3D石墨烯基气凝胶的制备及在超级电容器中的应用

超级电容器作为一种新型的能源存储装置,由于其较高的功率密度、优良的充放电特性、超长的循环寿命,使其在移动电源,新能源汽车等众多领域具有非常广泛的应用前景.3D石墨烯基气凝胶具有多孔结构、大的比表面积、高的导电率、优异的机械性能和电子传输能力,它一直被认为是超级电容器的理想电极材料.本文综述了3D石墨烯基气凝胶的制备方法...     

A Simple Route to Produce Highly Efficient Porous Carbons Recycled from Tea Waste for High-Performance Symmetric Supercapacitor Electrodes

High-performance porous carbons derived from tea waste were prepared by hydrothermal treatment, combined together with KOH activation. The heat-treatment-processed materials possess an abundant hierarchical structure, with a large specific surface of 2235 m² g⁻¹ and wetting-complemental hydrophilicity for electrolytes. In a two-electrode system, the porous carbon electrodes’ built-in supercapacitor exhibited a high specific capacitance of 256 F g⁻¹ at 0.05 A g⁻¹, an excellent capacitance retention of 95.4% after 10,000 cycles, and a low leakage current of 0.014 mA. In our work, the collective results present that the precursor crafted from the tea waste can be a promising strategy to prepare valuable electrodes for high-performance supercapacitors, which offers a practical strategy to recycle biowastes into manufactured materials in energy storage applications.     

有机-无机复合气凝胶研究进展

气凝胶具有低密度、低热导率、高比表面积及高孔隙率等优异性能,在隔热、传感、催化、吸附、储能等领域显示出良好的应用前景。但气凝胶的多孔网络结构也造成了其强度低和韧性差等问题,严重制约了气凝胶的实际应用,有机-无机复合是一种增强气凝胶力学性能的有效方法。而且,采用有机-无机复合方法制备气凝胶还可以赋予气凝胶阻燃等其他新颖的性能。本文综述了有机-无机复合气凝胶的新研究进展,分析其原理、合成方法及相关性能,指出了有机无机复合气凝胶的优势和存在问题并展望了未来的发展方向。     

Fabrication of Cobaltosic Oxide Nanoparticle-Doped 3 D MXene/Graphene Hybrid Porous Aerogels for All-Solid-State Supercapacitors

MXenes are a new family of 2 D transition metal carbides and nitrides, which have attracted enormous attention in electrochemical energy storage, sensing technology, and catalysis owing to their good conductivity, high specific surface area, and excellent electrochemical properties. In this work, a series of Co₃O₄-doped 3 D MXene/RGO hybrid porous aerogels is designed and prepared through a facile in situ reduction and thermal annealing process, in which the reduced graphene oxide (RGO) conductive network can electrically link the separated Co₃O₄-MXene composite nanosheets, leading to enhanced electronic conductivity. It is found that upon using the Co₃O₄-MXene/RGO hybrid porous aerogel prepared with a mass ratio of Co₃O₄-MXene/RGO of 3:1 (CMR31) as an electrode for a supercapacitor, a superior specific capacitance of 345 F g⁻¹ at the current density of 1 A g⁻¹ is achieved, which is significantly higher than those of Ti₃C₂T_x MXene, RGO, and MXene/RGO electrodes. In addition, a high capacitance retention (85 % of the initial capacitance after 10 000 cycles at a high current density of 3 A g⁻¹) and a low internal resistance R_s (0.44 Ω) can be achieved. An all-solid-state asymmetric supercapacitor (ASC) device is assembled using CMR31, and it has the ability to light up a blue LED indicator for 5 min if four ASCs are connected in series. Therefore, these novel Co₃O₄-MXene/RGO hybrid porous aerogels have potential practical applications in high-energy storage devices.     

N-doped honeycomb-like porous carbon towards high-performance supercapacitor

Biomass-derived porous carbon with developed pore structure is critical to achieving high performance electrode materials. In this work, we report a grape-based honeycomb-like porous carbon (GHPC) prepared by KOH activation and carbonization, followed by N-doping (NGHPC). The obtained NGHPC exhibits a unique honeycomb-like structure with hierarchically interconnected micro/mesopores, and high specific surface area of 1268 m²/g. As a supercapacitor electrode, the NGPHC electrode exhibits a remarkable specific capacitance of 275 F/g at 0.5 A/g in a three-electrode cell. Moreover, the NGHPC//NGHPC symmetric supercapacitor displays a high energy density of 12.6 Wh/kg, and excellent cycling stability of approximately 95.2% capacitance retention after 5000 cycles at 5 A/g. The excellent electrochemical performance of NGHPC is ascribed to its high specific surface area, honeycomb-like structure and high-content of pyrodinic-N (36.29%). It is believed that grape-based carbon materials show great potential as advanced electrode materials for supercapacitors.     

Zinc-Guided 3D Graphene for Thermally Chargeable Supercapacitors to Harvest Low-Grade Heat

Low-grade heat energy recycling is the key technology of waste-heat utilization, which needs to be improved. Here, we use a zinc-assisted solid-state pyrolysis route to prepare zinc-guided 3D graphene (ZnG), a 3D porous graphene with the interconnected structure. The obtained ZnG, with a high specific surface area of 1817 m²·g⁻¹ and abundant micropores and mesopores, gives a specific capacitance of 139 F·g⁻¹ in a neutral electrolyte when used as electrode material for supercapacitors. At a high current density of 8 A·g⁻¹, the capacitance retention is 93% after 10,000 cycles. When ZnG is used for thermally chargeable supercapacitors, the thermoelectric conversion of the low-grade heat energy is successfully realized. This work thus provides a demonstration for low-grade heat energy conversion.     

Activated carbon felts with exfoliated graphene nanosheets for flexible all-solid-state supercapacitors

Porous activated carbon felts (ACFs) with exfoliated graphene nanosheets were prepared by a simple thermal treatment strategy. They exhibit high gravimetric and areal specific capacitances as well as long-term cycling stability. Impressively, the all-solid-state supercapacitors based on ACFs electrodes deliver stable electrochemical performance even under different bending states.     

Hierarchical Mn3O4 Anchored on 3D Graphene Aerogels via C−O−Mn Linkage with Superior Electrochemical Performance for Flexible Asymmetric Supercapacitor

Flexible asymmetric supercapacitors are more appealing in flexible electronics because of high power density, wide cell voltage, and higher energy density than symmetric supercapacitors in aqueous electrolyte. In virtues of excellent conductivity, rich porous structure and interconnected honeycomb structure, three dimensional graphene aerogels show great potential as electrode in asymmetric supercapacitors. However, graphene aerogels are rarely used in flexible asymmetric supercapacitors because of easily re-stacking of graphene sheets, resulting in low electrochemical activity. Herein, flower-like hierarchical Mn₃O₄ and carbon nanohorns are incorporated into three dimensional graphene aerogels to restrain the stack of graphene sheets, and are applied as the positive and negative electrode for asymmetric supercapacitors devices, respectively. Besides, a strong chemical coupling between Mn₃O₄ and graphene via the C-O-Mn linkage is constructed and can provide a good electron-transport pathway during cycles. Consequently, the asymmetric supercapacitor device shows high rate cycle stability (87.8 % after 5000 cycles) and achieves a high energy density of 17.4 μWh cm⁻² with power density of 14.1 mW cm⁻² (156.7 mW cm⁻³) at 1.4 V.     

Mesoporous Nickel Oxide Nanowires: Hydrothermal Synthesis,Characterisation and Applications for Lithium‐Ion Batteries and Supercapacitors with Superior Performance

Mesoporous nickel oxide nanowires were synthesized by a hydrothermal reaction and subsequent annealing at 400 °C. The porous one‐dimensional nanostructures were analysed by field‐emission SEM, high‐resolution TEM and N₂ adsorption/desorption isotherm measurements. When applied as the anode material in lithium‐ion batteries, the as‐prepared mesoporous nickel oxide nanowires demonstrated outstanding electrochemical performance with high lithium storage capacity, satisfactory cyclability and an excellent rate capacity. They also exhibited a high specific capacitance of 348 F g^?1 as electrodes in supercapacitors.     

Flexible Polyester Cellulose Paper Supercapacitor with a Gel Electrolyte

A low-cost polyester cellulose paper has been used as a substrate for a flexible supercapacitor device that contains aqueous carbon nanotube ink as the electrodes and a polyvinyl alcohol (PVA)-based gel as the electrolyte. Gel electrolytes have attracted much interest due to their solvent-holding capacity and good film-forming capability. The electrodes are characterized for their conductivity and morphology. Because of its high conductivity, the conductive paper is studied in supercapacitor applications as active electrodes and as separators after coating with polyvinylidene fluoride. Carbon nanotubes deposited on porous paper are more accessible to ions in the electrolyte than those on flat substrates, which results in higher power density. A simple fabrication process is achieved and paper supercapacitors are tested for their performance in both aqueous and PVA gel electrolytes by using galvanostatic and cyclic voltammetry methods. A high specific capacitance of 270 F g⁻¹ and an energy density value of 37 W h kg⁻¹ are achieved for devices with PVA gel electrolytes. Furthermore, this device can maintain excellent specific capacitance even under high currents. This is also confirmed by another counter experiment with aqueous sulfuric acid as the electrolyte. The cycle life, one of the most critical parameters in supercapacitor operations, is found to be excellent (6000 cycles) and less than 0.5 % capacitance loss is observed. Moreover, the supercapacitor device is flexible and even after twisting does not show any cracks or evidence of breakage, and shows almost the same specific capacitance of 267 F g⁻¹and energy density of 37 W h kg⁻¹. This work suggests that a paper substrate can be a highly scalable and low-cost solution for high-performance supercapacitors.     

Excellent electrochemical performance of nitrogen-enriched hierarchical porous carbon electrodes prepared using nano-CaCO3 as template

Recently, tremendous research efforts have been concentrated on developing high-performance electrode materials to meet the ever-increasing energy and power demands in supercapacitors. Herein, we presented a high-capacity supercapacitor material based on nitrogen-enriched hierarchical porous carbons (NHPCs) synthesized by the carbonization of melamine formaldehyde resins using eco-friendly and inexpensive nano-CaCO₃ as template. The effects of carbonization temperature and template content on the porous structure and electrochemical characteristics were compared and discussed in detail. The prepared NHPCs possessed large surface area up to 834 m² g^?1 and high nitrogen content up to 20.94 wt %. As electrode material for supercapacitors, NHPCs exhibited superior electrochemical performances with high specific capacitance (190 F g^?1 at 20 A g^?1), outstanding rate capability (80 %), and excellent cycling stability (over 2,000 cycles at 5 A g^?1) in 1 M sulfuric acid media. The excellent electrochemical performances are due to the synergic effects of unique hierarchical porous microstructure, abundant nitrogen and oxygen functionalities, as well as high degree of graphitization framework.     

Carbon-Encased Mixed-Metal Selenide Rooted with Carbon Nanotubes for High-Performance Hybrid Supercapacitors

Transition metal-based compounds with high theoretical capacitance and low cost represent one class of promising electrode materials for high-performance supercapacitors. However, their low intrinsic electrical conductivity impedes their capacitive effect and further limits their practical application. Rational regulation of their composition and structure is, therefore, necessary to achieve a high electrode performance. Herein, a well-designed carbon-encased mixed-metal selenide rooted with carbon nanotubes (Ni-Co-Se@C-CNT) was derived from nickel–cobalt bimetallic organic frameworks. Due to the unique porous structure, the synergistic effect of bimetal selenides and the in situ growth of carbon nanotubes, the composite exhibits good electrical conductivity, high structural stability and abundant redox active sites. Benefitting from these merits, the Ni-Co-Se@C-CNT exhibited a high specific capacity of 554.1 C g⁻¹ (1108.2 F g⁻¹) at 1 A g⁻¹ and a superior cycling performance, i.e., 96.4% of the initial capacity was retained after 5000 cycles at 10 A g⁻¹. Furthermore, a hybrid supercapacitor assembled with Ni-Co-Se@C-CNT cathode and activated carbon (AC) anode shows a superior energy density of 38.2 Wh kg⁻¹ at 1602.1 W kg⁻¹.     

Preparation,Structures and Mechanical Properties of Bamboo Shoot Shell Nanofiber/Konjac Glucomannan Aerogels

With bamboo shoot shell nanofibers(BSN) and konjac glucomannan(KGM) as precursor materials, the BSN/KGM aerogels were prepared in different proportions by sol-gel method. The surface morphology, microstructure, characteristic functional groups and thermal properties of BSN/KGM aerogels were characterized by scanning electron microscopy(SEM), infrared spectroscopy(IR), X-ray diffraction(XRD) and thermogravimetric analysis(TGA). The effect of BSN on the structure and properties of BSN/KGM aerogels was also studied. The results showed that the BSN/KGM aerogels possessed network porous structure with compact and homogeneous porosity, high specific surface area and low density. With the increase of BSN, the sheet structure of aerogels was converted into the 3D porous network structure, which contributes significantly higher thermal stability. In addition, the BSN/KGM aerogels showed excellent mechanical properties. The maximum relative compression rate was 62%, suggesting the addition of BSN can enhance the compression properties of the BSN/KGM aerogels.     

A facile synthesis of hierarchical porous carbon derived from renewable lignin for high-performance supercapacitor

In this work, we proposed a facile one-pot pyrolysis method to conveniently manufacture lignin-derived carbon materials with graded porous construction for use in supercapacitors. The renewable lignin was selected as precursor, while the potassium citrate was used as a pore-forming agent. The properties of the prepared lignin-derived carbon (LAC) and the performance for supercapacitor application were thoroughly evaluated. The LAC at optimal preparation conditions shows a layered porous structure with a large specific surface area of 3174 cm² g⁻¹ and pore volume of 2.796 cm³ g⁻¹, where the specific capacitance reach to 241 F g⁻¹ at 1 A g⁻¹ scan rate in 6 M KOH electrolyte solution. At the same time, the specific capacitance remains at 220 F g⁻¹ even at an excessive scan velocity of 20 A g⁻¹, while the capacitance retention is still close to 91.3%. The capacitance retention rate is stable above 95% after 10,000 charge/discharge cycles, which shows the desired long-time stability. All these results demonstrate the outstanding properties of the new prepared LAC material and the considerable application potential in the field of electrical energy storage.     

Conductive Microporous Covalent Triazine‐Based Framework for High‐Performance Electrochemical Capacitive Energy Storage

Nitrogen‐enriched porous nanocarbon, graphene, and conductive polymers attract increasing attention for application in supercapacitors. However, electrode materials with a large specific surface area (SSA) and a high nitrogen doping concentration, which is needed for excellent supercapacitors, has not been achieved thus far. Herein, we developed a class of tetracyanoquinodimethane‐derived conductive microporous covalent triazine‐based frameworks (TCNQ‐CTFs) with both high nitrogen content (>8 %) and large SSA (>3600 m² g^?1). These CTFs exhibited excellent specific capacitances with the highest value exceeding 380 F g^?1, considerable energy density of 42.8 Wh kg^?1, and remarkable cycling stability without any capacitance degradation after 10 000 cycles. This class of CTFs should hold a great potential as high‐performance electrode material for electrochemical energy‐storage systems.     

Manganese Oxide/Graphene Aerogel Composites as an Outstanding Supercapacitor Electrode Material

Graphene aerogels (GA), prepared with an organic sol–gel process, possessing a high specific surface area of 793 m² g^?1, a high pore volume of 3 cm³ g^?1, and a large average pore size of 17 nm, were applied as a support for manganese oxide for supercapacitor applications. The manganese oxide was electrochemically deposited into the highly porous GA to form MnO₂/GA composites. The composites, at a high manganese oxide loading of 61 wt. %, exhibited a high specific capacitance of 410 F g^?1 at 2 mV s^?1. More importantly, the high rate specific capacitances measured at 1000 mV s^?1 for these composites were two‐fold higher than those obtained with samples prepared in the absence of the GA support. The specific capacitance retention ratio, based on the specific capacitance obtained at 25 mV s^?1, was maintained high, at 85 %, even at the high scan rate of 1000 mV s^?1, in contrast with the significantly lower value of 67 % for the plain manganese oxide sample. For the cycling stability, the specific capacitance of the composite electrode decayed by only 5 % after 50,000 cycles at 1000 mV s^?1. The success of this MnO₂/GA composite may be attributed to the structural advantages of high specific surface areas, high pore volumes, large pore sizes, and three‐dimensionally well‐connected network of the GA support. These structural advantages made possible the high mass loading of the active material, manganese oxide, large amounts of electroactive surfaces for the superficial redox events, fast mass‐transfer within the porous structure, and well‐connected conductive paths for the involved charge transport.     

Large Scale Porous Structure in Gels and Relationship with Their Plastic Behavior

Silica gels (classical aerogels and composite aerogels) have been prepared by classical gelation and addition of silica soot in the gelifying solution before gelation. Due to the aggregation mechanisms, these structures are characterized by a fractal organization. The fractal network previously described in the literature (1–100 nm) which results from the aggregation mechanism of the organosiloxane is affected by the addition of the silica soots. Ultra Small Angle X-ray Scattering (USAXS) experiments (done at ESRF) shows that besides the fractal network built by the organosiloxane, the silica soots are forming another porous structure at a higher scale.The mechanical properties seem to be dependent on this large pore structure. Under isostatic pressure, aerogels display an irreversible shrinkage caused by plastic deformation. As a consequence of this plastic shrinkage it is possible to densify, by the pore collapse tending towards the silica glass. The densification mechanism is different from the one obtained by a sintering at high temperature. The pore collapse mechanism is favored by the large pores structure of the composite aerogels, in contrast to viscous sintering.     

用于超级电容器的锰钴氧化物/碳纤维材料

The development of high-performance supercapacitor electrode materials is imperative to alleviate the ongoing energy crisis. Numerous transition metals (oxides) have been studied as electrode materials for supercapacitors owing to their low cost, environmental-friendliness, and excellent electrochemical performance. Among the developed binary transition metal oxides, manganese cobalt oxides typically show high theoretical capacitance and stable electrochemical performance, and are widely used in the electrode materials of supercapacitors. However, the poor conductivity and active material utilization of manganese cobalt oxide-based electrode materials limit their potential capacitance application. Cotton is mainly composed of organic carbon-containing materials, which can be transformed to carbon fibers after calcination. The resultant carbonaceous material exhibits a large specific surface area and good conductivity. Such advantages could potentially suppress the negative effects caused by the poor conductivity and small specific surface area of manganese cobalt oxides, thereby improving the electrochemical performance. Herein, we firstly deposited manganese cobalt oxides on cotton by a simple hydrothermal method, yielding a composite of manganese cobalt oxides and carbon fibers via subsequent calcination, to improve the electrochemical performance of the electrode material. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), and electrochemical characterizations were used to investigate the physical, chemical, and electrochemical properties of the prepared samples. The fabricated manganese cobalt oxides in the composite were uniformly dispersed on the carbon fiber surface, which increased the contact between the interface of the electrode material and electrolyte, and enhanced electrode material utilization. The electrode material was confirmed to have well contacted with the electrolyte during a contact angle test. Hence, a pseudo-capacitance reaction completely occurred on the manganese cobalt oxide material. Moreover, the addition of carbon fibers reduced the resistance of the material, resulting in excellent capacitive performance. The capacitance of the prepared composite was 854 F∙g^-1 at a current density of 2 A∙g^-1. The capacitance was maintained at 72.3% after 2000 cycles at a current density of 2 A∙g^-1. These results indicate that the manganese cobalt oxide and carbon fiber composite is a promising electrode material for high-performance supercapacitors. The findings presented herein provide a strategy for coupling with carbon materials to enhance the performance of supercapacitor electrode materials based on manganese cobalt oxides. Thus, novel insights into the design of high-performance supercapacitors for energy management are provided.     

Excellent Capacitive Performance of a Three‐Dimensional Hierarchical Porous Graphene/Carbon Composite with a Superhigh Surface Area

Three‐dimensional hierarchical porous graphene/carbon composite was successfully synthesized from a solution of graphene oxide and a phenolic resin by using a facile and efficient method. The morphology, structure, and surface property of the composite were investigated intensively by a variety of means such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption, Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). It is found that graphene serves as a scaffold to form a hierarchical pore texture in the composite, resulting in its superhigh surface area of 2034 m²g^?1, thin macropore wall, and high conductivity (152 S m^?1). As evidenced by electrochemical measurements in both EMImBF₄ ionic liquid and KOH electrolyte, the composite exhibits ideal capacitive behavior, high capacitance, and excellent rate performance due to its unique structure. In EMImBF₄, the composite has a high energy density of up to 50.1 Wh kg^?1 and also possesses quite stable cycling stability at 100 °C, suggesting its promising application in high‐temperature supercapacitors. In KOH electrolyte, the specific capacitance of this composite can reach up to an unprecedented value of 186.5 F g^?1, even at a very high current density of 50 A g^?1, suggesting its prosperous application in high‐power applications.     

Versatile protonic acid mediated preparation of partially deacetylated chitin nanofibers/nanowhiskers and their assembling of nano-structured hydro- and aero-gels

The partially deacetylated α-chitin nanofiber/nanowhisker (DEChN) aqueous dispersions were prepared by alkali deacetylation. The following mechanical treatment under acidic conditions was mediated by five different organic protonic acids, including acetic acid, gluconic acid, itaconic acid, citric acid and ascorbic acid. Thereafter, these acidic DEChN dispersions were transformed into hydrogels under an alkali gas phase coagulation bath. After solvent exchange and freeze drying, the DEChN-based aerogels were prepared. Previous research showed that the kinds of acid used for the adjustment of the pH value during the fibrillation process influenced the nanofibrillation efficiency. In this study, it was discovered that the types of protonic acid also influenced the properties of the DEChN hydrogels and aerogels under the same mass concentration (0.6%) of DEChNs, including the appearance, strength of hydrogels, the pore size and specific surface area of aerogels, as well. Nevertheless, all of the hydrogels showed good mechanical strength and all of the aerogels possessed a porous nanostructure sustained by nanofibrillar networks. The highly porous chitin aerogels showed a broad size mainly distribution from 2 to 100 nm, and the specific surface area of chitin aerogels ranged from 90 to 170 m²g^?1. Although it was not clear how the types of protonic acids influenced the properties of the hydrogel and aerogel, we were able to obtain DEChN dispersions and gels by mechanical treatment of partially deacetylated chitin at acidic conditions mediated by versatile acids. In the meantime, the observed differences among the gels provided the possibility to use the acid medium to select the gels with certain mechanical strength, porosity or specific surface area for the prospective desired applications.