Extreme wetting surfaces have been the significant subject of surface engineering field. A superhydrophillc surface has an exceptionally strong affinity to water and provides outstanding properties such as self-cleaning, anti-fogging, which offers a broad range of potential applications in many fields. Compared with superhydrophobic surfaces, superhydrophilic surfaces have received relatively few attentions, and some problems still exist in both academic and application. In this review, the controversy about the definition of superhydrophilic surfaces is introduced, then we analyze the mechanism of superhydrophilic phenomenon. The preparation methods and practical application are also discussed. Furthermore, some challenges and the current international new research tendency of superhydrophilic surfaces are highlighted. The review aims to provide an introductory yet comprehensive overview about superhydrophilic surfaces.

Contents
1 Introduction
2 Definition and mechanism
2.1 Definition of superhydrophilic surfaces
2.2 Mechanism of superhydrophilic phenomenon
3 Fabrication and application
3.1 Fabrication of superhydrophilic surfaces
3.2 Application of superhydrophilic surfaces
4 Problem and progress
4.1 Existing problems

Anodic titania nanotubes (ATNTs) have recently attracted particular attention due to their ease of preparation, low cost, large surface area, alignment and self-ordering. Especially, ATNTs are of interest for a wide variety of applications, including dye-sensitized solar cells, electrochemical sensors, photocatalysts, supercapacitors, etc. However, compared with analogous porous anodic alumina, the synthesis of ATNTs with regular and controllable microscopic morphologies is still under development. Although a number of excellent reviews on ATNTs have appeared, most of them have generally focused on their formation mechanism, properties, modifications and applications. This review attempts to pay close attention to the controllable fabrication of ATNTs, i.e., length, tube diameter, and self-ordering of nanotubes can be adjusted over large length scales. The preparation techniques of ATNTs in the last decade are summarized and the key factors for synthesis of ATNTs with tunable morphologies are discussed. In this review, we first present the anodization conditions of fabricating conventional ATNTs in ethylene glycol (EG) electrolytes and the typical microscopic morphologies of as-obtained ATNTs. Then, we discuss the growth characteristics and morphological parameters of ATNTs anodized in other electrolyte systems, such as aqueous solution, glycerol, dimethyl sulfoxide. It has been demonstrated that anodization conditions, including the solvent, temperature, anodization voltage, anodization duration and F^- concentration, have profound effects on the morphologies of ATNTs. On the basis of these experimental findings, we overview how to adjust tube diameter, tube length, wall thickness and self-organization of ATNTs by changing anodization parameters. Some fabrication methods for nanotubes with a length of over several hundreds micrometers and the structural features of such thick ATNT films are also given. In addition, the strategies to detach as-formed ATNTs from the metallic substrate and to obtain free-standing ATNT membranes are described. Finally, we emphasize some related issues for fabrication of ATNTs with tunable morphologies and indicate the main challenges and potential future directions of the field.

Contents
1 Introduction
2 Anodization conditions of fabricating the conventional ATNTs
3 ATNTs grown in non-ethylene glycol (EG)-based electrolyte systems
4 Adjustment of tube diameter and ordering of ATNTs
4.1 Adjustment of tube diameter
4.2 Achievement of an improved ordering for ATNTs
5 Methods for fabricating ATNTs with ultralong nanotubes
6 Strategies to obtain free-standing ATNT membranes
7 Conclusion

The development of paradigms for diastereoselective control in electrophilic attack on trigonal carbon adjacent to a chiral centre, especially for the alkylation and protonation of enolate anions and equivalents, generated from nucleophilic conjugative additions of α,β-unsaturated carbonyl compounds, and nitrates yielded from nucleophilic additions of nitroolefins, is introduced and reviewed. The diastereoselectivity in the kinetic protonation of conformationally restricted cyclic or allenic enol and enolate derivatives can be rationalized by Zimmerman's early transition state model, which is considered to be governed by steric factors exculsively. When acyclic substrates bearing conformational flexibility are employed, Houk's argument which is based on ab initio MO calculation has placed great importance on the approach angle, acute or obtuse which determines the sense of the diastereoselectivity. Subsequently, Fleming's successive refinements incline to avoid destabilizing allylic 1,3-interactions in the reaction of enolate anions with electrophiles. Excepting rationally tuning A-1,3 strain, electronegative heteroatom substituents are considered to occupy an antiperiplanar position to the forming σ bond via the stereoelectronic interaction in Mohrig's general rule for controlling the diastereoselectivity of electrophilic attack on enolate anions.

Contents
1 Introduction
2 Zimmerman model
2.1 Intermolecular kinetic protonation of restricted cyclic enolate derivatives
2.2 Intramolecular kinetic protonation transfer by the proximate groups of cyclic enolate derivatives
2.3 Kinetic protonation of allenic enolate derivatives
2.4 Application of Zimmerman model in open-chain substrates
3 Houk's arguments model
4 Fleming's refinements for Houk model
4.1 Fleming's model governed by steric factors
4.2 Fleming's model governed by heteroatom-containing substituents on the chiral carbon atom
5 Mohrig model and the applications
5.1 Introduction to Mohrig model
5.2 Applications of Mohrig model
5.3 Stereoelectronic effect in the protonation of chelate-controlled cyclic nitronate anions
6 Conclusions and prospects

Indenes and their derivatives widely exists in natural world, and some of them bearing multi-functional groups are very potential to become the lead compounds in drug because of their important bioactivities. In particular, asymmetric syntheses of indenes have attracted the extensive attention of organic chemists. Recently, many synthetic methods of them have been reported, including resolution of racemic mixture, syntheses of chiral auxiliary or substrate's induction, as well as chiral catalytic synthesis. In this review, we summarize the asymmetric syntheses of these compounds, and focus on the transition metal-catalyzed and organocatalytic asymmetric reaction. Finally, the further research on this field is also discussed.

Contents
1 Introduction
2 Catalytic asymmetric syntheses of indenes and their derivatives
2.1 Indene
2.2 Indanone
2.3 Indane
2.4 Indanol
2.5 Other derivatives
3 Conclusion

Chenodeoxycholic acid as a natural primary bile acid is one of the main organic compounds in the bile of chicken, duck, goose and so on. It has the function of sterilization, anti-inflammatory and dissolution of gallstones. In clinical practice, chenodeoxycholic acid is the drug for treatment of cholesterol gallstones. Ursodeoxycholic acid is the largest amount of drug for the treatment of gallstone disease, and chenodeoxycholic acid is the raw material for the synthetic of ursodeoxycholic acid. The application value in medicine promotes the preparation methods of chenodeoxycholic acid gradually improved. In recent years, great progress has been made in the research of chenodeoxycholic acid derivatives. Study on application of chenodeoxycholic acid has been extended to biological medicine, molecular recognition, functional materials and other fields. In particular, chenodeoxycholic acid derivatives show broad application prospects in the field of biological medicine. This paper provides an overview of the methods of extraction, synthesis and chemical modification of chenodeoxycholic acid according to chenodeoxycholic acid related research progress. Meanwhile, synthesis methods, properties and applications of chenodeoxycholic acid derivatives are also reviewed. The development prospects of chenodeoxycholic acid and its derivatives is also prospected.

Contents
1 Introduction
2 The preparation of chenodeoxycholic acid
2.1 The extraction of chenodeoxycholic acid from bile
2.2 Chemical synthesis of chenodeoxycholic acid
3 The synthesis of chenodeoxycholic acid derivatives
3.1 Synthesis of derivatives modified at 6-position
3.2 Synthesis of derivatives modified at 3,7-position
3.3 Synthesis of derivatives modified at 24-position carboxyl
3.4 Synthesis of derivatives modified at other positions
4 Conclusion

In recent centuries, the traditional tank reaction provides a large number of chemical products thermolysis of azidoacrylates. However, potential safety hazard, environmental pollution, huge energy consumption, huge site area and scale-up difficulties are the shortcomings. Continuous flow micro-reactor, with its high efficient heat transfer and mass transfer, accurate temperature control, security and stability, no amplification effect and the advantages of real-time monitoring, can solve the problems which existing in the traditional reaction. This review focuses on new findings in continuous flow micro-reaction in the last five years. The nitration reaction, thermolysis of azidoacrylates, Grignard and Grignard-type reactions, coupled reaction, amination reaction, oxidation and reduction reaction, condensation reaction, cyclization reaction, multistep reaction in flow condition and the continuous flow micro-reactors are introduced. Meanwhile, the potential strengths of the continuous flow micro-reaction as well as the weaknesses are discussed.

Contents
1 Introduction
2 Liquid phase reaction in flow condition
2.1 Nitration reaction
2.2 Thermolysis of azidoacrylates
2.3 Grignard and Grignard-type reaction
2.4 Coupled reaction
2.5 Amination reaction
2.6 Oxidation and Reduction reaction
2.7 Condensation reaction
2.8 Cyclization reaction
2.9 Other reactions
3 The gas-liquid reaction and gas-liquid-solid reaction in flow condition
4 Multistep reaction in flow condition
5 The continuous flow micro-reactors
6 Others
7 Conclusion

1α,25-Dihydroxyvitamin D₃(1α,25-(OH)₂-D₃, 125D)is the most active metabolite of vitamin D₃, but the therapeutic application of 125D is limited by induction of hypercalcemia. The need for vitamin D compounds with selective biological profiles has stimulated the synthesis of more than three thousand analogues of 125D. This article reviews the recent progress of vitamin D research in the design and synthesis of the structural modifications in the A ring (including modification in the C2-, and C3-substitued, aromatic A ring and seco-A ring analogues), side chain, CD ring, seco-B ring, and non-secosteroidal vitamin D₃ analogs, and the relation between the structure and the biological activities.

Contents
1 Introduction
2 Structure-activity relationship of analogues modified in the A ring
2.1 Analogues modification of C-2-substitued
2.2 Aromatic A-ring 125D analogues
2.3 Ring-A-seco-19-nor analogues
2.4 C-3-subtitued-25-hydroxy analogues
3 Structure-activity relationship of analogues modified in the side chains
3.1 26-Desmethyl-2-methylene-22-ene-19-nor-analogues
3.2 C-22-oxa-analogues
3.3 Analogues with aromatic side chains attached at C-17
3.4 C-2 substituted analogues having ringed side chains
3.5 Analogues of combination of triple bond and adamantane ring on the side chain
4 Structure-activity relationship of analogues modified in CD-ring
4.1 13α-Substituted-des-C-ring-19-nor-125D analogues
4.2 Analogues with α-hydroxyalkyl substituents at C12
4.3 9-Alkylidene-19-nor-125D analogues with unnatural triene system
5 Structure-activity relation of analogues modified substituted in seco-B ring
5.1 6-Substituted analogues of 125D
5.2 C-7-methyl-19-nor-125D analogues
6 Structure-activity relationship of non-secosteroidal vitamin D analogues
6.1 Bis- and tris-aromatic analogues
6.2 p-Carborane-based non-secosteroidal vitamin D analogues
7 Conclusion and outlook

Block copolymers(BCPs) have been attracting significant attentions owning to their wide industrial applications such as elastomer materials, optics, electronics, information, chemistry and biology in the past decades. The unique properties and materials performances of BCPs arise from their rich nanostructures. The chemistry difference between covalently bonded blocks leads to microphase separation and characteristic nanosized domains, which is a function of temperature, block composition and the degree of polymerization of blocks. The consequent self-assembly behavior displays rich ordered morphologies, which typically include sphere, cylinder, gyroid and lamellae. Among the mesostructures, network morphologies are especially interesting and useful because of their three-dimensionally co-continuous, interpenetrated meso-networks. Their character of high porosity and huge interface area generates practical merits in various applications such as outstanding mechanical anti-creep and high charge transport efficiency of optoelectronic devices.However, the rarely observed network morphologies of BCPs gain insufficient attentions. This review introduces fundamental principles of BCPs self-assembly and emphasizes the network morphologies of diBCPs. Three main types of network morphologies are discussed, including ordered bicontinuous double diamond (OBDD), double gyroid (DG) and Fddd. It also reviews three kinds of network preparation methods that appear in recent literatures: precise synthesis of diBCPs with specific chemistry, order-order phase transition from other nanostructures, and blending with homopolymer. Several typical applications are also reviewed. In the last part, the current research highlights are summarized and the future research directions of network mesosturctures are predicted.

Contents
1 Introduction
2 Self-assembly of diblock copolymers
2.1 Block copolymers
2.2 Self-assembly principles of diblock copolymers
2.3 Network morphologies
3 Preparation methods of network mesostructures of diblock copolymers
3.1 Precise synthesis
3.2 Order-order transition
3.3 Blending
4 Applications
5 Conclusion

Recently, all-polymer solar cells, in which both the donor and acceptor materials that absorb light and transport charges are semiconducting polymers, have a great potential to replace fullerene/polymer devices. The use of n-type polymers as acceptors has potential to overcome the high cost, poor thermal/photochemical stability, limited light absorption in the visible-near infrared region, and other limitations of fullerene derivatives. Among the various n-type polymers investigated as electron acceptors in all-PSCs to date, nanphthalene diimide (NDI)-based polymers with high carrier mobility and electron affinity have emerged as the most promising. Compared to fullerene derivatives, NDI-based n-type polymer acceptors exhibit better thermo/mechanical properties, light absorption and durability of the devices. The optical properties, electronic structure, crystallinity, solubility and charge transport of these materials can be easily tuned to enhance the devices performance. The greater thermal stability and mechanical strength of n-type polymers can ensure more morphologically and environmentally rugged all-polymer solar cells. In the paper, the research progress about the NDI-based D-A polymer acceptors is typically summed up according to the polymer structure. Meanwhile, the effects of corresponding donors, devices structure and post-process condition on the performances are described in detail. Finally, the all-polymer solar cells composed of NDI-based polymer acceptor and polymer donor are commented and we look forward to their development prospects in All-PSCs field.

Contents
1 Introduction
2 D-A polymers based on NDI
2.1 D-A polymers based on NDI which D unit has changed
2.2 D-A polymers based on NDI which A unit has changed
3 The devices post-processing technique
3.1 Solvent effect
3.2 The effect of D/A blend ratio on the device performance
3.3 The effect of additive on active layer morphology and device photovoltaic property
3.4 Film self-assembly aging
3.5 Invert structure of polymer solar cells
3.6 The cathode buffer layer
4 Conclusion and outlook

Hydroxyapatite (HA) is a kind of main minerals in vertebrate bones including human and animals. The synthesized HA possess good biocompatibility, bioactivity and bone conductivity. Acting as novel biological material, HA has been successfully used for repairing and replacing bone tissue. In this review, based on introducing preparation and applications of hydroxyapatite and its composite, the progress of HA composite materials with various natural polymers has been summarized. The main synthesis methods of HA are precipitation, emulsion, hydrothermal method, sol-gel method, mechanical chemical method, hydrolysis, pyrolysis, sonochemistry, template method, and electrodeposition method. Here, the natural polymer includes polysaccharide and protein, which polysaccharide includes cellulose, starch, chitin, chitosan and heparin, and protein includes collagen, gelatin, keratin, fibroin and plant protein. After being combined with hydroxyapatite, their mechanical properties and bioactive properties of the natural polymer composite material are improved with keeping their biocompatibility. Therefore, the natural polymer/HA composite materials have been applied as biological medicine, carriers, absorption and separation. The development trend is also suggested in the end of paper. In order to match special environment of biological body, such as strong resilience or bone growth speed matching performance, the new kind of natural polymer/HA composite materials will be investigated.

Contents
1 HA and its composites
2 Preparation and applications of HA and its composite
2.1 The main synthesis methods of HA
2.2 The applications of HA composite
3 Polysaccharide HA composites
3.1 Cellulose/HA and starch/HA composites
3.2 Chitin/HA and chitosan/HA composites
3.3 Heparin/HA composites
4 Protein/HA composites
4.1 Collagen/HA composites
4.2 Gelatin/HA composites
4.3 Keratin/HA composites
4.4 Fibroin/HA composites
4.5 Plant protein/HA composites
5 Conclusion and outlook

Small molecular fluorescent probe possess such advantages as high selectivity, high sensitivity and visualization when applied in detecting the pollutants. However, the drawback of low detection efficiency, difficulty to separate and recovery from bulk solution and pollution to the environment can notbe overcome. Small molecules fluorescent probes loaded on the surface of mesoporous materials by chemical methods can combine the advantages of fluorescent probes and mesoporous materials. The mesoporous material-based fluorescence probe can not only possess the function of detection and clearance of small molecular fluorescent probe, but also may achieve lower concentration detection and enhance the detection sensitivity by adjusting the pore size and components of mesoporous materials. This paper reviews the research progress of different mesoporous materials-based fluorescent probes firstly. The applications of different mesoporous materials-based fluorescent probes in the detection of heavy metal ions, organic small molecules, biological molecules and anions are elucidated emphasizedly. Lastly, the future studies for mesoporous materials-based fluorescent probes are also expected.

Contents
1 Introduction
2 Fluorescent probes for metal ions
2.1 Fluorescent probes for copper ions
2.2 Fluorescent probes for mercury ions
2.3 Fluorescent probes for lead ions
2.4 Fluorescent probes for iron ions
2.5 Fluorescent probes for other metal ions
3 Fluorescent probes for small organic molecules
4 Fluorescent probes for biological molecules
5 Fluorescent probes for anions
5.1 Pyrophosphate ions
5.2 Dichromate ions
6 Conclusion and outlook

Since introduced by Allen J. Bard and co-workers in 1986, scanning electrochemical microscopy (SECM) has been used as a powerful scanning probe technique in wide variety of fields, such as metal anti-corrosion, material characterization, biomedicine and new energy technology. In recent years, SECM plays a more and more important role in the field of photoelectrochemical energy research. In this paper, we introduce the basic principle as well as feedback and generation-collection operation-modes of SECM and highlight some of the recent advances on SECM applied to studies of solar cell and solar water splitting. SECM coupling with light source used as an effective tool for investigating interfacial charge transfer process and the regeneration kinetics of dyes in dye-sensitized solar cell are described. Additionally, SECM used as a powerful screening technique for developing efficient photocatalysts is discussed. Furthermore, we provide a brief research example that related SECM used as a combinatorial screening technique to investigate Ⅲ A, Ⅳ A and ⅤA group metal ions as dopants for WO₃ for photoelectrochemical water oxidation. This work has been conducted in our group recently, and it is reported for the first time. The details of this work are presented, including preparing doped WO₃ arrays on FTO glass substrate, setting up SECM testing system, photoelectrochemical scanning doped WO₃ arrays, screening scan results and proving scan results on scaled-up films. The SECM screening results show that 2%~4% In³⁺ doped WO₃, 2%~4% Sn⁴⁺ doped WO₃ and 4%~6% Sb⁵⁺ doped WO₃ have higher photoelectrochemical activity than un-doped WO₃. On the basis of research results, it is concluded that SECM is a convenient and efficient screening technique, has a promising application prospect in the development of photocatalysts. Finally, we briefly describe and forecast the development trend of SECM in the field of photoelectrochemical energy research.

Contents
1 Introduction
2 SECM operation modes
2.1 Feedback mode
2.2 Generation-collection mode
3 SECM used as tool for photoelectrochemical energy research
4 SECM used as screening technique for developing metal ion doped WO₃ photocatalysts
5 Conclusion and outlook

Particulate pollution is a major air pollution problem in Chinese mega-cities. Under such conditions, the atmospheric gas-phase chemistry is strongly influenced by heterogeneous reactions, of which to quantify the heterogeneous reaction processes of N₂O₅ is essential for the understanding of the nighttime oxidation capacity, regional NO_x budget, photochemical ozone prodution, etc. In this paper, we extensively review the research progress of the N₂O₅ heterogeneous reaction processes such as its reaction mechanism, measurement techniques of the corresponding uptake coefficient (γ_N2O5) and the measurement results on different aerosol substrates. The heterogeneous reaction processes of N₂O₅ is a typical reactive uptake process which can be ideally studied by the aerosol flow tube system. The corresponding laboratory kinetic studies are started from model aerosols (sulfate), and evolved to be more realistic aerosols according to the accumulated knowledges on the aerosol properties obtained in field studies. It is found that the γ_N2O5 varied from 0.001 to 0.2 on different aerosol substrates, more than two orders of magnitude. The variation is influenced by the ambient temperature, relative humidity, mixing state, phase state, aerosol chemical compositions like NO₃^-, Cl^-, SO₄^2-, liquid water content (LWC), organics, etc., of which the uptake coefficient is higher with higher LWC, Cl^-, SO₄^2- while lower with higher NO₃^- and organics. The avaiable field studies in the United States and Europe showed that, to describe γ_N2O5, these impact factors can't be independently expressed; and the dependence seems to be very complicated and cross correlated. Therefore the state of art parameterization methods of γ_N2O5 developed from lab kinetic studies are still not able to describe the field observations. Since high aerosol loading and high N₂O₅ are always co-located at urban aeras, more field observations and sucessful parameterization of γ_N2O5 is proposed to be conducted in typical urban conditions including Chinese megacity regions.

Contents
1 Introduction
2 Proposed Mechanisms of the N₂O₅ heterogeneous uptake
3 Measurement of the heterogeneous uptake coefficient of N₂O₅ in the simulated system
3.1 Measurement techniques
3.2 Measurement results on different aerosol substrates
4 Measurement of the heterogeneous uptake coefficient of N₂O₅ in the field
5 The parameterization of the heterogeneous uptake coefficient of N₂O₅
6 Conclusion and outlook

During the past three years, a new group of water and wastewater treatment technologies, called advanced reduction processes (ARPs), has been developed by combining activation methods with reducing reagents to yield reducing free radicals, including hydrated electron (e_aq^-) and hydrogen atom (H·), etc. The most commonly used activation method is UV, and the reducing agent is usually sulfite (SO₃^2-) or dithionite (S₂O₄^2-). The produced reducing radicals can donate an unpaired electron to a target contaminant and thereby chemically reduce it. Many kinds of stubborn contaminants can be degraded by ARPs, such as chlorinated organic compounds, fluorinated compounds and some inorganic pollutants (perchlorate, nitrate, bromate, etc.). So this novel process has a bright future in control of environmental pollutions. However, the ARPs are short of systematic research now. In order to promote the development of ARPs, the present research situation and prospect are reviewed in this paper. And the existing problems are also presented based on the analysis of its basic principles.

Contents
1 Introduction
2 Reaction mechanism of ARPs
2.1 Production of free radicals
2.2 The reaction between contaminant and free radicals
3 The research progress of ARPs
3.1 Influencial factors
3.2 Mechanism of degradation
3.3 Kinetic model
4 Conclusion and prospection
4.1 A further study of factors
4.2 Making clear of the degradation mechanism
4.3 Evaluating removal efficiency of different senior reduction technology for different pollutants
4.4 The extension of ARPs

Methanol is a kind of important basic chemical raw material. With the increase of global methanol production capacity, the catalytic conversion of methanol to methanol downstream high value-added downstream products is very important. The bifunctional catalysts for one-step oxidation of methanol to dimethoxymethane (DMM) and methyl formate (MF) with high value-added are very useful and have received considerable attention. In this paper, the recent applications of bifunctional catalysts for one-step oxidation of methanol to DMM and MF in recent are reviewed and summarized. The catalysis of bifunctional catalysts and the distribution of the products, especially the precious metal catalysts, metal oxide catalysts and heteropolyacid catalysts are carefully analyzed in order to provide a wide range of references for the catalytic conversion of methanol through synthesis step process of DMM and MF.

Contents
1 Introduction
2 The bifunctional catalysts for one-step catalytic conversion of methanol to DMM
2.1 The precious metal catalysts
2.2 The metal oxide catalysts
2.3 The supported heteropoly acid catalysts
3 The bifunctional catalysts for one-step synthesis of methyl formate from methanol
3.1 The precious metal catalysts
3.2 The metal oxide catalysts
4 Conclusion and outlook

Due to the lack of a living functional layer of endothelial cells (ECs) on the surface of artificial vascular scaffolds, especially small-diameter artificial vascular scaffolds, usually encounter long-term low patency and restenosis, limiting their clinical application. Nevertheless, it has been proved that re-endothelialization of artificial vascular scaffolds can be aquired rapidly via gene transfection towards endothelial cells, which is mediated by gene complexes. At present, gene carriers modified with targeting peptides provide a useful approach to promote transfection efficiency as well as decrease cytotoxicity. We introduce the desired genes and gene carriers applied in gene transfection detailedly. Based on polycationic gene carriers, the recent developments of gene carriers with targeting peptides for promoting the proliferation of ECs and endothelialization are highlighted in this review. Combined with the progress of small diameter artificial blood vessels, some perspectives on accomplishing rapid endothelialization via gene transfection are also presented.

Contents
1 Introduction
2 Non-viral gene carriers
3 Peptides for selective adhesion of endothelial cells
4 Gene carriers for targeting transfection of endothelial cells
5 Artificial vascular scaffolds modified by targeting carrier/gene complexes
6 Conclusion and outlook

Solid oxide fuel cells (SOFCs) have attracted considerable attention because of their high energy conversion efficiency (reach up to 80%), low emission of pollutants, and excellent fuel flexibility. Conventional SOFCs need to be operated at high temperature typically at ~1000 ℃ to obtain the required performance. This high operating temperature leads to the degradation of fuel cell performance, interfacial reactions among the components, and limited choice of materials. Therefore, intermediate temperature solid oxide fuel cell (IT-SOFCs) would be a development trend for the next generation of SOFCs which could be commercialized in the future. Lowing the operating temperature from traditional 1000 ℃ to 500~800 ℃ or even lower not only significantly prolongs the lifetime of materials and reduces the SOFCs system costs, but also provides a broader range for material selection. Therefore, it is necessary to develop a new electrode material with high electrochemical activity in intermediate temperature range to improve electrochemical performance. As one of the mixed ionic-electronic conductors (MIECs), the reaction sites of double perovskite materials extend the active sites from the three phase boundary to the entire exposed surface, which affords low polarization resistance and high performance at intermediate operating temperature. Meanwhile, due to the high ability of transporting oxygen ions, the low thermal expansion coefficient, good catalytic activity and high tolerance to sulfur poisoning and strong resistance against carbon deposition, the double-perovskite oxide becomes a promising electrode material for the IT-SOFCs. This review focuses on the structure stability, electronic and ionic conductivity as well as catalytic activity of perovskite materials. The main concerns about current double perovskite based electrode materials are summarized and the main future research directions are proposed.

Contents
1 Introduction
2 Solid oxide fuel cells
2.1 Introduction of SOFCs
2.2 Principle of SOFCs
2.3 Advantages of SOFCs
2.4 Problems of SOFCs
3 Cathode of SOFCs
3.1 LnBaCo₂O₆ layered double perovskite
3.2 Other Co-base double perovskite
3.3 Co-free double perovskite
4 Anode of SOFCs
5 Symmetric solid oxide fuel cells
6 Conclusion and outlook