Synthesis of Organized Layered Carbon by Self-Templating of Dithiooxamide

Molecular Engineering of Porous Fe-N-C Catalyst with Sulfur Incorporation for Boosting CO2 Reduction and Zn-CO2 Battery

Transition metal-nitrogen-carbon (M-N-C) catalysts have emerged as promising candidates for electrocatalytic CO2 reduction reaction (CO2RR) due to their uniform active sites and high atomic utilization rate. However, poor efficiency at low overpotentials and unclear reaction mechanisms limit the application of M-N-C catalysts. In this study, Fe-N-C catalysts are developed by incorporating S atoms onto ordered hierarchical porous carbon substrates with a molecular iron thiophenoporphyrin. The well-prepared FeSNC catalyst exhibits superior CO2RR activity and stability, attributes to an optimized electronic environment, and enhances the adsorption of reaction intermediates. It displays the highest CO selectivity of 94.0% at -0.58 V (versus the reversible hydrogen electrode (RHE)) and achieves the highest partial current density of 13.64 mA cm-2 at -0.88 V. Furthermore, when employed as the cathode in a Zn-CO2 battery, FeSNC achieves a high-power density of 1.19 mW cm-2 and stable charge-discharge cycles. Density functional theory calculations demonstrate that the incorporation of S atoms into the hierarchical porous carbon substrate led to the iron center becoming more electron-rich, consequently improving the adsorption of the crucial reaction intermediate *COOH. This study underscores the significance of hierarchical porous structures and heteroatom doping for advancing electrocatalytic CO2RR and energy storage technologies.

Dual Activation for Tuning N, S Co-Doping in Porous Carbon Sheets Toward Superior Sodium Ion Storage

Porous carbon has been widely focused to solve the problems of low coulombic efficiency (ICE) and low multiplication capacity of Sodium-ion batteries (SIBs) anodes. The superior energy storage properties of two-dimensional(2D) carbon nanosheets can be realized by modulating the structure, but be limited by the carbon sources, making it challenging to obtain 2D structures with large surface area. In this work, a new method for forming carbon materials with high N/S doping content based on combustion activation using the dual activation effect of K2SO4/KNO3 is proposed. The synthesized carbon material as an anode for SIBs has a high reversible capacity of 344.44 mAh g-1 at 0.05 A g-1. Even at the current density of 5 Ag-1, the capacity remained at 143.08 mAh g-1. And the ICE of sodium-ion in ether electrolytes is ≈2.5 times higher than that in ester electrolytes. The sodium storage mechanism of ether/ester-based electrolytes is further explored through ex-situ characterizations. The disparity in electrochemical performance can be ascribed to the discrepancy in kinetics, wherein ether-based electrolytes exhibit a higher rate of Na+ storage and shedding compared to ester-based electrolytes. This work suggests an effective way to develop doubly doped carbon anode materials for SIBs.

Nanohybrids of BCN-Fe1-xS for Sodium and Lithium Hybrid Ion Capacitors

Hybrid ion capacitors (HIC) are receiving a lot of attention due to their potential to achieve high energy and power densities, but they remain insufficient. It is imperative to explore outstanding and environmentally benign electrode materials to achieve high-performing HIC systems. Here, a unique boron carbon nitride (BCN)-based HIC system that comprises a microporous BCN structure and Fe1-xS nanoparticle incorporated BCN nanosheets (BNF) as cathode and anode, respectively is reported. The BNF is prepared through a facile one-pot calcination process using dithiooxamide (DTO), boric acid, and iron source. In situ, crystal growth of Fe1-xS facilitates the formation of BCN structure through the creation of holes/defects in the polymeric structure. The first principle density functional (DFT) theory simulations demonstrate the structural and electronic properties of the hybrid of BCN and Fe1-xS as compelling anode materials for HIC applications. The DFT calculations reveal that both BCN and BNF structures have excellent metallic characters with Li+ storage capacities of 128.4 and 1021.38 mAh g-1 respectively. These findings are confirmed experimentally where the BCN-based HIC system delivers exceptional energy and power densities of 267.5 Wh kg-1/749.5 W kg-1 toward Li+ storage, which outweighs previous HIC performances and demonstrates favorable performance for Li+ and Na+ storages.

Boosting the lithium storage performance by synergistically coupling ultrafine heazlewoodite nanoparticle with N, S co-doped carbon

Transition metal sulfides, as an important class of inorganics, have been shown to be potential high-performance electrode candidates for lithium-ion batteries (LIBs) in account of their high activity towards lithium storage, rich types and diverse structures. Despite these advantages, structure degradation related with volume variations upon electrochemical cycling restricts their further development. In this present study, a unique hybrid structure with ultrafine heazlewoodite nanoparticles (less than 10 nm) in-situ confined in nitrogen and sulfur dual-doped carbon (Ni₃S₂@NSC) was constructed though a facile pyrolysis process, using a novel Ni-based metal chelates as the precursor. Specifically, enhanced structure stability, shortened Li⁺ migration distance and improved reaction dynamics can be obtained simultaneously in the designed structure, thereby allowing to realize high lithium storage performance. Consequently, a remarkable reversible capacity of 955.9 mAh g^-1 (0.1 A g^-1 after 100 cycles) and a superior long-term cycling stability up to 1200 cycles (863.7 mAh g^-1 at 1.0 A g^-1) are obtained. Importantly, the fundamental understanding on the improved lithium storage of Ni₃S₂@NSC based on the synergistic coupling reveals that the combination between Ni₃S₂ and NSC at the hetero-interface through the doped sulfur atoms contributes to the integrity of electrode and improved kinetics.

Self-Assembled Carbon Superstructures Achieving Ultra-Stable and Fast Proton-Coupled Charge Storage Kinetics

Designing ingenious and stable carbon nanostructures is critical but still challenging for use in energy storage devices with superior electrochemistry kinetics, durable capacitive activity, and high rate survivability. To pursue the objective, a simple self-assembly strategy is developed to access carbon superstructures built of nanoparticle embedded plates. The carbon precursors, 2,4,6-trichloro-1,3,5-triazine and 2,6-diaminoanthraquinone can form porous organic polymer with "protic salt"-type rigid skeleton linked by -NH₂ ⁺ Cl^- - "rivets", which provides the cornerstone for hydrogen-bonding-guided self-assembly of the organic backbone to superstructures by π-π plane stacking. The ameliorative charge density distribution and decreased adsorption energy in as-fabricated carbon superstructures allow the high accessibility of the build-in protophilic sites and efficient ion diffusion with a low energy barrier. Such superstructures thus deliver ultra-stable charge storage and fast proton-coupled kinetics at the structural-chemical defects, contributing to unprecedented lifespan (1 000 000 cycles), high-rate capability (100 A g^-1 ) for carbon-based supercapacitors, and an ultrahigh energy density (128 Wh kg^-1 ) for Zn-ion hybrid supercapacitors. The self-assembled carbon superstructures significantly improve the all-round electrochemical performances, and hold great promise for efficient energy storage.

Facile in-situ synthesis of heazlewoodite on nitrogen-doped reduced graphene oxide for enhanced sodium storage

Nickel sulfide based anode materials, featuring rich types, high specific capacities and favorable conversion kinetics, have been proved to be promisingly applied in high-performance sodium-ion batteries (SIBs). Unfortunately, the poor electronic/ionic conductivity, together with the structure change induced degraded capacity upon cycling, restricts their further development. In this work, heazlewoodite nanoparticles decorated on nitrogen doped reduced graphene oxide (Ni₃S₂/NrGO) were fabricated via a facile combined approach with freeze-drying and subsequent in-situ sulfidation. In the obtained hybrid structure, the synergistic effect between Ni₃S₂ and NrGO endows the composite with highly conductive pathways, thus accelerating the charge transfer. Benefitting from the buffering matrix offered by NrGO as well as the tight combination between Ni₃S₂ and NrGO, this novel Ni₃S₂/NrGO demonstrates satisfying sodium storage performance, with a stable reversible capacity of 299.2 mAh g^-1 up to 100 cycles (0.1 A g^-1) and a high initial Coulombic efficiency of 76.8%. Importantly, the rational structure design and synthesis method, as well as the insights on the improved electrochemical performance reported in this work, should be helpful for the development of new-type host materials with high performance for SIBs.

Folic Acid Coordinated Cu-Co Site N-Doped Carbon Nanosheets for Oxygen Reduction Reaction

The design and development of carbon materials with high-efficiency oxygen reduction activity is still a problem. Folic acid (FA) has unique structural characteristics, and it can provide multiple coordination sites for metal ions. Here, folic acid (FA) was used as a metal complex ligand, and Cu-Co-based N-doped porous carbon nanosheets (Cu-CoNCNs) were synthesized by the solvothermal method, the molten salt template-assisted calcination method, and the chemical etching method. The Cu-CoNCNs synthesized by this method have highly efficient oxygen reduction reaction (ORR) activity. In 0.1 mol/L KOH electrolytes, the catalyst exhibits excellent ORR activity and has a fairly high half-wave potential (0.905 V vs reversible hydrogen electrode (RHE)). X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, infrared spectroscopy, and X-ray diffraction (XRD) were used to investigate the reasons why the catalyst has excellent catalytic activity and long-life stability. It was proved that the impressive ORR activity of Cu-CoNCNs comes from Cu doping, which can regulate the surface electronic structure of the catalyst, thereby optimizing the binding ability between the intermediate and adsorbed species and improving the catalytic activity.

Monomeric vanadium oxide: a very efficient species for promoting aerobic oxidative dehydrogenation of N-heterocycles

The isolated monomeric VO₄ species, controlled by natural ligand tartaric acid, in the VO_x/NbO_y@C catalysts exhibited excellent performances and good recyclability in the dehydrogenation of N-heterocycles.

Single-Step Synthesis of Mesoporous Carbon Nitride/Molybdenum Sulfide Nanohybrids for High-Performance Sodium-Ion Batteries

Molybdenum disulfide (MoS₂ ) is a promising candidate as a high-performing anode material for sodium-ion batteries (SIBs) due to its large interlayer spacing. However, it suffers from continued capacity fading. This problem could be overcome by hybridizing MoS₂ with nanostructured carbon-based materials, but it is quite challenging. Herein, we demonstrate a single-step strategy for the preparation of MoS₂ coupled with ordered mesoporous carbon nitride using a nanotemplating approach which involves the pyrolysis of phosphomolybdic acid hydrate (PMA), dithiooxamide (DTO) and 5-amino-1H-tetrazole (5-ATTZ) together in the porous channels of 3D mesoporous silica template. The sulfidation to MoS₂ , polymerization to carbon nitride (CN) and their hybridization occur simultaneously within a mesoporous silica template during a calcination process. The CN/MoS₂ hybrid prepared by this unique approach is highly pure and exhibits good crystallinity as well as delivers excellent performance for SIBs with specific capacities of 605 and 431 mAhg^-1 at current densities of 100 and 1000 mAg^-1 , respectively, for SIBs.

Atomically Dispersed Fe-N4 Modified with Precisely Located S for Highly Efficient Oxygen Reduction

Immobilizing metal atoms by multiple nitrogen atoms has triggered exceptional catalytic activity toward many critical electrochemical reactions due to their merits of highly unsaturated coordination and strong metal-substrate interaction. Herein, atomically dispersed Fe-NC material with precise sulfur modification to Fe periphery (termed as Fe-NSC) was synthesized, X-ray absorption near edge structure analysis confirmed the central Fe atom being stabilized in a specific configuration of Fe(N3)(N-C-S). By enabling precisely localized S doping, the electronic structure of Fe-N4 moiety could be mediated, leading to the beneficial adjustment of absorption/desorption properties of reactant/intermediate on Fe center. Density functional theory simulation suggested that more negative charge density would be localized over Fe-N4 moiety after S doping, allowing weakened binding capability to *OH intermediates and faster charge transfer from Fe center to O species. Electrochemical measurements revealed that the Fe-NSC sample exhibited significantly enhanced oxygen reduction reaction performance compared to the S-free Fe-NC material (termed as Fe-NC), showing an excellent onset potential of 1.09 V and half-wave potential of 0.92 V in 0.1 M KOH. Our work may enlighten relevant studies regarding to accessing improvement on the catalytic performance of atomically dispersed M-NC materials by managing precisely tuned local environments of M-Nx moiety.

Mesoporous Iron-doped MoS2/CoMo2S4 Heterostructures through Organic-Metal Cooperative Interactions on Spherical Micelles for Electrochemical Water Splitting

Mesoporous metal sulfide hybrid (meso-MoS₂/CoMo₂S₄) materials via a soft-templating approach using diblock copolymer polystyrene-block-poly(acrylic acid) micelles are reported. The formation of the meso-MoS₂/CoMo₂S₄ heterostructures is based on the sophisticated coassembly of dithiooxamide and metal precursors (i.e., Co²⁺, PMo₁₂), which are subsequently annealed in nitrogen atmosphere to generate the mesoporous material. Decomposing the polymer leaves behind mesopores throughout the spherical MoS₂/CoMo₂S₄ hybrid particles, generating numerous electrochemical active sites in a network of pores that enable faster charge transfer and mass/gas diffusion that enhance the electrocatalytic performance of MoS₂/CoMo₂S₄. Doping the spherical meso-MoS₂/CoMo₂S₄ heterostructures with iron improves the electronic properties of the hybrid meso-Fe-MoS₂/CoMo₂S₄ material and consequently results in its superior electrochemical activities for both hydrogen evolution reaction and oxygen evolution reaction.

Metal chelate induced in situ wrapping of Ni3S2 nanoparticles into N, S-codoped carbon networks for highly efficient sodium storage

Metal-dithiooxamide chelate derived Ni₃S₂ nanoparticles wrapped in N, S codoped carbon networks exhibit excellent sodium storage performance.

A Simple Route to Porous Graphene from Carbon Nanodots for Supercapacitor Applications

A facile method to convert biomolecule-based carbon nanodots (CNDs) into high-surface-area 3D-graphene networks with excellent electrochemical properties is presented. Initially, CNDs are synthesized by microwave-assisted thermolysis of citric acid and urea according to previously published protocols. Next, the CNDs are annealed up to 400 °C in a tube furnace in an oxygen-free environment. Finally, films of the thermolyzed CNDs are converted into open porous 3D turbostratic graphene (3D-ts-graphene) networks by irradiation with an infrared laser. Based upon characterizations using scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman spectroscopy, a feasible reaction mechanism for both the thermolysis of the CNDs and the subsequent laser conversion into 3D-ts-graphene is presented. The 3D-ts-graphene networks show excellent morphological properties, such as a hierarchical porous structure and a high surface area, as well as promising electrochemical properties. For example, nearly ideal capacitive behavior with a volumetric capacitance of 27.5 mF L^-1 is achieved at a current density of 560 A L^-1 , which corresponds to an energy density of 24.1 mWh L^-1 at a power density of 711 W L^-1 . Remarkable is the extremely fast charge-discharge cycling rate with a time constant of 3.44 ms.

Thermal Exfoliation of Layered Metal-Organic Frameworks into Ultrahydrophilic Graphene Stacks and Their Applications in Li-S Batteries

2D nanocarbon-based materials with controllable pore structures and hydrophilic surface show great potential in electrochemical energy storage systems including lithium sulfur (Li-S) batteries. This paper reports a thermal exfoliation of metal-organic framework crystals with intrinsic 2D structure into multilayer graphene stacks. This family of nanocarbon stacks is composed of well-preserved 2D sheets with highly accessible interlayer macropores, narrowly distributed 7 Å micropores, and ever most polar pore walls. The surface polarity is quantified both by its ultrahigh water vapor uptake of 14.3 mmol g^-1 at low relative pressure of P/P₀ = 0.4 and ultrafast water wetting capability in less than 10.0 s. Based on the structural merits, this series hydrophilic multilayer graphene stack is showcased as suitable model cathode host for unveiling the challenging surface chemistry issue in Li-S batteries.

Supernormal Conversion Anode Consisting of High-Density MoS2 Bubbles Wrapped in Thin Carbon Network by Self-Sulfuration of Polyoxometalate Complex

Large-capacity conversion electrodes are highly required to raise the energy density of batteries. However, their undesired phase segregation and volume expansion during cycling lead to the motivation for nanofabrication and nanochemistry of active species in order to decrease "dead mass" and promote better construction of conductive networks. However, the inactivity of the conductive skeleton and loose nanostructure would compromise the energy density of the electrode. The integration of large-sized (high-density) grains into an electroactive conductive network in a compact way is still a big challenge. Here we report a proof-of-concept prototype consisting of unusual MoS₂ solid bubbles of hundreds of nanometers in size, which are conformally encapsulated by thin-layer carbon. The seamless welding between this carbon coating and the surrounding broader carbon substrate can effectively avoid the peel-off of active species and breakage of the conductive network. This MoS₂-C composite is achieved by simultaneous self-sulfuration and self-carbonization of a polyoxometalate (POM)-based chelate, and its Li-storage performance is superior to most MoS₂-based anodes even with ultrathin 2D nanosheets. Partially benefiting from the electroactivity of a dithiooxamide (DTO)-derivate carbon network, the reversible capacity of MoS₂-C by pyrolyzing the POM-DTO chelate can reach 1500-2000 mAh/g at 0.5-1 A/g even after 700 cycles and be maintained around 1000 mAh/g under as high as 10-20 A/g.

Sulfur-Doped Carbon Nitride Polymers for Photocatalytic Degradation of Organic Pollutant and Reduction of Cr(VI)

As a promising conjugated polymer, binary carbon nitride has attracted extensive attention as a metal-free and visible-light-responsive photocatalyst in the area of photon-involving purification of water and air. Herein, we report sulfur-doped polymeric carbon nitride microrods that are synthesized through thermal polymerization based on trithiocyanuric acid and melamine (TM) supramolecular aggregates. By tuning the polymerization temperature, a series of sulfur-doped carbon nitride microrods are prepared. The degradation of Rhodamine B (RhB) and the reduction of hexavalent chromium Cr(VI) are selected as probe reactions to evaluate the photocatalytic activities. Results show that increasing pyrolysis temperature leads to a large specific surface area, strong visible-light absorption, and accelerated electron-hole separation. Compared to bulk carbon nitride, the highly porous sulfur-doped carbon nitride microrods fabricated at 650 °C exhibit remarkably higher photocatalytic activity for degradation of RhB and reduction of Cr(VI). This work highlights the importance of self-assembly approach and temperature-control strategy in the synthesis of photoactive materials for environmental remediation.

"Installation art"-like hierarchical self-assembly of giant polymeric elliptical platelets

This paper reports the aqueous self-assembly of giant elliptical platelets over 20 μm in axial length, from a novel polyamide. Both the self-assembly pathway and mechanism were studied using morphology and X-ray characterizations. The polymer first self-organizes into small quadrangular frustum pyramid platelets, and then these small platelets can be further installed into giant elliptical platelets through an "installation art"-like hierarchical self-assembly process driven by crystallization. The as-prepared regular giant platelets can further aggregate together into multi-horned or flower-like superstructures.

Synthesis of nitrogen and sulfur co-doped hierarchical porous carbons and metal-free oxidative coupling of silanes with alcohols

Hierarchically porous N and S co-doped carbon was used as an efficient and robust metal-free catalyst for oxidative coupling of silanes with alcohols.