Anchoring zero valence single atoms of nickel and iron on graphdiyne for hydrogen evolution

Efficient Hydrogen Evolution on Nanoscale Graphdiyne

Self-active metal-free graphdiyne (GDY) is used, which has a precise chemical structure, as a model carbon-based metal-free electrocatalyst to assess its activity in the hydrogen evolution reaction (HER) and to understand the origin of electrocatalytic performance at the atomic level. The studies reveal that the unusual electrocatalytic properties of GDY originate from its unique nanostructure, which can simultaneously provide highly active sites for hydrogen adsorption and facilitate the electron-transfer process for proton reduction. Accordingly, GDY can act as a metal-free efficient HER electrocatalyst with Pt-like HER activity, but with long-term durability superior to that of Pt/C under the wide pH range (from acidic to basic). To the best of knowledge, such HER performance is better than that of other reported metal-free electrocatalysts and most transition-metal electrocatalysts-even Pt-based ones.

MXene-Based Materials for Solar Cell Applications

MXenes are a class of two-dimensional nanomaterials with exceptional tailor-made properties, making them promising candidates for a wide variety of critical applications from energy systems, optics, electromagnetic interference shielding to those advanced sensors, and medical devices. Owing to its mechano-ceramic nature, MXenes have superior thermal, mechanical, and electrical properties. Recently, MXene-based materials are being extensively explored for solar cell applications wherein materials with superior sustainability, performance, and efficiency have been developed in demand to reduce the manufacturing cost of the present solar cell materials as well as enhance the productivity, efficiency, and performance of the MXene-based materials for solar energy harvesting. It is aimed in this review to study those MXenes employed in solar technologies, and in terms of the layout of the current paper, those 2D materials candidates used in solar cell applications are briefly reviewed and discussed, and then the fabrication methods are introduced. The key synthesis methods of MXenes, as well as the electrical, optical, and thermoelectric properties, are explained before those research efforts studying MXenes in solar cell materials are comprehensively discussed. It is believed that the use of MXene in solar technologies is in its infancy stage and many research efforts are yet to be performed on the current pitfalls to fill the existing voids.

Stabilizing Interface pH by N-Modified Graphdiyne for Dendrite-Free and High-Rate Aqueous Zn-ion Batteries

Zn dendrite issue was intensively studied via tuning zinc ion flux. pH change seriously influences dendrite formation, while its importance has not been revealed. Here, we construct a N-modification graphdiyne interface (NGI) to stabilize pH by mediating hydrated zinc ion desolvation. Operando pH detection reveals pH stabilization by NGI. This works with pores in NGI to achieve dendrite-free Zn deposition and an increased symmetric cell lifespan by 116 times. Experimental and theoretical results owe pH stabilization to desolvation with a reduced activation energy achieved by electron transfer from solvation sheath to N atom. The efficient desolvation ensures that electron directly transfers from substrate to Zn2+ (rather than the coordinated H2O), avoiding O-H bond splitting. Hence, Zn-V6O13 battery achieves a long lifespan at 20.65 mA cm-2 and 1.07 mAh cm-2. This work reveals the significance of interface pH and provides a new approach to address Zn dendrite issue.

Single-Atom Engineering to Ignite 2D Transition Metal Dichalcogenide Based Catalysis: Fundamentals, Progress, and Beyond

Single-atom catalysis has been recognized as a pivotal milestone in the development history of heterogeneous catalysis by virtue of its superior catalytic performance, ultrahigh atomic utilization, and well-defined structure. Beyond single-atom protrusions, two more motifs of single-atom substitutions and single-atom vacancies along with synergistic single-atom motif assemblies have been progressively developed to enrich the single-atom family. On the other hand, besides traditional carbon material based substrates, a wide variety of 2D transitional metal dichalcogenides (TMDs) have been emerging as a promising platform for single-atom catalysis owing to their diverse elemental compositions, variable crystal structures, flexible electronic structures, and intrinsic activities toward many catalytic reactions. Such substantial expansion of both single-atom motifs and substrates provides an enriched toolbox to further optimize the geometric and electronic structures for pushing the performance limit. Concomitantly, higher requirements have been put forward for synthetic and characterization techniques with related technical bottlenecks being continuously conquered. Furthermore, this burgeoning single-atom catalyst (SAC) system has triggered serial scientific issues about their changeable single atom-2D substrate interaction, ambiguous synergistic effects of various atomic assemblies, as well as dynamic structure-performance correlations, all of which necessitate further clarification and comprehensive summary. In this context, this Review aims to summarize and critically discuss the single-atom engineering development in the whole field of 2D TMD based catalysis covering their evolution history, synthetic methodologies, characterization techniques, catalytic applications, and dynamic structure-performance correlations. In situ characterization techniques are highlighted regarding their critical roles in real-time detection of SAC reconstruction and reaction pathway evolution, thus shedding light on lifetime dynamic structure-performance correlations which lay a solid theoretical foundation for the whole catalytic field, especially for SACs.

Chemistry, Functionalization, and Applications of Recent Monoelemental Two-Dimensional Materials and Their Heterostructures

The past decades have witnessed a rapid expansion in investigations of two-dimensional (2D) monoelemental materials (Xenes), which are promising materials in various fields, including applications in optoelectronic devices, biomedicine, catalysis, and energy storage. Apart from graphene and phosphorene, recently emerging 2D Xenes, specifically graphdiyne, borophene, arsenene, antimonene, bismuthene, and tellurene, have attracted considerable interest due to their unique optical, electrical, and catalytic properties, endowing them a broader range of intriguing applications. In this review, the structures and properties of these emerging Xenes are summarized based on theoretical and experimental results. The synthetic approaches for their fabrication, mainly bottom-up and top-down, are presented. Surface modification strategies are also shown. The wide applications of these emerging Xenes in nonlinear optical devices, optoelectronics, catalysis, biomedicine, and energy application are further discussed. Finally, this review concludes with an assessment of the current status, a description of existing scientific and application challenges, and a discussion of possible directions to advance this fertile field.

Selective Conversion of CO2 into Cyclic Carbonate on Atom Level Catalysts

The conversion of carbon dioxide (CO₂) into organic carbonates under ambient temperatures and pressures with high conversion and selectivity still faces a great challenge. The zerovalent atomic catalysts (ACs), featuring accurate structure and valence states, provide a new and accurate model system for catalysis. Herein we developed a general preadsorption-reduction strategy to synthesize zerovalent cobalt AC on graphdiyne (Co⁰/GDY). The Co⁰/GDY ACs were used for efficient and selective CO₂ fixation. We were surprised to find that Co⁰/GDY ACs reached nearly 100% conversion at 80 °C and 1 atm in CO₂ fixation and with a significantly high turnover frequency (TOF) of 3024.8 h^-1, which is almost several orders larger than that of benchmarked catalysts. Such high conversion and selectivity represent the advantages of emerging catalysts.

Single-Atom (Iron-Based) Catalysts: Synthesis and Applications

Supported single-metal atom catalysts (SACs) are constituted of isolated active metal centers, which are heterogenized on inert supports such as graphene, porous carbon, and metal oxides. Their thermal stability, electronic properties, and catalytic activities can be controlled via interactions between the single-metal atom center and neighboring heteroatoms such as nitrogen, oxygen, and sulfur. Due to the atomic dispersion of the active catalytic centers, the amount of metal required for catalysis can be decreased, thus offering new possibilities to control the selectivity of a given transformation as well as to improve catalyst turnover frequencies and turnover numbers. This review aims to comprehensively summarize the synthesis of Fe-SACs with a focus on anchoring single atoms (SA) on carbon/graphene supports. The characterization of these advanced materials using various spectroscopic techniques and their applications in diverse research areas are described. When applicable, mechanistic investigations conducted to understand the specific behavior of Fe-SACs-based catalysts are highlighted, including the use of theoretical models.

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.

Direct Charge Trapping Multilevel Memory with Graphdiyne/MoS2 Van der Waals Heterostructure

Direct charge trapping memory, a new concept memory without any dielectric, has begun to attract attention. However, such memory is still at the incipient stage, of which the charge-trapping capability depends on localized electronic states that originated from the limited surface functional groups. To further advance such memory, a material with rich hybrid states is highly desired. Here, a van der Waals heterostructure design is proposed utilizing the 2D graphdiyne (GDY) which possesses abundant hybrid states with different chemical groups. In order to form the desirable van der Waals coupling, the plasma etching method is used to rapidly achieve the ultrathin 2D GDY with smooth surface for the first time. With the plasma-treated 2D GDY as charge-trapping layer, a direct charge-trapping memory based on GDY/MoS2 is constructed. This bilayer memory is featured with large memory window (90 V) and high degree of modulation (on/off ratio around 8 × 107 ). Two operating mode can be achieved and data storage capability of 9 and 10 current levels can be obtained, respectively, in electronic and opto-electronic mode. This GDY/MoS2 memory introduces a novel application of GDY as rich states charge-trapping center and offers a new strategy of realizing high performance dielectric-free electronics, such as optical memories and artificial synaptic.

Bimetallic Mixed Clusters Highly Loaded on Porous 2D Graphdiyne for Hydrogen Energy Conversion

There is no doubt that hydrogen energy can play significant role in promoting the development and progress of modern society. The utilization of hydrogen energy has developed rapidly, but it is far from the requirement of human. Therefore, it is very urgent to develop methodologies and technologies for efficient hydrogen production, especially high activity and durable electrocatalysts. Here a bimetallic oxide cluster on heterostructure of vanadium ruthenium oxides/graphdiyne (VRuOx /GDY) is reported. The unique acetylene-rich structure of graphdiyne achieves outstanding characteristics of electrocatalyst: i) controlled preparation of catalysts for achieving multiple-metal clusters; ii) regulation of catalyst composition and morphology for synthesizing high-performance catalysts; iii) highly active and durable hydrogen evolution reaction (HER) properties. The optimal porous electrocatalyst (VRu0.027 Ox /GDY) can deliver 10 mA cm-2 at low overpotentials of 13 and 12 mV together with robust long-term stability in alkaline and neutral media, respectively, which are much smaller than Pt/C. The results reveal that the synergism of different components can efficiently facilitate the electron/mass transport properties, reduce the energy barrier, and increase the active site number for high catalytic performances.

Facile and large-scale synthesis of polymorphic graphdiyne catalyzed by transition metal salts for organic pollutant removal

Organic pollutants widely exist in the environment, causing a lot of potential harm. On account of excellent physical and chemical properties, graphdiyne (GDY) has been widely used in many potential fields. However, it is crucial to develop more synthetic methods to achieve mass production of GDY and explore its universality in the removal of organic pollutants. Herein, six transition metal salts including Cu salts and Pd salts were selected as catalysts to successfully synthesize GDY with different morphologies by a coupling reaction. The method is simple, safe, easy to operate and suitable for large-scale production. Among them, CuSO4-catalyzed GDY has higher yield (>90%), lower density and fewer defects. Furthermore, it can efficiently remove organic pollutants from water such as dyes, tetracycline antibiotics and neonicotinoid pesticides, demonstrating that the adsorption material has a certain universality. In particular, the adsorption effect of GDY on dye is comparable to that of MWCNTs and stronger than that of conventional adsorbents such as graphene and activated carbon. This work provides more possibilities for the industrial production of GDY and its promising application for the removal of organic pollutants.

2D Silicene Nanosheets for High-Performance Zinc-Ion Hybrid Capacitor Application

Supercapacitors possessing fast-charging characteristics and long lifespan are becoming increasingly important for powering portable and smart energy storage devices, and combining capacitive and battery-type materials into an integrated device is an effective method for increasing the overall performance of capacitors. Silicene is being designed as a cathode for the development of enhanced capacitance and ultra-cycle stable zinc-ion hybrid capacitors. Possessing a maximum areal capacity of 14 mF cm^-2, a maximum power density of 9 mW cm^-2, capacitance retention of 112% even after 10 000 cycles, and an unexpectedly high energy density of 23 mJ cm^-2, this achievement of the zinc-ion hybrid capacitor would be superior to that of previously reported silicon-based supercapacitors. The DFT calculations further reveal that Zn ions dominate the capacitive behavior of the silicene electrode. The support association between silicene and zinc-ion hybrid capacitors so that they can take advantage of each other's strengths, which takes electrochemical energy technology to a stage, offering a straightforward proposal for integration and implementation of silicon-based materials.

Graphdiyne: from Preparation to Biomedical Applications

Graphdiyne(GDY) is a kind of two-dimensional carbon nanomaterial with specific configurations of sp and sp 2 carbon atoms. The key progress in the preparation and application of GDY is bringing carbon materials to a brand-new level. Here, the various properties and structures of GDY are introduced, including the existing strategies for the preparation and modification of GDY. In particular, GDY has gradually emerged in the field of life sciences with its unique properties and performance, therefore, the development of biomedical applications of GDY is further summarized. Finally, the challenges of GDY toward future biomedical applications are discussed.

High Voltage-Stabilized Graphdiyne Cathode Interface

Suppressing the irreversible interfacial reactions is an important scientific bottleneck in the development of stable high-energy-density lithium-ion battery. The interfacial chemistry of graphdiyne (GDY) on the high-voltage cathode of LiNi_0.5 Mn_1.5 O₄ (LNMO) shows a very interesting process, in which the sp-hybridization carbon atoms chemically scavenge the hydrofluoric acid (HF) and in situ form the fluorinated GDY interface. It first turns the harmful HF into profit, and greatly enhances the interfacial stability and restrains the side reaction on the cathode under high working voltage. The GDY-coated LNMO cathode obviously alleviates the electrolyte degradation, achieves high Coulombic efficiency and reliability. Due to atomic-level selectivity and chemical trapping of HF by GDY, it effectively suppresses the dissolution of Mn, Ni elements. These results highlight the unparalleled advantages of GDY in the formation of high stable interfaces and protection of high-energy-density electrodes.

Spectroscopic Analyses of Changes in Photocatalytic and Catalytic Activities of Mn- and Ni-Ion Doped and Base-Treated Reduced Graphene Oxide

While reduced graphene oxide (rGO) is used widely as a catalyst, its catalytic activity can be improved significantly by modifying it with a metal. In this study, we compared the photocatalytic and catalytic properties of base-treated rGO particles and transition-metal-ion-doped rGO based on the oxidation reaction of thiophenol and the photocatalytic degradation of 4-chlorophenol. Since the two catalytic activities are related to the changes in the electronic structure of rGO, X-ray photoemission spectroscopy, X-ray absorption spectroscopy, and Raman spectroscopy were performed. When rGO was doped with Mn2+ ions, its catalytic properties improved with respect to both reactions. The changes in the electronic structure of rGO are attributed to the formation of defect structures on the rGO surface via a reaction between the doped Mn2+ ions and oxygen of the rGO surface. Thus, the results show that the doping of rGO with Mn ions in the +2-charge state (stable oxide form: MnO) enhances its catalytic and photocatalytic activities. Hence, this study provides new insights into the use of defect-controlled rGO as a novel catalyst.

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.

Defect and Doping Engineered Penta-graphene for Catalysis of Hydrogen Evolution Reaction

Water electrolysis is a sustainable and clean method to produce hydrogen fuel via hydrogen evolution reaction (HER). Using stable, effective and low-cost electrocatalysts for HER to substitute expensive noble metals is highly desired. In this paper, by using first-principles calculation, we designed a defect and N-, S-, P-doped penta-graphene (PG) as a two-dimensional (2D) electrocatalyst for HER, and its stability, electronic properties and catalytic performance were investigated. The Gibbs free energy (ΔG_H), which is the best descriptor for the HER, is calculated and optimized, the calculation results show that the ΔG_H can be 0 eV with C2 vacancies and P doping at C1 active sites, which should be the optimal performance for a HER catalyst. Moreover, we reveal that the larger charge transfer from PG to H, the closer ΔG_H is to zero according to the calculation of the electron charge density differences and Bader charges analysis. Ulteriorly, we demonstrated that the HER performance prefers the Volmer-Heyrovsky mechanism in this study.

Graphdiyne-based metal atomic catalysts for synthesizing ammonia

Development of novel catalysts for nitrogen reduction at ambient pressures and temperatures with ultrahigh ammonia (NH3) yield and selectivity is challenging. In this work, an atomic catalyst with separated Pd atoms on graphdiyne (Pd-GDY) was synthesized, which shows fascinating electrocatalytic properties for nitrogen reduction. The catalyst has the highest average NH3 yield of 4.45 ± 0.30 mgNH3 mgPd -1 h-1, almost tens of orders larger than for previously reported catalysts, and 100% reaction selectivity in neutral media. Pd-GDY exhibits almost no decreases in NH3 yield and Faradaic efficiency. Density functional theory calculations show that the reaction pathway prefers to perform at the (Pd, C1, C2) active area because of the strongly coupled (Pd, C1, C2), which elevates the selectivity via enhanced electron transfer. By adjusting the p-d coupling accurately, reduction of self-activated nitrogen is promoted by anchoring atom selection, and side effects are minimized.

Designing Undercoordinated Ni-Nx and Fe-Nx on Holey Graphene for Electrochemical CO2 Conversion to Syngas

In this study, we propose a top-down approach for the controlled preparation of undercoordinated Ni-N_x (Ni-hG) and Fe-N_x (Fe-hG) catalysts within a holey graphene framework, for the electrochemical CO₂ reduction reaction (CO₂RR) to synthesis gas (syngas). Through the heat treatment of commercial-grade nitrogen-doped graphene, we prepared a defective holey graphene, which was then used as a platform to incorporate undercoordinated single atoms via carbon defect restoration, confirmed by a range of characterization techniques. We reveal that these Ni-hG and Fe-hG catalysts can be combined in any proportion to produce a desired syngas ratio (1-10) across a wide potential range (-0.6 to -1.1 V vs RHE), required commercially for the Fischer-Tropsch (F-T) synthesis of liquid fuels and chemicals. These findings are in agreement with our density functional theory calculations, which reveal that CO selectivity increases with a reduction in N coordination with Ni, while unsaturated Fe-N_x sites favor the hydrogen evolution reaction (HER). The potential of these catalysts for scale up is further demonstrated by the unchanged selectivity at elevated temperature and stability in a high-throughput gas diffusion electrolyzer, displaying a high-mass-normalized activity of 275 mA mg^-1 at a cell voltage of 2.5 V. Our results provide valuable insights into the implementation of a simple top-down approach for fabricating active undercoordinated single atom catalysts for decarbonized syngas generation.

1 T-MoSe2 monolayer supported single Pd atom as a highly-efficient bifunctional catalyst for ORR/OER

The development of highly-efficient catalysts for oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) is highly crucial for the commercial applications of some novel energy-related devices. Herein, using comprehensive first-principles computations, the potential of a variety of single metal-based catalysts supported by MoSe₂ nanosheet to boost the ORR or OER process was evaluated. The computations revealed that these considered metal atoms can be more stably anchored on 1 T-MoSe₂ than those of on 2H-MoSe₂. In particular, the supported Ni and Pd catalysts on 1 T-MoSe₂ exhibit high OER activity due to their quite low overpotential (0.47 and 0.49 V). Meanwhile, the anchored Pd atom on 1 T-MoSe₂ also displays excellent ORR performance with an ultra-low overpotential of 0.32 V, thus implying its superior bifunctional activity for ORR/OER. Our results provide a quite promising avenue to design a new class of MoSe₂-based single atom catalysts for fuel cells, which also further enriches the application fields of MoSe₂ nanosheets in advanced catalysis.

Post-modified Strategies of Graphdiyne for Electrochemical Applications

The new carbon material graphdiyne (GDY) has been verified to have a great application prospect in electrochemical field. In order to study its properties and expand its scope of application, various experiments including structural control tests are imposed on GDY. Among them, as one of the most commonly used methods to modify the structure, heteroatom doping is favored for its advantages in synthesis methods and the control of mechanical, electrical and even magnetic properties of carbon materials. According to the published studies, the top-down methods of doping heteroatoms for GDY only need cheap raw materials, simple synthetic route and strong controllability, which is conducive to rapid performance breakthroughs in electrochemical applications. This review selects the typical cases in the development of that post-modification method from the application of GDY in the electrochemical field. Here, based on the existed reports, the commonly used non-metal elements (such as nitrogen, sulfur) and metal elements (such as iron) have been introduced to post-modify GDY. Then, a detailed analysis is made for corresponding electrochemical applications, such as energy storage and electrocatalysis. Finally, the challenges and prospects of post-modified GDY in synthesis and electrochemical applications are proposed. This review provides us a useful guidance for the development of high-quality GDY suitable for electrochemical applications.

Silver incorporated into g-C3N4/Alginate as an efficient and heterogeneous catalyst for promoting click and A3 and KA2 coupling reaction

Fe3O4/g-C3N4/Alginate-Ag nanocomposite as a novel and effective nanocatalyst was successfully prepared. This nanocomposite was fully characterized using several techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy with energy dispersive spectroscopy (FESEM-EDS), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). In addition, the catalytic activity of this novel and characterized nanocatalyst was investigated in the regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles via click reaction and A3 and KA2 coupling reaction in aqueous media. The prepared nanocatalyst was simply recovered by using an external magnet and reused for several times with a slight loss of catalytic activity.

Two-Dimensional Conductive π-d Frameworks with Multiple Sensory Capabilities

Two-dimensional (2D) metal-molecule hybrid frameworks have attracted great attention due to their π-d interactions for the charge-spin-lattice coupling, promising for next-generation molecular electronics. However, a high electrical conductivity is indispensable to realize such potential. Herein, we design and assemble a conductive 2D conjugated coordination thin film through an interfacial reaction between the aqueous and organic phases. Its electronic conducting properties are derived from the π-d coupling interactions to achieve an electrical conductivity of 1.05 S/cm, while the stimulus-dependent π-d interactions induce multifunctional sensory capabilities. The Co-DABDT (DABDT = 2,5-diamino-1,4-benzenedithiol dihydrochloride) thin films demonstrate an excellent performance for sensing light, strain, temperature, and humidity, as well as robust mechanical stability. The 2D frameworks with multisensing properties for real-time static and dynamic monitoring are promising for smart wearable electronic systems.

Interfacial sp C-O-Mo Hybridization Originated High-Current Density Hydrogen Evolution

High-current density (≥1 A cm^-2) is a critical factor for large-scale industrial application of water-splitting electrocatalysts, especially seawater-splitting. However, it still remains a great challenge to reach high-current density due to the lack of active and stable intrinsic catalytic active sites in catalysts. Herein, we report an original three-dimensional self-supporting graphdiyne/molybdenum oxide (GDY/MoO₃) material for efficient hydrogen evolution reaction via a rational design of "sp C-O-Mo hybridization" on the interface. The "sp C-O-Mo hybridization" creates new intrinsic catalytic active sites (nonoxygen vacancy sites) and increases the amount of active sites (eight times higher than pure MoO₃). The "sp C-O-Mo hybridization" facilitates charge transfer and boosts the dissociation process of H₂O molecules, leading to outstanding HER activity with high-current density (>1.2 A cm^-2) in alkaline electrolyte and a decent activity and stability in natural seawater. Our results show that high-current density electrocatalysts can be achieved by interfacial chemical bond engineering, three-dimensional structure design, and hydrophilicity optimization.

Incorporating MoO3 Patches into a Ni Oxyhydroxide Nanosheet Boosts the Electrocatalytic Oxygen Evolution Reaction

The electrocatalytic oxygen evolution reaction from H₂O (OER) is essential in a number of areas like electrocatalytic hydrogen production from H₂O. A Ni oxyhydroxide nanosheet (NiNS) is among the most widely studied OER catalysts but still suffers from low activity, sluggish kinetics, and poor stability. Herein, we incorporate MoO₃ patches into NiNS to form a nanosheet with an intimate Ni-Mo interface (NiMoNS) for the OER. The overpotential at 10 mA cm^-2 and Tafel slope on NiMoNS (260 mV, 54.7 mV dec^-1) are lower than those on NiNS (296 mV, 89.3 mV dec^-1), implying that higher activity and faster kinetics are achieved on NiMoNS. There is no change in electrocatalytic efficiency of NiMoNS after 18 h of OER, but the electrocatalytic efficiency of NiNS decreases by 56% after only 8 h of OER. Thus, NiMoNS has better stability. The intimate Ni-Mo interface promotes two-dimensional lateral growth of NiMoNS to form a surface area 1.5 times larger than that of NiNS, and facilitates electron transfer from Ni to Mo. This makes the Ni³⁺/Ni²⁺ ratio on the NiMoNS surface (1.32) higher than that on the NiNS surface (0.68). Moreover, the Ni³⁺/Ni²⁺ ratio on NiMoNS surface increases to 1.81 after 18 h of OER but the Ni³⁺/Ni²⁺ ratio on the NiNS surface decreases to 0.51 after 8 h of OER. Therefore, the NiMoNS surface has more abundant and stable Ni³⁺ sites which are catalytically active toward OER. This could be the reason for the enhanced activity, kinetics, and stability of NiMoNS. The results are very valuable for fabricating more efficient catalysts for electrocatalysis.

Engineering the Coordination Sphere of Isolated Active Sites to Explore the Intrinsic Activity in Single-Atom Catalysts

Reducing the dimensions of metallic nanoparticles to isolated, single atom has attracted considerable attention in heterogeneous catalysis, because it significantly improves atomic utilization and often leads to distinct catalytic performance. Through extensive research, it has been recognized that the local coordination environment of single atoms has an important influence on their electronic structures and catalytic behaviors. In this review, we summarize a series of representative systems of single-atom catalysts, discussing their preparation, characterization, and structure-property relationship, with an emphasis on the correlation between the coordination spheres of isolated reactive centers and their intrinsic catalytic activities. We also share our perspectives on the current challenges and future research promises in the development of single-atom catalysis. With this article, we aim to highlight the possibility of finely tuning the catalytic performances by engineering the coordination spheres of single-atom sites and provide new insights into the further development for this emerging research field.

Graphdiyne Based Ternary GD-CuI-NiTiO3 S-Scheme Heterjunction Photocatalyst for Hydrogen Evolution

As the demand of fossil fuels continues to expand, hydrogen energy is considered a promising alternative energy. In this work, the NiTiO₃-CuI-GD ternary system was successfully constructed based on morphology modulation and energy band structure design. First, the one-pot method was used to cleverly embed the cubes CuI in the stacked graphdiyne (GD) to prepare the hybrid CuI-GD, and CuI-GD was anchored on the surface of NiTiO₃ by simple physical stirring. The unique spatial arrangement of the composite catalyst was utilized to improve the hydrogen production activity under light. Second, to combine various characterization tools and energy band structures, we proposed an step-scheme (S-scheme) heterojunction photocatalytic reaction mechanism, among them, the tubular NiTiO₃ formed by the self-assembled of nanoparticles provided sufficient sites for the anchoring of CuI-GD, and the thin layer GD acted as an electron acceptor to capture a large number of electrons with the help of the conjugated carbon network; cubes CuI could consume holes in the reaction system; the loading of CuI-GD greatly improved the oxidation and reduction ability of the whole catalytic system. The S-scheme heterojunction accelerated the transfer of carriers and improved the separation efficiency. The experiment provides a new insight into the construction of an efficient and eco-friendly multicatalytic system.

Graphdiyne/Graphene Heterostructure: A Universal 2D Scaffold Anchoring Monodispersed Transition-Metal Phthalocyanines for Selective and Durable CO2 Electroreduction

Electrochemical CO₂ reduction (CO₂R) is a sustainable way of producing carbon-neutral fuels, yet the efficiency is limited by its sluggish kinetics and complex reaction pathways. Developing active, selective, and stable CO₂R electrocatalysts is challenging and entails intelligent material structure design and tailoring. Here we show a graphdiyne/graphene (GDY/G) heterostructure as a 2D conductive scaffold to anchor monodispersed cobalt phthalocyanine (CoPc) and reduce CO₂ with an appreciable activity, selectivity, and durability. Advanced characterizations, e.g., synchrotron-based X-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculation disclose that the strong electronic coupling between GDY and CoPc, together with the high surface area, abundant reactive centers, and electron conductivity provided by graphene, synergistically contribute to this distinguished electrocatalytic performance. Electrochemical measurements revealed a high FE_CO of 96% at a partial current density of 12 mA cm^-2 in a H-cell and an FE_CO of 97% at 100 mA cm^-2 in a liquid flow cell, along with a durability over 24 h. The per-site turnover frequency of CoPc reaches 37 s^-1 at -1.0 V vs RHE, outperforming most of the reported phthalocyanine- and porphyrin-based electrocatalysts. The usage of the GDY/G heterostructure as a scaffold can be further extended to other organometallic complexes beyond CoPc. Our findings lend credence to the prospect of the GDY/G hybrid contributing to the design of single-molecule dispersed CO₂R catalysts for sustainable energy conversion.

Multifunctional Graphdiyne-Cerium Oxide Nanozymes Facilitate MicroRNA Delivery and Attenuate Tumor Hypoxia for Highly Efficient Radiotherapy of Esophageal Cancer

Radioresistance is an important challenge for clinical treatments. The main causes of radioresistance include hypoxia in the tumor microenvironment, the antioxidant system within cancer cells, and the upregulation of DNA repair proteins. Here, a multiple radiosensitization strategy of high-Z-element-based radiation enhancement is designed, attenuating hypoxia and microRNA therapy. The novel 2D graphdiyne (GDY) can firmly anchor and disperse CeO2 nanoparticles to form GDY-CeO2 nanocomposites, which exhibit superior catalase-mimic activity in decomposing H2 O2 to O2 to significantly alleviate tumor hypoxia, promote radiation-induced DNA damage, and ultimately inhibit tumor growth in vivo. The miR181a-2-3p (miR181a) serum levels in patients are predictive of the response to preoperative radiotherapy in locally advanced esophageal squamous cell carcinoma (ESCC) and facilitate personalized treatment. Moreover, miR181a can act as a radiosensitizer by directly targeting RAD17 and regulating the Chk2 pathway. Subsequently, the GDY-CeO2 nanocomposites with miR181a are conjugated with the iRGD-grafted polyoxyethylene glycol (short for nano-miR181a), which can increase the stability, efficiently deliver miR181a to tumor, and exhibit low toxicity. Notably, nano-miR181a can overcome radioresistance and enhance therapeutic efficacy both in a subcutaneous tumor model and human-patient-derived xenograft models. Overall, this GDY-CeO2 nanozyme and miR181a-based multisensitized radiotherapy strategy provides a promising therapeutic approach for ESCC.

Single-atom catalysts for high-energy rechargeable batteries

Clean and sustainable electrochemical energy storage has attracted extensive attention. It remains a great challenge to achieve next-generation rechargeable battery systems with high energy density, good rate capability, excellent cycling stability, efficient active material utilization, and high coulombic efficiency. Many catalysts have been explored to promote electrochemical reactions during the charge and discharge process. Among reported catalysts, single-atom catalysts (SACs) have attracted extensive attention due to their maximum atom utilization efficiency, homogenous active centres, and unique reaction mechanisms. In this perspective, we summarize the recent advances of the synthesis methods for SACs and highlight the recent progress of SACs for a new generation of rechargeable batteries, including lithium/sodium metal batteries, lithium/sodium-sulfur batteries, lithium-oxygen batteries, and zinc-air batteries. The challenges and perspectives for the future development of SACs are discussed to shed light on the future research of SACs for boosting the performances of rechargeable batteries.

Density functional theory study of transition metal single-atoms anchored on graphyne as efficient electrocatalysts for the nitrogen reduction reaction

Ammonia (NH3) is the main raw material for the organic chemical industry and a critical feedstock for the fertilizer industry with great significance for the global economy. The NH3 demand has gradually increased with modern society development. Moreover, the electrocatalytic nitrogen reduction reaction (NRR) is a promising NH3 synthesis technology. However, the design of efficient electrocatalysts for the NRR is still challenging. In this study, we systematically analyzed transition metal (TM) single-atoms (Ti, V, Cr, Mn, Zr, Nb, and Mo) anchored on graphyne (GY) as NRR catalysts using density functional theory calculations. The calculation results for the first and last hydrogenation steps (*NNH formation and *NH3 desorption, respectively) revealed that Mn@GY (with an end-on configuration) and V@GY (with a side-on configuration) were the most suitable catalytic substrates for the NRR. The free-energy profiles of the TM@GY catalysts indicated that Mn@GY was the best NRR electrocatalyst owing to its distal pathway with a minimum free-energy barrier of 0.36 eV. In addition, the electronic properties, namely the Bader charge, charge density difference, partial density of states, and crystal orbital Hamilton population, of the TM@GY catalysts were analyzed in detail, and the results further confirmed that Mn@GY was an efficient electrocatalyst. The insights obtained from this comprehensive study can provide useful guidelines for designing new and efficient electrocatalysts.

Pt Single Atoms Supported on N-Doped Mesoporous Hollow Carbon Spheres with Enhanced Electrocatalytic H2 -Evolution Activity

The electronic metal-support interaction (EMSI) plays a crucial role in catalysis as it can induce electron transfer between metal and support, modulate the electronic state of the supported metal, and optimize the reduction of intermediate species. In this work, the tailoring of electronic structure of Pt single atoms supported on N-doped mesoporous hollow carbon spheres (Pt₁ /NMHCS) via strong EMSI engineering is reported. The Pt₁ /NMHCS composite is much more active and stable than the nanoparticle (Pt_NP ) counterpart and commercial 20 wt% Pt/C for catalyzing the electrocatalytic hydrogen evolution reaction (HER), exhibiting a low overpotential of 40 mV at a current density of 10 mA cm^-2 , a high mass activity of 2.07 A mg^-1 _Pt at 50 mV overpotential, a large turnover frequency of 20.18 s^-1 at 300 mV overpotential, and outstanding durability in acidic electrolyte. Detailed spectroscopic characterizations and theoretical simulations reveal that the strong EMSI effect in a unique N₁ -Pt₁ -C₂ coordination structure significantly tailors the electronic structure of Pt 5d states, resulting in promoted reduction of adsorbed proton, facilitated H-H coupling, and thus Pt-like HER activity. This work provides a constructive route for precisely designing single-Pt-atom-based robust electrocatalysts with high HER activity and durability.

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.

Single-atom Fe catalytic amplification-gold nanosol SERS/RRS aptamer as platform for the quantification of trace pollutants

Bisphenol A (BPA), as a typical endocrine disruptor, poses a serious threat to human health. Therefore, it is urgent to establish a rapid, sensitive, and simple method for the determination of BPA. In this paper, based on the aptamer-mediated single-atom Fe carbon dot catalyst (SA_Fe) catalyzing the HAuCl₄-ethylene glycol (EG) nanoreaction, a new SERS/RRS di-mode detection method for BPA was established. The results show that SA_Fe exhibits a strong catalytic effect on the HAuCl₄-EG nanoreaction, which could generate purple gold nanoparticles (AuNPs) with resonance Rayleigh scattering (RRS) signals and surface-enhanced Raman scattering (SERS) effects. After the addition of BPA aptamer (Apt), it could encapsulate SA_Fe through intermolecular interaction, thus inhibiting its catalytic action, resulting in the reduction of AuNPs generated and the decrease of RRS and SERS signals of the system. With the addition of BPA, Apt was specifically combined with BPA, and SA_Fe was re-released to restore the catalytic ability; the generated AuNPs increased. As a result of this RRS and SERS signals of the system recovered, and their increment was linear with the concentration of BPA. Thus, the quantification of 0.1-4.0 nM (RRS) and 0.1-12.0 nM (SERS) BPA was realized, and the detection limits were 0.08 nM and 0.03 nM, respectively. At the same time, we used molecular spectroscopy and electron microscopy to study the SA_Fe-HAuCl₄-ethylene glycol indicator reaction, and proposed a reasonable SA_Fe catalytic reaction mechanism. Based on Apt-mediated SA_Fe catalysis gold nanoreaction amplification, a SERS/RRS di-mode analytical platform was established for targets such as BPA.

Close band center and rapid adsorption kinetics facilitate selective electrochemical sensing of heavy metal ions

Combining density functional theory calculation with experiments and kinetics simulation, a multiscale framework describing the influence of reactant-substrate interaction on electrochemical performance was proposed. It was found that the close band center and the rapid adsorption kinetics facilitated the highly selective response of Ni(111) toward Cu(ii), providing a useful tactic to investigate the mechanism of electro-selectivity. This work not only verified that the interaction strength in the ex situ conditions, and kinetics rate could be applied to evaluate the electrochemical selectivity, but also contributed to the options and forecasting of selective electrode materials for heavy metal ions.

In Situ Identifying the Dynamic Structure behind Activity of Atomically Dispersed Platinum Catalyst toward Hydrogen Evolution Reaction

Single-atom catalysts (SAs) with the maximum atom utilization and breakthrough activities toward hydrogen evolution reaction (HER) have attracted considerable research interests. Uncovering the nature of single-atom metal centers under operating electrochemical condition is highly significant for improving their catalytic performance, yet is poorly understood in most studies. Herein, Pt single atoms anchoring on the nitrogen-carbon substrate (Pt_SA /N-C) as a model system are utilized to investigate the dynamic structure of Pt single-atom centers during the HER process. Via in situ/operando synchrotron X-ray absorption spectroscopy and X-ray photoelectron spectroscopy, an intriguing structural reconstruction at atomic level is identified in the Pt_SA /N-C when it is subjected to the repetitive linear sweep voltammetry and cyclic voltammetry scanning. It demonstrates that the PtN bonding tends to be weakened under cathodic potentials, which induces some Pt single atoms to dynamically aggregate into forming small clusters during the HER reaction. More importantly, experimental evidence and/or indicator is offered to correlate the observed Tafel slope with the dynamic structure of Pt catalysts. This work provides an evident understanding of SAs under electrocatalytic process and offers informative insights into constructing efficient catalysts at atomic level for electrochemical water-splitting system.

Single-Atom Catalysts: A Sustainable Pathway for the Advanced Catalytic Applications

A heterogeneous catalyst is a backbone of modern sustainable green industries; and understanding the relationship between its structure and properties is the key for its advancement. Recently, many upscaling synthesis strategies for the development of a variety of respectable control atomically precise heterogeneous catalysts are reported and explored for various important applications in catalysis for energy and environmental remediation. Precise atomic-scale control of catalysts has allowed to significantly increase activity, selectivity, and in some cases stability. This approach has proved to be relevant in various energy and environmental related technologies such as fuel cell, chemical reactors for organic synthesis, and environmental remediation. Therefore, this review aims to critically analyze the recent progress on single-atom catalysts (SACs) application in oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and chemical and/or electrochemical organic transformations. Finally, opportunities that may open up in the future are summarized, along with suggesting new applications for possible exploitation of SACs.