Atomically dispersed Mn-N_(x) catalysts derived from Mn-hexamine coordination frameworks for oxygen reduction reaction

Metal-organic frameworks recently have been burgeoning and used as precursors to obtain various metal-nitrogen-carbon catalysts for oxygen reduction reaction(ORR).Although rarely studied,Mn-N-C is a promising catalyst for ORR due to its weak Fenton reaction activity and strong graphitization catalysis.Here,we developed a facile strategy for anchoring the atomically dispersed nitrogen-coordinated single Mn sites on carbon nanosheets(MnNCS)from an Mn-hexamine coordination framework.The atomically dispersed Mn-N_(4) sites were dispersed on ultrathin carbon nanosheets with a hierarchically porous structure.The optimized MnNCS displayed an excellent ORR performance in half-cells(0.89 V vs.reversible hydrogen electrode(RHE)in base and 0.76 V vs.RHE in acid in half-wave potential)and Zn-air batteries(233 mW cm^(−2)in peak power density),along with significantly enhanced stability.Density functional theory calculations further corroborated that the Mn-N_(4)-C(12)site has favorable adsorption of*OH as the rate-determining step.These findings demonstrate that the metal-hexamine coordination framework can be used as a model system for the rational design of highly active atomic metal catalysts for energy applications.

Cellulose nanofiber-derived carbon aerogel for advanced room-temperature sodium–sulfur batteries

Room-temperature sodium–sulfur(RT/Na–S)batteries are regarded as promising large-scale stationary energy storage systems owing to their high energy density and low cost as well as the earth-abundant reserves of sodium and sulfur.However,the diffusion of polysulfides and sluggish kinetics of conversion reactions are still major challenges for their application.Herein,we developed a powerful and functional separator to inhibit the shuttle effect by coating a lightweight three-dimensional cellulose nanofiber-derived carbon aerogel on a glass fiber separator(denoted NSCA@GF).The hierarchical porous structures,favorable electronic conductivity,and three-dimensional interconnected network of N,S-codoped carbon aerogel endow a multifunctional separator with strong polysulfide anchoring capability and fast reaction kinetics of polysulfide conversion,which can act as the barrier layer and an expanded current collector to increase sulfur utilization.Moreover,the hetero-doped N/S sites are believed to strengthen polysulfide anchoring capability via chemisorption and accelerate the redox kinetics of polysulfide conversion,which is confirmed from experimental and theoretical results.As a result,the assembled Na–S coin cells with the NSCA@GF separator showed a high reversible capacity(788.8 mAh g^(−1) at 0.1 C after 100 cycles)and superior cycling stability(only 0.059%capacity decay per cycle over 1000 cycles at 1 C),thereby demonstrating the significant potential for application in high-performance RT/Na–S batteries.

二次电池研究进展

能源的存储和利用是当今科学和技术发展中的重大课题之一,尤其是作为高效的电能/化学能转化装置的二次电池相关技术一直是科学家研究的热点领域。在此背景下,本文较为系统地介绍目前二次电池的重要研究进展,将从二次电池的发展历史引入,再到其相关的基础理论知识的介绍。随后较为详细地讨论当前不同体系的二次电池及相关应的关键材料的研究进展,涉及到锂离子电池、钠离子电池、钾离子电池、镁离子电池、锌离子电池、钙离子电池、铝离子电池、氟离子电池、氯离子电池、双离子电池、锂-硫(硒)电池、钠-硫(硒)电池、钾-硫(硒)电池、多价金属-硫基电池、锂-氧电池、钠-氧电池、钾-氧电池、多价金属-氧气电池、锂-溴(碘)电池、水系金属离子电池、光辅助电池、柔性电池、有机电池、金属-二氧化碳电池等。此外,也介绍了电池研究中常见的电极反应过程表征技术,包括冷冻电镜、透射电镜、同步辐射、原位谱学表征、磁性表征等。本文将有助于研究人员对二次电池进行全面系统的了解与把握,并为之后二次电池的研究提供很好的指导作用。

Porous carbon coupled with an interlaced MoP–MoS2 heterojunction hybrid for efficient hydrogen evolution reaction

The design and development of electrocatalysts composed of non-noble-metal catalysts with both large surface area and high electrical conductivities are crucial for the hydrogen evolution reaction(HER).Here,a xylose-based porous carbon is coupled with a MoS2-Mo P heterojunction(MoS2-Mo P/FPC)hybrid and used as a promising catalyst for HER.The hybrid is prepared by immobilizing petal-like MoS2 nanosheets on porous carbon(MoS2/FPC),followed by controlling the phosphidation in Ar/H2 to form MoS2-Mo P/FPC.Red phosphorus provides the P species that can induce the construction of the heterojunction under the reducing atmosphere,along with the generation of a Mo P phase and the splitting of the MoS2 phase.The as-prepared MoS2-Mo P/FPC catalyst offers a low overpotential of 144 mV at a current density of 10 m A cm^-2 and a small Tafel slope of 41 m V dec^-1 for the HER in acidic media,as well as remarkable stability.Apart from the active nature of the hybrid,its outstanding activity is attributed to the MoS2-Mo P heterojunction,and the good charge/mass-transfer ability of porous carbon.This strategy provides a new method to develop and design low-cost and high-performance catalysts for the HER.

Biomass-based N doped carbon as metal-free catalyst for selective oxidation of D-xylose into D-xylonic acid

Rational design and facile preparation of low-cost and efficient catalysts for the selective converting of biomass-derived monosaccharides into high value-added chemicals is highly demanded,yet challenging.Herein,we first demonstrate a N doped defect-rich carbon(NC-800-5)as metal-free catalyst for the selective oxidation of D-xylose into D-xylonic acid in alkaline aqueous solution at 100℃ for 30 min,with 57.4%yield.The doped graphitic N is found to be the active site and hydroxyl ion participating in the oxidation of D-xylose.Hydroxyl ion and D-xylose first adsorb on NC-800-5 surface,and the aldehyde group of D-xylose is catalyzed to form germinal diols ion.Then,C–H bond break to yield carboxylic group.Furthermore,NC-800-5 catalyst shows high stability in recycled test.

Defect reduction to enhance the mechanical strength of nanocellulose carbon aerogel

Carbon aerogels prepared from renewable nano building blocks are rising-star materials and hold great promise in many fields.However,various defects formed during carbonization at high temperature disfavor the stress transfer and thus the fabrication of flexible carbon aerogel from renewable nano building blocks.Herein,a structural defect-reducing strategy is proposed by altering the pyrolysis route of cellulose nanofiber.Inorganic salt that inhibits the generation of tar volatilization during pyrolysis can prevent the formation of various structural defects.Microstructure with fewer defects can reduce stress concentration and remarkably enhance the compressibility of carbon aerogel,thus increasing the maximum stress retention of carbon aerogel.The carbon aerogel also has high stress sensor sensitivity and excellent temperature coefficient of resistance.The structural defect-reducing strategy will pave a new way to fabricate high-strength carbon materials for various fields.

Base-free selective oxidation of monosaccharide into sugar acid by surface-functionalized carbon nanotube composites

Selective oxidation of biomass-derived monosaccharide into high value-added chemicals is highly desirable from sustainability perspectives.Herein,we demonstrate a surface-functionalized carbon nanotubesupported gold(Au/CNT-O and Au/CNT-N)catalyst for base-free oxidation of monosaccharide into sugar acid.Au/CNT-O and Au/CNT-N surfaces successfully introduced oxygen-and nitrogen-containing functional groups,respectively.The highest yields of gluconic acid and xylonic acid were 93.3%and 94.3%,respectively,using Au/CNT-N at 90℃ for 240 min,which is higher than that of using Au/CNT-O.The rate constants for monosaccharide decomposition and sugar acid formation in Au/CNT-N system were higher,while the corresponding activation energy was lower than in Au/CNT-O system.DFT calculation revealed that the mechanism of glucose oxidation to gluconic acid involves the adsorption and activation of O_(2),adsorption of glucose,dissociation of the formyl C-H bond and formation of O-H bond,and formation and desorption of gluconic acid.The activation energy barrier for the glucose oxidation over Au/CNT-N is lower than that of Au/CNT-O.The nitrogen-containing functional groups are more beneficial for accelerating monosaccharide oxidation and enhancing sugar acid selectivity than oxygen-containing functional groups.This work presents a useful guidance for designing and developing highly active catalysts for producing high-value-added chemicals from biomass.

Self-assembly fabrication of lignin-derived carbon with dual heteroatoms doping for high-performance supercapacitor

Renewable and low-cost biomass is an ideal sustainable alternative to petroleum-based resources,but producing biomass-based carbon electrode with high performances remains a challenge.Herein,we propose a facile self-assembly strategy to fabricate a biomass-derived N,S co-doping carbon electrode from lignosulfonate without any activation or template process.Taking advantage of the coordination between Fe ions and lignosulfonate,the resultant carbon exhibits a spherical structure with abundant graphitized nanosheets,leading to a high specific surface area with rational pore structure,which are beneficial to the electron/ion transport and storage.The high contents of doping N(8.47 wt%)and S(2.56 wt%)significantly boost the electrochemical performances.As a supercapacitor electrode,the carbon material displays high specific capacitance of 390 F g^(-1),excellent cycling stability and high energy density of 14.7 W h kg^(-1)at a power density of 450 W kg^(-1).This study provides a potential strategy for synthesizing cost-effective heteroatom-doped carbon materials from biomass with abundant functional groups and heteroatom sources,such as chitosan,collagen,and gelatin.

Recent progress and future perspectives of flexible metal‐air batteries

With the rapid development of wearable and intelligent flexible electronic devices(FEDs),the demand for flexible energy storage/conversion devices(ESCDs)has also increased.Rechargeable flexible metal‐air batteries(MABs)are expected to be one of the most ideal ESCDs due to their high theoretical energy density,cost advantage,and strong deformation adaptability.With the improvement of the device design,material assemblies,and manufacturing technology,the research on the electrochemical performance of flexible MABs has made significant progress.However,achieving the high mechanical flexibility,high safety,and wearable comfortability required by FEDs while maintaining the high performance of flexible MABs are still a daunting challenge.In this review,flexible Zn‐air and Li‐air batteries are mainly exemplified to describe the most recent progress and challenges of flexible MABs.We start with an overview of the structure and configuration of the flexible MABs and discuss their impact on battery performance and function.Then it focuses on the research progress of flexible metal anodes,gel polymer electrolytes,and air cathodes.Finally,the main challenges and future research perspectives involving flexible MABs for FEDs are proposed.

Thermoelectric generator based on anisotropic wood aerogel for low-grade heat energy harvesting

Thermoelectric generators(TEGs)have received increasing attention due to their potential to harvest low-grade heat energy(<100℃ )and provide power for the Internet of Things(IoT)and wearable electronic devices.Herein,a wood-based ordered framework is used to fabricate carbon nanotube/poly(3,4-ethylenedioxythiophene)(CNT/PEDOT)wood aerogel for TEG.The prepared CNT/PEDOT wood aerogel with an anisotropic structure exhibits a low thermal conductivity of 0.17 W m^(−1)K^(−1)and is advantageous to develop a sufficient temperature gradient.Meanwhile,CNT/PEDOT composites effectively decouple the relationship between the Seebeck coefficient and electrical conductivity by energy filtering effect to enhance thermoelectric(TE)output properties.The vertical TEG assembled by the CNT/PEDOT wood aerogels reveals an output power of 1.5μW and a mass-specific power of 15.48μW g^(−1)at a temperature difference of 39.4 K.Moreover,the layered structure renders high compressibility and fatigue resistance.The anisotropic structure,high mechanical performance,and rapid thermoelectric response,enabling the TEG based on CNT/PEDOT wood aerogel offer opportunities for continuous power supply to low-power electronic devices.

Reversible aqueous zinc-ion battery based on ferric vanadate cathode

Rechargeable aqueous zinc-ion batteries have attracted extensive interest because of low cost and high safety.However,the relationship between structure change of cathode and the zinc ion storage mechanism is still complex and challenging.Herein,open-structured ferric vanadate(Fe_(2)V_(4)O_(13))has been developed as cathode material for aqueous zinc-ion batteries.Intriguingly,two zinc ion storage mechanism can be observed simultaneously for the Fe2V4O13 electrode,i.e.,classical intercalation/deintercalation storage mechanism in the tunnel structure of Fe_(2)V_(4)O_(13),and reversible phase transformation from ferric vanadate to zinc vanadate,which is verified by combined studies using various in-situ and ex-situ techniques.As a result,the Fe_(2)V_(4)O_(13) cathode delivers a high discharge capacity of 380 mAh/g at 0.2 A/g,and stable cyclic performance up to 1000 cycles at 10 A/g in the operating window of 0.2-1.6 V with 2 mol/L Zn(CF_(3)SO_(3))_(2) aqueous solution.Moreover,the assembled Fe_(2)V_(4)O_(13)//Zn flexible quasi-solid-state battery also exhibits a relatively high mechanical strength and good cycling stability.The findings reveal a new perspective of zinc ion storage mechanism for Fe_(2)V_(4)O_(13),which may also be applicable to other vanadate cathodes,providing a new direction for the investigation and design of zinc-ion batteries.

Metal coordination assists fabrication of multifunctional aerogel

Interfacial design is one of the most promising ways in improving mechanical properties of nanocomposites.In this work,a multifunctional aerogel with excellent mechanical performances,sensing sensitivity,and fire retardancy is fabricated by taking advantage of metal coordination between biopolymer and Fe3+.Montmorillonite(MMT)nanosheets are added to induce a‘brick and mortar’structure.The coordination remarkably reduces structural defects,leading to well-formed lamellas that can effectively distribute stress under sever compression without plastic deformation.The structural merits impart the aerogel highly reversible compressibility even at 99%strain and superior durability.Besides,it demonstrates high sensing performance in wearable health monitoring devices,and shows fire resistance property that can maintain elasticity in a flame.The work offers a facile and effective method to create multifunctional aerogels from various polymers.