Defective Carbon Research Articles

Investigation of vacancy-type defects in diamond-like carbon films using slow positron beam

Positron annihilation spectroscopy was used to investigate vacancy-type defects in diamond-like carbon (DLC) films. From Doppler broadening measurements of the γ-rays produced by annihilation and positron annihilation lifetime (PAL) using a slow positron beam on DLC films deposited by various deposition methods and conditions, it was found that there is a good correlation between the S parameter obtained by Doppler broadening and PAL. The result of PAL correlates well with film density and hardness, indicating that PAL measurements can be used as an indicator of these film properties. The hydrogen content in the DLC film was roughly proportional to the PAL. However, there were also cases in which PAL differed greatly even with almost the same hydrogen content, and the sp 2/(sp 2+sp 3) ratio of carbon in DLC films has no direct relationship with PAL.

Photo-induced CO2 cycloaddition and tetracycline degradation over novel FeOx modified defective graphitic carbon nitride composite

Utilizing sunlight to achieve CO2 conversion and environmental remediation has been a key focus. Herein, “all-in-one” graphitic carbon nitride (g-C3N4) composite-based photocatalysts were synthesized by a simple one-step low-temperature calcination. Lower calcination temperature resulted in defective g-C3N4 enriched in cyano and hydroxyl groups. It was found that by incorporating amorphous FeOX, the resulted FeOX/O-g-C3N4 photocatalyst shows very good performance towards both CO2 cycloaddition reaction and photo-Fenton degradation of tetracycline (TC). It was also found that the photocatalyst shows the highest styrene carbonate yield of 83% (23 mmol g−1 h−1) under ambient conditions, which is 13.8 times higher than that obtained over pure g-C3N4. The photocatalyst also exhibits a 4.7 times faster TC removal rate than that of pure g-C3N4. Systematic characterization and mechanism study demonstrate the role of defects and photo-induced charge carriers.

Comparison of Interatomic Potentials for Modeling Defects in Graphene Using Molecular Dynamics

In this work, we tested the ability of classical interatomic potentials to describe the energy characteristics of defects of various dimensionality in graphene crystals. Brenner's Reactive Empirical Bond Order potentials (second generation REBO, AIREBO, AIREBO-M), Tersoff potentials, as well as BOP and LCBOP potentials were considered. The data obtained in this work using the molecular dynamics method was compared with literature data obtained using the density functional theory. It is noted that when modeling point and linear defects, the potentials of the REBO family and the LCBOP potential demonstrate the best agreement with the literature data. For modeling pseudo-graphene crystals, the best fit is demonstrated by the Tersoff B-N-C potential, which shows slightly overestimated energy values for linear and point defects, but most accurately describes the geometry of the crystal lattice. The potential of BOP demonstrates its inability to correctly model defect configurations with high densities of eight-member defect rings. When simulating four-member carbon defect rings, most potentials exhibit distortions in the crystal lattice that are not observed in the density functional theory calculations.

Cyano and defective co-modified carbon nitride for optimized photoreformation of glucose to arabinose

In this study, NaNO2 and NH4I were introduced during the calcination process of melamine to construct cyano-modified defective carbon nitride (NICN). The presence of cyano groups, defects, and halogens was demonstrated through a series of characterizations, and their positions in NICN were inferred. The electronic structure of NICN was simulated through theoretical calculations (DFT) to prove the rationality of our inference. The experiments on the photocatalytic conversion of glucose using these catalysts revealed that NICN has a high conversion rate for glucose (91.04%, 1 h) and a certain selectivity for arabinose in the product (the yield reaches 0.262 g/L). In addition, the adjustment of the solvent and the atmosphere have a great impact on the product. After six cycle experiments, the material's conversion rate to glucose was almost unchanged and the structure of the material was very stable. Theoretical calculations of the Fukui function of glucose, free radical capture experiments, electron paramagnetic resonance and isotope labeling proved that superoxide radicals, electrons and holes are the main reactive activities species, which further clarify the reaction mechanism of glucose into arabinose. This work affords new ideas for designing functional carbon nitride-based photocatalysts for the photocatalytic oxidation of glucose to produce arabinose.

Oxygen-containing functional groups of activated carbon fibers as efficient oxygen transfer channels for H2S catalytic oxidation at room temperature

Activated carbon fibers (ACFs) with different activation degrees were developed by KOH activation method. And then, series of Na2CO3 loaded ACF catalysts were prepared and tested for H2S catalytic oxidation at room temperature. Among them, Na/ACF-8 presented the highest saturation sulfur capacity (1.22 gH2S/g). Importantly, it was found that COOH, COC/COH and COOCO were the main active oxygen species, and acted as oxygen transfer channels during the reaction. The reaction process mainly involved the dissociation of H2S, the reaction of HS− with C-O bond containing groups to form C-S bonds and sulfur-containing products. Moreover, the oxygen-containing functional groups were just responsible for water generation and the superoxide radical (O2•−) was responsible for SS bond oxidation. The O2•− was activated by ring carbon defects for Na/ACF-6 and Na/ACF-8 catalysts. And the ring carbon defects and ultramicropores were jointly responsible for the activation of O2•− for Na/ACF-2 and Na/ACF-4 catalysts.

Catalytic activation of peroxymonosulfate by intrinsic defects in amorphous carbon: Enhanced electronic transfer and oxygen-functional groups

Inherent defects in carbon material serve as an important way to enhance peroxymonosulfate (PMS) activity, however, the mechanism that activates PMS has always been ambiguous. Herein, the pyrolysis of straw with Prussian blue nanoparticles to prepare CoFe2O4/C (Carbon) was applied to analyze the mechanism of defective amorphous-C catalyzed activation of PMS. Amorphous-C structural defects increased the specific surface area of CoFe2O4/C (from 44.19 to 108.73 m2/g) with triggered electronic rearrangement, resulting in more PMS adsorption. CoFe2O4/C ensured the supply of low-valent metals (≡Co2+ and ≡Fe2+) simultaneously introduced a large number of surface oxygen-containing functional groups, which facilitated free radical generation. The structural defects enhanced electron transfer contributing to the direct oxidative degradation of BPA. Thus, 100 % removal of 450 µM BPA was achieved within 40 min attributed to the combined effect of catalyst-mediated ∙OH, 1O2, and electron transfer. Furthermore, the CoFe2O4/C/PMS system for BPA degradation exhibited universal pH suitability (4 ∼ 10) and low metal leaching (452.10 and 19.53 μg/L for Co and Fe, respectively). This study constructs systematic support for proposing the catalytic mechanism of carbon intrinsic defects activated PMS.

In situ confined growth of Cu2-xSe nanoparticles in highly defective nitrogen-doped carbon for high-rate sodium-ion battery anodes

Transition metal selenides are considered as hopeful anode materials for sodium-ion battery (SIB) due to the high specific capacity and rich reserves in nature. However, the inherent low conductivity of these anode materials, as well as the inevitable volume expansion and structural collapse during cycling, result in their poor rate performance and cycling stability. Herein, a universal selenization-co-carbonization strategy is proposed to synthesize Cu2-xSe nanoparticles in-situ confined in highly defective nitrogen-doped carbon (Cu2-xSe@NC) with superior architectural features, which involves simultaneous selenization and carbonization procedure of octahedral metal–organic framework (Cu-BTC) precursor. The nitrogen-doped carbon matrix stabilizes/confines the Cu2-xSe nanoparticles to prevent their agglomeration and volume expansion during cycling while endowing high electrical conductivity to the hybrid materials. As anode for SIBs, the Cu2-xSe@NC exhibits a high reversible capacity of 340 mAh/g at 0.1 A/g with a high initial coulombic efficiency of 70 %, superior rate performance (capacity retention of 82.4 % from 0.02 to 5 A/g), and long-cycle durability. The ex-situ XRD and HRTEM techniques confirmed that Cu2-xSe undergoes complex intercalation and crystal evolution accompanied by reversible intermediate phases (NaCuSe and Na2Se) transformation during charge/discharge cycle. First-principles calculations and in-situ EIS confirmed that the intercalation of Na+ can greatly reducing the energy band gap and improving the electrical conductivity of Cu2-xSe@NC, thereby achieving excellent rate performance. Moreover, the Cu2-xSe@NC anode is also evaluated by matching with Na3V2(PO4)3 cathode to assemble a full SIB, which can provide high initial capacity and capacity retention, revealing its potential for practical application.

Modulating Intrinsic Defect Structure of Fibrous Hard Carbon for Super‐Fast and High‐Areal Sodium Energy Storage

AbstractCreating defects by heteroatom doping is commonly approved in respect of enhancing fast sodium‐ion storage of carbonaceous anodes ascribing to rich external defects, but the contribution of intrinsic carbon defects (e.g., vacancy) in improving rate‐capability has rarely been investigated. Here, a bio‐derived fibrous hard carbon with high‐reversible intrinsic defects is synthesized via metal‐assisted‐catalytic strategy. It is found that sp2‐hybridized carbon is united through catalytic‐tuning during thermal‐etching process along with the formation of low‐potential planar intrinsic carbon defects (vacancies and non‐hexagonal carbon rings) by sacrificing poor‐reversible carbon edges. Such integrated structures greatly improve the reversibility of defective sites and charge transfer kinetics, thus enhancing the slope sodium‐storage capacity of carbon below 1 V even at high current densities. Thus‐obtained fibrous carbon anodes enable boosted initial coulombic efficiency (≈90%) and ultrahigh‐rate capability in both half‐ (222.2 mAh g−1at 50 A g−1) and full‐cell (200 C, charged/discharged in ≈10 s). Interestingly, compared with meso‐/macroporous structures, such micropore‐dominated carbon fibers are more beneficial for fabricating high‐mass‐loading, crack‐free thick electrodes (>10 mg cm−2) with considerable areal‐capacity over 3.0 mAh cm−2. Paired with high‐loading Na3V2PO4 cathode (14.4 mg cm−2), full‐cell achieves admirable areal‐capacity over 1.4 mAh cm−2 and peak areal‐energy/power‐density of 3.2/74 mW cm−2.

Surface engineered carbon felt toward highly reversible Fe anode for all-iron flow batteries

Low-cost all-iron flow batteries recently promise a great alternative to conventional flow battery technologies for large-scale energy storage. However, inferior Fe deposition/dissolution reversibility at anode largely impedes further advance of all-iron flow battery in application. Here, we report a surface engineered carbon felt with abundant carbon defects, which realizes highly reversible Fe deposition/dissolution for all-iron flow batteries. By introducing nano-scale pores on carbon fibers via a multistep electrode treatment approach, the modified carbon felt features a high degree of defects and proves effective in promoting Fe/Fe2+ kinetics and improving Fe nucleation and growth morphology, which is beneficial for both uniform Fe deposition and complete Fe dissolution rendering a substantially enhanced reversibility for Fe anode. Theoretical calculations further ascribe the enhanced Fe/Fe2+ reversibility to strong adsorption and intensified hybridization between Fe2+ and carbon defects, while all-iron flow cell tests adopting the modified carbon felt finally demonstrates a high power density of 80 mW cm−2 as well as stable charge–discharge operation over 250 cycles with a Coulombic efficiency of 99 %, which highlights the importance of electrode design in developing stable Fe anode for use in high-performance all-iron flow batteries.

Intrinsic Defect‐Rich Carbon‐Supported Iron Phthalocyanine as Beyond‐Pt Oxygen Reduction Catalysts for Zinc–Air Batteries

Molecular iron phthalocyanine (FePc) bearing a single‐atom Fe–N4 moiety is a high‐profile non‐platinum catalyst toward the oxygen reduction reaction (ORR), but its unsatisfactory activity and inadequate stability hinder the practical application. Herein, a novel strategy by hybridizing FePc with fullerene‐derived intrinsic defect‐rich carbon to improve its ORR activity and stability is reported. Via alkali‐assisted thermal pyrolysis, C60 molecules are disintegrated into tiny fragments that then restructure into pentagon‐ and edge‐rich carbon (FC). Utilizing FC as a support of FePc leads to a significantly improved ORR activity compared to other supports including reduced graphene oxide and carbon nanotube that hold distinct structural features. The optimized FePc/FC with a Fe loading of 3 wt% presents a half‐wave potential of 0.917 V, far beyond that of Pt/C (0.846 V), via selective four‐electron ORR pathway and excellent stability under accelerated stress test. The practical applicability of FePc/FC is also demonstrated as a high‐performing cathode catalyst of aqueous zinc–air batteries. It is, for the first time, explicitly disclosed that strong interactions between FePc molecules and intrinsic carbon defects (e.g., pentagons and edges) not only strengthen the anchoring effect of supported FePc but also enhance the intrinsic ORR activity of single‐atom Fe–N4 sites.

Defective nitrogen doped carbon material derived from nano-ZIF-8 for enhanced in-situ H2O2 generation and tetracycline hydrochloride degradation in electro-Fenton system

Tetracycline hydrochloride (TC) accumulates in large quantities in the water environment, causing a serious threat to human health and ecological environment safety. This research focused on developing cost-effective catalysts with high 2e- selectivity for electro-Fenton (EF) technology, a green pollution treatment method. Defective nitrogen-doped porous carbon (d-NPC) was prepared using the metal-organic framework as the precursor to achieve in-situ H2O2 production and self-decomposition into high activity ·OH for degradation of TC combined with Co2+/Co3+. The d-NPC produced 172.1 mg L−1 H2O2 within 120 min, and could degrade 96.4% of TC in EF system. The self-doped defects and graphite-nitrogen in d-NPC improved the oxygen reduction performance and increased the H2O2 yield, while pyridine nitrogen could catalyze H2O2 to generate ·OH. The possible pathway of TC degradation was also proposed. In this study, defective carbon materials were prepared by ball milling, which provided a new strategy for efficient in-situ H2O2 production and the degradation of pollutants.

Stable hydrogen evolution reaction at high current densities via designing the Ni single atoms and Ru nanoparticles linked by carbon bridges

Continuous and effective hydrogen evolution under high current densities remains a challenge for water electrolysis owing to the rapid performance degradation under continuous large-current operation. In this study, theoretical calculations, operando Raman spectroscopy, and CO stripping experiments confirm that Ru nanocrystals have a high resistance against deactivation because of the synergistic adsorption of OH intermediates (OHad) on the Ru and single atoms. Based on this conceptual model, we design the Ni single atoms modifying ultra-small Ru nanoparticle with defect carbon bridging structure (UP-RuNiSAs/C) via a unique unipolar pulse electrodeposition (UPED) strategy. As a result, the UP-RuNiSAs/C is found capable of running steadily for 100 h at 3 A cm−2, and shows a low overpotential of 9 mV at a current density of 10 mA cm−2 under alkaline conditions. Moreover, the UP-RuNiSAs/C allows an anion exchange membrane (AEM) electrolyzer to operate stably at 1.95 Vcell for 250 h at 1 A cm−2.

Regulation of oriented NO photooxidation to circumvent NO2 with high-coordinated M–N5 (M = Fe, Co, Mn, Ti) sites and far–carbon defects

The targeted oxidization of trace NO to NO3- instead of toxic NO2via photocatalytic process represents one of the promising protocols for assuring environmental benefits. A novel type of graphite carbon nitride (CN) photocatalysts with high coordination sites (M–N5; M = Fe, Co, Mn, Ti) and far–carbon defects were manufactured by reconstructing the low coordination structure (M–N4). The mingled characterizations and theoretical calculations demonstrated that the reconstructed sites could improve the charge and energy transfer process of the exciton to precisely regulate the activation process of O2, while inhibiting the activation of adsorbed H2O. Superior orientation to form superoxide radical and singlet oxygen, rather than hydroxyl radical, showed excellent NO removal rates (68.6%) and superior NO3- selectivity (about 100%) under visible–light irradiation. This work proposes a unique mechanism via tailored construction of highly coordinated structures for selective NO oxidation to achieve the goal of atmospheric purification.

Carbon Mediated Multifunctional Sb2Se3–WSe2 Heterostructure Nanofiber Facilitates Rapid and Stable Na+ Transport

AbstractAlloying metal selenides as advanced anode materials for sodium‐ion devices requires overcoming the challenges of high diffusion energy barriers and large volume expansion at high‐power densities. The typical dealloying process is difficult to trigger under fast kinetics, leading to limited capacity utilization. Here, Sb/W‐hybridization precursor is synthesized by one‐step reaction, followed by electrostatic spinning strategy to achieve a localized domain‐limiting effect. Finally, the carbon mediated Sb2Se3–WSe2 heterostructure nanofiber (SbWSe/C/NF) are obtained after carbonization/selenization process. Physical characterization and theoretical calculations reveal that the SbWSe/C/NF‐500 has a heterogeneous structure and abundant edge carbon defects, facilitating rapid Na+ transfer from exterior to interior. Furthermore, compared with the Sb2Se3/C monomer, the SbWSe/C heterostructure shows a significant dealloying reaction at high current densities, enhancing capacity utilization. Resultantly, the Na half‐cell with SbWSe/C/NF‐500 electrode demonstrates excellent rate capability and a high specific capacity of 553.7 mA h g−1 after 250 cycles at 2 A g−1. Meanwhile, the assembled sodium‐ion capacitor exhibits 80.83% capacity retention after 8000 cycles at 3800 W kg−1. The structure design strategy of cationic heterostructures with dual‐carbon introduction provides a reference for developing high‐power anodes.

Synthesis of Fe–N doped porous carbon/silicate composites regulated by minerals in coal gasification fine slag for synergistic electrocatalytic treatment of phenolic wastewater

Coal gasification fine slag (CGFS), as a difficult-to-dispose solid waste in the coal chemical industry, consists of minerals and residual carbon. Due to the aggregate structure of minerals blocking pores and encapsulating active substances, the high-value utilization of CGFS still remains a challenge. Based on the intrinsic characteristics of CGFS, this study synthesized Fe–N doped porous carbon/silicate composites (Fe-NC) by alkali activation and pyrolysis for electrocatalytic degradation of phenolic wastewater. Meanwhile, minerals were utilized to regulate the surface chemical and pore structure, turning their disadvantages into advantages, which caused a sharp increase in m-cresol mineralization. The positive effect of minerals on composite properties was investigated by characterization techniques, electrochemical analyses and density functional theory (DFT) calculations. It was found that the mesoporous structure of the mineral-regulated composites was further developed, with more carbon defects and reactive substances on its surface. Most importantly, silicate mediated iron conversion through strong interaction with H2O2, high work function gradient with electroactive iron, and excellent superoxide radical (•O2−) production capacity. It effectively improved the reversibility and kinetics of the entire electrocatalytic reaction. Within the Fe-NC311 electrocatalytic system, the m-cresol removal rate reached 99.55 ± 1.24%, surpassing most reported Fe–N-doped electrocatalysts. In addition, the adsorption and electrooxidation experiment confirmed that the synergistic effect of Fe–N doped porous carbon and silicate simultaneously promoted the capture of pollutants and the transformation of electroactive molecules, and hence effectively shortened the diffusion path of short-lived radicals, which was further supported by molecular dynamics simulation. Therefore, this research provides new insights into the problem of mineral limitations and opens an innovative approach for CGFS recycling and environmental remediation.

Nitrogen-doped graphene-decorated FeSex-Sb2Se3/C nanofibers as advanced anode materials for potassium ion batteries

Low operating voltage, high theoretical capacity conversion alloyed anodes ideal for potassium ion anodes. However, how to address the structural deformation and volume expansion of the changed alloyed materials throughout the reaction process is a crucial topic. A novel nitrogen-doped graphene-decorated FeSex-Sb2Se3/C nanofibers (FeSbSe-NGCNFs) composite is synthesized by adding dicyandiamide (DCDA) during electrospinning. Benefiting from porous one-dimensional nanostructure, graphene-decoration and rich nitrogen doping, the best electrochemical performance is shown by FeSbSe-NGCNFs when used as an anode in PIBs. FeSbSe-NGCNFs provide a reversible discharge specific capacity of 279.9 mAh/g at 100 mA g−1 after 100 cycles with a capacity retention of 87.6 %, in addition to a high capacity of 169.9 mAh/g at a high current of 3000 mA g−1. After 1000 cycles, the composite retained 115.8 mAh/g of capacity at 1000 mA g−1. The main causes of these exceptional cycling multiplicity properties are the porous structure that produces more carbon defects and active sites, increasing the amount of storage capacity for K+ and speeding up K+ transport and electron transfer, as well as the graphene nanosheet structure that enhances electrical conductivity and increases its specific surface area. Therefore, PIBs might benefit from the developed FeSbSe-NGCNFs as anode material.

Graphitic Armor: A Natural Molecular Sieve for Robust Hydrogen Electroxidation.

Carbon coating layers have been found to improve the catalytic performance of transition metals, which is usually explained as an outcome of electronic synergistic effect. Herein we reveal that the defective graphitic carbon, with a unique interlayer gap of 0.342 nm, can be a highly selective natural molecular sieve. It allows efficient diffusion of hydrogen molecules or radicals both along the in-plane and out-of-plane direction, but sterically hinders the diffusion of molecules with larger kinetic diameter (e.g., CO and O2) along the in-plane direction. As a result, poisonous species lager than 0.342 nm are sieved out, even when their adsorption on the metal is thermodynamically strong; at the same time, the interaction between H2 and the metal is not affected. This natural molecular sieve provides a very chance for constructing robust metal catalysts for hydrogen-relevant processes, which are more tolerant to chemical or electrochemical oxidation or CO-relevant poisoning.

Graphitic Armor: A Natural Molecular Sieve for Robust Hydrogen Electroxidation

AbstractCarbon coating layers have been found to improve the catalytic performance of transition metals, which is usually explained as an outcome of electronic synergistic effect. Herein we reveal that the defective graphitic carbon, with a unique interlayer gap of 0.342 nm, can be a highly selective natural molecular sieve. It allows efficient diffusion of hydrogen molecules or radicals both along the in‐plane and out‐of‐plane direction, but sterically hinders the diffusion of molecules with larger kinetic diameter (e.g., CO and O2) along the in‐plane direction. As a result, poisonous species lager than 0.342 nm are sieved out, even when their adsorption on the metal is thermodynamically strong; at the same time, the interaction between H2 and the metal is not affected. This natural molecular sieve provides a very chance for constructing robust metal catalysts for hydrogen‐relevant processes, which are more tolerant to chemical or electrochemical oxidation or CO‐relevant poisoning.

A functional cathode sodium compensation agent for stable sodium-ion batteries

Hard carbon (HC) is widely used in sodium-ion batteries (SIBs), but its performance has always been limited by low initial Coulombic efficiency (ICE) and cycling stability. Cathode compensation agent is a favorable strategy to make up for the loss of active sodium ions consumed by HC anode. Yet it lacks agent that effectively decomposes to increase the active sodium ions as well as regulate carbon defects for decreasing the irreversible sodium ions consumption. Here, we propose 1,2-dihydroxybenzene Na salt (NaDB) as a cathode compensation agent with high specific capacity (347.9 mAh g−1), lower desodiation potential (2.4–2.8 V) and high utilization (99%). Meanwhile, its byproduct could functionalize HC with more CO groups and promotes its reversible capacity. Consequently, the presodiation hard carbon (pHC) anode exhibits highly reversible capacity of 204.7 mAh g−1 with 98% retention at 5 C rate over 1000 cycles. Moreover, with 5 wt% NaDB initially coated on the Na3V2(PO4)3 (NVP) cathode, the capacity retention of NVP + NaDB|HC cell could increase form 36%–89% after 1000 cycles at 1 C rate. This work provides a new avenue to improve SIBs reversible capacity and cycling performance through designing functional cathode compensation agent.

Enhanced photocatalytic hydrogen production performance of g-C3N4 with rich carbon vacancies

Hydrogen energy is globally recognized as one of the clean and renewable chemical energy sources. Development of photocatalysts that can efficiently utilize sunlight for photocatalytic hydrogen production is an urgent mission at present. In this study, g-C3N4 with abundant pore structure and carbon defects for photocatalytic hydrogen generation was prepared by heat treatment of g-C3N4 using ammonium carbonate. The results of photocatalytic hydrogen evolution experiments demonstrate that the 5NHC sample (2 g g-C3N4 was mixed with 5.0 g ammonium carbonate) exhibits the highest hydrogen precipitation rate (972.3 μmol g-1h−1), which is 4.29 times higher than that of the reference g-C3N4 (183.6 μmol g-1h−1). Moreover, the 5NHC sample shows excellent structural stability during the hydrogen production cycling experiments, confirmed by the experimental results. Cr(VI) reduction results further demonstrate excellent photocatalytic performance of 5NHC, which is 1.54 times higher than that of the reference g-C3N4. The defective energy levels induced by carbon vacancies will lead to a rapid separation of photoinduced charge pairs, which will result in boosted photocatalytic performance. This work provides an effective strategy for development of highly performance g-C3N4.