High-density oxygen-enriched graphene hydrogels for symmetric supercapacitors with ultrahigh gravimetric and volumetric performance

The contradiction between the porous structure and density of graphene materials makes it unable to meet the dual requirements of the next generation supercapacitors for gravimetric capacitance and volumetric capacitance. Herein, we successfully synthesized high-density oxygen-enriched graphene hydrogels (HOGHs) by a one-step hydrothermal method using high concentration graphene oxide (GO) solution and trometamol as precursors. The as-prepared HOGHs samples present a dense 3D network structure and moderate specific surface areas, which leads to a high packing density. In addition, the HOGHs samples also contain abundant oxygen-containing functional groups and some nitrogen-containing functional groups. These heteroatomic functional groups can provide pseudocapacitance for the electrode materials. Therefore, the HOGH-140 based symmetric supercapacitor shows ultrahigh gravimetric and volumetric specific capacitance (325.7 F g⁻¹, 377.8 F cm⁻³), excellent rate performance and cycling stability. Simultaneously, the symmetric binder-free supercapacitor exhibits high gravimetric specific energy density (11.3 Wh kg⁻¹) and volumetric specific energy density (13.1 Wh L⁻¹) in 6 M KOH, respectively. These outstanding properties make the material have a good application prospect in the field of compact energy storage devices.     

Electrode and electrolyte materials for electrochemical capacitors

Among different electric energy storage technologies electrochemical capacitors are used for energy storage applications when high power delivery or uptake is needed. Their energy and power densities, durability and efficiency are influenced by electrode and electrolyte materials however due to a high cost/performance ratio; their widespread use in energy storage systems has not been attained yet.Thanks to their properties such as high surface area, controllable pore size, low electrical resistance, good polarizability and inertness; activated carbons derived from polymeric precursors are the most used electrode materials in electrochemical capacitors at present. Other electrode materials such as shaped nano-carbons or metal oxides are also investigated as electrode materials in electrochemical capacitors, but only as useful research tools.Most commercially used electrochemical capacitors employ organic electrolytes when offering concomitant high energy and high power densities. The use of aqueous based electrolytes in electrochemical capacitor applications is mainly limited to research purposes as a result of their narrow operating voltage. Recent studies on room temperature ionic liquids to be employed as electrolyte for electrochemical capacitor applications are focused on fine tuning their physical and transport properties in order to bring the energy density of the device closer to that of batteries without compromising the power densities.In this paper a performance analysis, recent progress and the direction of future developments of various types of materials used in the fabrication of electrodes for electrochemical capacitors are presented. The influence of different types of electrolytes on the performance of electrochemical capacitors such as their output voltage and energy/power densities is also discussed.     

A hybrid PEMFC/supercapacitor device with high energy and power densities based on reduced graphene oxide/Nafion/Pt electrode

Proton exchange membrane fuel cells (PEMFCs) possess high energy and low power densities, while supercapacitors are characterized by high power and low energy densities. A hybrid PEMFC/supercapacitor device (HPSD) with high energy and power densities was proposed and fabricated for the first time using a reduced graphene oxide/Nafion/Pt electrode in this study. The reduced graphene oxide (rGO) was a capacitive material, and Pt was used as the electrocatalyst. Nafion ionomers adsorbed onto the rGO sheets surface and connected the rGO sheets and the electrolyte (Nafion membrane), thus increasing the utilization rate and specific capacitance of rGO. During the half-cell tests, the rGO/Nafion/Pt electrode exhibited better pulse discharge and galvanostatic discharge performance than the conventional Nafion/Pt electrode. Due to the unique synergy of electrochemical reaction current and capacitance current during the discharge process, the HPSD exhibited a higher power density (26.2 kW kg⁻¹) than the PEMFC (23.9 kW kg⁻¹). The energy density (12.7 kWh kg⁻¹) exhibited by HPSD was close to that of the PEMFC (13.5 kWh kg⁻¹). Therefore, the concept of HPSD is to create a new method for developing next-generation electrochemical devices with high energy and power densities.     

The choice of noble electrolyte for symmetric polyurethane-graphene composite supercapacitors

Simple, low cost, highly conducting, flexible, lightweight and porous electrodes are prepared using reduced graphene oxide (rGO) for energy storage device applications. Graphene oxide (GO) slurry is prepared using graphite powder through oxidation followed by solvothermal reduction. A simple dip and dry method to fabricate flexible electrodes by depositing GO on the skeleton of foams is reported. These electrodes are chemically reduced to enhance the conductivity and are used as an electrode material to facilitate large surface area and fast ionic diffusion. The state of the art of present work is all the devices studied under open air condition. The electrochemical studies demonstrate that the constructed supercapacitors exhibit a high specific capacitance of 69 F/g in 1 M NaOH electrolyte at 2 mVs⁻¹ scan rate which is significantly high. Also, the devices showed encouraging performance when constructed with different electrolytes, which helps to understand the electrolytic effect and to choose the best electrolyte for the high performance of supercapacitors.     

Recent progress about graphene for chemical energy storage applications

石墨烯独特的二维空间结构使其具有优异的导电性能,力学性能以及超大的比表面积,被认为是颇具潜力的新型储能材料,是目前储能研究的热点之一.本文综述了石墨烯在储氢,超级电容器,锂离子电池,锂硫电池以及锂-空气电池等化学储能领域中的应用,探讨了不同制备方法对其性能的影响.石墨烯以其特殊的空间结构而成为极具前景的储氢材料,同时与其它材料复合后形成三维导电网络结构而提高电极材料的电化学性能,还可以缓冲电极材料在循环过程中的体积变化,有效提升储能材料的循环寿命.通过优化复合材料的微观结构,将进一步提高其电化学性能.本文最后就石墨烯在储能应用中的关键问题进行了简要分析.     

Calculation on energy densities of lithium ion batteries and metallic lithium ion batteries

锂电池是理论能量密度最高的化学储能体系,估算各类锂电池电芯和单体能达到的能量密度,对于确定锂电池的发展方向和研发目标具有重要的参考价值。本工作根据主要正负极材料的比容量、电压,同时考虑非活性物质集流体、导电添加剂、黏结剂、隔膜、电解液、封装材料占比,计算了不同材料体系组成的锂离子电池和采用金属锂负极、嵌入类化合物正极的金属锂离子电池电芯的预期能量密度,并计算了18650型小型圆柱电池单体的能量密度,为电池发展路线的选择和能量密度所能达到的数值提供参考依据。同时指出,电池能量密度只是电池应用考虑的一个重要指标,面向实际应用,需要兼顾其它技术指标的实现。     

Nanomaterials for on-board solid-state hydrogen storage applications

Hydrogen has the highest gravimetric density (energy density per unit mass) of any fuel. The combustion of hydrogen releases energy in the form of heat. When hydrogen reacts with oxygen in a fuel cell, the reaction releases energy in the form of electricity. Unlike hydrocarbon-based fuels, the generation of energy from either the combustion of hydrogen or the reaction of hydrogen with oxygen in a fuel cell is not accompanied by the emission of greenhouse gases. This makes hydrogen a promising solution to solve global warming issues. However, hydrogen has a low volumetric density (low energy density per unit volume) which makes storing or transporting hydrogen extremely difficult and expensive. To accelerate the utilization of hydrogen as an energy carrier, it is necessary to develop advanced hydrogen storage methods that have the potential to have a higher energy density.The hydrogen storage market is segmented by application into: (1) Stationary power: stored hydrogen is consumed for example in a fuel cell for use in backup power stations, refueling stations, power stations; (2) Portable power: hydrogen storage applications for electronic devices such as mobile phones, flash lights, and portable generators; and (3) Transportation: industries including automobiles, aerospace, unmanned aerial systems, and hydrogen tanks used throughout the hydrogen supply chain. The increasing development of light and heavy fuel cell vehicles is expected to drive the development of on-board solid-state hydrogen technologies.A large number of research groups worldwide for many years have been trying to develop materials having the right set of thermodynamic and kinetic properties, along with all of the physical properties (high gravimetric density, high volumetric density, etc.) to allow for low-pressure storage system in ambient conditions. However, to date, no material has been found that satisfies all the desired properties to be viably used in many applications. Even if we consider only three parameters namely gravimetric density, volumetric density, and system cost, no materials that can meet the ultimate targets of the U.S. Department of Energy (DOE) or the 2030 targets of the European Union's Fuel Cells and Hydrogen Joint Undertaking (FCH JU) and the New Energy and Industrial Technology Development Organization (NEDO) in Japan.The present article reviews advances in solid-state hydrogen storage technology and compares the opportunities and challenges of selected materials. The materials reviewed in this article have a wider spectrum than the materials reviewed in other existing articles, including carbon nanotubes (CNTs), metal–organic frameworks (MOFs), graphene, boron nitride (BN), fullerene, silicon, amorphous manganese hydride molecular sieve, and metal hydrides. Pioneering works, important breakthroughs, as well as the latest developments for promising materials are also reviewed.In addition, for the first time the targets set by several official regulatory agencies for solid-state hydrogen storage are summarized. Achievements in academic and industrial research are compared against these targets.The future prospects of promising materials are analyzed based on how its practical application can be implemented according to market needs.     

Recent progress of electrode materials for room-temperature sodium-ion stationary batteries

随着风能、太阳能等可再生能源的不断发展,储能作为影响其发展的关键技术越来越受到人们的关注。在储能领域,锂离子电池以高能量密度、长循环寿命、高电压等诸多优点在电子领域已得到广泛的应用,并成为未来电动汽车动力电池的最佳选择。但因锂资源储量有限、分布不均匀,而且原材料成本比较高,所以锂离子电池在电网大规模储能方面的应用遇到了瓶颈。与锂相比,钠不但具有与锂相似的物理化学性质,更具有资源丰富、分布广泛、原料成本低廉等优势。近些年室温钠离子电池再次引起了人们的研究兴趣,特别是在电网储能方面表现出极大的应用潜力。虽然目前已报道了多种钠离子电池电极材料,但大都离实用化以及进一步产业化尚有一定的距离。本文重点介绍一些性能较为突出的室温钠离子电池电极材料,并指出要实现钠离子电池的产业化,需要开发空气中稳定、高安全、高容量、高倍率、循环稳定、低成本的新型正、负极材料。     

Emerging 2D-Nanostructured materials for electrochemical and sensing Application-A review

The discovery of novel 2D-monoelemental materials with extraordinary physical, mechanical, thermal, optical and electronic properties has predicted many potential applications in various areas of technology based on the grounds of advanced sciences. The monoelemental two dimensional (2D) materials arouse a tremendous attention in different areas of science due to their unique properties and extensive applications. The 2D nanomaterials like Borophene and Bismuthene have emerged as effective nanomaterials due to their unique properties including large surface area, structural anisotropy, tunable band gap, and high carrier mobility. They are attracting increasing research interest in electronics, optoelectronics, and catalysis and also in energy storage and energy conversion applications. These materials are massively studied under theoretical approaches but many of its physical characteristics have still to be analyzed experimentally. This review article gives a detail theoretical and experimental information about the 2D-nanostructured Borophene and Bismuthene materials including their synthesis techniques, properties and also analyzed their advantages and disadvantages over each other. Further we performed an overview of the status of Borophene and Bismuthene in electrochemical and sensing applications including batteries, sensors, catalysis, and gas storage devices. Furthermore, we present our insight into the challenges, future perspective and opportunities, which would hopefully shed light on the great potential of this ever-expanding field. The nanomaterials like borophene and bismuthene have emerged as effective alternatives to graphene with excellent electrochemical properties finding potential applications in detecting and sensing devices. It is established that Borophene and Bismuthene find a large area of applications in developing conductors for electric and thermal appliances. Borophene has demonstrated incredible flexibility and high structural anisotropy and it is a material massively studied by theoretical approaches. However, many of its physical characteristics have still to be realized experimentally. In this review, we present a brief survey on preparation methods of 2D-nanostructured materials Borophene and Bismuthene. Also, an overview of the applications’ status of Borophene in electrochemical area, batteries, sensors, and catalysis and gas storage devices is covered along with an assessment on 2D-nanostructured Bismuthene being an extremely efficient electrocatalyst. It is described that Bismuthene shows a modest cyclability for Li-ion batteries, Na-ion batteries and K-ion batteries. Bismuthene is typically obtained through a low-cost liquid exfoliation synthesis method, for batteries and other energy conversion devices. In the synthesis of 2D-nanomaterials, the removal of dissolved chemicals from the reaction solutions and improving the device efficiency are still challenging. Herein, electrochemical and sensing applications of 2D-nanostructured materials, along with the advantages and disadvantages are comprehensively reviewed.     

Biomass-derived graphene-based nanocomposite: A facile template for decoration of ultrathin nickel–aluminum layered double hydroxide nanosheets as high-performance supercapacitors

One promising approach to design of high performance supercapacitors is based on the coupling the conductive porous carbon matrixes and the electroactive components. However, the main challenge to this goal is the maintaining the long cycling life, high power and high energy densities of the related capacitors. Herein, we reported on an electroactive composite based on biomass derived 3D graphene coupled with nickel-aluminum layer double hydroxides for manufacturing a cathode material in a supercapacitor. The electrode exhibits a remarkable specific capacitance of 1390 F g⁻¹ at 1 Ag^-1, and ultrahigh rate capability of 60% from 1 to 30 Ag^-1, as well as excellent cycling stability with a capacitance retention of 92% after 5000 cycles. Furthermore, the electrode was used as the positive electrode against a Vulcan XC-72R as the negative electrode to assemble an asymmetric supercapacitor. The asymmetric supercapacitor device exhibited a maximum energy density of 173 Wh kg⁻¹ and power density of 28.8 kW kg⁻¹ as well as excellent cycling stability of 92% after 5000 cycles. The asymmetric supercapacitor could lighted up LED lamps with different colors more than 24 min. The work showed promising performance of further application in electrochemical devices.     

A brief overview of secondary zinc anode development: The key of improving zinc‐based energy storage systems

Electricity will increasingly be produced from sources that are geographically decentralized and/or intermittent in their nature. In consequents, there is an urgent need to increase the storage of energy to guarantee the continuity of energy supply. Rechargeable zinc‐air battery is a promising technology due to the high theoretical energy density and the abundant and environmentally benign materials that are used. In the state of the art, the information about secondary zinc anode for rechargeable zinc‐air batteries is scarce. The main development of the technology has been lately concentrated on the bifunctional air electrodes while the used zinc anode is mainly based on a planar zinc electrode providing low specific energy densities for the full system. This overview compiles the available information in the literature regarding the development and manufacturing of zinc anodes for electrical rechargeable batteries applications, where secondary porous zinc electrodes are generally desired. In this context, the zinc‐based anode electrode composition (namely, active material, binder, conductive material, current collector, and additives), pretreatments, and processing techniques are described and their impact on the zinc anode performance analyzed.     

Graphene‐based ternary composites for supercapacitors

The research on electrode materials for supercapacitor application continues to evolve as the request of high‐energy storage system has increased globally due to the demand for energy consumption. Over the past decades, various types of carbon‐based materials have been employed as electrode materials for high‐performance supercapacitor application. Among them, graphene is 1 of the most widely used carbon‐based materials due to its excellent properties including high surface area and excellent conductivity. To exploit more of its interesting properties, graphene is tailored to produce graphene oxide and reduced graphene oxide to improve the dispersibility in water and easy to be incorporated with other materials to form binary composites or even ternary composites. Nowadays, ternary composites have attracted enormous interest as 2 materials (binary composites) cannot satisfy the requirement of the high‐performance supercapacitor. Thus, many approaches have been employed to fabricate ternary composites by combining 3 different types of electroactive materials for high‐performance supercapacitor application. This review focuses on the supercapacitive performance of graphene‐based ternary composites with different types of active materials, ie, conducting polymers, metal oxide, and other carbon‐based materials.     

Recent advances on graphene-based materials as cathode materials in lithium-sulfur batteries

Representing one of the advanced energy storage devices, lithium-sulfur batteries have a wide range of possible applications. While it serves as a promising energy storage system, it should adhere to multiple important criteria before a large-scale application can be realized. The novel uses of graphene can resolve the deficiencies of lithium-sulfur batteries. Graphene is an exceptional conductive material with excellent mechanical stability and is extremely flexible. Because of its large porosity value, it enables a high sulfur loading within its matrix and effectively encapsulates polysulfide. Graphene oxide, on the other hand, often exhibits a number of functional groups capable of chemically bonding to polysulfides, resulting in good capability for polysulfide entrapping. Physical containment of sulfur by graphene materials and its chemical interactions with sulfur can be further improved by designing 3D graphene-sulfur configurations through doping of functional groups or heteroatoms. This review article offers an insight into the strategies for achieving a high sulfur loading cathode with a long cycle life and high retention potential through sulfur containment and carbon host functionalization, for which this review focuses on the functionalization of graphene. Throughout these strategies, significant performance improvements can be achieved.     

Synthesis of PEDOT-modified graphene composite materials as flexible electrodes for energy storage and conversion applications

In this study, poly(3,4-ethylenedioxythiophene) (PEDOT)-modified graphene composite materials have been shown to exhibit excellent energy storage and conversion properties. Flexible, conducting and porous carbon cloth (CC) and graphene paper (GP)-modified CC (GP/CC) were used as substrates for comparison in all experiments. PEDOT was electrodeposited on these substrates, and their capacitance properties were measured for supercapacitor applications. Furthermore, the adsorption of size-selected Pt colloidal nanoparticles has also been performed using two substrates to form the electrode materials for fuel cell applications. We found that the PEDOT/GP/CC is the excellent flexible electrode material for both supercapacitors and fuel cells.     

Progress in carbon fibers based flexible electrodes for supercapacitors

目前，环境友好的清洁能源的开发和设计是能源领域的研究重点。超级电容器是一种新型的储能器件，具有快速充放电的特点，在储能领域有很好的应用潜力。但是能量密度的不足，在一定程度上限制超级电容器的发展。另一方面，柔性电子器件的兴起要求储能器件必须也具备柔性的特质。因此，如何开发一个高能量密度，又同时保有高功率密度、长循环寿命特性的柔性超级电容器是研究人员致力解决的问题。目前常用的方法是将具有高理论比电容的赝电容材料和碳纤维柔性基底结合。本文结合本课题组在碳纤维基柔性超级电容器方面的探索，简单介绍超级电容器的存储机理和系统分类，综述了碳纤维基柔性超级电容器的研究情况和相应的柔性电极的制备方法。最后，讨论了碳纤维基柔性超级电容器在实际应用中的相关前景和挑战。     

Recent developments in Li-ion prismatic cells

The development of new materials is required to improve the energy density of Li-ion batteries. A new graphite type with optimised physical–chemical characteristics has been studied and developed to improve negative electrode performance. Lithium ion charge and discharge acceptance have been improved by the enhanced intrinsic properties of the material. The new material has higher efficiency electrode porosity/tortuosity, and increases electrical conductivity. This allows better charge performance at low temperatures and discharge performance at high rates.Combined with an optimised electrolyte composition, it also gives low and reproducible fading, good discharge performance in very low temperature conditions, and long term storage at high temperatures.Due to this and other design modifications that will be discussed, a 22% improvement in energy density is obtained in the new generation of Saft Li-ion medium prismatic cells (MP).     

Enhanced volumetric hydrogen density in sodium alanate by compaction

Powder compaction is a potential process for the enhancement of the volumetric and gravimetric capacities of hydrogen storage systems based on metal hydrides. This paper presents the hydrogen absorption and desorption behaviour of compacts of sodium alanate material prepared under different levels of compaction pressure. It is shown that even at high compaction levels and low initial porosities, hydrogen absorption and desorption kinetics can proceed comparatively fast in compacted material. Furthermore, experimental hydrogen weight capacities of compacted material are higher than the experimental values obtained in case of loose powder. It is demonstrated that the kinetic behaviour of the compacted material during cycling is directly associated to the volumetric expansion of the compact, which is quantitatively measured and analyzed during both hydrogen absorption and desorption processes. The cycling behaviour and dimensional changes of compacted sodium alanate material are a key consideration point if it is used as hydrogen storage materials in practical tank systems.     

Construction and preparation of nitrogen-doped porous carbon material based on waste biomass for lithium-ion batteries

Biomass derived carbon materials have been widely studied as electrodes in energy storage devices due to their renewable nature, low-cost and tunable physical/chemical properties. However, the influences of different treatments for biomass derived carbon materials are still lack of in-depth discussion. In this work, we investigate the effects of the treatment for biomass on the structure and composition of the resulted carbon materials. Especially, the optimal N-doped porous carbon (NPCCS), which was fabricated by H₂SO₄-assisted hydrothermal treatment and subsequent pyrolysis process using corn silk as raw material, shows a unique interconnected layered nanostructure with ultra-high nitrogen content (18.79 at%). As a result, the NPCCS electrode displays excellent cycling stability and outstanding rate performance in lithium-ion half-cell test and shows high first reversible specific capacity of 523.6 mAh g^?1 in full-cell test. This work provides some guidance for preparing biomass derived carbon materials with superior electrochemical performance for the applications in advanced energy storage devices.     

Research progress of metal oxides as anode materials for lithium ion capacitors

锂离子电容器是一种介于超级电容器和锂离子电池之间的新型储能器件,具有高能量密度、高功率密度以及长循环寿命等优点,在电动汽车、轨道交通、智能电网、可移动电子设备等领域具有非常广泛的应用前景。金属氧化物具有脱/嵌锂能力优异,理论比容量普遍较高,而且自然资源丰富、环境友好的优点,是一类理想的锂离子电容器负极材料,但电子导电率不高,脱/嵌锂过程中不可逆体积畸变较大,影响了其商业化的应用。本文综述了金属氧化物负极材料的制备方法,并分析了其作为锂离子电容器负极材料的电化学性能与优缺点,最后展望了金属氧化物负极材料未来的发展方向。