The synthesis and performance analysis of various biomass-based carbon materials for electric double-layer capacitors: A review

Biomass is one of the most promising clean energy sources. The porous carbon materials prepared by biomass as electrode materials of electric double-layer capacitors (EDLCs) are easily available at a low price, which would greatly reduce the cost of the production. However, carbon materials made with biomass generally have many disadvantages such as low specific surface area (SSA), poor pore size structure, and difficulty to control the pore diameter, which results in the poor EDLC performance. In this paper, the prime purpose is to expose the recent progress of biomass carbon in the fields of electrode materials of EDLC. The review provides a comprehensive literature review that is focused on EDLC electrodes derived from biochar of the evidence of 181 publications published over a period of 30 years from 1989 to 2019. Various carbon materials derived from different biomass for electrode of EDLC are discussed. The most promising methods for the preparation of several biomass carbons are described in detail. Some factors such as SSA, pore size structure, surface functional groups, and electrolyte are further analyzed to discuss the effects on the electrochemical performance of the EDLC. Notably, current deficiencies and possible solutions of preparation methods of biomass carbon as electrode materials are outlined. And the future research trends in this field are prospected.     

Biomass carbon & its prospects in electrochemical energy systems

Activated carbon has now become a vital active material in multifarious applications such as catalytic supports, removal of pollutants, battery electrodes, capacitors, gas storage etc., and these applications require carbon powders with desirable functionalities like surface area, chemical constituents and pore structure. Hence the production of activated carbon materials, especially from cheap and natural bio-precursors (biomass) is a highly attractive research theme in today's science of advanced materials. Though abundant and detailed reports on activated carbons for these applications are available in the literature, creating a consolidated account on the biomass derived activated carbon would serve as a database for the researchers and thus appears justified. Hence an overview on activated carbons (preparation, physical and electrochemical properties) derived especially from biomass for the specific application as electrodes in electrochemical energy devices has been presented to stress the importance of biomass, bioenergy and conversion of wastes into energy concept further. It is certain from the survey of around 100 recent published articles that the biomass carbons have outstanding capability of being applied as electrodes in the energy devices. Particularly, carbon (unactivated) derived from pyrolized peanut shells exhibited a maximum specific capacity of 4765 mAhg⁻¹ in the case of lithium-ion batteries and coconut shell derived carbon in KOH electrolyte gave capacitance of 368 Fg⁻¹ and ZnCl₂ activated carbon from waste coffee grounds exhibited 368 Fg⁻¹ in H₂SO₄. Undoubtedly the study indicates that the biomass derived carbons have economic and commercial promise in the near future.     

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.     

N,P, S co-doped biomass-derived hierarchical porous carbon through simple phosphoric acid-assisted activation for high-performance electrochemical energy storage

Porous carbon materials are the most widely used electrode materials in Electric Double Layer Supercapacitor (EDLS). Optimize specific surface area, improving hierarchical pores structure, and doping heteroatoms are all important methods to improve the capacitance performance of electrodes. Herein, we synthesize walnut shell-derived hierarchical porous carbon (WSPC) with cost-effective and well-developed pore for electrochemical energy storage via simple phosphoric acid-assisted activation method. The final porous carbon products have perfect microporous structure, abundant heteroatom functional groups (the atomic content ratio of nitrogen, phosphorus and sulfur reaches 10.3%), and high specific surface area and pore volume (up to 2583 m² g^?1 and 1.236 cm³ g^?1, respectively). In the three-system, the electrode shows an optimal specific capacitance of up to 332 F g^?1 and excellent rate performance. In the symmetric system, the symmetric device WSPC//WSPC shows a maximum gravimetric specific energy of ~14.08 Wh kg^?1. And the device still has a specific energy of 9.75 Wh kg^?1 even under the high gravimetric specific power of 7 kW kg^?1. In addition, the device has excellent cycle stability and retains an initial specific capacitance of 90.2% after 8000 galvanostatic charge-discharge (GCD) cycle. In summary, these outstanding results suggest the biomass derived porous carbon possessing the potential and will show great commercial value for the fabrication of high performance supercapacitors.     

生物炭应用于超级电容器电极的研究进展

生物质资源储量丰富,可通过热化学等方法转化制备性能优良的生物炭.生物炭材料具有较大的比表面积、较高的孔隙率、丰富多样的孔道结构以及优良的导电率,将其作为超级电容器电极材料有利于提高双电层超级电容器的电化学性能,应用前景良好.通过介绍两种超级电容器工作原理,总结了生物炭作为电极材料的制备和改性方法,论述了生物炭的比表面积...     

Green synthesis of molybdenum-based nanoparticles and their applications in energy conversion and storage: A review

In the scope of the rapid technological advancements, nanoparticles (NPs) have gained prominence due to their excellent and tunable biological, and physicochemical properties. Nowadays, different methods are used for their synthesis. In particular, the green synthesis of metal precursors for the synthesis of NPs, represents a cost-effective, environmentally friendly, and hazardous chemical-free method for developing a large variety of NPs. By exploiting plant extracts, the production rate of NPs is relatively faster. Due to fossil reserves and high fuel consumption, renewable and clean energy materials are urgently needed to improve environmental sustainability. With outstanding electrochemical and physicochemical characteristics, molybdenum-based NPs (Mo-NPs) are gaining increasing attention in the fields of energy conversion and storage. Considering the significance of Mo-NPs synthesized from greener routes and their energy applications, it is necessary to review recent trends and developments in this field. This review summarizes important research studies and future research guidelines for the preparation of Mo-NPs through green routes and their applications to meet global energy and environmental demands. Moreover, future research directions are also highlighted to achieve sustainable greener precursors and Mo-NPs based energy storage devices.     

Degradation of biomass components to prepare porous carbon for exceptional hydrogen storage capacity

Porous carbon has been constructed in various strategies for hydrogen storage. In this work, a simple-effective strategy was proposed to transform sustainable biomass into porous carbon by degrade partial lignin and hemicellulose with Na₂SO₃ and NaOH aqueous mixture. This method collapses the biomass structure to provide more active sites, and also avoid the generation and accumulation of non-porous carbon nanosheets. As a result, the as-prepared sample possesses high specific surface area (2849 m² g^?1) and large pore volume (1.08 cm³ g^?1) concentrating almost completely on micropore. Benefit to these characteristics, the as-prepared sample exhibits appealing hydrogen storage capacity of 3.01 wt% at 77 K, 1 bar and 0.85 wt% at 298 K, 50 bar. The isosteric heat of hydrogen adsorption is as high as 8.0 kJ mol^?1, which is superior to the most biochars. This strategy is of great significance to the conversion of biomass and the preparation of high-performance hydrogen storage materials.     

核壳结构材料的制备及其应用

核壳材料可以通过不同的包覆技术进行制备,其在许多方面的性能优于普通材料。包覆技术可以对内核微粒表面性质进行剪裁,如改变内核表面电荷、官能团和反应特性等,从而提高内核的分散性与稳定性。同时,核壳材料还具有组成种类多、形貌多样、组分间具有协同效应等特点,已被广泛用于生物质能利用催化剂、新型储能材料、光电材料等新能源领域。本文综述了多种核壳材料的制备方法,总结了核壳结构材料的发展现状,归纳了应用过程中存在的问题,并对核壳结构材料的进一步研究方向——向着微观操纵方向发展和达到性能可控的目的进行了展望。     

Carbon nanotubes: A potential material for energy conversion and storage

Carbon nanotube-based materials are gaining considerable attention as novel materials for renewable energy conversion and storage. The novel optoelectronic properties of CNTs (e.g., exceptionally high surface area, thermal conductivity, electron mobility, and mechanical strength) can be advantageous for applications toward energy conversion and storage. Although many nanomaterials are well known for the unique structure-property relations, such relations have been sought most intensively from CNTs due to their extreme diversity and richness in structures. For the development of energy-related devices (like photovoltaic cells, supercapacitors, and lithium ion batteries), it is critical to conduct pre-evaluation of their design, operation, and performance in terms of cost, life time, performance, and environmental impact. This critical review was organized to address the recent developments in the use of CNT-based materials as working/counter electrodes and electrolytes in photovoltaic devices and as building blocks in next-generation flexible energy storage devices. The most promising research in the applications of CNTs toward energy conversion and storage is highlighted based on both computational and experimental studies along with the challenges for developing breakthrough products.     

Photo-Isomerization Energy Storage Using Azobenzene and Nanoscale Templates: A Topical Review

Azobenzene(AZO) has attached tremendous attention in the field of photo-isomerization energy storage due to its advantages of absorbing light in ultraviolet-visible range and reversible isomerization. However, the issues of low energy density and short half-lifetime restrict the further development of AZO. Therefore, a method, by preparing hybrid photo-isomerization energy storage materials using nanoscale templates, was proposed to handle the above two issues. In this paper, a summary of hybrid photo-isomerization energy storage materials with AZO and nanoscale templates is conducted from the aspects of templates, preparation methods, derivatives and applications. The performances of template candidates, i.e. carbon nanotubes(CNTs) and graphene(GO) are reviewed and compared based on the analysis of grafting density, energy density, and half-lifetime of hybrid materials. Then, two major preparation methods of AZO hybrid materials including non-covalent and covalent functionalizations are discussed. Furthermore, the studies on AZO derivatives functionalized on nanoscale templates are summarized to further point to the direction of derivatization towards high performance AZO-functionalized materials. Finally, due to the superiority of AZO hybrid solid-state films in large-scale utilization, their current applications are reviewed to find out some promising applications.     

生物质基掺氮多孔炭材料研究进展*

掺氮多孔炭材料因其发达的孔结构、丰富的官能团以及良好的稳定性等特点,应用广泛。生物质来源广且价格低廉,以其为原料制备掺氮多孔炭材料是当前研究的热点。针对不同生物质制备生物基掺氮多孔炭材料的工艺及关键影响因素进行综述,分析了氮的赋存形态及形成机理,介绍了其在储能、催化、吸附等领域的应用,并对未来的研究方向进行了展望。     

Hydrogen storage ability of porous carbon material fabricated from coffee bean wastes

The hydrogen storage ability at 298 and 77 K of porous carbon materials with microporous structures fabricated from coffee bean wastes through KOH activation was investigated regarding pore structure. The dependence of hydrogen storage ability on the pore structure of porous carbon materials was investigated at 298 and 77 K to clarify the storage mechanism of carbon materials. Hydrogen storage ability at 298 K was increased linearly with increasing of specific surface area increasing. The maximum amount of stored hydrogen was 0.6 wt.% on porous carbon material with 2070 m²/g specific surface area. The hydrogen storage ability at 77 K was 4.0 wt.% on the same sample. The hydrogen storage ability showed a linear relationship with the micro-pore volume size. These changes in the dependence of the hydrogen storage ability on pore size suggested that the storage configuration changed from two- to three-dimensional. The stored hydrogen densities in porous carbon materials calculated from these values were 5.7 and 69.6 mg/cm³ at 298 and 77 K, respectively. The change in density indicated that the state of stored hydrogen in porous carbon materials was filled up aggregational state, which is extremely close to the liquid state, and suggested the realizing of high hydrogen storage ability on carbon materials fabricated from agricultural waste.     

Nitrogen-doped hierarchically porous carbon obtained via single step method for high performance supercapacitors

In the present work, nitrogen doped hierarchically activated porous carbon (APC) samples have been synthesized via single step scalable method using ethylene di-amine tetra acetic acid (EDTA) as precursor and KOH as activating agent. Activated porous carbons with different pore sizes have been developed by varying the activation temperature. SEM, TEM and SAXS analysis suggest that with variation of activation temperature, a hierarchical porous structure with interconnected meso-pore and micro pores has been achieved. The sufficiently high surface area of the synthesized materials provides active sites to enhance the diffusion of ions between the electrolyte and the carbon electrodes. The electrode prepared at 800 °C activated sample exhibited highest specific capacitance of 274 Fg^-1 in two electrode setup, at a current density of 0.1 Ag^-1 in 1 M aqueous H₂SO₄. Along with this, it showed maximum energy density of 9.5 Whkg^?1 at a power density of 64.5 Wkg^-1. The remarkable electrochemical performance reveals that the synthesized nitrogen doped activated carbon electrodes derived from EDTA can be tuned to have optimum pore structure and pore size distribution for better electrochemical performance, so it can be considered as a potential electrode material for applications in electrochemical energy storage.     

Nitrogen-doped porous carbons derived from sustainable biomass via a facile post-treatment nitrogen doping strategy: Efficient CO2 capture and DRM

Nitrogen (N)-doped carbon materials have become promising candidates for many applications. In this paper, the biomass activated carbon (BC) was obtained by carbonization and activation of soybean meal. Using soybean meal as the precursor, potassium hydroxide (KOH) as the activator and melamine as the nitrogen source, a series of N-doped porous biomass carbons (H-NC-X) with different N contents were achieved via a facile post-treatment nitrogen doping strategy. Then these samples were used as a catalyst for dry reforming of methane (DRM) reaction and an adsorbent for CO₂ capture. Among all the investigated samples, BC has the largest specific surface area and the best pore structure characteristics, showing the best CO₂ adsorption capacity. However, when BC was used as a catalyst for DRM reaction, it showed the worst catalytic performance. After nitrogen doping treatment, the CO₂ adsorption capacity of the prepared N-doped biomass porous carbon decreased gradually with the increase of the introduced N content. This is mainly due to the destruction of the microporous structure of porous carbon by post-processing nitrogen doping. In contrast, when nitrogen-doped porous carbon was used as the reforming catalyst, the catalytic activity increased with the increase of the introduced N content. The order was: H-NC-30>H-NC-20>H-NC-10. This indicates that when nitrogen-doped porous carbon was used as an adsorbent, the pore structure plays a major role; while when it was used as a reforming catalyst, nitrogen functional groups are the major active sites. This study provides a promising N-doped carbon material for effect CO₂ adsorption and DRM reactions.     

Three-dimensional nitrogen rich bubbled porous carbon sponge for supercapacitor & pressure sensing applications

Three-dimensional (3D) porous carbonaceous materials offer numerous merits such as light-weight, high surface area, flexibility, and thus hold immense potential in energy storage applications. In this work, we report preparation of nitrogen-rich free-standing compressible porous neuron-like carbon sponge using commercially available kitchen sponge by a facile, cost-effective, and scalable synthetic strategy. The unique neuron-like bubbled interconnected carbon structure with enhanced N/O functionalities improves the electrochemical performance by providing sufficient space for ion transport and large accessible surface-active sites. This material also delivers high current response under compressive stress acting as a pressure sensor. This bubbled carbon material achieves an improved specific capacitance of 268.5 F g⁻¹ at 0.5 A g⁻¹. As a self-supporting electrode in a symmetrical supercapacitor cell, it still delivers a good specific capacitance of 167 F g⁻¹ at 0.35 A g⁻¹, retaining 92.5% of capacitance over 7000 charge/discharge cycles. Furthermore, the device delivers a maximum energy density of 14.8 Wh Kg⁻¹, demonstrating its immense potential for multi-functional applications owing to its unique features.     

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.     

Experimental investigation of a new thermal energy storage system using thermo‐sensitive magnetic fluid and porous medium

In this paper, a novel thermal energy storage (TES) system based on a thermo‐sensitive magnetic fluid (MF) in a porous medium is proposed to store low‐temperature thermal energy. In order to have a better understanding about the fluid flow and heat‐transfer mechanism in the TES system, four different configurations, using ferrofluid as the basic fluid and either copper foam or porous carbon with different porosity (90 and 100 PPI, respectively) as the packed bed, are investigated experimentally. Furthermore, two thermal performance parameters are evaluated during the heat charging cycle, which are thermal storage velocity and thermal storage capacity of the materials under a range of magnetic field strength. It is shown that heat conduction is the primary heat‐transfer mechanism in copper foam TES system, while magnetic thermal convection of the magnetic fluid is the dominating heat‐transfer mechanism in the porous carbon TES. In practical applications in small‐scale systems, the 90‐PPI copper foam should be selected among the four porous materials because of its cost efficiency, while porous carbon should be used in industrial scale systems because of its sensitivity to magnetic field and cost efficiency.     

Transformation of biomass into carbon nanofiber for supercapacitor application – A review

This paper starts with a review on challenges and need of improved supercapacitor application, which is then followed by advantages of biomass compared with other materials for use in supercapacitor application. The conversion of biomass into carbon nanofiber using different techniques was extensively reviewed for its advantages and limitations. It was revealed that the materials currently used are yet to be fully sustainable or feasible for energy storage application. In contrast, biomass represents a widely available and sustainable material to be converted into carbon nanofiber for energy storage application. Different techniques were employed for carbon nanofiber production to achieve different objectives, comprising high product yield, feasible diameter adjustment, low electric consumption, and shorter production time. Nevertheless, it was revealed that many key properties of the biomass-derived carbon nanofiber have yet to be fully investigated, as there are still knowledge gaps to be filled for each technique. Thus, more studies are needed to broaden the existing understanding in the key parameters of different techniques in order to develop a highly desirable carbon nanofiber from biomass for sustainable energy storage application.     

Recent progress in the application of carbon materials to supercapacitors and lead-carbon batteries

新型炭材料是电化学储能领域中非常重要的一类储能材料,目前广泛应用于各种电化学储能器件.本文综述了具有电容特性的高比表面积炭材料在超级电容器与铅炭电池中的应用.采用不同的方法合成具有高比表面积的新型炭材料作为超级电容器电极材料,能够得到较高的比容量.适量高比表面积的炭材料应用于铅酸电池负极,形成铅炭电池,极大地提高了电池的储能特性.论文最后探讨了新型炭材料在超电容以及铅炭电池中应用的发展方向.     

Metal-organic frameworks as highly efficient electrodes for long cycling stability supercapacitors

Among a large variety of energy storage technologies, supercapacitors possess special advantages such as rapid charge/discharge, high power density, safety, and environmental friendliness to meet the requirement of specific applications. The common electrode materials of supercapacitors, including porous carbon, conductive polymers, and metal oxides/hydroxides, have their own benefits and drawbacks in energy density and stability. Owing to the big surface area and controllable porosity, the metal-organic frameworks (MOFs) have been explored as important candidates for supercapacitor applications. This mini-review focuses on the recent advances of MOF-based materials including pristine MOFs, MOFs composite materials, and MOF-derived materials in the development of long cycling life supercapacitors. The devices discussed here mean those with capacitive retention rates of more than 90% after 10,000 cycles and high energy density. In addition, we also describe the fundamental knowledge of supercapacitors, highlight the stabilization mechanism of MOFs, and propose the strategies to enhance the stability of MOF-based supercapacitor electrodes.