With the massive global consumption of fossil fuels, the energy crisis is getting worse and the emission of greenhouse gases such as CO₂ has made the environmental problems become increasingly prominent. Photocatalytic reduction of CO₂ to energy compounds is considered to be one of the best ways to effectively solve this problem. Covalent organic frameworks (COFs) are a new type of crystalline porous organic polymer materials with high stability and pre-design ability, which makes COFs own great potential ability in the field of photocatalytic CO₂ reduction. This paper summarizes the research progress of COFs in the field of photocatalytic CO₂ reduction, including the introduction of different metal ions to provide the active site and increasing the photosensitive functional groups to improve their utilization of visible light. Since the research of COFs as photocatalytic CO₂ reduction catalyst is still an initial field, further exploration of synthesis, modification, and mechanism of COFs for CO₂ reduction is still promising research work.

1 Introduction

2 Covalent organic frameworks

2.1 Basic information of COFs

2.2 Application of COFs in photocatalysis

3 Basic principles of photocatalytic CO₂ reduction

4 COFs for photocatalytic CO₂ reduction

5 Conclusion and outlook

As the largest supply end and demand end in daily production respectively, the conversion, storage and utilization of electric energy and thermal energy play an important role in energy systems. Therefore, it is of great significance to develop high-efficiency materials for electro-thermal conversion and storage, especially facing today’s energy crises, environmental pollution and extreme climates. Among heat storage materials, phase change materials (PCMs) own unique advantages because of their high latent heat storage density and constant temperature during heat absorption and release. However, the low intrinsic conductivity of most PCMs does not match the large power requirements of current energy storage systems. This issue can be effectively improved by combining PCMs with conductive materials to obtain electrically heatable PCM composites. In this article, the latest research progress of electro-thermal conversion PCMs from three aspects of the functional mechanism, affecting factors and applications are systematically reviewed. Moreover, PCMs composited with conductive fillers, conductive framework and serving as conductive polymers are summarized and compared critically. Finally, this article points out the potential direction of future research and emphasizes the key points of this field.

1 Introduction

2 Electrothermal conversion mechanism of phase change composites

3 Functional phase change composites for electrical energy conversion, storage and utilization

3.1 Phase change composites doped with conductive fillers

3.2 Phase change composites supported by conductive framework

3.3 Phase change composites composed of conductive polymer

4 Application of electrothermal phase change composites

5 Conclusion and outlook

Lithium-sulfur (Li-S) batteries are considered as a promising next-generation high-energy battery system due to their ultrahigh theoretical capacity, energy density and the merits of sulfur in terms of abundant resource and environmental friendliness. However, their practical application is confronted with several critical problems including insulation of sulfur and discharge products, shuttle effect of soluble lithium polysulfides, and sluggish reaction kinetics of sulfur, etc. Significant progress has been achieved in addressing these problems by sulfur electrode design, functional separator/interlayer, liquid-electrolyte modification, and solid-electrolyte strategy. Nevertheless, there is still a lack of in-depth understanding of real-time dynamic reaction process and mechanism as well as electrode/electrolyte interface regulation strategy in Li-S batteries. First-principles calculation has gradually developed into an important research tool in various disciplines such as materials, chemistry and energy, facilitating to understand the properties of reaction species, interactions between molecules or/and electrons, electrochemical reaction processes and laws, and dynamic evolution of electrode/electrolyte from the molecular/atomic level. It delivers distinct advantages beyond “experimental trial and error” method in studying the multi-electron and multi-ion redox process in Li-S battery. In this paper, important advances in the application of first principles calculation to study the interactions between electrodes and polysulfides, charge-discharge reaction mechanisms, and electrolytes in Li-S batteries are comprehensively reviewed, and the current challenge and enlightening directions for application of first-principles calculation to study Li-S batteries are also prospected.

1 Introduction

2 Overview of first-principles

3 Interaction between electrode materials and polysulfides

3.1 Carbon materials

3.2 Transition metal compounds

3.3 Heterostructure

3.4 MOF and COF

3.5 Other materials

4 Reaction mechanism during charge and discharge

5 Electrolyte

6 Conclusion and outlook

With the rapid development of portable electronic devices, electric vehicles, and smart grids, there is an increasing interest in high-energy-density lithium metal batteries. Uneven Li stripping or deposition on the surface of lithium metal will lead to the growth of lithium dendrites, which can easily pierce the separator and cause the short circuit in the battery. Moreover, the highly reactive lithium metal will continue to react with the electrolyte, resulting in an unstable solid electrolyte. interfacial (SEI) film and irreversible capacity loss. Taking high-energy-density and high safety into account is a key scientific problem that needs to be solved urgently in the development and application of lithium metal batteries. The interaction of strong electron withdrawing group (C≡N) in polyacrylonitrile (PAN) polymer and C=O in carbonate solvent can form a more stable SEI film. As a lithium anode coating, PAN can also inhibit the growth of lithium dendrites. In addition, due to the low lowest unoccupied molecular orbital, high electrochemical stability and wide electrochemical window, PAN can be regard as polymer electrolytes for lithium metal batteries, and matched with a high-voltage cathode to achieve both high energy density and safety. Thus, PAN polymer has significant potential application in electrolytes for lithium metal batteries. This review mainly starts from the different states of electrolytes (liquid, gel, and solid state). Recent research development of PAN polymer as separators and lithium anode protective layers in liquid electrolytes, as well as its application in gel electrolytes and solid-state electrolytes are presented. Finally, the review prospects the development trend of PAN polymer in lithium metal battery electrolytes.

1 Introduction

2 The application of PAN in liquid state electrolytes

2.1 As separator

2.2 As lithium anode protective layers

3 The application of PAN in gel electrolytes

4 The application of PAN in solid-state electrolyte

4.1 Monolayer electrolytes containing PAN

4.2 Heterogeneous multilayer electrolytes containing PAN

4.3 PAN electrospinning fiber membrane

5 Conclusion and outlook

Na-based seawater batteries are expected to become a new-generation of energy storage device due to its advantages of environmental friendliness, high energy density, and abundant and easy availability of seawater. Its working principle is that the conversion between the chemical energy and the electrical energy is achieved through redox reaction when seawater is considered as the electrolyte. In this review, the electrochemical principle, and design and optimization strategy of battery structure of Na-based seawater batteries are summarized. The latest research progress of Na-based seawater batteries is reviewed. Finally, the challenges to overcome the performance improvement and commercialization of Na-based seawater batteries are discussed, and the future development directions of the batteries are forecasted. The review provides the theoretical guidance for the development of Na-based seawater batteries, and then promotes Na-based seawater batteries support for major national needs such as the deep-sea energy supply and extremely environmental-energy source.

1 Introduction

2 The introduction of Na-based seawater battery

2.1 The concept of Na-based seawater battery

2.2 The electrochemical principle of Na-based seawater battery

2.3 The characteristics of Na-based seawater battery

2.4 Battery design and optimization

3 Key components and challenges of Na-based seawater battery

3.1 Anode

3.2 Organic electrolyte

3.3 Solid electrolyte

3.4 Catalysts

4 Conclusion and prospect

Carbon nanotubes (CNTs) are ideal materials for building photovoltaic cells due to their unique one-dimensional structure and excellent photoelectric properties. In this paper, we review recent structural design, fabrication method and device performance of CNT-based photovoltaic cells and different functional roles of CNTs in these devices. Firstly, the structure and photoelectric properties of CNTs are introduced. Then, we emphatically discuss the operation principles, the fabrication methods and the advantages and shortage of the photovoltaic cells with CNTs used as the photoelectric conversion materials, conducting electrodes and carrier transport layers in the devices. The applications of carbon nanotubes in Micro photovoltaic cell,carbon nanotube/silicon heterojunction photovoltaic cells, dye sensitized photovoltaic cells, perovskite photovoltaic cells, organic photovoltaic cells and flexible photovoltaic cells are introduced. Finally, the advantages and challenges of CNT-based photovoltaic cells are summarized. This paper will provide new idea and reference for the design and fabrication of novel carbon-based photovoltaic cells.

1 Introduction

2 Structure and properties of carbon nanotubes

2.1 Structure of carbon nanotubes

2.2 Photoelectric properties of carbon nanotubes

3 Carbon nanotubes act as photoelectric conversion materials

3.1 Photovoltaic cells based on pure carbon nanotubes

3.2 Carbon nanotube/silicon heterojunction photovoltaic cells

3.3 Photovoltaic cells with carbon nanotubes as part of photosensitive materials

4 Carbon nanotubes act as conductive electrodes

4.1 Application in organic photovoltaic cells

4.2 Application in perovskite photovoltaic cells

4.3 Application in dye-sensitized photovoltaic cells

4.4 Application in flexible photovoltaic cells

5 Carbon nanotubes act as carrier transport materials

6 Conclusion and outlook

Thermoelectric materials, as one new kind of energy materials, can realize the direct conversion of thermal and electrical energy, which have important applications in power generation and refrigeration. Compared with traditional thermoelectric materials, flexible thermoelectric materials demonstrate excellent application prospects in wearable devices and flexible electronics fields, due to the advantages of being bendable, a lightweight and environmentally friendly. At present, how to further improve the performance of flexible thermoelectric materials is the focus, especially the collaborative optimization of flexibility andthermoelectric properties. In this paper, we have reviewed the research progress of polymer-based flexible thermoelectric materials, carbon-based flexible thermoelectric materials and inorganic semiconductor flexible thermoelectric materials, introduced their characteristics, performance optimization and preparation methods, and summarized the applications of flexible thermoelectric materials in the fields of electronics, medicine and industry. Also, based on the shortcomings of flexible thermoelectric materials, the future research directions are prospected.

1 Introduction

2 Types of flexible thermoelectric materials and their thermoelectric properties

2.1 Polymer-based flexible thermoelectric materials

2.2 Carbon-based flexible thermoelectric materials

2.3 Inorganic semiconductor flexible thermoelectric materials

3 Preparation method of flexible thermoelectric materials

3.1 Physical vapor deposition

3.2 In-situ polymerization

3.3 Electrospinning

3.4 High temperature melting method

4 Applications of flexible thermoelectric materials

5 Conclusion and outlook

Recently, structure modification has been used more and more widely in enhancing the performance of electromagnetic wave absorbing materials. Porous structure is not only conducive for the incidence of electromagnetic waves into the interior of the material, but also can effectively improve the impedance matching between electromagnetic wave and materials, resulting in enhanced absorption of electromagnetic waves. Additionally, multiple scattering and reflection endowed by the different scale pores in materials extend the propagation path of electromagnetic wave, and further increase its loss. Meanwhile, the lightweight nature of porous material provides a feasible way for the application of some absorbing materials with high performance but unduly density. In this paper, the research status and problem of zero- and three-dimensional porous electromagnetic wave absorbing materials (PEMAM) are summarized and the possible research hotspots and development directions of porous electromagnetic wave absorbing materials in the future are also proposed.

1 Introduction

2 Zero-dimensional PEMAM

2.1 Magnetic loss type PEMAM

2.2 Dielectric loss type PEMAM

2.3 Magnetoelectric composite type PEMAM

3 Three-dimensional PEMAM

3.1 Graphene/carbon nanosheet and carbon nanotubes-based PEMAM

3.2 Green carbon material-based PEMAM

3.3 Other three-dimensional PEMAM

4 Conclusion and outlook

MIL-101(Fe) is a typical Fe-based metal-organic framework (Fe-MOF), which demonstrates the advantages of flexible structure, large specific surface area, large porosity, and adjustable pore size. In recent years, MIL-101(Fe) and its composites have been extensively studied in the field of water pollution remediation, especially in the hexavalent chromium (Cr(Ⅵ)) reduction and advanced oxidation processes for removing organic pollutants in water. The water stability, light absorption activity and the carrier separation efficiency can be significantly improved by functional modification with specific functional materials. In this review, the preparation strategies of MIL-101(Fe) and its composites, as well as their application as heterogeneous catalysts for photocatalysis, H₂O₂ activation, and persulfate activation were introduced. The future development of MIL-101(Fe) and its composites as catalysts for water purification is prospected.

1 Introduction

2 Preparation of MIL-101(Fe) and its composites

2.1 MIL-101(Fe)

2.2 MIL-101(Fe) composites

3 MIL-101(Fe) and its composites for reduction of Cr(Ⅵ)

4 Advanced oxidative degradation of organic pollutants in wastewater by MIL-101(Fe) and their composites

4.1 Photocatalysis

4.2 Activation of H₂O₂

4.3 Activation of persulfate

5 Water stability and biotoxicity of MIL-101(Fe)

6 Conclusions and prospective

Covalent organic frameworks (COFs) are a class of crystalline organic porous polymers with long-range ordered structures prepared by reversible reactions. Due to high radiation resistance, structural designability and functionalization, COFs are expected to play a role in the efficient adsorption of radionuclides and the exploration of interaction mechanism. However, the reversibility of typical linkage bonds causes the limited chemical stability of COFs. This paper reviews the improvement strategies towards chemical stability of COFs (including the decrease of reversibility of linkage bonds, the post synthetic transformation from reversible bonds to irreversible ones, and the construction of hydrophobic environment around linkage bonds), crystalline control (including the influence of synthesis conditions, in layer coplanar and interlayer interaction for two-dimensional COFs and the crystallization of amorphous polymers), functionalization methods and the applications of COFs in the separation and enrichment of radionuclides. The interaction between radionuclides and COFs could be optimized by enhancing the strength of COFs skeleton, introducing special functional groups or changing the size of monomers. The application prospect and research focus of COFs in radionuclide separation are prospected.

1 Introduction

2 Typical reversible reactions of COFs

2.1 B—O bond formation

2.2 C=N bond formation

2.3 C—N bond formation

2.4 C—O bond formation

2.5 C=C bond formation

2.6 Others

3 Improvement of COFs linkage stability

3.1 COFs linkage cyclization reaction

3.2 Oxidation or reduction of imine linkage

3.3 COF to COF transformation via monomer exchange

3.4 Others

4 Regulation of crystallinity

4.1 Effect of synthesis conditions on crystallinity

4.2 Intralayer coplanarity of 2D COFs

4.3 Interlayer stacking force of 2D COFs

4.4 Crystallization of amorphous polymer

5 Functionalized syntheses of COFs

6 Applications of COFs in separation and enrichment of radionuclides

6.1 {\mathrm{UO}}_2^{2+}

6.2 I₂ vapor

6.3 {\mathrm{TcO}}_4^{-}/ {\mathrm{ReO}}_4^{-}

7 Conclusion and outlook

With the large-scale spread of COVID-19 around the world, it has caused serious damage to the health of people around the world. In addition to being transmitted by various droplets, viruses can also be transmitted by human touch of contaminated surfaces. However, as a commonly used surface antiviral method, disinfectants have the disadvantage of discontinuously inactivating viruses, which is bad for inhibiting the spread of various infectious viruses. Therefore, it is urgent to protect the surface of daily objects from virus pollution to eliminate the spread of various respiratory viruses (such as Corona Virus Disease 2019, SARS-CoV-2). From this point of view, it is very important to design and develop effective antiviral coatings. This paper discusses the working mechanisms, performance evaluation methods, processing technologies, practical applications and research progress of nanoparticle antiviral coatings and polymer antiviral coatings for SARS-CoV-2, and also proposes some strategies to design more effective antiviral coatings from the perspective of different types of antiviral coatings. Although some of these antiviral coatings are still in the experimental stage, they still show great potential in the antiviral field.

1 Introduction

2 Antiviral mechanism

2.1 Direct inactivation of virus

2.2 Inhibiting virus infection of host cells

2.3 Inhibition of virus proliferation

3 Antiviral coatings

3.1 Nanomaterial antiviral coatings

3.2 Antiviral polymer coatings

4 Evaluation methods of antiviral coatings

5 Processing technologies of antiviral coatings

6 Practical applications of antiviral coatings

6.1 Antivirus mask

6.2 Antivirus fabrics

6.3 Surface of other solid objects

7 Conclusion and outlook