Insights into Nano-and Micro-Structured Scaffolds for Advanced Electrochemical Energy Storage

Adopting a nano-and micro-structuring approach to fully unleashing the genuine potential of electrode active material benefits in-depth understandings and research progress toward higher energy density electrochemical energy stor-age devices at all technology readiness levels.Due to various challenging issues,especially limited stability,nano-and micro-structured(NMS)electrodes undergo fast electrochemical performance degradation.The emerging NMS scaffold design is a pivotal aspect of many electrodes as it endows them with both robustness and electrochemical performance enhancement,even though it only occupies comple-mentary and facilitating components for the main mechanism.However,extensive efforts are urgently needed toward optimizing the stereoscopic geometrical design of NMS scaffolds to minimize the volume ratio and maximize their functionality to fulfill the ever-increasing dependency and desire for energy power source supplies.This review will aim at highlighting these NMS scaffold design strategies,summariz-ing their corresponding strengths and challenges,and thereby outlining the potential solutions to resolve these challenges,design principles,and key perspectives for future research in this field.Therefore,this review will be one of the earliest reviews from this viewpoint.

Dual-Functional Electrode Promoting Dendrite-Free and CO_(2) Utilization Enabled High-Reversible Symmetric Na-CO_(2) Batteries

Sodium-carbon dioxide(Na-CO_(2))batteries are regarded as promising energy storage technologies because of their impressive theoretical energy density and CO_(2)reutilization,but their practical applications are restricted by uncontrollable sodium dendrite growth and poor electrochemical kinetics of CO_(2)cathode.Constructing suitable multifunctional electrodes for dendritefree anodes and kinetics-enhanced CO_(2)cathodes is considered one of the most important ways to advance the practical application of Na-CO_(2)batteries.Herein,RuO2 nanoparticles encapsulated in carbon paper(RuCP)are rationally designed and employed as both Na anode host and CO_(2)cathode in Na-CO_(2)batteries.The outstanding sodiophilicity and high catalytic activity of RuCP electrodes can simultaneously contribute to homogenous Na+distribution and dendrite-free sodium structure at the anode,as well as strengthen discharge and charge kinetics at the cathode.The morphological evolution confirmed the uniform deposition of Na on RuCP anode with dense and flat interfaces,delivering enhanced Coulombic efficiency of 99.5%and cycling stability near 1500 cycles.Meanwhile,Na-CO_(2)batteries with RuCP cathode demonstrated excellent cycling stability(>350 cycles).Significantly,implementation of a dendrite-free RuCP@Na anode and catalytic-site-rich RuCP cathode allowed for the construction of a symmetric Na-CO_(2)battery with long-duration cyclability,offering inspiration for extensive practical uses of Na-CO_(2)batteries.

Recent progress and future prospects of high-entropy materials for battery applications

Due to the energy crisis caused by limited fossil fuel reserves,extensive use of the renewable energy sources such as wind or solar energy is deemed to replace the use of traditional fossil fuels in the future^([1−3]).However,most renewable energy sources face the same problem,which is the intermittency of energy.For example,solar energy cannot be utilized at night.That means the continuous energy demand required for large-scale power grids can’t be satisfied by a single solar panel model.

Anode materials for potassium-ion batteries: Current status and prospects

Potassium-ion batteries(KIBs)as one of the most promising alternatives to lithium-ion batteries have been highly valued in recent years.However,progress in KIBs is largely restricted by the sluggish development in anode materials.Therefore,it is imperative to systematically outline and evaluate the recent research advances in the field of anode materials for KIBs toward promoting the development of high-performance anode materials for KIBs.In this review,the recent achievements in anode materials for KIBs are summarized.The electrochemical properties(ie.charge storage mechanism,capacity,rate performance,and cycling stability)of these reported anode materials,as well as their advantages/disadvantages,are discerned and analyzed,enabling high-performance KIBs to meet the requirements for practical applications.Finally,technological developments,scientific challenges,and future research opportunities of anode materials for KIBs are briefly reviewed.

Highly-rough surface carbon nanofibers film as an effective interlayer for lithium–sulfur batteries

Lithium–sulfur(Li–S)battery with a new configuration is demonstrated by inserting a flexible nitrogen-doping carbon nanofiber(N-CNFs)interlayer between the sulfur cathode and the separator.The N-CNFs film with high surface roughness and surface area is fabricated by electrospinning and a subsequent calcination process.The N-CNFs film interlayer not only effectively traps the shuttling migration of polysulfides but also gives the whole battery reliable electronic conductivity,which can effectively enhance the electrochemical performance of Li–S batteries.Finally,Li–S batteries with long cycling stability of 785 mAh/g after 200 cycles and good rate capability of 573 mAh/g at 5 C are achieved.

Recent progress and future prospect of novel multi-ion storage devices

Rechargeable batteries,especially lithium-ion batteries(LIBs),have made rapid development since the 21st century,greatly facilitating people's lives[1−6].Based on considerations of cost and existing problems(such as safety issues due to LIBs stacking strategy and unsatisfactory performance for various applications),researchers have explored alternative technologies to LIBs to meet the needs for wide application scenarios[5].Among them,multi-ion storage devices such as dual-ion batteries(DIBs)and metal-ion hybrid capacitors(MIHCs)are considered promising alternative energy storage devices of LIBs due to their unique multi-ion storage mechanism.In a multi-ion storage device,cations and anions carry charges back and forth between the electrolyte and the electrodes at the same time,unlike the rocking chair mechanism of LIBs[7].Generally,the anodes of DIBs and MIHCs work in a similar mechanism to LIBs,storing charge through redox reactions.The main difference among them is the mechanism of the cathodes during charging and discharging[8].In DIBs,the battery-type cathode stores anions through the Faraday reaction.

Micro-nano structural electrode architecture for high power energy storage

The necessity and superiorities of micro-nano structural electrodes toward high power:Electrochemical energy storage(EES)technologies have achieved great success in portable electronics and electric vehicles owing to their environmental friendliness and cost effectiveness.With the promotional concepts such as the Internet of Things and ultra-high efficiency self-powered systems in recent years,there are substantial demand for superior EES systems,including but not limited to high-performance,miniaturization and multifunction[1−4].In a particular EES cell,active materials are carried by electrodes as the basic building blocks of energy storage or release.Material innovation(includes composition,structure,size and morphology)has revealed remarkable energy density,power density and lifespan for associated devices in the lab setting of low mass loading slurry-coating electrodes[5].

Preface to the Special Issue on Challenges and Possibilities of Energy Storage

The utilization of renewable energy is the ultimate way to meet the increasing energy demands of our modern society.The efficient storage and utilization of the energy in different ways are the current hot topics in the research community.Among them,the solar water splitting,photocatalysis,and lithium–sulfur batteries are with great application promise.The research will provide strategies for the production,storage,and application of energy for industry.

An in-depth understanding of photophysics in organic photocatalysts

The urgent need to replace conventional fossil fuels with clean energy has stimulated a large number of research efforts on photocatalytic hydrogen evolution[1−4].Alternatively,organic semiconductors with tunable light absorption,well-positioned band edges,and excellent charge separation are highly expected[5−8].Conventionally,a semiconductor material with a wide band gap has a larger exciton binding energy,while a semiconductor material with a narrow band gap has a smaller exciton binding energy[9].Since smaller exciton binding energies are favorable for exciton separation,choosing a semiconductor with a suitable bandgap seems to be the first step toward high solar-to-hydrogen efficiency.The tunable light-harvesting ability determines the advantage and potential of organic semiconductors as photocatalysts.However,the insufficient external quantum efficiency(EQE)and the un-derlying photophysical mechanism remain restricting the orientation toward industrialization[10].

Review on Recent Advances of Cathode Materials for Potassium-ion Batteries

Potassium-ion batteries(PIBs) as a promising supplement to lithium-ion batteries have drawn great attention attributing to the abundant potassium resources, the fast-ionic conductivity of potassium ions in electrolyte, and the low standard redox potential of potassium. However, the development of PIBs is still in its infancy, which is largely restricted by the fact that the electrode materials, especially the cathode materials of PIBs, are far from satisfactory in practical applications regarding the capacity, voltage, and cycle life. Therefore, most of current research efforts have been devoted to exploring new and high-performance electrode materials for achieving PIBs with high capacity and voltage as well as excellent cyclability. In this review,the recent advancements on cathode materials for PIBs are specially summarized. Besides, technological developments, scientific challenges, and future research opportunities of cathode materials for PIBs are also briefly outlooked.

Research progress of transition metal compounds as bifunctional catalysts for zinc-air batteries

Zinc-air batteries(ZABs)are widely studied because of their high theoretical energy density,high battery voltage,environmental protection,and low price.However,the slow kinetics of oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)on the air electrode limits the further application of ZABs,so that how to develop a cheap,efficient,and stable catalyst with bifunctional catalytic activity is the key to solving the development of ZABs.Transition metal compounds are widely used as cathode materials for ZABs due to their low cost,high electrocatalytic activity,and stable structure.This review summarizes the research progress of transition metal compounds as bifunctional catalysts for ZABs.The development history,operation principle,and mechanism of ORR and OER reactions are introduced first.The application and development of transition metal compounds as bifunctional catalysts for ZABs in recent years are systematically introduced,including transition metal oxides(TMOs),transition metal nitrides(TMNs),transition metal sulfides(TMSs),transition metal carbides(TMCs),transition metal phosphates(TMPs),and others.In addition,the shortcomings of transition metal compounds as bifunctional catalysts for ZABs were summarized and reasonable design strategies and improvement measures were put forward,aiming at providing a reference for the design and construction of high-performance ZABs cathode materials.Finally,the challenges and future in this field are discussed and prospected.

Graphitic carbons:preparation,characterization,and application on K-ion batteries

K-ion batteries(KIBs)have drawn much attention due to the abundant potassium reserves and wide accessibility as well as high energy density,which can be designed for large-scale energy storage systems.As the most promising anode materials for KIBs,graphitic carbons,especially those with an intermediate structure between the crystalline graphite and amorphous carbons become a hot research focus because of the improved rate capability and enhanced diffusion-controlled capacity at low voltage regions.Herein,we first review the structures of graphitic carbons in the view of graphitic domains and the structure changes in their K-ion intercalation compounds.Then,we summarize the preparation mechanisms and characterizations of graphitic carbons and the influence factors in their degree of graphitization.Furtherly,we illustrate the strategies to optimize their K-ion storage properties from four aspects,namely graphitic domain design,microstructure engineering,electrochemical active component regulation,and defect engineering.Finally,we propose the issues that urgently need to be solved in graphitic carbons and the possible solutions.We hope that this view could offer some inspiration for the further designing and optimizing of graphitic carbons for practical KIBs.

Dissociation of singlet excitons dominates photocurrent improvement in high-efficiency non-fullerene organic solar cells

In organic solar cells,the singlet and triplet excitons dissociate into free charge carriers with different mechanisms due to their opposite spin state.Therefore,the ratio of the singlet and triplet excitons directly affects the photocurrent.Many methods were used to optimize the performance of the low-efficiency solar cell by improving the ratio of triplet excitons,which shows a long diffusion length.Here we observed that in high-efficiency systems,the proportion of singlet excitons under linearly polarized light excitation is higher than that of circularly polarized light.Since the singlet charge transfer state has lower binding energy than the triplet state,it makes a significant contribution to the charge carrier generation and enhancement of the photocurrent.Further,the positive magnetic field effect reflects that singlet excitons dissociation plays a major role in the photocurrent,which is opposite to the case of low-efficiency devices where triplet excitons dominate the photocurrent.

Interfacial molecular screening of polyimide dielectric towards high-performance organic field-effect transistors

The compatibility of the gate dielectrics with semiconductors is vital for constructing efficient conducting channel for high charge transport.However,it is still a highly challenging mission to clearly clarify the relationship between the dielectric layers and the chemical structure of semiconductors,especially vacuum-deposited small molecules.Here,interfacial molecular screening of polyimide(Kapton)dielectric in organic field-effect transistors(OFETs)is comprehensively studied.It is found that the semiconducting small molecules with alkyl side chains prefer to form a high-quality charge transport layer on polyimide(PI)dielectrics compared with the molecules without alkyl side chains.On this basis,the fabricated transistors could reach the mobility of 1.2 cm^(2) V^(−1)s^(−1) the molecule with alkyl side chains on bare PI dielectric.What is more,the compatible semiconductor and dielectric would further produce a low activation energy(E_(A))of 3.01 meV towards efficient charge transport even at low temperature(e.g.,100 K,0.9 cm^(2) V^(−1)s^(−1)).Our research provides a guiding scheme for the construction of high-performance thin-film field-effect transistors based on PI dielectric layer at room and low temperatures.

Advances on three-dimensional electrodes for micro-supercapacitors:A mini-review

Owing to the high power density,long cycle life and maintain-free,micro-supercapacitors(MSCs)stand out as preferred miniaturized energy source for themiscellaneous autonomous electronic components.However,the shortage of energy density is the main stumbling block for their practical applications.To solve this energy issue,constructing a three-dimensional(3D)electrode within the limited footprint area is proposed as a new solution for improving the energy storage capacity ofMSCs.In the last few years,extensive efforts have been devoted to developing 3D electrodes for MSCs,and significant progress and breakthrough have been achieved.While,there is still lack of systematic summary on the 3D electrode design strategies.To this end,it is imperative to outline the basic design conception,summarize the current states,and discuss the future research about 3D electrodes in MSCs based on the latest development.

Emerging smart design of electrodes for micro-supercapacitors:A review

Owing to high power density and long cycle life,micro-supercapacitors(MSCs)are regarded as a prevalent energy storage unit for miniaturized electronics in modern life.A major bottleneck is achieving enhanced energy density without sacrificing both power density and cycle life.To this end,designing electrodes in a“smart”way has emerged as an effective strategy to achieve a trade-off between the energy and power densities of MSCs.In the past few years,considerable research efforts have been devoted to exploring new electrode materials for high capacitance,but designing clever configurations for electrodes has rarely been investigated from a structural point of view,which is also important for MSCs within a limited footprint area,in particular.This review article categorizes and arranges these“smart”design strategies of electrodes into three design concepts:layer-by-layer,scaffoldassisted and rolling origami.The corresponding strengths and challenges are comprehensively summarized,and the potential solutions to resolve these challenges are pointed out.Finally,the smart design principle of the electrodes of MSCs and key perspectives for future research in this field are outlined.

Unexpected intercalation-dominated potassium storage in WS2 as a I potassium-ion battery anode

Unexpected intercalation-dominated process is observed duri ng K^+insertion in WS2 in a voltage range of 0.01-3.0 V.This is different fromthe previously reported two-dimensional(2D)transition metal dichalcogenides that undergo a conversion reaction in a low voltage rangewhen used as anodes in potassium-ion batteries.Charge/discharge processes in the K and Na cells are studied in parallel to demonstrate thedifferention storage mechanisms.The Na^+storage proceeds through intercalation and conversion reactions while the K^+storage is governedby an intercalation reaction.Owing to the reversible K^+intercalation in the van der Waals gaps,the WS2 anode exhibits a low decay rate of 0.07%per cycle,delivering a capacity of 103 mAh·g^-1 after 100 cycles at 100 mA·g^-1.It maintains 57%capacity at 800 mA·g^-1 and shows stablecyclability up to 400 cycles at 500 mA·g^-1.Kinetics study proves the facilitation of K^+transport is derived from the intercalation-dominatedmecha nism.Furthermore,the mechanismis verified by the density functional theory(DFT)calculations,showing that the progressive expansion of the interlayer space can account for the observed results.

Activated carbon prepared from waste tire pyrolysis carbon black via CO_(2)/KOH activation used as supercapacitor electrode

As the quantity of waste tires increases,more pyrolysis carbon black(CBp),a type of low value-added carbon black,is being produced.However,the application of CBp has been limited.Therefore,it is necessary to identify and expand applications of CBp.This work focuses on the preparation of activated carbon(AC)from CBp using the physicochemical activation of carbon dioxide(CO_(2))and potassium hydroxide(KOH).Thereafter,AC is applied to the electrode of the electrical double-layer capacitor(EDLC).The AC prepared by CO_(2)/KOH activation exhibited a hierarchical pore structure.The specific surface area increased from 415 to 733 m^(2)g^(−1),and in combination with low ash content of 1.51%,ensured abundant ion diffusion channels and active sites to store charge.The EDLC comprising the AC(AC-2)electrode prepared by excitation of CO_(2)(300 sccm)and KOH had a reasonable gravimetric specific capacitance of 192 F g^(−1)at 0.5 A g^(−1),and exhibited a good rate capability of 73%at 50 A g^(−1)in a three-electrode system.Moreover,the EDLC device comprising the AC-2 electrode delivered excellent cycling stability(capacitance retention of 106%after 10000 cycles at 2 A g^(−1)in a two-electrode system).Furthermore,a symmetric supercapacitor based on an AC electrode that exhibits a supreme energy density of 4.7 Wh kg^(−1)and a maximum power density of 6362.6 W kg^(−1)is demonstrated.

Deep Ultraviolet Phototransistor Based on Thiophene-Fluorobenzene Oligomer with High Mobility and Performance

Deep ultraviolet(UV)photodetectors have important applications in the industrial and military fields.However,little research has been reported on organic phototransistors(OPTs)in the deep ultraviolet range.Here,a novel organic semiconductor containing a small torsion angle and lowπ-conjugation 2,2':5',2"-terthiophene groups,oF-PTTTP,is designed and synthesized,which exhibits high carrier mobility and unique deep ultraviolet response.Accordingly,an OPT based on oF-PTTTP single crystal shows high responsivity to deep-UV light.The photodetectors achieve high photoresponsivity(R)of 857 A/W and detectivity(D*)of 3.2×10^(15)Jones under 280 nm light illumination(only 95 nW·cm^(–2)).To the best of our knowledge,280 nm is the deepest detection wavelength reported for organic phototransistors and this work presents a new molecule design concept for organic phototransistors with deep-UV detection.

Submicrometer optical frequency combs based on SPPs metallic multi-ring resonators

Optical frequency combs(OFCs)have great potential in communications,especially in dense wavelength-division multiplexing.However,the size of traditional OFCs based on conventional optical microcavities or dispersion fibers is at least tens of micrometers,far larger than that of nanoscale electronic chips.Therefore,reducing the size of OFCs to match electronic chips is of necessity.Here,for the first time to our knowledge,we introduce surface plasmon polaritons(SPPs)to the construction of OFCs to realize a miniature device.The thickness of our device is reduced below 1μm.Though the presence of SPPs may induce ohmic and scattering loss,the threshold of the device is obtained as 9μW,comparable to the conventional device.Interestingly,the response time is 13.2 ps,much faster than the optical counterparts.This work provides a feasible strategy for the miniaturization of OFCs.