Energy band and charge-carrier engineering in skutterudite thermoelectric materials

The binary CoSb_(3) skutterudite thermoelectric material has high thermal conductivity due to the covalent bond between Co and Sb, and the thermoelectric figure of merit, ZT, is very low. The thermal conductivity of CoSb_(3) materials can be significantly reduced through phonon engineering, such as low-dimensional structure, the introduction of nano second phases,nanointerfaces or nanopores, which greatly improves their ZT values. The phonon engineering can optimize significantly the thermal transport properties of CoSb_(3)-based materials. However, the improvement of the electronic transport properties is not obvious, or even worse. Energy band and charge-carrier engineering can significantly improve the electronic transport properties of CoSb_(3)-based materials while optimizing the thermal transport properties. Therefore, the decoupling of thermal and electronic transport properties of CoSb_(3)-based materials can be realized by energy band and charge-carrier engineering. This review summarizes some methods of optimizing synergistically the electronic and thermal transport properties of CoSb_(3) materials through the energy band and charge-carrier engineering strategies. Energy band engineering strategies include band convergence or resonant energy levels caused by doping/filling. The charge-carrier engineering strategy includes the optimization of carrier concentration and mobility caused by doping/filling, forming modulation doped structures or introducing nano second phase. These strategies are effective means to improve performance of thermoelectric materials and provide new research ideas of development of high-efficiency thermoelectric materials.

Digital twin driven and intelligence enabled content delivery in end-edge-cloud collaborative 5G networks

The rapid development of 5G/6G and AI enables an environment of Internet of Everything(IoE)which can support millions of connected mobile devices and applications to operate smoothly at high speed and low delay.However,these massive devices will lead to explosive traffic growth,which in turn cause great burden for the data transmission and content delivery.This challenge can be eased by sinking some critical content from cloud to edge.In this case,how to determine the critical content,where to sink and how to access the content correctly and efficiently become new challenges.This work focuses on establishing a highly efficient content delivery framework in the IoE environment.In particular,the IoE environment is re-constructed as an end-edge-cloud collaborative system,in which the concept of digital twin is applied to promote the collaboration.Based on the digital asset obtained by digital twin from end users,a content popularity prediction scheme is firstly proposed to decide the critical content by using the Temporal Pattern Attention(TPA)enabled Long Short-Term Memory(LSTM)model.Then,the prediction results are input for the proposed caching scheme to decide where to sink the critical content by using the Reinforce Learning(RL)technology.Finally,a collaborative routing scheme is proposed to determine the way to access the content with the objective of minimizing overhead.The experimental results indicate that the proposed schemes outperform the state-of-the-art benchmarks in terms of the caching hit rate,the average throughput,the successful content delivery rate and the average routing overhead.

3D N,O-Codoped Egg-Box-Like Carbons with Tuned Channels for High Areal Capacitance Supercapacitors

Functional carbonaceous materials for supercapacitors(SCs)without using acid for post-treatment remain a substantial challenge.In this paper,we present a less harmful strategy for preparing three-dimensional(3D)N,O-codoped egg-box-like carbons(EBCs).The as-prepared EBCs with opened pores provide plentiful channels for ion fast transport,ensure the e ective contact of EBCs electrodes and electrolytes,and enhance the electron conduction.The nitrogen and oxygen atoms doped in EBCs improve the surface wettability of EBC electrodes and provide the pseudocapacitance.Consequently,the EBCs display a prominent areal capacitance of 39.8μF cm-2(340 F g-1)at 0.106 m A cm-2 in 6 M KOH electrolyte.The EBC-based symmetric SC manifests a high areal capacitance to 27.6μF cm-2(236 F g-1)at 0.1075 m A cm-2,a good rate capability of 18.8μF cm-2(160 F g-1)at 215 m A cm-2 and a long-term cycle stability with only 1.9%decay after 50,000 cycles in aqueous electrolyte.Impressively,even in all-solid-state SC,EBC electrode shows a high areal capacitance of 25.0μF cm-2(214 F g-1)and energy density of 0.0233 m Wh cm-2.This work provides an acid-free process to prepare electrode materials from industrial by-products for advanced energy storage devices.

Nitrogen-doped graphene:Synthesis,characterizations and energy applications

Nitrogen-doped（N-doped） graphene has attracted increasing attentions because of the significantly enhanced properties in physic, chemistry, biology and material science, as compared with those of pristine graphene. By date, N-doped graphene has opened up an exciting new field in the science and technology of two-dimensional materials. From the viewpoints of chemistry and materials, this article presents an overview on the recent progress of N-doped graphene, including the typical synthesis methods, characterization techniques, and various applications in energy fields. The challenges and perspective of Ndoped graphene are also discussed. We expect that this review will provide new insights into the further development and practical applications of N-doped graphene.

Guest editorial: AI and edge computing driven technologies and applications

1.Introduction Emerging networking paradigms,including Information-Centric Networking(ICN)[1],Software-Defined Networking(SDN)[2],Mobile Satellite Communication Networks(MSCN)[3],and Internet of Vehicles(IoV)[4],have faced some severe challenges.For example,the dynamic network environment makes it very hard to optimize resource allocation.In addition,these networking paradigms usually have heterogeneous features,making it difficult to schedule traffic among different kinds of networks.These challenges can be addressed by the adaptive learning of Artificial Intelligence(AI)[5,6]and the edge caching of edge computing.AI can also help establish a relatively optimal routing strategy and perform congestion control by learning the dynamic network state.Just like AI,edge computing[7–10]can help provide fast response to users,and deploy edge servers with strong computing and storage capabilities can greatly improve the performance of 4K/8K and VR/AR.However,despite their ability to improve network performance,there are still many challenges.For example,the integrated architectures and frameworks need to be clearly identified,and the related protocols need to be better defined.

Conversion mechanism of NiCo_(2)Se_(4)nanotube sphere anodes for potassium-ion batteries

Given the abundance of potassium resources,potassium-ion batteries are considered a low-cost alternative to lithium-ion types.However,their electrochemical performance remains rather unsatisfactory because potassium ions have sluggish kinetics and large ionic radius.In this study,NiCo_(2)Se_(4)nanotube spheres are synthesized as efficient potassium storage hosts via a facile two-step hydrothermal process.The rationally designed electrode has various ameliorating morphological and functional features,including the following:(i)A hollow structure allows for relief of the volume expansion while offering an excellent electrochemical reac-tivity to accelerate the conversion kinetics;(ii)a high electrical conductivity for enhanced electron transfer;and(iii)myriad vacancies to supply active sites for electrochemical reactions.As such,the electrode delivers an initial reversible capacity of 458.1 mAh g^(−1)and retains 346.6 mAh g^(−1)after 300 cycles at 0.03 A g^(−1).The electrode sustains a high capacity of 101.4 mAh g^(−1)even at a high current density of 5 A g^(−1)and outperforms the majority of state-of-the-art anodes in terms of both cyclic capacity and rate capability,especially at above 1.0 A g^(−1).This study not only proves bimetallic selenides are promising candidates for potassium storage devices but also offers new insight into the rational design of electrode materials for high-rate potassium-ion batteries.

Recent advances in anode materials for potassium-ion batteries:A review

Potassium-ion batteries(PIBs)are appealing alternatives to conventional lithium-ion batteries(LIBs)because of their wide potential window,fast ionic conductivity in the electrolyte,and reduced cost.However,PIBs suffer from sluggish K+reaction kinetics in electrode materials,large volume expansion of electroactive materials,and the unstable solid electrolyte interphase.Various strategies,especially in terms of electrode design,have been proposed to address these issues.In this review,the recent progress on advanced anode materials of PIBs is systematically discussed,ranging from the design principles,and nanoscale fabrication and engineering to the structure-performance relationship.Finally,the remaining limitations,potential solutions,and possible research directions for the development of PIBs towards practical applications are presented.This review will provide new insights into the lab development and real-world applications of PIBs.

High-performance Li-ion capacitor based on black-TiO2-x/graphene aerogel anode and biomass-derived microporous carbon cathode

Lithium-ion capacitor (LIC) has been regarded as a promising energy storage system with high powder density and high energy density.However,the kinetic mismatch between the anode and the cathode is a major issue to be solved.Here we report a high-performance asymmetric LIC based on oxygen-deficient black-TiO2-x/graphene (B-TiO2-x/G) aerogel anode and biomass derived microporous carbon cathode.Through a facile one-pot hydrothermal process,graphene nanosheets and oxygen-vacancy-rich porous B-TiO2-x/G nanosheets were self-assembled into three-dimensional (3D) interconnected B-TiO2-x/G aerogel.Owing to the rich active sites,high conductivity and fast kinetics,the B-TiO2-x/G aerogel exhibits remarkable reversible capacity,high rate capability and long cycle life when used as anode material for lithium ion storage.Moreover,density functional theory (DFT) calculation reveals that the incorporation of graphene nanosheets can reduce the energy barrier of Li^+ diffusion in B-TiO2-x.The asymmetric LIC based on B-TiO2-x/G aerogel anode and naturally-abundant pine-needles derived microporous carbon (MPC) cathode work well within a large voltage window (1.0-4.0 V),and can deliver high energy density (166.4 Wh·kg^-1 at 200 mA·g^-1),and high power density (7.9 kW·kg^-1 at 17.1 Wh·kg^-1).Moreover,the LIC shows a high capacitance retention of 87% after 3,000cycles at 2,000 mA·g^-1.The outstanding electrochemical performances indicate that the rationally-designed LICs have promising prospect to serve as advanced fast-charging energy storage devices.

Designing metal sulfide-based cathodes and separators for suppressing polysulfide shuttling in lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries,known for their high energy density,are attracting extensive research interest as a promising next-generation energy storage technology.However,their widespread use has been hampered by certain issues,including the dissolution and migration of polysulfides,along with sluggish redox kinetics.Metal sulfides present a promising solution to these obstacles regarding their high electrical conductivity,strong chemical adsorption with polysulfides,and remarkable electrocatalytic capabilities for polysulfide conversion.In this review,the recent progress on the utilization of metal sulfide for suppressing polysulfide shuttling in Li-S batteries is systematically summarized,with a special focus on sulfur hosts and functional separators.The critical roles of metal sulfides in realizing high-performing Li-S batteries have been comprehensively discussed by correlating the materials’structure and electrochemical performances.Moreover,the remaining issues/challenges and future perspectives are highlighted.By offering a detailed understanding of the crucial roles of metal sulfides,this review dedicates to contributing valuable knowledge for the pursuit of high-efficiency Li-S batteries based on metal sulfides.

Controlled growth and photoconductive properties of hexagonal SnS2 nanoflakes with mesa-shaped atomic steps

We demonstrated the controlled growth of two-dimensional （2D） hexagonal tin disulfide （SnS2） nanoflakes with stacked monolayer atomic steps. The morphology was similar to flat-topped and step-sided mesa plateaus or step pyramids. The SnS2 nanoflakes were grown on mica substrates via an atmospheric-pressure chemical vapor deposition process using tin monosulfide and sulfur powder as precursors. Atomic force microscopy （AFM）, electron microscopy, and Raman characterizations were performed to investigate the structural features, and a sequential layer-wise epitaxial growth mechanism was revealed. In addition, systematic Raman characterizations were performed on individual SnS2 nanoflakes with a wide range of thicknesses （1-100 nm）, indicating that the A1g peak intensity and Raman shifts were closely related to the thickness of the SnS2 nanoflakes. Moreover, photoconductive AFM was performed on the monolayer-stepped SnS2 nanoflakes, revealing that the flat surface and the edges of the SnS2 atomic steps had different electrical conductive properties and photoconductive behaviors. This is ascribed to the dangling bonds and defects at the atomic step edges, which caused a height difference of the Schottky barriers formed at the interfaces between the PtIr-coated AFM tip and the step edges or the flat surface of the SnS2 nanoflakes. The 2D SnS2 crystals with regular monolayer atomic steps and fast photoresponsivity are promising for novel applications in photodetectors and integrated optoelectronic circuits.

Review Article Electrocatalysts in lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries with the merits of high theoretical capacity and high energy density have gained significant attention as the next-generation energy storage devices.Unfortunately,the main pressing issues of sluggish reaction kinetics and severe shuttling of polysulfides hampered their practical application.To overcome these obstacles,various strategies adopting high-efficient electrocatalysts have been explored to enable the rapid polysulfide conversions and thereby suppressing the polysulfide shuttling.This review first summarizes the recent progress on electrocatalysts involved in hosts,interlayers,and protective layers.Then,these electrocatalysts in Li-S batteries are analyzed by listing representative works,from the viewpoints of design concepts,engineering strategies,working principles,and electrochemical performance.Finally,the remaining issues/challenges and future perspectives facing electrocatalysts are given and discussed.This review may provide new guidance for the future construction of electrocatalysts and their further utilizations in high-performance Li-S batteries.

Promoting polysulfide conversions via cobalt single-atom catalyst for fast and durable lithium-sulfur batteries

Although promising strategies have been developed to resolve the critical drawbacks of lithium-sulfur(Li-S)batteries,the intractable issues including undesirable shuttling of polysulfides and sluggish redox reaction kinetics have still been unresolved thoroughly.Herein,a cobalt single-atom(CoSA)catalyst comprising of atomic Co distributed homogeneously within nitrogen(N)-doped porous carbon(Co-NPC)nanosphere is constructed and utilized as a separator coating in Li-S batteries.The Co-NPC exposes abundant active sites participating in sulfur redox reactions,and remarkable catalytic activity boosting the rapid polysulfide conversions.As a result,Li-S batteries with Co-NPC coating layer realize significantly enhanced specific capacity(1295 mAh·g^(-1)at 0.2 C),rate capability(753 mAh·g^(-1)at 3.0 C),and long-life cyclic stability(601 mAh·g^(-1)after 500 cycles at 1.0 C).Increasing the areal sulfur loading to 6.2 mg·cm^(-2),an extremely high areal capacity of 7.92 mAh·cm^(-2)is achieved.Further in situ X-ray diffraction,density functional theory calculations,and secondary ion mass spectrometry confirm the high catalytic capability of CoSA towards reversible polysulfide conversion.This study supplies new insights for adopting single-atom catalyst to upgrade the electrochemical performance of Li-S batteries.

Zinc-based fiber-shaped rechargeable batteries:Insights into structures,electrodes,and electrolytes

The rapid evolution of flexible wearable electronics has spurred a growing demand for energy storage devices,characterized by low-cost manufacturing processes,high safety standards,exceptional electrochemical performance and robust mechanical properties.Among novel flexible devices,fiber-shaped batteries(FSBs)have emerged as prominent solutions exceptionally suited to future applications,owing to their unique one-dimensional(1D)architecture,remarkable flexibility,potential for miniaturization,adaptability to deformation and compatibility with the conventional textile industry.In the forefront research on fiber-shaped batteries,zincbased FSBs(ZFSBs)have garnered significant attentions,featured by the promising electrochemical properties of metallic Zn.This enthusiasm is driven by the impressive capacity of Zn(820 mAh·g^(-1))and its low redox potential(Zn/Zn^(2+):-0.76 V vs.standard hydrogen electrode).This review aims to consolidate recent achievements in the structural design,fabrication processes and electrode materials of flexible ZFSBs.Notably,we highlight three representative structural configurations:parallel type,twisted type and coaxial type.We also place special emphasis on electrode modifications and electrolyte selection.Furthermore,we delve into the promising development opportunities and anticipate future challenges associated with ZFSBs,emphasizing their potential roles in powering the next generation of wearable electronics.