“H_(2)-free” demethoxylation of guaiacol in subcritical water using Pt supported on N-doped carbon catalysts:A cost-effective strategy for biomass upgrading

"H_(2)-free" HDO is a revolutionary route to circumvent the limitations of H_(2)-fed HDO reactors for biomass upgrading.This work demonstrates the viability of this economically appealing route when an adequate catalyst is implemented.Herein,we have developed a new family of Pt catalysts supported on N-doped activated carbons for the H_(2)-free HDO process of guaiacol.Several N-donors have been used to tune the catalyst’s structural and electronic properties.As a general trend,the N-promoted samples are more selective towards oxygen-depleted products.The best performing material,namely Pt/PANI-AC reached outstanding guaiacol conversion values-ca.75% at 300℃ while displaying reasonable stability for multiple recycling operations.The advanced performance is ascribed to the modified electronic and acid-base properties which favor guaiacol activation and C-O cleavage,as well as the excellent dispersion of the Pt nano particles.

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.

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.

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.

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.

Engineering single-atom Mn on nitrogen-doped carbon to regulate lithium-peroxide reaction kinetics for rechargeable lithium-oxygen batteries

Precision engineering of catalytic sites to guide more favorable pathways for Li_(2)O_(2) nucleation and decom-position represents an enticing kinetic strategy for mitigating overpotential,enhancing discharge capac-ity,and improving recycling stability of Li-O_(2) batteries.In this work,we employ metal-organic frameworks(MOFs)derivation and ion substitution strategies to construct atomically dispersed Mn-N_(4) moieties on hierarchical porous nitrogen-doped carbon(Mn SAs-NC)with the aim of reducing the over-potential and improving the cycling stability of Li-O_(2) batteries.The porous structure provides more chan-nels for mass transfer and exposes more highly active sites for electrocatalytic reactions,thus promoting the formation and decomposition of Li_(2)O_(2).The Li-O_(2) batteries with Mn SAs-NC cathode achieve lower overpotential,higher specific capacity(14290 mA h g^(-1) at 100 mAg^(-1)),and superior cycle stability(>100 cycles at 200 mA g^(-1))compared with the Mn NPs-NC and NC.Density functional theory(DFT)cal-culations reveal that the construction of Mn-N_(4) moiety tunes the charge distribution of the pyridinic N-rich vacancy and balances the affinity of the intermediates(LiO_(2) and Li_(2)O_(2)).The initial nucleation of Li_(2)O_(2) on Mn SAs-NC favors the O_(2)-→LiO_(2)→Li_(2)O_(2) surface-adsorption pathway,which mitigates the overpoten-tials of the oxygen reduction(ORR)and oxygen evolution reaction(OER).As a result,Mn SAs-NC with Mn-N_(4) moiety effectively facilitates the Li_(2)O_(2) nucleation and enables its reversible decomposition.This work establishes a methodology for constructing carbon-based electrocatalysts with high activity and selectivity for Li-O_(2)batteries.

Hierarchically porous Co@N-doped carbon fiber assembled by MOF-derived hollow polyhedrons enables effective electronic/mass transport:An advanced 1D oxygen reduction catalyst for Zn-air battery

Developing advanced oxygen reduction reaction(ORR)electrocatalysts with rapid mass/electron transport as well as conducting relevant kinetics investigations is essential for energy technologies,but both still face ongoing challenges.Herein,a facile approach was reported for achieving the highly dispersed Co nanoparticles anchored hierarchically porous N-doped carbon fibers(Co@N-HPCFs),which were assembled by core-shell MOFs-derived hollow polyhedrons.Notably,the unique one-dimensional(1D)carbon fibers with hierarchical porosity can effectively improve the exposure of active sites and facilitate the electron transfer and mass transfer,resulting in the enhanced reaction kinetics.As a result,the ORR performance of the optimal Co@N-HPCF catalysts remarkably outperforms that of commercial Pt/C in alkaline solution,reaching a limited diffusion current density(J)of 5.85 m A cm^(-2)and a half-wave potential(E_(1/2))of 0.831 V.Particularly,the prepared Co@N-HPCF catalysts can be used as an excellent air-cathode for liquid/solid-state Zn-air batteries,exhibiting great potentiality in portable/wearable energy devices.Furthermore,the reaction kinetic during ORR process is deeply explored by finite element simulation,so as to intuitively grasp the kinetic control region,diffusion control region,and mixing control region of the ORR process,and accurately obtain the relevant kinetic parameters.This work offers an effective strategy and a reliable theoretical basis for the engineering of first-class ORR electrocatalysts with fast electronic/mass transport.

ZIF-Mediated Anchoring of Co species on N-doped Carbon Nanorods as an Efficient Cathode Catalyst for Zn-Air Batteries

Developing efficient oxygen reduction reaction(ORR)catalyst is essential for the practical application of Zn-air batteries(ZABs).In this contribution,we develop a novel zeolitic imidazolate framework(ZIF)-mediated strategy to anchor Co species on N-doped carbon nanorods for efficient ORR.Featuring ultrahigh N-doping(10.29 at.%),monodisperse Co nanocrystal decoration,and well-dispersed Co-N_(x)functionalization,the obtained Co-decorated N-doped carbon nanorods(Co@NCNR)exhibit a decent ORR performance comparable to commercial Pt/C in alkaline media.Aqueous ZABs have been assembled using Co@NCNR as the cathode catalyst.The assembled ZABs manifest high initial open-circuit voltage as well as high energy density.In addition,the Co@NCNR also demonstrates ideal ORR performance in quasi-solid-state ZABs.

Boron-doped lamellar porous carbon supported copper catalyst for dimethyl oxalate hydrogenation

Doping heteroatoms on carbon materials could bring some special advantages for using as catalyst support.In this work, a boron doped lamellar porous carbon(B-LPC) was prepared facilely and utilized as carbonbased support to construct Cu/B-LPC catalyst for dimethyl oxalate(DMO) hydrogenation. Doping boron could make the B-LPC own more defects on surface and bigger pore size than B-free LPC, which were beneficial to disperse and anchor Cu nanoparticles. Moreover, the interaction between Cu species and B-LPC could be strengthened by the doped B, which not only stabilized the Cu nanoparticles, but also tuned the valence of Cu species to maintain more Cu^(+). Therefore, the B-doped Cu/B-LPC catalyst exhibited stronger hydrogenation ability and obtained higher alcohols selectivity than Cu/LPC, as well as high stability without decrease of DMO conversion and ethylene glycol selectivity even after 300 h of reaction at 240℃.

Schiff-base polymer derived FeCo-N-doped porous carbon flowers as bifunctional oxygen electrocatalyst for long-life rechargeable zinc-air batteries

Rational design and exploration of low-cost and robust bifunctional oxygen electrocatalysts are vitally important for developing high-performance zinc-air batteries(ZABs).Herein,we reported a facile yet cost-efficient approach to construct a bifunctional oxygen reduction reaction(ORR)/oxygen evolution reaction(OER)electrocatalyst composed of N-doped porous carbon nanosheet flowers decorated with Fe Co nanoparticles(Fe Co/N-CF).Rational design of this catalyst is achieved by designing Schiff-base polymer with unique molecular structure via hydrogen bonding of cyanuramide and terephthalaldehyde polycondensate in the presence of metal cations.It exhibits excellent activity and stability for electrocatalysis of ORR/OER,enabling ZAB with a high peak power density of 172 m W cm^(-2)and a large specific capacity of 811 m A h g^(-1)Znat large current.The rechargeable ZAB demonstrates excellent durability for 1000 h with slight voltage decay,far outperforming a couple of precious Pt/Ir-based catalysts.Density functional theory(DFT)calculations reveal that high activity of bimetallic Fe Co stems from enhanced O_(2)and OH-adsorption and accelerated O_(2)dissociation by OAO bond activation.

Manipulating oxygenate adsorption on N-doped carbon by coupling with CoSn alloy for bifunctional oxygen electrocatalyst

Highly active bifunctional oxygen electrocatalysts accelerate the development of high-performance Zn-air battery,but suffer from the mismatched activities of oxygen evolution reaction(OER)and oxygen reduced reaction(ORR).Herein,highly integrated bifunctional oxygen electrocatalysts,cobalt-tin alloys coated by nitrogen doped carbon(CoSn@NC)are prepared by MOFs-derived method.In this hybrid catalyst,the binary CoSn nanoalloys mainly contribute to highly active OER process while the Co(or Sn)-N-C serves as ORR active sites.Rational interaction between CoSn and NC donates more rapid reaction kinetics than Pt/C(ORR)and IrO_(2)(OER).Such CoSn@NC holds a promise as air-cathode electrocatalyst in Zn-air battery,superior to Pt/C+IrO_(2)catalyst.First-principles calculations predict that CoSn alloys can upgrade charge redistribution on NC and promote the transfer to reactants,thus optimizing the adsorption strength of oxygen-containing intermediates to boost the overall reactivity.The tuning of oxygenate adsorption by interactions between alloy and heteroatom-doped carbon can guide the design of bifunctional oxygen electrocatalysts.

In situ formation of multiple catalysts for enhancing the hydrogen storage of MgH_(2) by adding porous Ni_(3)ZnC_(0.7)/Ni loaded carbon nanotubes microspheres

MgH_(2) is considered one of the most promising hydrogen storage materials because of its safety,high efficiency,high hydrogen storage quantity and low cost characteristics.But some shortcomings are still existed:high operating temperature and poor hydrogen absorption dynamics,which limit its application.Porous Ni_(3)ZnC_(0.7)/Ni loaded carbon nanotubes microspheres(NZC/Ni@CNT)is prepared by facile filtration and calcination method.Then the different amount of NZC/Ni@CNT(2.5,5.0 and 7.5 wt%)is added to the MgH_(2) by ball milling.Among the three samples with different amount of NZC/Ni@CNT(2.5,5.0 and 7.5 wt%),the MgH_(2)-5 wt%NZC/Ni@CNT composite exhibits the best hydrogen storage performances.After testing,the MgH_(2)-5 wt%NZC/Ni@CNT begins to release hydrogen at around 110℃ and hydrogen absorption capacity reaches 2.34 wt%H_(2) at 80℃ within 60 min.Moreover,the composite can release about 5.36 wt%H_(2) at 300℃.In addition,hydrogen absorption and desorption activation energies of the MgH_(2)-5 wt%NZC/Ni@CNT composite are reduced to 37.28 and 84.22 KJ/mol H_(2),respectively.The in situ generated Mg_(2)NiH_(4)/Mg_(2)Ni can serve as a"hydrogen pump"that plays the main role in providing more activation sites and hydrogen diffusion channels which promotes H_(2) dissociation during hydrogen absorption process.In addition,the evenly dispersed Zn and MgZn2 in Mg and MgH_(2) could provide sites for Mg/MgH_(2) nucleation and hydrogen diffusion channel.This attempt clearly proved that the bimetallic carbide Ni_(3)ZnC_(0.7) is a effective additive for the hydrogen storage performances modification of MgH_(2),and the facile synthesis of the Ni_(3)ZnC_(0.7)/Ni@CNT can provide directions of better designing high performance carbide catalysts for improving MgH_(2).

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.

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.

Tin-mediated carbon-confined Pt_(3)Co ordered intermetallic nanoparticles as highly efficient and durable oxygen reduction electrocatalysts for rechargeable zinc-air batteries

The development of electrocatalysts for the oxygen reduction reaction(ORR) that bears high selectivity,exceptional activity,and long-term stability is crucial for advancing various green energy technologies.Intermetallics composed of platinum and transition metals are considered to be promising candidates for this purpose.However,they typically face challenges such as unfavorable intrinsic activity and a propensity for particle aggregation,diminishing their ORR performance.Against this backdrop,we present our findings on a N-doped carbon confined Pt_(3)Co intermetallic doped with p-block metal tin(Pt_(3)Co_(x)Sn_(1-x)/NC).The introduction of Sn induces lattice strain due to its larger atomic size,which leads to the distortion of the Pt_(3)Co lattice structure,while the coupling of carbon polyhedra inhibits the particle aggregation.The optimized Pt_(3)Co_(0.8)Sn_(0.2)/NC catalyst demonstrates an impressive half-wave potential of 0.86 V versus RHE,surpassing both Pt_(3)Co/NC and Pt_(3)Sn/NC catalysts.Moreover,the Pt_(3)Co_(0.8)Sn_(0.2)/NC exhibits a mass-specific activity as high as 1.4 A mg_(Pt)^(-1),ranking it in the top level among the intermetallicsbased ORR electrocatalysts.When further employed as a cathode material in a self-assembled zinc-air battery,it shows stable operation for over 80 h.These results underscore the significant impact of lattice strain engineering through the strategic doping of p-block metal in the carbon-confined Pt_(3)Co intermetallic,thereby enhancing the catalytic efficiency for the ORR.

Critical role of carbon support in metal nanoaggregate facilitating Fe-N-C catalyst for PEM fuel cell application

Metal nanoaggregates can simultaneously enhance the activity and stability of Fe-N-C catalysts in proton-exchange-membrane fuel cells(PEMFC).Previous studies on the relevant mechanism have focused on the direct interaction between FeN_(4)active sites and metal nanoaggregates.However,the role of carbon support that hosts metal nanoaggregates and active sites has been overlooked.Here,a Fe-N-C catalyst encapsulating inactive gold nanoparticles is prepared as a model catalyst to investigate the electronic tuning of Au nanoparticles(NPs)towards the carbon support.Au NPs donate electrons to carbon support,making it rich inπelectrons,which reduces the work function and regulates the electronic configuration of the FeN_(4)sites for an enhanced ORR activity.Meanwhile,the electron-rich carbon support can mitigate the electron depletion of FeN_(4)sites caused by carbon support oxidation,thereby preserving its high activity.The yield and accumulation of H_(2)O_(2)are thus alleviated,which delays the oxidation of the catalyst and benefits the stability.Due to the electron-rich carbon support,the composite catalyst achieves a top-level peak power density of 0.74 W/cm^(2) in a 1.5 bar H_(2)-air PEMFC,as well as the improved stability.This work elucidates the key role of carbon support in the performance enhancement of the FeN-C/metal nanoaggregate composite catalysts for fuel cell application.

Structure design and electrochemical properties of carbon-based single atom catalysts in energy catalysis:A review

Single atom catalysts(SACs) possessing regulated electronic structure, high atom utilization, and superior catalytic efficiency have been studied in almost all fields in recent years. Carbon-based supporting SACs are becoming popular materials because of their low cost, high electron conductivity, and controllable surface property. At the stage of catalysts preparation, the rational design of active sites is necessary for the substantial improvement of activity of catalysts. To date, the reported design strategies are mainly about synthesis mechanism and synthetic method. The level of understanding of design strategies of carbon-based single atom catalysts is requiring deep to be paved. The design strategies about manufacturing defects and coordination modulation of catalysts are presented. The design strategies are easy to carry out in the process of drawing up preparation routes. The components of carbon-based SACs can be divided into two parts: active site and carbon skeleton. In this review, the manufacture of defects and coordination modulation of two parts are introduced, respectively. The structure features and design strategies from the active sites and carbon skeletons to the overall catalysts are deeply discussed.Then, the structural design of different nano-carbon SACs is introduced systematically. The characterization of active site and carbon skeleton and the detailed mechanism of reaction process are summarized and analyzed. Next, the applications in the field of electrocatalysis for oxygen conversion and hydrogen conversion are illustrated. The relationships between the superior performance and the structure of active sites or carbon skeletons are discussed. Finally, the conclusion of this review and prospects on the abundant space for further promotion in broader fields are depicted. This review highlights the design and preparation thoughts from the parts to the whole. The detailed and systematic discussion will provide useful guidance for design of SACs for readers.

Ionic porous polyamide derived N-doped carbon towards highly selective electroreduction of CO_(2)

Electrochemical CO_(2) reduction reaction(CO_(2) RR) has attracted growing attention in energy storage and sustainable production of fuels and chemicals. N-doped carbon materials are preferred metal-free electrocatalysts, but it remains one challenge to finely engineer the active sites and porosity. Herein, we demonstrated that ionic porous polyamides were a kind of versatile precursors to prepare functional carbon materials in a one-step pyrolysis process. The polyamide precursors allowed the maintenance of abundant N species at high temperatures. The existence of ionic moieties and large specific surface area of the precursors promoted the formation of larger porosity carbon with a large specific surface area and sufficient active graphitic-N species by controlling the pyrolysis temperature. The catalyst was highly selective in the CO_(2) RR to produce CO with a maximum Faraday efficiency above 99%, attributable to the improved mass transfer in a large porosity system. This work shows that ionic polyamides are promising carbon precursors for the fabrication of metal-free electrocatalysts for CO_(2) RR.

Preparation of Co/S co-doped carbon catalysts for excellent methylene blue degradation

S and Co co-doped carbon catalysts were prepared via pyrolysis of MOF-71 and thiourea mixtures at 800℃at a mass ratio of MOF-71 to thiourea of 1:0.1 to effectively activate peroxymonosulfate(PMS)for methylene blue(MB)degradation.The effects of two different mixing routes were identified on the MB degradation performance.Particularly,the catalyst obtained by the alcohol solvent evaporation(MOF-AEP)mixing route could degrade 95.60%MB(50 mg/L)within 4 min(degradation rate:K=0.78 min^(-1)),which was faster than that derived from the direct grinding method(MOF-DGP,80.97%,K=0.39 min^(-1)).X-ray photoelectron spectroscopy revealed that the Co-S content of MOF-AEP(43.39at%)was less than that of MOF-DGP(54.73at%),and the proportion of C-S-C in MOF-AEP(13.56at%)was higher than that of MOF-DGP(10.67at%).Density functional theory calculations revealed that the adsorption energy of Co for PMS was -2.94 eV when sulfur was doped as C-S-C on the carbon skeleton,which was higher than that when sulfur was doped next to cobalt in the form of Co-S bond(-2.86 eV).Thus,the C-S-C sites might provide more contributions to activate PMS compared with Co-S.Furthermore,the degradation parameters,including pH and MOF-AEP dosage,were investigated.Finally,radical quenching experiments and electron paramagnetic resonance(EPR)measurements revealed that ^(1)O_(2)might be the primary catalytic species,whereas·O~(2-)might be the secondary one in degrading MB.

Unraveling the Role of Nitrogen-Doped Carbon Nanowires Incorporated with MnO_(2)Nanosheets as High Performance Cathode for Zinc-Ion Batteries

Manganese-based cathode materials are considered as a promising candidate for rechargeable aqueous zinc-ion batteries(ZIBs).Suffering from poor conductive and limited structure tolerance,various carbon matrix,especially N-doped carbon,were employed to incorporate with MnO_(2)for greatly promoted electrochemical performances.However,the related underlying mechanism is still unknown,which is unfavorable to guide the design of high performance electrode.Herein,by incorporating layered MnO_(2)with N-doped carbon nanowires,a free-standing cathode with hierarchical core-shell structure(denoted as MnO_(2)@NC)is prepared.Benefiting from the N-doped carbon and rational architecture,the MnO_(2)@NC electrode shows an enhanced specific capacity(325 mAh g^(−1)at 0.1 A g^(−1))and rate performance(90 mAh g^(−1)at 2 A g^(−1)),as well as improved cycling stability.Furthermore,the performance improvement mechanism of MnO_(2)incorporated by N-doped carbon is investigated by X-ray photoelectron spectroscopy(XPS),Raman spectrums and density functional theory(DFT)calculation.The N atom elongates the Mn-O bond and reduces the valence of Mn^(4+)ion in MnO_(2)crystal by delocalizing its electron clouds.Thus,the electrostatic repulsion will be weakened when Zn^(2+)/H^(+)insert into the host MnO_(2)lattices,which is profitable to more cation insertion and faster ion transfer kinetics for higher capacity and rate capability.This work elucidates a fundamental understanding of the functions of N-doped carbon in composite materials and shed light on a practical pathway to optimize other electrode materials.