Recent trends in hydrogen and oxygen electrocatalysis for anion exchange membrane technologies

This review aims at presenting recent findings in the understanding of oxygen and hydrogen electrocatalysis in alkaline electrolytes that are key processes for the emergence of sustainable energy storage and conversion devices such as anion exchange membrane fuel cells and electrolyzers. In these systems, the exchange of electrons through electrochemical reactions provides a unique pathway to reversibly convert the electricity vector into chemical one: hydrogen. A concise and critical review of advances made during the last past years in the design of catalysts is provided. Challenges and opportunities for the development of the next catalyst generation are also addressed.     

Lowering reaction temperature: Electrochemical ammonia synthesis by coupling various electrolytes and catalysts

Ammonia is a vital emerging energy carrier and storage medium in the future hydrogen economy, even presenting relevant advantages compared with methanol due to the higher hydrogen content(17.6 wt% for ammonia versus 12.5 wt% for methanol). The rapidly growing demand for ammonia is still dependent on the conventional high-temperature and high-pressure Haber–Bosch process, which can deliver a conversion rate of about 10%–15%. However, the overall process requires a large amount of fossil fuels,resulting in serious environmental problems. Alternatively, electrochemical routes show the potential to greatly reduce the energy consumption, including sustainable energy sources and simplify the reactor design. Electrolytes perform as indispensable reaction medium during electrochemical processes, which can be further classified into solid oxide electrolytes, molten salt electrolytes, polymer electrolytes, and liquid electrolytes. In this review, recent developments and advances of the electrocatalytic ammonia synthesis catalyzed by a series of functional materials on the basis of aforementioned electrolytes have been summarized and discussed, along with the presentation and evaluation of catalyst preparation, reaction parameters and equipment.     

低聚离子液体的体相与界面及其电化学储能应用

近年来,随着单阳离子液体的发展,新型低聚物离子液体被合成并应用。这类离子液体可看作是由几个重复的单阳离子组合而成,可以通过改变阳离子带电基团、间隔连接的长度或种类、末端链的长度以及阴离子种类来获得更多不同的结构。因此,低聚离子液体有更复杂的微观结构和内部相互作用,决定了其多特征的物化性质和电化学特性,有望满足更多对溶剂性能有特定要求的应用。例如,与单阳离子液体相比,低聚离子液体具有更大的可调节性、更宽的液态温度范围、更高的热稳定性等优点,使其在电化学储能设备中得到越来越多的应用,如用作超级电容器和锂离子电池的电解液。在本综述中,我们系统地总结并详细解释了低聚离子液体的性质和结构（包括单个离子的结构和本体液内部的纳米组织）之间的关联,主要是双阳离子液体和三阳离子液体;概括了低聚离子液体作为超级电容器和锂离子电池的电解液的相关研究,重点阐述了由低聚离子液体和不同类型电极组成的双电层的结构和性能,以及与相应单阳离子液体电解液的比较结果;提供了降低低聚离子液体粘度和加速离子扩散的优化措施,提出了低聚离子液体电解液未来可能面临的主要问题和发展前景。     

Recent Advances in Porous Carbon Materials for Electrochemical Energy Storage

Climate change and the energy crisis have promoted the rapid development of electrochemical energy‐storage devices. Owing to many intriguing physicochemical properties, such as excellent chemical stability, high electronic conductivity, and a large specific surface area, porous carbon materials have always been considering as a promising candidate for electrochemical energy storage. To date, a wide variety of porous carbon materials based upon molecular design, pore control, and compositional tailoring have been proposed for energy‐storage applications. This focus review summarizes recent advances in the synthesis of various porous carbon materials from the view of energy storage, particularly in the past three years. Their applications in representative electrochemical energy‐storage devices, such as lithium‐ion batteries, supercapacitors, and lithium‐ion hybrid capacitors, are discussed in this review, with a look forward to offer some inspiration and guidelines for the exploitation of advanced carbon‐based energy‐storage materials.     

Chemical and Physical Solutions for Hydrogen Storage

Hydrogen is a promising energy carrier in future energy systems. However, storage of hydrogen is a substantial challenge, especially for applications in vehicles with fuel cells that use proton‐exchange membranes (PEMs). Different methods for hydrogen storage are discussed, including high‐pressure and cryogenic‐liquid storage, adsorptive storage on high‐surface‐area adsorbents, chemical storage in metal hydrides and complex hydrides, and storage in boranes. For the latter chemical solutions, reversible options and hydrolytic release of hydrogen with off‐board regeneration are both possible. Reforming of liquid hydrogen‐containing compounds is also a possible means of hydrogen generation. The advantages and disadvantages of the different systems are compared.     

有机磷酸酯阻燃电解液的研究进展

随着锂离子电池的市场拓展,安全性问题已成为电动汽车、大规模储能等应用领域关注的首要问题. 目前商品化的锂离子电池普遍采用低沸点碳酸酯类电解液,其易燃性成为电池不安全性的主要隐患. 为了提高锂离子电池的本征安全性,阻燃或不燃性电解液成为近年来研究的热点,其中以磷酸酯为溶剂的阻燃型或不燃型电解液受到广泛关注. 本文主要介绍磷酸酯阻燃和不燃电解液的研究状况,分析了这类电解液与锂离子电池正负极的兼容性问题,讨论了改善磷酸酯电解液电化学兼容性的途径,提出了发展高效、安全、稳定的不燃电解液的一些思路.     

Water-in-salt electrolytes for high voltage aqueous electrochemical energy storage devices

If were not by their low electrochemical stability, aqueous electrolytes would be the preferred alternative to be used in electrochemical energy storage devices. Their abundance and nontoxicity are key factors for such application, especially in large scale. The development of highly concentrated aqueous electrolytes, so-called water-in-salt electrolytes, has expanded the electrochemical window of aqueous electrolyte up to 3.0 V (whereas salt-in-water electrolytes normally shows up to 1.6 V), showing that water can be an alternative after all. Many devices, ranging from metal-ion batteries to electrochemical capacitors, have been reported recently, making use of such wider electrochemical stability and enhancing devices energy density. Different salts have also been proposed not only to gain in costs but also to improve physicochemical properties.     

Progress on predicting the electrochemical stability window of electrolytes

The advancement of novel electrical energy storage systems with high energy density encourages the development of electrolytes with wide electrochemical stability windows (ESWs). For the design of electrolytes, atomistic simulations have been used to investigate their electrochemical stability, providing a fast and economical approach for electrolytes screening, in which the simulation models are the key to predicting the electrolyte ESWs. Herein, the completing progress of the simulation models on predicting electrolyte ESWs is overviewed, which ranges in complexity from an isolated molecule/ion model to a solvation model and finally to a complex model of the electrode–electrolyte interface. We highlight the limitation and applicability of these models in detail and advocate a perspective of possible future research on the prediction of the electrolyte ESWs.     

Silica sol–gel chemistry: creating materials and architectures for energy generation and storage

There is widespread recognition that the use of energy in the twenty-first century must be sustainable. Because of its extraordinary flexibility, silica sol–gel chemistry offers the opportunity to create the novel materials and architectures which can lead to significant advances in renewable energy and energy storage technologies. In this paper, we review some of the significant contributions of silica sol–gel chemistry to these fields with particular emphasis on electrolytes and separators where sol–gel approaches to functionalization and encapsulation have been of central importance. Examples are presented in the areas of dye-sensitized solar cells, biofuel cells, proton exchange membrane fuel cells, redox flow batteries and electrochemical energy storage. Original work is also included for the sol–gel encapsulation of a room temperature ionic liquid to create a solid state electrolyte for electrochemical capacitors. In view of the critical importance of energy and the versatility of the sol–gel process, we expect the sol–gel field to play an increasingly important role in the development of sustainable energy generation and storage technologies.     

Crystal Channel Engineering for Rapid Ion Transport: From Nature to Batteries

Ion transport behaviours through cell membranes are commonly identified in biological systems, which are crucial for sustaining life for organisms. Similarly, ion transport is significant for electrochemical ion storage in rechargeable batteries, which has attracted much attention in recent years. Rapid ion transport can be well achieved by crystal channels engineering, such as creating pores or tailoring interlayer spacing down to the nanometre or even sub-nanometre scale. Furthermore, some functional channels, such as ion selective channels and stimulus-responsive channels, are developed for smart ion storage applications. In this review, the typical ion transport phenomena in the biological systems, including ion channels and pumps, are first introduced, and then ion transport mechanisms in solid and liquid crystals are comprehensively reviewed, particularly for the widely studied porous inorganic/organic hybrid crystals and ultrathin inorganic materials. Subsequently, recent progress on the ion transport properties in electrodes and electrolytes is reviewed for rechargeable batteries. Finally, current challenges in the ion transport behaviours in rechargeable batteries are analysed and some potential research approaches, such as bioinspired ultrafast ion transport structures and membranes, are proposed for future studies. It is expected that this review can give a comprehensive understanding on the ion transport mechanisms within crystals and provide some novel design concepts on promoting electrochemical ion storage capability in rechargeable batteries.     

Electric Double‐Layer Capacitor Based on an Ionic Clathrate Hydrate

Herein, we suggest a new approach to an electric double‐layer capacitor (EDLC) that is based on a proton‐conducting ionic clathrate hydrate (ICH). The ice‐like structures of clathrate hydrates, which are comprised of host water molecules and guest ions, make them suitable for applications in EDLC electrolytes, owing to their high proton conductivities and thermal stabilities. The carbon materials in the ICH Me₄NOH ? 5 H₂O show a high specific capacitance, reversible charge–discharge behavior, and a long cycle life. The ionic‐hydrate complex provides the following advantages in comparison with conventional aqueous and polymer electrolytes: 1) The ICH does not cause leakage problems under normal EDLC operating conditions. 2) The hydrate material can be utilized itself, without requiring any pre‐treatments or activation for proton conduction, thus shortening the preparation procedure of the EDLC. 3) The crystallization of the ICH makes it possible to tailor practical EDLC dimensions because of its fluidity as a liquid hydrate. 4) The hydrate solid electrolyte exhibits more‐favorable electrochemical stability than aqueous and polymer electrolytes. Therefore, ICH materials are expected to find practical applications in versatile energy devices that incorporate electrochemical systems.     

Photocatalytic hydrogen production

The efficient storage of solar energy in chemical fuels, such as hydrogen, is essential for the large-scale utilisation of solar energy systems. Recent advances in the photocatalytic production of H(2) are highlighted. Two general approaches for the photocatalytic hydrogen generation by homogeneous catalysts are considered: HX (X = Cl, Br) splitting involving both proton reduction and halide oxidation via an inner-sphere mechanism with a single-component catalyst; and sensitized H(2) production, employing sacrificial electron donors to regenerate the active catalyst. Future directions and challenges in photocatalytic H(2) generation are enumerated.     

新型超级电容器的研发进展

传统超级电容器受低能量密度的限制,在当今器件研发中需更加关注电极材料结构-组成-性能研究。 本文总结了新型赝电容器的发展历程及其研发过程中存在的挑战与解决措施,着重从胶体离子超级电容器电极材料等新型的电极材料和氧化还原电解质两个方面进行综述。 原位合成的胶体离子超级电容器电极材料比非原位合成的电极材料具有更高的反应活性,并且以近似离子的状态存在,有效增加了电极材料的比容量。 氧化还原电解质的使用在不改变电极材料的前提下,进一步提高了超级电容器的能量密度。 初步介绍了新型锂离子电容器。 锂离子电容器同时使用电池型材料和电容型材料,可提高其能量密度。 依据当前超级电容器的研发现状,未来有望将电池材料和电容器材料结合使用,进而形成电池电容器或电容电池,使其同时具有高的能量密度和功率密度。     

Porous Carbon Hosts for Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) are considered to be one of the most promising alternatives to the current lithium-ion batteries (LIBs) to meet the increasing demand for energy storage owing to their high energy density, natural abundance, low cost, and environmental friendliness. Despite great success, LSBs still suffer from several problems, including undermined capacity arising from low utilization of sulfur, unsatisfactory rate performance and poor cycling life owing to the shuttle effect of polysulfides, and poor electrical conductivity of sulfur. Under such circumstances, the design/fabrication of porous carbon–sulfur composite cathodes is regarded as an effective solution to overcome the above problems. In this review, different synthetic methods of porous carbon hosts and their corresponding integration into carbon–sulfur cathodes are summarized. The pore formation mechanism of porous carbon hosts is also addressed. The pore size effect on electrochemical performance is highlighted and compared. The enhanced mechanism of the porous carbon host on the sulfur cathode is systematically reviewed and revealed. Finally, the combination of porous carbon hosts and high-profile solid-state electrolytes is demonstrated, and the challenges to realize large-scale commercial application of porous carbon–sulfur cathodes is discussed and future trends are proposed.     

全固态电池界面的研究进展

Owing to the serious energy crisis and environmental problems caused by fossil energy consumption, development of high-energy-density batteries is becoming increasingly significant to satisfy the rapidly growing social demands. Lithium-ion batteries have received widespread attention because of their high energy densities and environmental friendliness. At present, they are widely used in portable electronic devices and electric vehicles. However, security aspects need to be addressed urgently. Substantial advances in liquid electrolyte-based lithium-ion batteries have become a performance bottleneck in the recent years. Traditional lithium-ion batteries use organic liquids as electrolytes, but the flammability and corrosion of these electrolytes considerably limit their development. Continuous growth of lithium dendrites can pierce the separator, leading to electrolyte leakage and combustion, which is a serious safety hazard. Replacement of organic electrolytes with solid-state electrolytes is one of the promising solutions for the development of next-generation energy storage devices, because they have high energy densities and are safe. Solid electrolytes can remarkably alleviate the safety hazards involved in the use of traditional liquid-based lithium-ion batteries. In addition, the composite of solid-state electrolytes and lithium metal is expected to result in a higher energy density. However, due to the lack of fluidity of the solid electrolytes, problems such as limited solid-solid contact area and increased impedance at the interface when solid-state electrolytes are in contact with electrodes must be solved. The localized and buried interface is a major drawback that restricts the electrochemical performance and practical applications of the solid-state batteries. Fabrication of a stable interface between the electrodes and solid-state electrolyte is the main challenge in the development of solid-state lithium metal batteries. All these aspects are critical to the electrochemical performance and safety of the solid-state batteries. Current research mainly focuses on addressing the problems related to the solid-solid interface in solid-state batteries and improving the electrochemical performance of such batteries. In this review, we comprehensively summarize the challenges in the fabrication of solid-state batteries, including poor chemical and electrochemical compatibilities and mechanical instability. Research progress on the improvement strategies for interface problems and the advanced characterization methods for the interface problems are discussed in detail. Meanwhile, we also propose a prospect for the future development of solid-state batteries to guide the rational designing of next-generation high-energy solid-state batteries. There are many critical problems in solid-state batteries that must be fully understood. With further research, all-solid-state batteries are expected to replace the traditional liquid-based lithium-ion batteries and become an important system for a safe and reliable energy storage.     

Recent progress of composite solid polymer electrolytes for all-solid-state lithium metal batteries

In comparison with lithium-ion batteries (LIBs) with liquid electrolytes, all-solid-state lithium batteries (ASSLBs) have been considered as promising systems for future energy storage due to their safety and high energy density. As the pivotal component used in ASSLBs, composite solid polymer electrolytes (CSPEs), derived from the incorporation of inorganic fillers into solid polymer electrolytes (SPEs), exhibit higher ionic conductivity, better mechanical strength, and superior thermal/electrochemical stability compared to the single-component SPEs, which can significantly promote the electrochemical performance of ASSLBs. Herein, the recent advances of CSPEs applied in ASSLBs are presented. The effects of the category, morphology and concentration of inorganic fillers on the ionic conductivity, mechanical strength, electrochemical window, interfacial stability and possible Li⁺ transfer mechanism of CSPEs will be systematically discussed. Finally, the challenges and perspectives are proposed for the future development of high-performance CSPEs and ASSLBs.     

惰性小分子电催化还原反应的电解液调控

本文概述了惰性小分子电催化还原反应（如二氧化碳还原反应和氮气还原反应）中电解液的组成和作用机制,介绍了相关电解液研究的最新进展,并讨论了电解液调控在揭示反应机理、改善催化性能中的重要作用.     

Ordered porous carbon with tailored pore size for electrochemical hydrogen storage application

Ordered porous carbon with tailored pore size represents an innovative concept in electrochemical hydrogen storage. This work deals with physical characteristics and electrochemical hydrogen storage behavior of the ordered porous carbons with well-tailored pore size, synthesized by a replica technique using hexagonal mesoporous silica as templates. By using a mixture of two surfactants (HTAB and C16EO8) at different ratios, it is possible to control the wall thickness of silica and, consequently, the pore diameter of carbons within a narrow range of 2.1-2.8 nm. In addition, highly developed ultramicroporosity (pore size smaller than 0.7 nm), which plays a predominant role in hydrogen storage, can be produced in the ordered porous carbons. A discharge capacity of up to 527 mAh/g (corresponding to 1.95 wt % hydrogen storage) has been achieved in 6 M KOH for the ordered porous carbon. Furthermore, the ordered porous carbons also possess excellent capacity retainability after charge-discharge cycles and rate capability.     

当前和下一代锂离子电池电解液的原子尺度微观认识和研究进展

电解液及构筑电极电解液界面对于开发和应用高比容量储能系统至关重要。具体来说，电解液的机械（抗压性、粘度）、热（热导率和热容）、化学（溶解性、活度、反应性）、输运和电化学（界面及界面层）等性质，与其所组成的储能器件的性能直接相关。目前，大量的实验研究通过调控电解液的物理和/或化学组成来改善电解液性能，以满足新型电极材料的工作运行。与此同时，理论模拟方法近年来得到了迅速发展，使人们可以从原子尺度来理解电解液在控制离子输运和构筑功能化界面的作用。站在理论模拟研究的前沿上，人们可以利用其所揭示的机理性认识对新型电解液开展理性设计。本文首先总结了传统电解液的组成、溶剂化结构和输运性质以及电极电解液界面层的形成机理，进一步讨论了利用新型电解液设计稳定电极电解液界面层的方法，包括使用电解液添加剂、高浓电解液和固态电解质，并着重讨论了对这些新型电解液体系进行原子尺度模拟的最新进展，为了解和认识电解液提供更为基本的理解，并为未来电解液的设计提供系统的指导。最后，作者对新型电解液的理论筛选进行了展望。     

Cathode Materials for Hybrid Supercapacitors Based on Ozonated Reduced Graphene Oxide

A carbon material capable of reversible electrochemical oxidation and reduction with relatively high electrical conductivity was prepared by ozonation of thermally reduced graphene oxide. The specific discharge energy for such materials used in lithium ion electrochemical cell cathodes with non-aqueous electrolytes (LP-71) can reach 540 W h/kg at 40 mA/g current, while the average specific discharge power is 11.5 kW/kg at 5 A/g current. The specific charge after 2500 charge/discharge cycles at 5 A/g current was at a level of 93% of the initial value. The obtained materials appear promising for the design of new electricity storage systems.