Novel high-entropy oxides for energy storage and conversion:From fundamentals to practical applications

High-entropy oxides(HEOs)are gaining prominence in the field of electrochemistry due to their distinctive structural characteristics,which give rise to their advanced stable and modifiable functional properties.This review presents fundamental preparations,incidental characterizations,and typical structures of HEOs.The prospective applications of HEOs in various electrochemical aspects of electrocatalysis and energy conversion-storage are also summarized,including recent developments and the general trend of HEO structure design in the catalysis containing oxygen evolution reaction(OER)and oxygen reduction reaction(ORR),supercapacitors(SC),lithium-ion batteries(LIBs),solid oxide fuel cells(SOFCs),and so forth.Moreover,this review notes some apparent challenges and multiple opportunities for the use of HEOs in the wide field of energy to further guide the development of practical applications.The influence of entropy is significant,and high-entropy oxides are expected to drive the improvement of energy science and technology in the near future.

Polymer-/Ceramic-based Dielectric Composites for Energy Storage and Conversion

Dielectric composites boost the family of energy storage and conversion materials as they can take full advantage of both the matrix and filler.This review aims at summarizing the recent progress in developing highperformance polymer-and ceramic-based dielectric composites,and emphases are placed on capacitive energy storage and harvesting,solid-state cooling,temperature stability,electromechanical energy interconversion,and high-power applications.Emerging fabrication techniques of dielectric composites such as 3D printing,electrospinning,and cold sintering are addressed,following by highlighted challenges and future research opportunities.The advantages and limitations of the typical theoretical calculation methods,such as finite-element,phase-field model,and machine learning methods,for designing high-performance dielectric composites are discussed.This review is concluded by providing a brief perspective on the future development of composite dielectrics toward energy and electronic devices.

Single-atom catalysts for electrochemical energy storage and conversion

The expedited consumption of fossil fuels has triggered broad interest in the fabrication of novel catalysts for electrochemical energy storage and conversion. Especially, single-atom catalysts(SACs) have attracted more attention owing to their high specific surface areas and abundant active centers. This review summarizes recent synthetic strategies to fabricate SACs with different metal loadings on various supports, and the structural influence of supports on metal loading. Then, the functions of SACs are illustrated on electronic structure and electrocatalysis;the isolated SACs with an unsaturated coordination environment generally accelerate the electrocatalytic process and promote the selectivity. The applications of SACs to some typical electrocatalytic reactions are also introduced in detail, as well as to electrochemical energy storage and conversion systems. Finally, the challenges and the perspectives of SACs are discussed for future exploration.

Two-dimensional polymer-based nanosheets for electrochemical energy storage and conversion

Over the past decades, two-dimensional（2D） nanomaterials possessing planar layered architecture and unique electronic structures have been being quickly developed, due to their wide potential application in the fields of chemistry, physics, and materials science. As a new family of 2D nanomaterials, 2D polymerbased nanosheets, featuring excellent characters, such as tunable framework structures, light weight, flexibility, high specific surface, and good semiconducting properties, have been emerging as one kind of promising functional materials for optoelectronics, gas separation, catalysis and sensing, etc. In this review, the recent progress in synthetic approach and characterization of 2D polymer-based nanosheets were summarized, and their current advances in electrochemical energy storage and conversion including second batteries, supercapacitors, oxygen reduction and hydrogen evolution were discussed systematically.

Preface to Special Issue on Electrochemical Energy Storage and Conversion

Energy utilization includes two aspects of storage and conversion. Both the density of energy storage and the efficiency of energy conversion are particularly considered in the application of energy. It is well known that chemical energy can be easily stored in chemical substances with high-energy density such as those containing hydrogen and lithium. Meanwhile, chemical energy can be highly converted into clean and efficient electrical energy through the systems of electrochemical energy storage and conversion, which include batteries, fuel cells, and electrochemical capacitors （also called supercapacitors）. Thus, the combination of chemical energy and electrochemical reactions makes full use of the advantages of chemical energy and electrical energy. Nowadays, systems of electrochemical energy storage and conversion have already played an important role in powering an increasingly diverse range of applications from electronic devices to cars.

Energy storage and conversion:Driving human development

Energy scarcity and environmental pollution are worldwide issues which plague human development.According to projections for economic development and population growth,global energy demand is anticipated to double by 2050 and triple by2100.Better energy storage and conversion are glorious but arduous missions in the 21st century.Although the fossil

A Rising 2D Star:Novel MBenes with Excellent Performance in Energy Conversion and Storage

As a flourishing member of the two-dimen-sional(2D)nanomaterial family,MXenes have shown great potential in various research areas.In recent years,the continued growth of interest in MXene derivatives,2D transition metal borides(MBenes),has contributed to the emergence of this 2D material as a latecomer.Due to the excellent electrical conductivity,mechanical properties and electrical properties,thus MBenes attract more researchers’interest.Extensive experimental and theoretical studies have shown that they have exciting energy conversion and elec-trochemical storage potential.However,a comprehensive and systematic review of MBenes applications has not been available so far.For this reason,we present a comprehen-sive summary of recent advances in MBenes research.We started by summarizing the latest fabrication routes and excellent properties of MBenes.The focus will then turn to their exciting potential for energy storage and conversion.Finally,a brief summary of the challenges and opportunities for MBenes in future practical applications is presented.

Machine learning:Accelerating materials development for energy storage and conversion

With the development of modern society,the requirement for energy has become increasingly important on a global scale.Therefore,the exploration of novel materials for renewable energy technologies is urgently needed.Traditional methods are difficult to meet the requirements for materials science due to long experimental period and high cost.Nowadays,machine learning(ML)is rising as a new research paradigm to revolutionize materials discovery.In this review,we briefly introduce the basic procedure of ML and common algorithms in materials science,and particularly focus on latest progress in applying ML to property prediction and materials development for energyrelated fields,including catalysis,batteries,solar cells,and gas capture.Moreover,contributions of ML to experiments are involved as well.We highly expect that this review could lead the way forward in the future development of ML in materials science.

Tungsten disulfide: synthesis and applications in electrochemical energy storage and conversion

Recently,two-dimensional transition metal dichalcogenides,particularly WS_(2),raised extensive interest due to its extraordi-nary physicochemical properties.With the merits of low costs and prominent properties such as high anisotropy and distinct crystal structure,WS_(2) is regarded as a competent substitute in the construction of next-generation environmentally benign energy storage and conversion devices.In this review,we begin with the fundamental studies of the structure,properties and preparation of WS_(2),followed by detailed discussions on the development of various WS_(2) and WS_(2)-based composites for electrochemical energy storage and conversion applications.In the end,some prospective prospects and promising develop-ments of WS_(2) in these fields are proposed.

Laser irradiation construction of nanomaterials toward electrochemical energy storage and conversion:Ongoing progresses and challenges

The emerging use of laser irradiation in synthesis smartly bridges“nanotech-nology”and“light”,and has attracted enormous attention as an efficient syn-thetic methodology for versatile nanomaterials toward electrochemical energy storage and conversion devices(ESCDs).In this review,recent contributions and progress regarding the laser-induced nanomaterials for ESCDs are com-prehensively summarized,with a special focus on their practical utilization in rechargeable batteries,supercapacitors and electrocatalysis.The laser-induced synthesis strategies and corresponding mechanisms involved in nano-architecture generation/regulation,including pulsed laser deposition and laser irradiation in liquid,are also discussed in detail.With the in-depth insights into the mechanisms and revolutionary advancements of laser irradiation tech-nology,the comprehensive performances of ESCDs have been strikingly opti-mized.Finally,the existing challenges and future directions in this booming research field are outlined.This review will exert the significant guidance for future design and purposeful fabrication of advanced laser-induced nano-materials with appealing properties for advanced ESCDs and beyond.

Recent Advances in Two-dimensional Materials for Electrochemical Energy Storage and Conversion

With the increased energy demand,developing renewable and clean energy technologies becomes more and more significant to mitigate climate warming and alleviate the environmental pollution.The key point is design and synthesis of low cost and efficient materials for a wide variety of electrochemical reactions.Over the past ten years,two-dimensional(2D)nanomaterials that graphene represents have been paid much attention as a class of the most promising candidates for heterogeneous electrocatalysts in electrochemical storage and conversion.Their unique properties,such as good chemical stability,good flexibility,and good electronic properties,along with their nanosized thickness and large specific area,make them exhibit comprehensively good performances for energy storage and conversion.Here,we present an overview on the recent advances in electrochemical applications of graphene,graphdiyne,transition metal dichalcogenides(TMDs),and MXenes for supercapacitors(SCs),oxygen reduction reaction(ORR),and hydrogen evolution reaction(HER).

Three-dimensional printing of graphene-based materials for energy storage and conversion

Developing high-performance energy storage and conversion(ESC)device relies on both the utilization of good constituent materials and rational design of assembly structure.Graphene-based materials,due to their superior properties like high electrical/thermal conductivity,large surface area,and unique optical properties,have been extensively reported for ESC applications.The emerging three-dimensional(3D)printing techniques,especially extrusion-based direct ink writing technique,have brought a revolutionary improvement in structure control accuracy and designing capability to graphene-based macro-assemblies,triggering a boost in functionalities and performances of graphene-based ESC devices.In these circumstances,understanding the very recent progress of 3Dprinted graphene materials and their design philosophy to bring new concepts for material designs and address the requirements for high-performance ESC devices are urgently important.In this review,we aim to outline recent developments in 3D printing of graphene-based materials and their applications in ESC applications.Basic requirements and theoretical analysis for preparation printable inks are discussed,as well as feasible GO ink preparation strategies in existing literatures.The representative explorations of 3D-printed graphenematerials in ESC applications like batteries,supercapacitors,solar steam generators,and electro-thermal conversion are also reviewed.This study attempts to provide a comprehensive overview of the progresses and limitations of present 3D printed graphenematerials,and seeks to enlighten the opportunities and orientations of future research in this field.

Recent progress and perspectives on silicon anode:Synthesis and prelithiation for LIBs energy storage

The ever-increasing environmental/energy crisis as well as the rapid upgrading of mobile devices had stimulated intensive research attention on promising alternative energy storage and conversion devices.Among these devices,alkali metal ion batteries,such as lithium-ion batteries(LIBs) had attracted increasing research attention due to its several advantages including,environmental friendliness,high power density,long cycle life and excellent reversibility.It had been widely used in consumer electronics,electric vehicles,and large power grids et ac.Silicon-based(silicon and their oxides,carbides) anodes had been widely studied.Its several advantages including low cost,high theoretical capacity,natural abundance,and environmental friendliness,which shows great potential as anodes of LIBs.In this review,we summarized the recently progress in the synthetic method of silicon matrix composites.The empirical method for prelithiation of silicon-based materials were also provided.Further,we also reviewed some novel characterization methods.Finally,the new design,preparation methods and properties of these nano materials were reviewed and compared.We hoped that this review can provide a general overview of recent progress and we briefly highlighted the current challenges and prospects,and will clarify the future trend of silicon anode LIBs research.

Recent progress on mechanisms,principles,and strategies for high-activity and high-stability non-PGM fuel cell catalyst design

The commercialization of a polymer membrane H2-O2 fuel cell and its widespread use call for the development of cost-effective oxygen reduction reaction(ORR)nonplatinum group metal(NPGM)catalysts.Nevertheless,to meet the requests for the real-world fuel cell application and replacing platinum catalysts,it still needs to address some challenges for NPGM catalysts regarding the sluggish ORR kinetics in the cathode and their poor durability in acidic environment.In response to these issues,numerous efforts have been made to study NPGM catalysts both theoretically and experimentally,developed these into the atomically dispersed coordinated metal-nitrogen-carbon(M-N-C)form over the past decades.In this review,we present a comprehensive summary of recent advancements on NPGM catalysts with high activity and durability.Catalyst design strategies in terms of optimizing active-site density and enhancing catalyst stability against demetalization and carbon corrosion are highlighted.It is also emphasized the importance of understanding the mechanisms and principles behind those strategies through a combination of theoretical modeling and experimental work.Especially,further understanding the mechanisms related to the active-site structure and the formation process of the single-atom active site under pyrolysis conditions is critical for active-site engineering.Optimizing the active-site distance is the basic principle for improving catalyst activity through increasing the catalyst active-site density.Theoretical studies for the catalyst deactivation mechanism and modeling stable active-site structures provide both mechanisms and principles to improve the NPGM catalyst durability.Finally,currently remained challenges and perspectives in the future on designing high-performance atomically dispersed NPGM catalysts toward fuel cell application are discussed.

Recent progress on MOF-derived carbon materials for energy storage

Metal-organic frameworks(MOFs)are of quite a significance in the field of inorganic-organic hybrid crystals.Especially,MOFs have attracted increasing attention in recent years due to their large specific surface area,desirable electrical conductivity,controllable porosity,tunable geometric structure,and excellent thermal/chemical stability.Some recent studies have shown that carbon materials prepared by MOFs as precursors can retain the privileged structure of MOFs,such as large specific surface area and porous structure and,in contrast,realize in situ doping with heteroatoms(eg,N,S,P,and B).Moreover,by selecting appropriate MOF precursors,the composition and morphology of the carbon products can be easily adjusted.These remarkable structural advantages enable the great potential of MOF-derived carbon as high-performance energy materials,which to date have been applied in the fields of energy storage and conversion systems.In this review,we summarize the latest advances in MOF-derived carbon materials for energy storage applications.We first introduce the compositions,structures,and synthesis methods of MOF-derived carbon materials,and then discuss their applications and potentials in energy storage systems,including rechargeable lithium/sodium-ion batteries,lithium-sulfur batteries,supercapacitors,and so forth,in detail.Finally,we put forward our own perspectives on the future development of MOF-derived carbon materials.

Catalytic effect in lithium metal batteries: From heterogeneous catalyst to homogenous catalyst

Lithium metal batteries are regarded as prominent contenders to address the pressing needs owing to the high theoretical capacity.Toward the broader implementation,the primary obstacle lies in the intricate multi-electron,multi-step redox reaction associated with sluggish conversion kinetics,subsequently giving rise to a cascade of parasitic issues.In order to smooth reaction kinetics,catalysts are widely introduced to accelerate reaction rate via modulating the energy barrier.Over past decades,a large amount of research has been devoted to the catalyst design and catalytic mechanism exploration,and thus the great progress in electrochemical performance has been realized.Therefore,it is necessary to make a comprehensive review toward key progress in catalyst design and future development pathway.In this review,the basic mechanism of lithium metal batteries is provided along with corresponding advantages and existing challenges detailly described.The main catalysts employed to accelerate cathode reaction with emphasis on their catalytic mechanism are summarized as well.Finally,the rational design and innovative direction toward efficient catalysts are suggested for future application in metal-sulfur/gas battery and beyond.This review is expected to drive and benefit future research on rational catalyst design with multi-parameter synergistic impacts on the activity and stability of next-generation metal battery,thus opening new avenue for sustainable solution to climate change,energy and environmental issues,and the potential industrial economy.

A Unifi ed View of Carbon Neutrality:Solar-Driven Selective Upcycling of Waste Plastics

With the rapid development of plastic production and consumption globally,the amount of post-consumer plastic waste has reached levels that have posed environmental threats.Considering the substantial CO_(2)emissions throughout the plastic lifecycle from material production to its disposal,photocatalysis is considered a promising strategy for eff ective plastic recycling and upcycling.It can upgrade plastics into value-added products under mild conditions using solar energy,realizing zero carbon emissions.In this paper,we explain the basics of photocatalytic plastic reformation and underscores plastic feedstock reformation pathways into high-value-added products,including both degradation into CO_(2)followed by reformation and direct reformation into high-value-added products.Finally,the current applications of transforming plastic waste into fuels,chemicals,and carbon materials and the outlook on upcycling plastic waste by photocatalysis are presented,facilitating the realization of carbon neutrality and zero plastic waste.

A perspective on carbon materials for future energy application

Nanocarbon materials play a critical role in the development of new or improved technologies and devices for sustainable production and use of renewable energy. This perspective paper defines some of the trends and outlooks in this exciting area, with the effort of evidencing some of the possibilities offered from the growing level of knowledge, as testified from the exponentially rising number of publications, and putting bases for a more rational design of these nanomaterials. The basic members of the new carbon family are fullerene, graphene, and carbon nanotube. Derived from them are carbon quantum dots, nanohorn, nanofiber, nano ribbon, nanocapsulate, nanocage and other nanomorphologies. Second generation nanocarbons are those which have been modified by surface functionalization or doping with heteroatoms to create specific tailored properties. The third generation of nanocarbons is the nanoarchitectured supramolecular hybrids or composites of the first and second genera- tion nanocarbons, or with organic or inorganic species. The advantages of the new carbon materials, relating to the field of sustainable energy, are discussed, evidencing the unique properties that they offer for developing next generation solar devices and energy storage solutions.

Recent Progress on Asymmetric Carbon- and Silica-Based Nanomaterials: From Synthetic Strategies to Their Applications

Carbon-and silica-based nanomaterials possess a set of merits including large surface area,good structural stability,diversified morphology,adjustable structure,and biocompatibility.These outstanding features make them widely applied in different fields.However,limited by the surface free energy effect,the current studies mainly focus on the symmetric structures,such as nanospheres,nanoflowers,nanowires,nanosheets,and core-shell structured composites.By comparison,the asymmetric structure with ingenious adjustability not only exhibits a larger effective surface area accompanied with more active sites,but also enables each component to work independently or corporately to harness their own merits,thus showing the unusual performances in some specific applications.The current review mainly focuses on the recent progress of design principles and synthesis methods of asymmetric carbon-and silica-based nanomaterials,and their applications in energy storage,catalysis,and biomedicine.Particularly,we provide some deep insights into their unique advantages in related fields from the perspective of materials’structure-performance relationship.Furthermore,the challenges and development prospects on the synthesis and applications of asymmetric carbon-and silica-based nanomaterials are also presented and highlighted.

Micro/nano metal–organic frameworks meet energy chemistry: A review of materials synthesis and applications

Micro/nano metal–organic frameworks(MOFs)have attracted significant attention in recent years due to their numerous unique properties,with many synthetic methods and strategies being reported for constructing MOFs with specific micro/nano structures.In addition,the design of micro/nano MOFs for energy storage and conversion applications and the study of the structure–activity relationship have also become research hotspots.Herein,a comprehensive overview of the recent progress on micro/nano MOFs is presented.We begin with a brief introduction to the various synthesis methods for controlling the morphology of micro/nano MOFs.Subsequently,the structure-dependent properties of micro/nano MOFs as electrode materials or catalysts in terms of batteries,supercapacitors,and catalysis are discussed.Finally,the remaining challenges and future perspectives in this field are presented.Overall,this review is expected to inspire the design of advanced micro/nano MOFs for efficient energy storage and conversion technologies.