Probing the electric double layer structure at nitrogen-doped graphite electrodes by constant-potential molecular dynamics simulations

Electric double layer(EDL)is a critical topic in electrochemistry and largely determines the working performance of lithium batteries.However,atomic insights into the EDL structures on heteroatom-modified graphite anodes and EDL evolution with electrode potential are very lacking.Herein,a constant-potential molecular dynamics(CPMD)method is proposed to probe the EDL structure under working conditions,taking N-doped graphite electrodes and carbonate electrolytes as an example.An interface model was developed,incorporating the electrode potential and atom electronegativities.As a result,an insightful atomic scenario for the EDL structure under varied electrode potentials has been established,which unveils the important role of doping sites in regulating both the EDL structures and the following electrochemical reactions at the atomic level.Specifically,the negatively charged N atoms repel the anions and adsorb Li~+at high and low potentials,respectively.Such preferential adsorption suggests that Ndoped graphite can promote Li~+desolvation and regulate the location of Li~+deposition.This CPMD method not only unveils the mysterious function of N-doping from the viewpoint of EDL at the atomic level but also applies to probe the interfacial structure on other complicated electrodes.

Preparation of N-doped graphite oxide for supercapacitors by NH_(3) cold plasma

In this work,N-doped graphite oxide(GO-P)was prepared by cold plasma treatment of GO using a mixture of NH_(3) and Ar as the working gas.When the ratios of NH_(3):Ar were 1:2,1:3,and 1:4,the specific capacitances of the GO-P(NH_(3):Ar=1:2),GO-P(NH_(3):Ar=1:3),and GO-P(NH_(3):Ar=1:4)were 124.5,187.7,and 134.6 F·g^(-1),respectively,which were 4.7,7.1,and 5.1 times that of GO at the current density of 1 A·g^(-1).The capacitance retention of the GO-P(NH_(3):Ar=1:3)was 80%when it was cycled 1000 times.The characterization results showed that the NH_(3)cold plasma could effectively produce N-doped GO and generate more active defects.The N/C ratio and the contents of pyridinic nitrogen and graphitic nitrogen of the GO-P(NH_(3):Ar=1:3)were the highest.These were conducive to providing pseudocapacitance and reducing the internal resistance of the electrode.In addition,the ID/IGof the GO-P(NH_(3):Ar=1:3)(1.088)was also the highest,indicating the highest number of defects.The results of discharge parameters measurement and in situ optical emission spectroscopy diagnosis of NH_(3) plasma showed that the discharge is the strongest when the ratio of NH_(3):Ar was 1:3,thereby the generated nitrogen active species can effectively promote N-doping.The N-doping and abundant defects were the keys to the excellent electrochemical performance of the GO-P(NH_(3):Ar=1:3).NH_(3) cold plasma is a simple and rapid method to prepare N-doped GO and regulate the N-doping to prepare high-performance supercapacitors.

N-doped graphene quantum dot-decorated N-TiO2/P-doped porous hollow g-C_(3)N_(4) nanotube composite photocatalysts for antibiotic photodegradation and H2 production

Exclusive responsiveness to ultraviolet light (~3.2 eV) and high photogenerated charge recombination rate are the two primary drawbacks of pure TiO_(2). We combined N-doped graphene quantum dots (N-GQDs), morphology regulation, and heterojunction construction strategies to synthesize N-GQD/N-doped TiO_(2)/P-doped porous hollow g-C_(3)N_(4) nanotube (PCN) composite photocatalysts (denoted as G-TPCN). The optimal sample (G-TPCN doped with 0.1wt% N-GQD, denoted as 0.1% G-TPCN) exhibits significantly enhanced photoabsorption, which is attributed to the change in bandgap caused by elemental doping (P and N), the improved light-harvesting resulting from the tube structure, and the upconversion effect of N-GQDs. In addition, the internal charge separation and transfer capability of0.1% G-TPCN are dramatically boosted, and its carrier concentration is 3.7, 2.3, and 1.9 times that of N-TiO_(2), PCN, and N-TiO_(2)/PCN(TPCN-1), respectively. This phenomenon is attributed to the formation of Z-scheme heterojunction between N-TiO_(2) and PCNs, the excellent electron conduction ability of N-GQDs, and the short transfer distance caused by the porous nanotube structure. Compared with those of N-TiO_(2), PCNs, and TPCN-1, the H2 production activity of 0.1%G-TPCN under visible light is enhanced by 12.4, 2.3, and 1.4times, respectively, and its ciprofloxacin (CIP) degradation rate is increased by 7.9, 5.7, and 2.9 times, respectively. The optimized performance benefits from excellent photoresponsiveness and improved carrier separation and migration efficiencies. Finally, the photocatalytic mechanism of 0.1% G-TPCN and five possible degradation pathways of CIP are proposed. This study clarifies the mechanism of multiple modification strategies to synergistically improve the photocatalytic performance of 0.1% G-TPCN and provides a potential strategy for rationally designing novel photocatalysts for environmental remediation and solar energy conversion.

High-efficiency sodium storage of Co_(0.85)Se/WSe_(2) encapsulated in N-doped carbon polyhedron via vacancy and heterojunction engineering

With the advantage of fast charge transfer,heterojunction engineering is identified as a viable method to reinforce the anodes'sodium storage performance.Also,vacancies can effectively strengthen the Na+adsorption ability and provide extra active sites for Na+adsorption.However,their synchronous engineering is rarely reported.Herein,a hybrid of Co_(0.85)Se/WSe_(2) heterostructure with Se vacancies and N-doped carbon polyhedron(CoWSe/NCP)has been fabricated for the first time via a hydrothermal and subsequent selenization strategy.Spherical aberration-corrected transmission electron microscopy confirms the phase interface of the Co_(0.85)Se/WSe_(2) heterostructure and the existence of Se vacancies.Density functional theory simulations reveal the accelerated charge transfer and enhanced Na+adsorption ability,which are contributed by the Co_(0.85)Se/WSe_(2) heterostructure and Se vacancies,respectively.As expected,the CoWSe/NCP anode in sodium-ion battery achieves outstanding rate capability(339.6 mAh g^(−1) at 20 A g^(−1)),outperforming almost all Co/W-based selenides.

Highly N-doped carbon with low graphitic-N content as anode material for enhanced initial Coulombic efficiency of lithium-ion batteries

N-doped carbons as one of the most prominent anode materials to replace standard graphite exhibit outstanding Li+storage performance.However,N-doped carbon anodes still suffer from low N-doping levels and low initial Coulombic efficiency(ICE).In this study,high N-doped and low graphitic-N carbons(LGNCs)with enhanced ICE were synthesized by taking advantage of a denitrification strategy for graphitic carbon nitride(g-C_(3)N_(4)).In brief,more than 14.5 at%of N from g-C_(3)N_(4)(55.1 at%N)was retained by reacting graphitic-N with lithium,which was subsequently removed.As graphitic-N is largely responsible for the irreversible capacity,the anode's performance was significantly increased.Compared to general N-doped carbons with high graphitic-N proportion(>50%)and low N content(<15 at%),LGNCs delivered a low proportion of 10.8%-17.2% within the high N-doping content of 14.5-42.7 at%,leading to an enhanced specific capacity of 1499.9mAh g^(-1) at an ICE of 93.7% for the optimal sample of LGNC(4:1).This study provides a facile strategy to control the N content and speciation,achieving both high Li+storage capacity and high ICE,and thus promoting research and application of N-doped carbon materials.

Targeted regeneration and upcycling of spent graphite by defect‐driven tin nucleation

The recycling of spent batteries has become increasingly important owing to their wide applications,abundant raw material supply,and sustainable development.Compared with the degraded cathode,spent anode graphite often has a relatively intact structure with few defects after long cycling.Yet,most spent graphite is simply burned or discarded due to its limited value and inferior performance on using conventional recycling methods that are complex,have low efficiency,and fail in performance restoration.Herein,we propose a fast,efficient,and“intelligent”strategy to regenerate and upcycle spent graphite based on defect‐driven targeted remediation.Using Sn as a nanoscale healant,we used rapid heating(~50 ms)to enable dynamic Sn droplets to automatically nucleate around the surface defects on the graphite upon cooling owing to strong binding to the defects(~5.84 eV/atom),thus simultaneously achieving Sn dispersion and graphite remediation.As a result,the regenerated graphite showed enhanced capacity and cycle stability(458.9 mAh g^(−1) at 0.2 A g^(−1) after 100 cycles),superior to those of commercial graphite.Benefiting from the self‐adaption of Sn dispersion,spent graphite with different degrees of defects can be regenerated to similar structures and performance.EverBatt analysis indicates that targeted regeneration and upcycling have significantly lower energy consumption(~99%reduction)and near‐zero CO_(2) emission,and yield much higher profit than hydrometallurgy,which opens a new avenue for direct upcycling of spend graphite in an efficient,green,and profitable manner for sustainable battery manufacture.

Enhancing capacitive deionization performance and cyclic stability of nitrogen-doped activated carbon by the electro-oxidation of anode materials

Electrode materials with high desalination capacity and long-term cyclic stability are the focus of capacitive deionization(CDI) community. Understanding the causes of performance decay in traditional carbons is crucial to design a high-performance material. Based on this, here, nitrogen-doped activated carbon(NAC) was prepared by pyrolyzing the blend of activated carbon powder(ACP) and melamine for the positive electrode of asymmetric CDI. By comparing the indicators changes such as conductivity, salt adsorption capacity, pH, and charge efficiency of the symmetrical ACP-ACP device to the asymmetric ACP-NAC device under different CDI cycles, as well as the changes of the electrochemical properties of anode and cathode materials after long-term operation, the reasons for the decline of the stability of the CDI performance were revealed. It was found that the carboxyl functional groups generated by the electro-oxidation of anode carbon materials make the anode zero-charge potential(E_(pzc)) shift positively,which results in the uneven distribution of potential windows of CDI units and affects the adsorption capacity. Furthermore, by understanding the electron density on C atoms surrounding the N atoms, we attribute the increased cyclic stability to the enhanced negativity of the charge of carbon atoms adjacent to quaternary-N and pyridinic-oxide-N.

Insight to the enhanced microwave absorption of porous N-doped carbon driven by ZIF-8:Competition between graphitization and porosity

Porous carbon-based materials are promised to be lightweight dielectric microwave absorbents.Deeply understanding the influence of graphitization grade and porous structure on the dielectric parameters is urgently required.Herein,utilizing the low boiling point of Zn,porous N-doped carbon was fabricated by carbonization of ZIF-8(Zn)at different temperature,and the microwave absorption performance was investigated.The porous N-doped carbon inherits the high porosity of ZIF-8 precursor.By increasing the carbonization temperature,the contents of Zn and N elements are decreased;the graphitization degree is improved;however,the specific surface area and porosity are increased first and then decreased.When the carbonization temperature is 1000°C,the porous N-doped carbon behaves enhanced microwave absorption.With an ultrathin thickness of 1.29 mm,the ideal RL reaches-50.57 dB at 16.95 GHz and the effective absorption bandwidth is 4.17 GHz.The mechanism of boosted microwave absorption is ascribed to the competition of graphitization and porosity as well as N dopants,resulting in high dielectric loss capacity and good impedance matching.The porous structure can prolong the pathways and raise the contact opportunity between microwaves and porous carbon,causing multiple scattering,interface polarization,and improved impedance matching.Besides,the N dopants can induce electron polarization and defect polarization.These results give a new insight to construct lightweight carbon-based microwave absorbents by regulating the graphitization and porosity.

Recycled graphite for more sustainable lithium-ion batteries

The demand for lithium-ion batteries(LIBs)is driven largely by their use in electric vehicles,which is projected to increase dramatically in the future.This great success,however,urgently calls for the efficient recycling of LIBs at the end of their life.Herein,we describe a froth flotation-based process to recycle graphite—the predominant active material for the negative electrode—from spent LIBs and investigate its reuse in newly assembled LIBs.It has been found that the structure and morphology of the recycled graphite are essentially unchanged compared to pristine commercial anode-grade graphite,and despite some minor impurities from the recycling process,the recycled graphite provides a remarkable reversible specific capacity of more than 350 mAh g^(−1).Even more importantly,newly assembled graphite‖NMC532 cells show excellent cycling stability with a capacity retention of 80%after 1000 cycles,that is,comparable to the performance of reference full cells comprising pristine commercial graphite.

The preparation and properties of N-doped carbon materials and their use for sodium storage

Defect engineering by heteroatom doping gives carbon materials some new characteristics such as a different electronic structure and a high electrochemical activity,making them suitable for high-performance applications.N-doping has been widely investigated because of its similar atom radius to carbon,high electronegativity as well as many different configurations.We summarize the preparation methods and properties of N-doped carbon materials,and discuss their possible use in sodium ion storage.The relationships between N content/configuration and crystallinity,electronic conductivity,wettability,chemical reactivity as well as sodium ion storage performance are discussed.

Spent graphite regeneration:Exploring diverse repairing manners with impurities-catalyzing effect towards high performance and low energy consumption

Spent battery recycling has received considerable attention because of its economic and environmental potential.A large amount of retired graphite has been produced as the main electrode material,accompanied by a detailed exploration of the repair mechanism.However,they still suffer from unclear repair mechanisms and physicochemical evolution.In this study,spent graphite was repaired employing three methodologies:pickling-sintering,pyrogenic-recovery,and high-temperature sintering.Owing to the catalytic effect of the metal-based impurities and temperature control,the as-obtained samples displayed an ordered transformation,including the interlayer distance,crystalline degree,and grain size.As anodes of lithium ions batteries,the capacity of repaired samples reached up to 310 mA h g^(-1)above after 300loops at 1.0 C,similar to that of commercial graphite.Meanwhile,benefitting from the effective assembly of carbon atoms in internal structure of graphite at>1400℃,their initial coulombic efficiency were>87%.Even at 2.0 C,the capacity of samples remained approximately 244 mA h g^(-1)after 500 cycles.Detailed electrochemical and kinetic analyses revealed that a low temperature enhanced the isotropy,thereby enhancing the rate properties.Further,economic and environmental analyses revealed that the revenue obtained through suitable pyrogenic-recovering manners was approximately the largest value(5500$t^(-1)).Thus,this study is expected to clarify the in-depth effect of different repair methods on the traits of graphite,while offering all-round evaluations of repaired graphite.

Growth kinetics of titanium carbide coating by molten salt synthesis process on graphite sheet surface

The synthesis of carbide coatings on graphite substrates using molten salt synthesis(MSS),has garnered significant interest due to its cost-effective nature.This study investigates the reaction process and growth kinetics involved in MSS,shedding light on key aspects of the process.The involvement of Ti powder through liquid-phase mass transfer is revealed,where the diffusion distance and quantity of Ti powder play a crucial role in determining the reaction rate by influencing the C content gradient on both sides of the carbide.Furthermore,the growth kinetics of the carbide coating are predominantly governed by the diffusion behavior of C within the carbide layer,rather than the chemical reaction rate.To analyze the kinetics,the thickness of the carbide layer is measured with respect to heat treatment time and temperature,unveiling a parabolic relationship within the temperature range of 700-1300℃.The estimated activation energy for the reaction is determined to be 179283 J·mol^(-1).These findings offer valuable insights into the synthesis of carbide coatings via MSS,facilitating their optimization and enhancing our understanding of their growth mechanisms and properties for various applications.

Enhanced stability of nitrogen-doped carbon-supported palladium catalyst for oxidative carbonylation of phenol

Enhancing the stability of supported noble metal catalysts emerges is a major challenge in both science and industry.Herein,a heterogeneous Pd catalyst(Pd/NCF)was prepared by supporting Pd ultrafine metal nanoparticles(NPs)on nitrogen-doped carbon;synthesized by using F127 as a stabilizer,as well as chitosan as a carbon and nitrogen source.The Pd/NCF catalyst was efficient and recyclable for oxidative carbonylation of phenol to diphenyl carbonate,exhibiting higher stability than Pd/NC prepared without F127 addition.The hydrogen bond between chitosan(CTS)and F127 was enhanced by F127,which anchored the N in the free amino group,increasing the N content of the carbon material and ensuring that the support could provide sufficient N sites for the deposition of Pd NPs.This process helped to improve metal dispersion.The increased metal-support interaction,which limits the leaching and coarsening of Pd NPs,improves the stability of the Pd/NCF catalyst.Furthermore,density functional theory calculations indicated that pyridine N stabilized the Pd^(2+)species,significantly inhibiting the loss of Pd^(2+)in Pd/NCF during the reaction process.This work provides a promising avenue towards enhancing the stability of nitrogen-doped carbon-supported metal catalysts.

An efficient recycling strategy to eliminate the residual“impurities”while heal the damaged structure of spent graphite anodes

The recycling of graphite from spent lithium-ion batteries(LIBs)is overlooked due to its relatively low added value and the lack of efficient recovering methods.To reuse the spent graphite anodes,we need to eliminate their useless components(mainly the degraded solid electrolyte interphase,SEI)and reconstruct their damaged structure.Herein,a facile and efficient strategy is proposed to recycle the spent graphite on the basis of the careful investigation of the composition of the cycled graphite anodes and the rational design of the regeneration processes.The regenerated graphite,which is revitalized by calcination treatment and acid leaching,delivers superb rate performance and a high specific capacity of 370 mAh g^(-1)(~99% of its theoretical capacity)after 100 cycles at 0.1 C,superior to the commercial graphite anodes.The improved electrochemical performance could be attributed to unchoked Li^(+) transport channels and enhanced charge transfer reaction due to the effective destruction of the degraded SEI and the full recovery of the damaged structure of the spent graphite.This work clarifies that the electrochemical performance of the regenerated graphite could be deteriorated by even a trace amount of the residual“impurity”and provides a facile method for the efficient regeneration of graphite anodes.

High-Efficiency Photo-Induced Charge Transfer for SERS Sensing in N-Doped 3D-Graphene on Si Heterojunction

Nitrogen-doped three-dimensional graphene(N-doped 3D-graphene)is a graphene derivative with excellent adsorption capacity,large specific surface area,high porosity,and optoelectronic properties.Herein,N-doped 3D-graphene/Si heterojunctions were grown in situ directly on silicon(Si)substrates via plasma-assisted chemical vapor deposition(PACVD),which is promising for surface-enhanced Raman scattering(SERS)substrates candidates.Combined analyses of theoretical simulation,incorporating N atoms in 3D-graphene are beneficial to increase the electronic state density of the system and enhance the charge transfer between the substrate and the target molecules.The enhancement of the optical and electric fields benefits from the stronger light-matter interaction improved by the natural nano-resonator structure of N-doped 3D-graphene.The as-prepared SERS substrates based on N-doped 3D-graphene/Si heterojunctions achieve ultra-low detection for various molecules:10^(-8)M for methylene blue(MB)and 10^(-9)M for crystal violet(CRV)with rhodamine(R6G)of 10^(10)M.In practical detected,10^(-8)M thiram was precisely detected in apple peel extract.The results indicate that N-doped 3D-graphene/Si heterojunctions based-SERS substrates have promising applications in low-concentration molecular detection and food safety.

Stable and reversible zinc metal anode with fluorinated graphite nanosheets surface coating

A highly stable zinc metal anode modified with a fluorinated graphite nanosheets(FGNSs)coating was designed.The porous structure of the coating layer effectively hinders lateral mass transfer of Zn ions and suppresses dendrite growth.Moreover,the high electronegativity exhibited by fluorine atoms creates an almost superhydrophobic solid-liquid interface,thereby reducing the interaction between solvent water and the zinc substrate.Consequently,this leads to a significant inhibition of hydrogen evolution corrosion and other side reactions.The modified anode demonstrates exceptional cycling stability,as symmetric cells exhibit sustained cycling for over 1400 h at a current density of 5 mA/cm^(2).Moreover,the full cells with NH_(4)V_(4)O_(10)cathode exhibit an impressive capacity retention rate of 92.2%after undergoing 1000 cycles.

Edge and lithium concentration effects on intercalation kinetics for graphite anodes

Graphite interfaces are an important part of the anode in lithium-ion batteries(LIBs),significantly influencing Li intercalation kinetics.Graphite anodes adopt different stacking sequences depending on the concentration of the intercalated Li ions.In this work,we performed first-principles calculations to comprehensively address the energetics and dynamics of Li intercalation and Li vacancy diffusion near the no n-basal edges of graphite,namely the armchair and zigzag-edges,at high Li concentration.We find that surface effects persist in stage-Ⅱ that bind Li strongly at the edge sites.However,the pronounced effect previously identified at the zigzag edge of pristine graphite is reduced in LiC_(12),penetrating only to the subsurface site,and eventually disappearing in LiC_(6).Consequently,the distinctive surface state at the zigzag edge significantly impacts and restrains the charging rate at the initial lithiation of graphite anodes,whilst diminishes with an increasing degree of lithiation.Longer diffusion time for Li hopping to the bulk site from either the zigzag edge or the armchair edge in LiC_(6) was observed during high state of charge due to charge repulsion.Effectively controlling Li occupation and diffusion kinetics at this stage is also crucial for enhancing the charge rate.

Thermal fatigue and wear of compacted graphite iron brake discs with various thermomechanical properties

The increase in payload capacity of trucks has heightened the demand for cost-effective yet high performance brake discs.In this work,the thermal fatigue and wear of compacted graphite iron brake discs were investigated,aiming to provide an experimental foundation for achieving a balance between their thermal and mechanical properties.Compacted graphite iron brake discs with different tensile strengths,macrohardnesses,specific heat capacities and thermal diffusion coefficients were produced by changing the proportion and strength of ferrite.The peak temperature,pressure load and friction coefficient of compacted graphite iron brake discs were analyzed through inertia friction tests.The morphology of thermal cracks and 3D profiles of the worn surfaces were also discussed.It is found that the thermal fatigue of compacted graphite iron discs is determined by their thermal properties.A compacted graphite iron with the highest specific heat capacity and thermal diffusion coefficient exhibits optimal thermal fatigue resistance.Oxidization of the matrix at low temperatures significantly weakens the function of alloy strengthening in hindering the propagation of thermal cracks.Despite the reduced hardness,increasing the ferrite proportion can mitigate wear loss resulting from low disc temperatures and the absence of abrasive wear.

Oxidation Evolution and Activity Origin of N-Doped Carbon in the Oxygen Reduction Reaction

N-doped carbon materials,with their applications as electrocatalysts for the oxygen reduction reaction(ORR),have been extensively studied.However,a negletcted fact is that the operating potential of the ORR is higher than the theoretical oxida-tion potential of carbon,possibly leading to the oxidation of carbon materials.Consequently,the infl uence of the structural oxidation evolution on ORR performance and the real active sites are not clear.In this study,we discover a two-step oxida-tion process of N-doped carbon during the ORR.The fi rst oxidation process is caused by the applied potential and bubbling oxygen during the ORR,leading to the oxidative dissolution of N and the formation of abundant oxygen-containing functional groups.This oxidation process also converts the reaction path from the four-electron(4e)ORR to the two-electron(2e)ORR.Subsequently,the enhanced 2e ORR generates oxidative H_(2)O_(2),which initiates the second stage of oxidation to some newly formed oxygen-containing functional groups,such as quinones to dicarboxyls,further diversifying the oxygen-containing functional groups and making carboxyl groups as the dominant species.We also reveal the synergistic eff ect of multiple oxygen-containing functional groups by providing additional opportunities to access active sites with optimized adsorption of OOH*,thus leading to high effi ciency and durability in electrocatalytic H_(2)O_(2) production.

Residual fluoride self-activated effect enabling upgraded utilization of recycled graphite anode

Recycling graphite anode from spent lithium-ion batteries(SLIBs)is regarded as a crucial approach to promoting sustainable energy storage industry.However,the recycled graphite(RG)generally presents degraded structure and performance.Herein,the residual fluoride self-activated effect is proposed for the upgraded utilization of RG.Simple and low-energy water immersion treatment not only widens the interlayer spacing,but also retains appropriate fluoride on the surface of RG.Theoretical analysis and experiments demonstrate that the residual fluoride can optimize Li~+migration and deposition kinetics,resulting in better Li~+intercalation/deintercalation in the interlayer and more stable Li metal plating/stripping on the surface of RG,As a result,the designed LFP||RG full cells achieve ultrahigh reversibility(~100%Coulombic efficiency),high capacity retention(67%after 200 cycles,0.85 N/P ratio),and commendable adaptability(stable cycling without short-circuiting,0.15 N/P ratio).The energy density is improved from 334 Wh kg^(-1)of 1.1 N/P ratio to 367 Wh kg^(-1)of 0.85 N/P ratio(total mass based on cathode and anode).The exploration of RG by residual fluoride self-activated effect achieves upgraded utilization beyond fresh commercial graphite and highlights a new strategy for efficient reuse of SLIBs.