Superior Anodic Lithium Storage in Core–Shell Heterostructures Composed of Carbon Nanotubes and Schiff-Base Covalent Organic Frameworks

Covalent organic frameworks(COFs)after undergoing the superlithiation process promise high-capacity anodes while suffering from sluggish reaction kinetics and low electrochemical utilization of redox-active sites.Herein,integrating carbon nanotubes(CNTs)with imine-linked covalent organic frameworks(COFs)was rationally executed by in-situ Schiff-base condensation between 1,1′-biphenyl]-3,3′,5,5′-tetracarbaldehyde and 1,4-diaminobenzene in the presence of CNTs to produce core–shell heterostructured composites(CNT@COF).Accordingly,the redox-active shell of COF nanoparticles around one-dimensional conductive CNTs synergistically creates robust three-dimensional hybrid architectures with high specific surface area,thus promoting electron transport and affording abundant active functional groups accessible for electrochemical utilization throughout the whole electrode.Remarkably,upon the full activation with a superlithiation process,the as-fabricated CNT@COF anode achieves a specific capacity of 2324 mAh g^(−1),which is the highest specific capacity among organic electrode materials reported so far.Meanwhile,the superior rate capability and excellent cycling stability are also obtained.The redox reaction mechanisms for the COF moiety were further revealed by Fourier-transform infrared spectroscopy in conjunction with X-ray photoelectron spectroscopy,involving the reversible redox reactions between lithium ions and C=N groups and gradual electrochemical activation of the unsaturated C=C bonds within COFs.

Electrospun carbon nanofiber-supported V_(2)O_(3) with enriched oxygen vacancies as a free-standing high-rate anode for an all-vanadium-based full battery

Synergistic regulation of hierarchical nanostructures and defect engineering is effective in accelerating electron and ion transport for metal oxide electrodes.Herein,carbon nanofiber-supported V_(2)O_(3) with enriched oxygen vacancies(OV-V_(2)O_(3)@CNF)was fabricated using the facile electrospinning method,followed by thermal reduction.Differing from the traditional particles embedded within carbon nanofibers or irregularly distributed between carbon nanofibers,the free-standing OV-V_(2)O_(3)@CNF allows for V_(2)O_(3) nanosheets to grow vertically on one-dimensional(1D)carbon nanofibers,enabling abundant active sites,shortened ion diffusion pathway,continuous electron transport,and robust structural stability.Meanwhile,density functional theory calculations confirmed that the oxygen vacancies can promote intrinsic electron conductivity and reduce ion diffusion energy barrier.Consequently,the OV-V_(2)O_(3)@CNF anode delivers a large reversible capacity of 812 mAh g^(-1) at 0.1 A g^(-1),superior rate capability(405 mAh g^(-1) at 5 A g^(-1)),and long cycle life(378 mAh g^(-1) at 5 A g^(-1) after 1000 cycles).Moreover,an all-vanadium full battery(V2O5//OV-V_(2)O_(3)@CNF)was assembled using an OV-V_(2)O_(3)@CNF anode and a V2O5 cathode,which outputs a working voltage of 2.5 V with high energy density and power density,suggesting promising practical application.This work offers fresh perspectives on constructing hierarchical 1D nanofiber electrodes by combining defect engineering and electrospinning technology.

Photothermal‐boosted polaron transport in Fe_(2)O_(3)photoanodes for efficient photoelectrochemical water splitting

Introduction of the photothermal effect into transition-metal oxide photoanodes has been proven to be an effective method to improve the photoelectrochemical(PEC)water-splitting performance.However,the precise role of the photothermal effect on the PEC performance of photoanodes is still not well understood.Herein,spinel-structured ZnFe_(2)O_(4)nanoparticles are deposited on the surface of hematite(Fe_(2)O_(3)),and the ZnFe_(2)O_(4)/Fe_(2)O_(3)photoanode achieves a high photocurrent density of 3.17 mA cm^(-2)at 1.23 V versus a reversible hydrogen electrode(VRHE)due to the photothermal effect of ZnFe_(2)O_(4).Considering that the hopping of electron small polarons induced by oxygen vacancies is thermally activated,we clarify that the main reason for the enhanced PEC performance via the photothermal effect is the promoted mobility of electron small polarons that are bound to positively charged oxygen vacancies.Under the synergistic effect of oxygen vacancies and the photothermal effect,the electron conductivity and PEC performance are significantly improved,which provide fundamental insights into the impact of the photothermal effect on the PEC performance of small polaron-type semiconductor photoanodes.

Engineering Fe‑N_(4)Electronic Structure with Adjacent Co‑N_(2)C_(2)and Co Nanoclusters on Carbon Nanotubes for Efficient Oxygen Electrocatalysis

Regulating the local configuration of atomically dispersed transition-metal atom catalysts is the key to oxygen electrocatalysis performance enhancement.Unlike the previously reported singleatom or dual-atom configurations,we designed a new type of binary-atom catalyst,through engineering Fe-N_(4)electronic structure with adjacent Co-N_(2)C_(2)and nitrogen-coordinated Co nanoclusters,as oxygen electrocatalysts.The resultant optimized electronic structure of the Fe-N_(4)active center favors the binding capability of intermediates and enhances oxygen reduction reaction(ORR)activity in both alkaline and acid conditions.In addition,anchoring M-N-C atomic sites on highly graphitized carbon supports guarantees of efficient charge-and mass-transports,and escorts the high bifunctional catalytic activity of the entire catalyst.Further,through the combination of electrochemical studies and in-situ X-ray absorption spectroscopy analyses,the ORR degradation mechanisms under highly oxidative conditions during oxygen evolution reaction processes were revealed.This work developed a new binary-atom catalyst and systematically investigates the effect of highly oxidative environments on ORR electrochemical behavior.It demonstrates the strategy for facilitating oxygen electrocatalytic activity and stability of the atomically dispersed M-N-C catalysts.

Boosting Lithium Storage in Graphene-Sandwiched Cathodes Containing Multi-Carbonyl Polyquinoneimine Nanosheets

Carbonyl polymers as booming electrode materials for lithium-organic batteries are currently limited by low practical capacities and poor rate performance due to their inherent electronic insulation and microscopic agglomeration morphologies.Herein graphene/carbonyl-enriched polyquinoneimine(PQI@Gr)composites were readily prepared by in situ hydrothermal polycondensation of dianhydride and anthraquinone co-monomer salts in the presence of graphene oxide(GO).Conductive graphene sheets derived from hydrothermal reduction of GO are fully sandwiched between densely interlaced quinone-containing polyimide nanosheets.Remarkably,the as-fabricated PQI@Gr cathodes exhibit much larger specific capacity(205 mAh g^(-1)at 0.1 A g^(-1)),higher carbonyl utilization(up to 89.9%),and better rate capability(179.4 mAh g^(-1)at 5.0 A g^(-1))due to a surface-dominated capacitive process via fast kinetics compared to bare PQI electrode(162.5 mAh g^(-1)at 0.1 A g^(-1);67.5%;96.9 mAh g^(-1)at 5 A g^(-1)).The capacity retention as high as 73%for PQI@Gr is also achieved over ultra-long 10000 cycles at 5.0 A g^(-1).Such outstanding electrochemical performances are attributable to the combined merits of polyimides and polyquinones,and robust 3D hierarchical heterostructures with efficient conductive networks,abundant porous channels for electrolyte infiltration and ion accessibility,and highly exposed carbonyl groups.This work offers new insights into the development of high-performance polymer electrodes for sustainable batteries.

Interwoven Poly(Anthraquinonyl Sulfide)Nanosheets-Decorated Carbon Nanotubes as Core-Sheath Heteroarchitectured Cathodes for Polymer-Based Asymmetrical Full Batteries

Organic redox-active polymers provide promising alternatives to metal-containing inorganic compounds in Li-ion batteries(LIBs),whereas suffer from low actual capacities,poor rate/power capabilities,and inferior cycling stability.Herein,poly(anthraquinonyl sulfide)-coated carbon nanotubes(CNT@PAQS)are readily performed by in situ polymerization to form core-sheath nanostructures.Remarkably,flower-like PAQS nanosheets are interwoven around CNTs to synergistically create robust 3D hierarchical networks with abundant cavities,internal channels,and sufficiently-exposed surfaces/edges,thereby promoting electron transport and making more active sites accessible for electrolytes and guest ions.Apparently,the as-fabricated CNT@PAQS cathode delivers the large reversible capacity(200.5 mAh g^(-1)at 0.05 A g^(-1)),high-rate capability(161.5 mAh g^(-1)at 5.0 A g^(-1)),and impressive cycling stability(retaining 88.0%over 1000 cycles).In addition,an asymmetric full-battery using CNT@PAQS as a cathode and cyclized polyacrylonitrile-encapsulated CNTs as an anode is assembled that delivers a high energy density of 86.3 Wh kg^(-1),and retains 81.3%of initial capacity after 1000 cycles.This work opens up an efficient strategy to combine highly conductive and redox-active phases into core-sheath heterostructures to unlock the barrier of high-rate charge storage.The further integration of two polymer-based electrodes into asymmetric full cells would also consolidate the development of low-cost,sustainable,and powerful batteries.

Designing Advanced Aqueous Zinc-Ion Batteries:Principles,Strategies,and Perspectives

Aqueous zinc-ion batteries(AZIBs)are an appealing battery system due to their low cost,intrinsic safety,and environmental-friendliness,while their application is plagued by the obstacles from the cathode,electrolyte,and zinc anode.Summarizing the design principles and strategies toward the optimization of cathode,electrolyte,and zinc anode is crucial for the development of AZIBs.Herein,we present a comprehensive analysis of the design principles and promising strategies toward the improvement of AZIBs.Firstly,the various reaction mechanisms are summarized and the existing issues associated with the cathode,electrolyte,and zinc anode are discussed to guide the rational design of AZIBs.Subsequently,we provide an in-depth and comprehensive discussion on the design principles and strategies for the electrodes/electrolyte/separator optimization,and analyze the advantages and disadvantages of various strategies.Importantly,the design principles and strategies of the newly appeared conversion-type AZIBs,such as Zn-S battery and Zn-Se battery,are also discussed and analyzed.The effect of design strategies on the electrochemical performance and the relationship between the current issues and strategies are also unveiled in detail.Finally,some research trends and perspectives are provided for designing better AZIBs.

Emerging Carbonyl Polymers as Sustainable Electrode Materials for Lithium-Free Metal-Ion Batteries

Lithium-ion batteries using inorganic electrode materials have been long demonstrated as the most promising power supplies for portable electronics,electric vehicles,and smart grids.However,the increasing cost and descending availability of lithium resources in combination with the limited electrochemical performance and eco-sustainability have created serious concerns with the competitiveness of lithium-ion batteries.There is a pressing need for the discovery of new redox chemistries between the alternative host materials and charge carriers.Organic nonlithium batteries using organic electrodes have recently attracted considerable interests as the future substitutes for energy storage systems,because of their combined merits(e.g.,natural abundance,rich chemistry of organics,rapid kinetics,and multielectron redox)of Li-free batteries and organic electrodes.Herein,an overview on the state-of-the-art developments of emerging carbonyl polymers for nonlithium metal-ion batteries is comprehensively presented with a primary focus on polyquinones and polyimides from the perspective of chain engineering.Six distinct categories,including monovalent(Na^(+),K^(+)) and multivalent(Mg^(2+),Zn^(2+),Ca^(2+),Al^(3+)) metal-ions batteries are individually outlined.Advantages of polymer electrode materials and characteristics of charge storage mechanisms are highlighted.Some key performance parameters such as specific capacity,rate capability,and cycle stability are carefully discussed.Moreover,aqueous nonlithium batteries based on carbonyl polymers are specially scrutinized due to the less reactivity of Li-free metals when exposed in aqueous electrolytes and ambient atmosphere.Current challenges and future prospects of developing polymer-based batteries are proposed finally.This review provides a fundamental guidance for the future advancement of next-generation sustainable batteries beyond lithium-ion batteries.

Electrochemically Active Phosphotungstic Acid Assisted Prevention of Graphene Restacking for High-Capacitance Supercapacitors

Direct reduction of graphene oxide usually leads to the agglomeration of the as-generated graphene sheets,thus suppressing the surface exposed for energy storage.Herein,graphene oxide was reduced by a one-pot hydrothermal process in the presence of an electrochemically active phosphotungstic acid to produce three-dimensional porous phosphotungstic acid/reduced graphene oxide composites.Phosphotungstic acid molecules were found to be uniformly anchored on the surface of reduced graphene oxide sheets through the electrostatic interaction to prevent the reduced graphene oxide sheets from restacking.

A Hierarchical Helical Carbon Nanotube Fiber Artificial Ligament

For the optimal functional recovery of force-transmitting connective tissues,obtaining grafts that are mechanically robust and integrating them with host bone effectively to tolerate high loads during violent joint motions is both crucial and challenging.Recent research proposes that a hierarchical helical carbon nanotube fiber,which has the considerably high mechanical strength,and can integrate with the host bone and restore movement in animals,is a very promising artificial ligament.The above research marks a significant development in artificial ligament via the innovative utilization of hierarchical helical carbon nanotube fiber.

Control on self-assembly structures of rod-coil-rod (PANI)_(98) -(PEG)_(136) -(PANI)_(98) triblock copolymer

The self-assembly behaviors of the rod-coil-rod(PANI)_(98)-(PEG)_(136)-(PANI)_(98) triblock copolymer are investigated in different solvents,such as N-methyl-2-pyrrolidone(NMP),dimethyl formamide(DMF),ethanol and water.The effects of solvents,concentration and ultrasonic irradiation on self-assembly are discussed.The results indicate that the triblock copolymer forms particles,rods,fiber,networks and fiber bands in the above solvents,respectively.Especially,the triblock copolymer can form a multi-layer,tri-dimensional fibrous network and a petaline structure from the mono-layer fibrous network with the increase of its concentration in ethanol.Also,the ultrasonic irradiation has a great effect on the self-assembly of the triblock copolymer.