable disparity in the C 1s ionization potentials (IPs) between substituted and adsorbed structures is observed upon doping with a boron atom. By analyzing the C and B 1s NEXAFS spectra on energy positions, spectral widths, spectral intensities, and different spectral profiles, we found that the six single boron-doped graphdiyne configurations can be sensitively identified. Moreover, this study provides a reliable theoretical reference for distinguishing different single boron-doped graphdiyne structures, enabling accurate selection of B-GDY structures for diverse practical applications.

Properties, Synthesis and Emerging Applications of Graphdiyne: A Journey Through Recent Advancements

Graphdiyne (GDY) is a new variant of nano-carbon material with excellent chemical, physical and electronic properties. It has attracted wide attention from researchers and industrialists for its extensive role in the fields of optics, electronics, bio-medics and energy. The unique arrangement of sp-sp2 carbon atoms, linear acetylenic linkages, uniform pores and highly conjugated structure offer numerous potentials for further exploration of GDY materials. However, since the material is at its infancy, not much understanding is available regarding its properties, growth mechanism and future applications. Therefore, in this review, readers are guided through a brief discussion on GDY's properties, different synthesis procedures with a special focus on surface functionalization and a list of applications for GDY. The review also critically analyses the advantages and disadvantages of each synthesis route and emphasizes the future scope of the material.

Graphdiyne/metal oxide hybrid materials for efficient energy and environmental catalysis

Graphdiyne (GDY)-based materials, owing to their unique structure and tunable electronic properties, exhibit great potential in the fields of catalysis, energy, environmental science, and beyond. In particular, GDY/metal oxide hybrid materials (GDY/MOs) have attracted extensive attention in energy and environmental catalysis. The interaction between GDY and metal oxides can increase the number of intrinsic active sites, facilitate charge transfer, and regulate the adsorption and desorption of intermediate species. In this review, we summarize the structure, synthesis, advanced characterization, small molecule activation mechanism and applications of GDY/MOs in energy conversion and environmental remediation. The intrinsic structure-activity relationship and corresponding reaction mechanism are highlighted. In particular, the activation mechanisms of reactant molecules (H2O, O2, N2, etc.) on GDY/MOs are systemically discussed. Finally, we outline some new perspectives of opportunities and challenges in developing GDY/MOs for efficient energy and environmental catalysis.

Self-Assembly of Wheel-Shaped Nanographdiynes and Self-Template Growth of Graphdiyne

Graphdiyne (GDY) multilayers show stacking-style-dependent physical properties; thus, controlling the stacking style of nanostructures is crucial for utilizing their electrical, optical, and transport properties in electro-optical devices. Herein, we report the assemblies of nanographdiynes decorated with substituents with different steric hindrances to adjust the stacking style. We show that the π-stacked aggregates were influenced by peripheral substituents and the substrate. Steric hexaterphenyl-substituted nanoGDY scaffolds led to dimer structures stacked in the AB-3 configuration with a twist angle of 26.01° or the AB-1 configuration with an in-plane shift along one diyne link. With the interval replacement of steric substituents with long C12 alkyl chains, nanoGDYs were stacked in the AB-2 configuration to decrease the steric congestion, eventually leading to one-dimensional (1D) nanofibrous aggregates. Self-assembly in the presence of substrates can result in ABC-stacked nanoGDYs, which endowed us with the possibility of using nanoGDY as the template for GDY growth in a homogeneous reaction. High-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and near-infrared-ultraviolet-visible (NIR-UV-vis) absorption spectroscopy indicate that the crystalline GDY prepared in this way is a 1.18 eV bandgap semiconductor.

Theoretic Study of Sulfur-Doped Graphdiynes by X-ray Spectroscopy

Sulfur-doped graphdiyne at different sites has a tremendous impact on its electronic structure and properties. Due to the large number of S-doping sites, there is no comprehensive and systematic experimental and theoretical study regarding the identification of S-doped graphdiyne configurations. In this paper, X-ray photoelectron (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra as well as geometries of 10 sulfur-doped graphdiyne molecules have been simulated at the density functional theory (DFT) level. Different types of carbon spectra were theoretically modeled to analyze the contribution of the spectra. Calculated results show that the NEXAFS spectra exhibit a clear dependence on the local structure. The theoretically simulated XPS spectra are in good agreement with the experimental spectra. The XPS spectra combined with the NEXAFS spectra can provide effective information for identifying the 10 S-doped conformations. Our research results provide further theoretical prediction and guidance for the experimental synthesis of S-doped graphdiyne, which solves the difficult problem of identification of S-doped carbon-based materials.

First-principles simulation of X-ray spectra of graphdiyne and graphdiyne oxides at the carbon K-edge

The experimental C 1s near-edge X-ray absorption fine-structure (NEXAFS) spectra of graphdiyne (GDY) show an evident change at different exposure periods, which is explained by oxidation. Herein, to better understand the structure-spectra relationship and the influence of oxidization, we performed a first-principles simulation of the NEXAFS spectra and X-ray photoelectron spectra (XPS) of both pure GDY and its four typical graphdiyne oxides (GDO) at the carbon K-edge. Pure GDY contains one sp2-hybridized (C1) and two sp-hybridized (C2, C3) carbons, while oxidation introduces more nonequivalent carbons. The experimental NEXAFS spectrum exhibits the lowest peak at ca. 285.8 eV. It was found that the C 1s → π* excitation from the sp2-hybridized carbon atoms (C1) in pure GDY and the sp-hybridized atoms (C2, C3) in GDOs contributes to this peak. The two weak resonances at around 289.0 and 290.6 eV in the experiment are contributed by the carbon atoms bonded to the oxygen atoms. Meanwhile, we found that oxidization leads to an increase in the C 1s ionization potentials (IPs) by 0.3-2.7 eV, which is consistent with the XPS experiments. Our calculations provide a clear explanation of the structure-spectra relationships of GDY and GDOs, and the signatures are useful for estimating the degree of oxidation.

Two-Dimensional Carbon Graphdiyne: Advances in Fundamental and Application Research

Graphdiyne (GDY), a rising star of carbon allotropes, features a two-dimensional all-carbon network with the cohybridization of sp and sp² carbon atoms and represents a trend and research direction in the development of carbon materials. The sp/sp²-hybridized structure of GDY endows it with numerous advantages and advancements in controlled growth, assembly, and performance tuning, and many studies have shown that GDY has been a key material for innovation and development in the fields of catalysis, energy, photoelectric conversion, mode conversion and transformation of electronic devices, detectors, life sciences, etc. In the past ten years, the fundamental scientific issues related to GDY have been understood, showing differences from traditional carbon materials in controlled growth, chemical and physical properties and mechanisms, and attracting extensive attention from many scientists. GDY has gradually developed into one of the frontiers of chemistry and materials science, and has entered the rapid development period, producing large numbers of fundamental and applied research achievements in the fundamental and applied research of carbon materials. For the exploration of frontier scientific concepts and phenomena in carbon science research, there is great potential to promote progress in the fields of energy, catalysis, intelligent information, optoelectronics, and life sciences. In this review, the growth, self-assembly method, aggregation structure, chemical modification, and doping of GDY are shown, and the theoretical calculation and simulation and fundamental properties of GDY are also fully introduced. In particular, the applications of GDY and its formed aggregates in catalysis, energy storage, photoelectronic, biomedicine, environmental science, life science, detectors, and material separation are introduced.

Synthesis of a Wheel-Shaped Nanographdiyne

Graphdiyne, a sp- and sp²-hybridized 2D π-conjugated carbon material with well-dispersed pores and unique electronic properties, was well investigated and applied in catalysis, electronics, optics, and energy storage and conversion. Graphdiyne fragments with conjugation in 2D can provide in-depth insights for understanding the intrinsic structure-property relationships of graphdiyne. Herein, an atomic precise wheel-shaped nanographdiyne composed of six dehydrobenzo [18] annulenes ([18]DBAs, the smallest macrocyclic unit of graphdiyne), was realized through the sixfold intramolecular Eglinton coupling in the hexabutadiyne precursors obtained by the sixfold Cadiot-Chodkiewicz cross-coupling of hexaethynylbenzene. Its planar structure was revealed by X-ray crystallographic analysis. The full cross-conjugation of the six 18π electron circuits yields the π-electron conjugation along the giant π core. This work provides a realizable method for the synthesis of future graphdiyne fragments with different functional groups and/or heteroatom doping, as well as the study of the unique electronic/photophysical properties and aggregation behavior of graphdiyne.

Second Sphere Effects Promote Formic Acid Dehydrogenation by a Single-Atom Gold Catalyst Supported on Amino-Substituted Graphdiyne

Regulating the second sphere of homogeneous molecular catalysts is a common and effective method to boost their catalytic activities, while the second sphere effects have rarely been investigated for heterogeneous single-atom catalysts primarily due to the synthetic challenge for installing functional groups in their second spheres. Benefiting from the well-defined and readily tailorable structure of graphdiyne (GDY), an Au single-atom catalyst on amino-substituted GDY is constructed, where the amino group is located in the second sphere of the Au center. The Au atoms on amino-decorated GDY displayed superior activity for formic acid dehydrogenation compared with those on unfunctionalized GDY. The experimental studies, particularly the proton inventory studies, and theoretical calculations revealed that the amino groups adjacent to an Au atom could serve as proton relays and thus facilitate the protonation of an intermediate Au-H to generate H₂ . Our study paves the way to precisely constructing the functional second sphere on single-atom catalysts.

Single-metal atom sandwiched by graphdiyne and BN-doped graphdiyne sheets as an electrocatalyst for nitrogen reduction: a first-principles study

The exploration of efficient single-atom catalysts provides a prospective pattern for the sustainable development of electrocatalytic nitrogen fixation. We systematically researched the nitrogen reduction properties of catalysts with a single transition metal (TM) atom sandwiched between BN-doped graphdiyne and graphdiyne (labeled BN-TM-G) by first-principles calculations. The TM atom in the novel sandwich structure provides electrons to the adjacent B atom, which acts as the active site, thus driving the fixation and reduction of N₂. In the BN-TM-G system, the NRR catalytic activity is bound up with the positive charge polarization level of the TM atom. Among them, BN-Sc-G, BN-Ti-G, BN-V-G, and BN-Cr-G systems showed higher catalytic ability, and the competitive HER was inhibited. In particular, the lowest limiting potential of BN-Cr-G is -0.63 V is promising for the NRR catalyst.

A Deprotection-free Method for High-yield Synthesis of Graphdiyne Powder with In Situ Formed CuO Nanoparticles

With a direct band gap, superior charge carrier mobility, and uniformly distributed pores, graphdiyne (GDY) has stimulated tremendous interest from the scientific community. However, its broad application is greatly limited by the complicated multistep synthesis process including complex deprotection of hexakis-[(trimethylsilyl)ethynyl]benzene (HEB-TMS) and peeling of GDY from the substrates. Here, we describe a deprotection-free strategy to prepare GDY powder by directly using HEB-TMS as the monomer. When CuCl was used as the catalysts in DMF solvent, the yield of GDY powder reached ≈100 %. More interestingly, uniformly dispersed CuO nanoparticles with an average diameter of ≈2.9 nm were in situ formed on GDY after the reaction. The prepared CuO/GDY was demonstrated an excellent co-catalyst for photocatalytic hydrogen evolution, comparable to the state-of-art Pt co-catalyst. The deprotection-free approach will widen the use of GDY and facilitate its scaling up to industrial level.

Revealing the Mechanism of sp-N Doping in Graphdiyne for Developing Site-Defined Metal-Free Catalysts

Due to the limited reserves of metals, scientists are devoted to exploring high-performance metal-free catalysts based on carbon materials to solve environment-related issues. Doping would build up inhomogeneous charge distribution on surface, which is an efficient approach for boosting the catalytic performance. However, doping sites are difficult to control in traditional carbon materials, thus hindering their development. Taking the advantage of unique sp-C in graphdiyne (GDY), a new N doping configuration of sp-hybridized nitrogen (sp-N), bringing a Pt-comparable catalytic activity in oxygen reduction reaction is site-defined introduced. However, the reaction intermediate of this process is never captured, hindering the understanding of the mechanism and the precise synthesis of metal-free catalysts. After the four-year study, the fabrication of intermediate-like molecule is realized, and finally sp-N doped GDY via the pericyclic reaction is obtained. Compared with GDY doped with other N configurations, the designed sp-N GDY shows much higher catalytic activity in electroreduction of CO₂ toward CH₄ production, owing to the unique electronic structure introduced by sp-N, which is more favorable in stabilizing the intermediate. Thus, besides opening the black-box for the site-defined doping, this work reveals the relationship between doping configuration and products of CO₂ reduction.

Graphdiyne Electrochemistry: Progress and Perspectives

Graphdiyne, a carbon allotrope, was synthesized in 2010 for the first time. It consists of two acetylene bonds between adjacent benzene rings. Graphdiyne and its composites thus exhibit ultrahigh intrinsic electrochemical activities. As "star" electrode materials, they have been utilized for various electrochemical applications. With the aim of giving a full screen of graphdiyne electrochemistry, this review starts from the history of graphdiyne materials, followed by their structural and electrochemical features. Recent progress and achievements in the synthesis of graphdiyne materials and their composites are overviewed. Subsequently, various electrochemical applications of graphdiyne materials and their composites are summarized, covering those in the fields of electrochemical energy conversion, electrochemical energy storage, and electrochemical sensing. The perspectives of graphdiyne electrochemistry are also discussed and outlined.

2D graphdiyne: an emerging carbon material

As a new member of carbon allotropes, graphdiyne (GDY) has the characteristics of being one-atom-thick with two-dimensional layers comprising sp and sp² hybridized carbon atoms, and represents a trend in the development of carbon materials. Its unique chemical and electronic structures give GDY many unique and fascinating properties such as rich chemical bonds, highly conjugated and super-large π structures, infinitely distributed pores and high inhomogeneity of charge distribution. GDY has entered a period of rapid development, especially with the significant emergence of fundamental research and applied research achievements over the past five years. As one of the frontiers of chemistry and materials science, graphdiyne was listed in the Top 10 research areas in the 2020 Research Frontiers report and was jointly released in the Top 10 in the world by Clarivate and the Chinese Academy of Sciences. The research results have shown the great potential of GDY in the applications of energy, catalysis, environmental science, electronic devices, detectors, biomedicine and therapy, etc. Scientists are eager to explore and fully reveal the new properties, discover new scientific concepts and phenomena, discover the new conversion modes and mechanisms of GDY in photoelectricity, energy, and catalysis, etc., and build the important scientific value of new conversion devices. This review covers research on the foundation and application of GDY, such as the controlled preparation of new methods of GDY and GDY-based materials, studies on new mechanisms and properties in chemistry and physics, and the foundation and applications in energy, catalysis, photoelectric and devices.

π-Conjugation Induced Anchoring of Ferrocene on Graphdiyne Enable Shuttle-Free Redox Mediation in Lithium-Oxygen Batteries

Soluble redox mediators (RMs), an alternative to conventional solid catalysts, have been considered an effective countermeasure to ameliorate sluggish kinetics in the cathode of a lithium-oxygen battery recently. Nevertheless, the high mobility of RMs leads to serious redox shuttling, which induces an undesired lithium-metal degeneration and RM decomposition during trade-off catalysis against the sustainable operation of batteries. Here, a novel carbon family of graphdiyne matrix is first proposed to decouple the charge-carrying redox property of ferrocene and the shuttle effects. It is demonstrated that a ferrocene-anchored graphdiyne framework can function as stationary RM, not only preserving the redox-mediating capability of ferrocene, but also promoting the local orientated three-dimensional (3D) growth of Li₂ O₂ . As a result, the RM-assisted catalysis in lithium-oxygen battery remains of remarkable efficiency and stability without the depletion of oxidized RMs or lithium degradation, resulting in a significantly enhanced electrochemical performance.

Amorphous materials for elementary-gas-involved electrocatalysis: an overview

Given the critical demands on energy conversion, storage, and transportation, tremendous interest has been devoted to the field of material development related to energy harvesting, recently. As the only route towards energy utilization, the carriers with the characteristics of low carbon are regarded as the future choice, e.g., hydrogen and ammonia. To this end, electrocatalysis provides a green way to access these substances. However, the unfulfilled conversion efficiency is the bottleneck for practical application. In this review, the promising characteristics of amorphous materials and the amorphous-induced electrocatalytic enhancement (AIEE) were emphasized. In the beginning, the characteristics of amorphous materials are briefly summarized. The basic mechanism of heterogeneous electrocatalytic reactions is illustrated, including the hydrogen/oxygen evolution and oxygen/nitrogen reduction. In the third part, the electrocatalytic performance of amorphous materials is discussed in detail, and the mechanism of AIEE is highlighted. In the last section of this review, the challenges and outlook for the development of amorphous enhanced electrocatalysis are presented.

A two-dimensional porous conjugated porphyrin polymer for uniform lithium deposition

Uniform lithium deposition is a benefit to achieving high-energy-density lithium metal batteries. There are many effective methods to suppress the dendritic growth of metallic lithium and promote the application of the lithium anode. However, the designation of lithiophilic sites at the atomic level remains a huge challenge. Herein, a two-dimensional porous conjugated porphyrin polymer linked by two acetylenic linkages from an in situ coupling reaction has been prepared on copper foil and employed as the lithiophilic host. The four electron-rich pyrrolic nitrogen atoms in the porphyrin building block and the linkage electron-rich sp-hybridized carbon atoms were regarded as precise lithiophilic sites, resulting in a decreased nucleation overpotential and dendrite free morphology. With uniform lithium deposition, the electrochemical performance of the electrode was significantly improved in regard to the overpotential, coulombic efficiency and lifespan. This work expands the precise construction of lithiophilic sites at the atomic level and benefits to further development of high-energy density lithium metal batteries.

2D Graphdiyne: A Rising Star on the Horizon of Energy Conversion

Two-dimensional (2D) graphdiyne (GDY), a rapidly rising star on the horizon of carbon materials, is a new carbon allotrope featuring sp- and sp² -cohybridized carbon atoms and 2D one-atom-thick network. Since the first successful synthesis of GDY by Professor Li's group in 2010, GDY has attached great interests from both scientific and industrial viewpoints based on its unique structure and physicochemical properties, which provides a fertile ground for applications in various fields including electrocatalysis, energy conversion, energy storage and optoelectronic devices. In this work, various potential properties of the GDY-based electrocatalysts and their recent advances in energy conversion are reviewed, including atomic catalysts, heterogeneous catalysts, and metal-free catalysts. The critical role of GDY in improving catalytic activity and stability is analyzed. The perspectives of the challenges and opportunities faced by GDY-based materials for energy conversion are also outlined.

Decorating graphdiyne on ultrathin bismuth subcarbonate nanosheets to promote CO2 electroreduction to formate

Electrocatalytic reduction of CO₂ is one of the most attractive approaches for converting CO₂ into valuable chemical feedstocks and fuels. This work reports a catalyst comprising graphdiyne-decorated bismuth subcarbonate (denoted as BOC@GDY) for efficient electroreduction of CO₂ to formate. The BOC@GDY shows a stable current density of 200 mA cm^-2 at -1.1 V in a flow cell configuration, with a faradaic efficiency of 93.5% for formate. Experimental results show that the synergistic effect in BOC@GDY is beneficial for the CO₂ adsorption affinity, the reaction kinetics and the selectivity for formate. In addition, in-situ X-ray absorption and Raman spectroscopy indicate that the electron-rich GDY could facilitate the reduction from Bi(III) to Bi(0), thus leading to more active sites. We also demonstrate that the promoting effect of GDY in CO₂ electroreduction can be further extended to other metal catalysts. To the best of our knowledge, such general promoting functions of GDY for CO₂ electroreduction have not been documented thus far.

Advances on Graphyne-Family Members for Superior Photocatalytic Behavior

Graphyne (GY) and graphdiyne (GDY) have been employed in photocatalysis since 2012, presenting intriguing electronic and optical properties, such as high electron mobility and intrinsic bandgap due to their high π-conjugated structures. Authors are reporting the enhanced photocatalytic efficiency of these carbon allotropes when combined with different metal oxides or other carbon materials. However, the synthesis of graphyne-family members (GFMs) is still very recent, and not much is known about the true potential of these photocatalytic materials. In this review article, the implications of different synthesis routes on the structural features and photocatalytic properties of these materials are elucidated. The application of GFMs in the nicotinamide adenine dinucleotide (NADH) regeneration, hydrogen and oxygen evolution, and carbon dioxide reduction is discussed, as well as in the degradation of pollutants and bacteria inactivation in water and wastewater treatment.

Forming electron traps deactivates self-assembled crystalline organic nanosheets toward photocatalytic overall water splitting

Most biological photoredox reactions occur in sophisticated molecular assemblies consisting of highly organized light-harvesting moieties and catalytic centers. Mimicking these prototypes by creating supramolecular assemblies could be a potentially viable approach toward artificial photosynthesis. Although self-assembled organic materials are known to carry out water splitting reactions, developing self-assembled organic materials for photocatalytic overall water splitting still remains a critical challenge. Herein, we first demonstrate that crystalline organic nanosheets assembled from linear oligo(phenylene butadiynylene) (OPB) are able to catalyze overall water splitting under visible light irradiation. Further investigations reveal that the photocatalytic activity of self-assembled organic structures is closely related to the crystalline structure along with the corresponding electronic structure. Structural disorders in OPB nanosheets and extrinsic factors such as adsorbed water molecules will induce the formation of electron traps which can make the OPB nanosheets thermodynamically unfavorable for photocatalytic overall water splitting. The deactivation mechanism unveiled in this study provides crucial insights into the assembling of artificial organic materials for future solar-to-chemical energy conversion.

Graphdiyne nanosheets as a platform for accurate copper(ii) ion detection via click chemistry and fluorescence resonance energy transfer

A novel sensing platform for sensitive detection of copper(ii) ions (Cu²⁺) in living cells and body fluids was developed by taking advantage of the excellent fluorescence quenching ability of graphdiyne (GDY) and the high specificity of click chemistry for the first time.

Cu²⁺ detection was performed by taking advantage of the fluorescence quenching ability of graphdiyne and the high specificity of click chemistry.

Structural, Electronic, and Vibrational Properties of a Two-Dimensional Graphdiyne-like Carbon Nanonetwork Synthesized on Au(111): Implications for the Engineering of sp-sp2 Carbon Nanostructures

Graphdiyne, atomically thin two-dimensional (2D) carbon nanostructure based on sp-sp2 hybridization is an appealing system potentially showing outstanding mechanical and optoelectronic properties. Surface-catalyzed coupling of halogenated sp-carbon-based molecular precursors represents a promising bottom-up strategy to fabricate extended 2D carbon systems with engineered structure on metallic substrates. Here, we investigate the atomic-scale structure and electronic and vibrational properties of an extended graphdiyne-like sp-sp2 carbon nanonetwork grown on Au(111) by means of the on-surface synthesis. The formation of such a 2D nanonetwork at its different stages as a function of the annealing temperature after the deposition is monitored by scanning tunneling microscopy (STM), Raman spectroscopy, and combined with density functional theory (DFT) calculations. High-resolution STM imaging and the high sensitivity of Raman spectroscopy to the bond nature provide a unique strategy to unravel the atomic-scale properties of sp-sp2 carbon nanostructures. We show that hybridization between the 2D carbon nanonetwork and the underlying substrate states strongly affects its electronic and vibrational properties, modifying substantially the density of states and the Raman spectrum compared to the free standing system. This opens the way to the modulation of the electronic properties with significant prospects in future applications as active nanomaterials for catalysis, photoconversion, and carbon-based nanoelectronics.

Spontaneously Splitting Copper Nanowires into Quantum Dots on Graphdiyne for Suppressing Lithium Dendrites

As an emerging carbon allotrope, the controllable growth of graphdiyne has been an important means to explore its unique scientific properties and applications. In this work, the effect of the crystal structure of copper (Cu) on the growth of graphdiyne is systematically studied. It is found that the crystal boundaries are the origin of the reaction activity. The polycrystalline Cu nanowire with many crystal boundaries is spontaneously split into Cu quantum dots (about 3 nm) by the grown graphdiyne. These Cu quantum dots are uniformly dispersed on the graphdiyne, and they block the long-range ordered growth of the graphdiyne. These Cu quantum dots in situ supported on graphdiyne demonstrate high efficiency in inhibiting the growth of lithium dendrites in lithium metal batteries. Based on this interesting finding, the Cu quantum dots anchored on the all-carbon graphdiyne can be prepared on a large scale, and unique applications of Cu quantum dots in electrochemical fields can be implemented.

Using graphdiyne (GDY) as a catalyst support for enhanced performance in organic pollutant degradation and hydrogen production: A review

The development of carbon materials brings a new two-dimensional catalyst support, graphdiyne (GDY), which is attracting increasing interest in the field of catalysis. This article presents a systematical review of recent studies about the characteristics, design strategies, and applications of GDY-supported catalysts. The sp- and sp²-hybridized carbon, high electrical conductivity, direct band gap, and high intrinsic carrier mobility are key characteristics for GDY to serve as a competitive catalyst support. Hydrothermal method (or solvothermal method), GDY in-situ growth, and electrochemical deposition are commonly used to load catalysts on GDY support. In the applications of GDY-supported photocatalysts, GDY mainly serves as an electron or hole transfer material. For the electrocatalytic hydrogen production, the unique electronic structure and high electrical conductivity of GDY can promote the electron transfer and water splitting kinetics. This review is expected to provide meaningful insight and guidance for the design of GDY-supported catalysts and their applications.

Artificial Carbon Graphdiyne: Status and Challenges in Nonlinear Photonic and Optoelectronic Applications

The creative integration of sp-hybridized carbon atoms into artificial carbon graphdiyne has led to graphdiyne with superior properties in terms of uniformly distributed pores, ambipolar carrier transport, natural bandgap, and broadband absorption. Consequently, graphdiyne, regarded as a promising carbon material, has garnered particular attention in light-matter interactions. Light-matter interactions play an important role in optical information technology and meet the increasing demand for various energy sources. Herein, the status and challenges in nonlinear photonic and optoelectronic applications of graphdiyne, which are still in the infancy stage, are summarized. Furthermore, the bottleneck and perspective of graphdiyne in these aspects are discussed. It is therefore anticipated that this review could promote the development of graphdiyne in photonic and optoelectronic fields.

Computational studies on triphenyldiyne as a two-dimensional visible-light-driven photocatalyst for overall water splitting

The high carrier mobility, porous configurations and tunable electronic structures of two-dimensional (2D) carbon materials hold great promise in energy conversion and storage. However, few of them are capable of photocatalytic overall water splitting. Here, by means of first-principles calculations within the quasi-particle approximation and the Bethe-Salpeter equation, we demonstrated a unique framework of triphenylenes (sp2) and acetylenic linkages (sp), namely triphenyldiyne (TDY) that has the electronic band structure suitable for photocatalytic overall water splitting along with pronounced optical absorbance in visible light. The redox ability of its photogenerated electrons is high enough to drive the hydrogen evolution reaction (HER). Through Ni doping with TDY, its overpotential for the oxygen evolution reaction (OER) can be reduced to match the redox ability of its photogenerated holes, enabling the photocatalytic overall water splitting in sunlight without the need of sacrificial reagents. This work offers not only a low-cost, earth-abundant and environmental-friendly photocatalyst, but also a promising strategy for designing highly efficient photocatalysts for overall water splitting.

Atomic-Level Functionalized Graphdiyne for Electrocatalysis Applications

Graphdiyne (GDY) is a two-dimensional (2D) electron-rich full-carbon planar material composed of sp2- and sp-hybridized carbon atoms, which features highly conjugated structures, uniformly distributed pores, tunable electronic characteristics and high specific surface areas. The synthesis strategy of GDY by facile coupling reactions under mild conditions provides more convenience for the functional modification of GDY and offers opportunities for realizing the special preparation of GDY according to the desired structure and unique properties. These structural characteristics and excellent physical and chemical properties of GDY have attracted increasing attention in the field of electrocatalysis. Herein, the research progress in the synthesis of atomic-level functionalized GDYs and their electrocatalytic applications are summarized. Special attention was paid to the research progress of metal-atom-anchored and nonmetallic-atom-doped GDYs for applications in the oxygen reduction reaction (ORR), the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) catalytic processes. In addition, several potential development prospects and challenges of these 2D highly conjugated electron-rich full-carbon materials in the field of electrocatalysis are presented.

A Graphdiyne Oxide-Based Iron Sponge with Photothermally Enhanced Tumor-Specific Fenton Chemistry

Fenton reaction-mediated oncotherapy is an emerging strategy which uses iron ions to catalytically convert endogenous hydrogen peroxide into hydroxyl radicals, the most reactive oxygen species found in biology, for efficient cancer therapy. However, Fenton reaction efficiency in tumor tissue is typically limited due to restrictive conditions. One strategy to overcome this obstacle is to increase the temperature specifically at the tumor site. Herein, a tumor-targeting iron sponge (TTIS) nanocomposite based on graphdiyne oxide, which has a high affinity for iron is described. TTIS can accumulate in tumor tissue by decoration with a tumor-targeting polymer to enable tumor photoacoustic and magnetic resonance imaging. With its excellent photothermal conversion efficiency (37.5%), TTIS is an efficient photothermal therapy (PTT) agent. Moreover, the heat produced in the process of PTT can accelerate the release of iron ions from TTIS and simultaneously enhance the efficiency of the Fenton reaction, thus achieving a combined PTT and Fenton reaction-mediated cancer therapy. This work introduces a graphdiyne oxide-based iron sponge that exerts an enhanced antitumor effect through PTT and Fenton chemistry.

Graphdiyne-Based Flexible Photodetectors with High Responsivity and Detectivity

Graphdiyne (GDY), a newly emerging 2D carbon allotrope, has been widely explored in various fields owing to its outstanding electronic properties such as the intrinsic bandgap and high carrier mobility. Herein, GDY-based photoelectrochemical-type photodetection is realized by spin-coating ultrathin GDY nanosheets onto flexible poly(ethylene terephthalate) (PET) substrates. The GDY-based photodetectors (PDs) demonstrate excellent photo-responsive behaviors with high photocurrent (P_ph , 5.98 µA cm^{- 2} ), photoresponsivity (R_ph , 1086.96 µA W^{- 1} ), detectivity (7.31 × 10¹⁰ Jones), and excellent long-term stability (more than 1 month). More importantly, the PDs maintain an excellent P_ph after 1000 cycles of bending (4.45 µA cm^{- 2} ) and twisting (3.85 µA cm^{- 2} ), thanks to the great flexibility of the GDY structure that is compatible with the flexible PET substrate. Density functional theory (DFT) calculations are adopted to explore the electronic characteristics of GDY, which provides evidence for the performance enhancement of GDY in alkaline electrolyte. In this way, the GDY-based flexible PDs can enrich the fundamental study of GDY and pave the way for the exploration of GDY heterojunction-based photodetection.

2D graphdiyne: an excellent ultraviolet nonlinear absorption material

With an sp2-hybridized carbon atom structure, graphene is recognized as a nonlinear absorption (NLA) material, which has motivated scientists to explore new allotropes of carbon. Different from graphene, graphdiyne (GDY) consists of sp- and sp2-hybridized carbon atoms. An sp-hybridized carbon-carbon triple bond structure will bring in novel nonlinear optical properties, which are different from other allotropes of carbon. In this study, we investigated the broadband NLA properties (ultraviolet-infrared waveband) of GDY nanosheets, exfoliated using a liquid-phase exfoliation (LPE) method. The short ultraviolet cut-off wavelength (around 200 nm-220 nm) forebodes the potential application of GDY as an ultraviolet optical material. The outstanding NLA resulting in an ultraviolet waveband attests that the GDY nanosheets are veritable ultraviolet NLA materials, which have potential applications in ultraviolet optics. Our study broadens the application scopes of nanomaterials.

Metal-Tuned Acetylene Linkages in Hydrogen Substituted Graphdiyne Boosting the Electrochemical Oxygen Reduction

Different from graphene with the highly stable sp² -hybridized carbon atoms, which shows poor controllability for constructing strong interactions between graphene and guest metal, graphdiyne has a great potential to be engineered because its high-reactive acetylene linkages can effectively chelate metal atoms. Herein, a hydrogen-substituted graphdiyne (HsGDY) supported metal catalyst system through in situ growth of Cu₃ Pd nanoalloys on HsGDY surface is developed. Benefiting from the strong metal-chelating ability of acetylenic linkages, Cu₃ Pd nanoalloys are intimately anchored on HsGDY surface that accordingly creates a strong interaction. The optimal HsGDY-supported Cu₃ Pd catalyst (HsGDY/Cu₃ Pd-750) exhibits outstanding electrocatalytic activity for the oxygen reduction reaction (ORR) with an admirable half-wave potential (0.870 V), an impressive kinetic current density at 0.75 V (57.7 mA cm^-2 ) and long-term stability, far outperforming those of the state-of-the-art Pt/C catalyst (0.859 V and 15.8 mA cm^-2 ). This excellent performance is further highlighted by the Zn-air battery using HsGDY/Cu₃ Pd-750 as cathode. Density function theory calculations show that such electrocatalytic performance is attributed to the strong interaction between Cu₃ Pd and CC bonds of HsGDY, which causes the asymmetric electron distribution on two carbon atoms of CC bond and the strong charge transfer to weaken the shoulder-to-shoulder π conjugation, eventually facilitating the ORR process.