In order to make full utilization of the high intrinsic surface area of graphene, recently, porous graphene materials including graphene nanomesh, crumpled graphene and graphene foam, have attracted ...tremendous attention and research interest, owing to their exceptional porous structure (high surface area, and high pore volume) in combination with the inherent properties of graphene, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Interestingly, porous graphene materials and their derivatives have been explored in a wide range of applications in the fields of electronic and photonic devices, energy storage, gas separation/storage, oil absorption and sensors. This article reviews recent progress in the synthesis, characterization, properties, and applications of porous graphene materials. We aim to highlight the importance of designing different porous structures of graphene to meet future challenges, and the trend on future design of porous graphene materials is analyzed.
Porous graphene materials including graphene nanomesh, crumpled graphene and graphene foam, have attracted tremendous attention and research interest due to their exceptional porous structure combining with inherent properties of graphene.
Volumetric performance, a much more reliable and precise parameter for evaluating the charge-storage capacity of supercapacitors compared with gravimetric performance, has aroused more and more ...interest in recent years owing to the rapid development of miniaturized, portable and wearable electronic devices as well as electric vehicles. Various carbon materials are widely used as electrode materials in supercapacitors. However, their intrinsically low specific capacitance and relatively low bulk density lead to a relatively low volumetric performance, significantly limiting their future application. This critical review points out the crucial importance of volumetric performance and reviews recent achievements of high volumetric performances obtained through the rational design and development of novel carbon-based materials. Particular emphasis is focused on discussing the factors influencing the volumetric performance of carbon materials from a structural design point of view. We then make an in-depth summary of various promising approaches used to make significant research breakthroughs in recent years. Current challenges, future research directions and opportunities in this fascinating field of supercapacitors with high gravimetric and volumetric performances are also discussed.
This review summarizes recent progress in the design and fabrication of carbon materials for high volumetric performance supercapacitors.
A facile one-step pyrolysis and activation synthesis method is utilized to convert a common biomass of willow catkin into interconnected porous carbon nanosheets (PCNs), and then followed by ...effective nitrogen and sulfur co-doping. Owing to the unique hollow and multilayered structure of willow catkin fiber, the pore structure of obtained carbons can be controlled by adjusting the mass ratio of raw material to alkali. As a result, the nitrogen and sulfur co-doped PCNs demonstrate a high specific capacitance of 298Fg−1 at 0.5Ag−1 and 233Fg−1 at 50Ag−1, revealing excellent rate performance. In addition, the electrode demonstrates superb cycling stability with only 2% capacitance loss after 10,000 cycles. Furthermore, the assembled symmetric cell with a wide voltage range of 1.8V yields a remarkable specific energy of 21.0Whkg−1 at 180Wkg−1. These exciting results exhibit a green and low-cost design of electrode materials for high performance supercapacitors.
The willow catkin derived nitrogen and sulfur co-doped porous carbon nanosheets (N,S-PCNs1-1) are prepared by a facile one-step pyrolysis and activation synthesis method, and then followed by effective nitrogen and sulfur co-doping. As a result, the as-obtained carbon processes cross-linked graphene-like structure with high specific surface area and interconnected pore texture, resulting in high specific capacitance, excellent rate performance and cycling stability.
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•Willow catkin is effectively converted into cross-linked porous carbon nanosheets.•N,S-PCNs1-1 electrode shows excellent capacitive performance.•The assembled symmetric supercapacitor exhibits high energy density.
Highlights
The development of transition metal compounds-carbon hybrid electrodes for high energy/power supercapacitors is summarized.
Effects of the conductive carbon skeleton, interfacial ...engineering, and electronic structure for transition metal compounds-carbon hybrid are discussed.
Some perspectives and issues in the future are provided.
Due to their rapid power delivery, fast charging, and long cycle life, supercapacitors have become an important energy storage technology recently. However, to meet the continuously increasing demands in the fields of portable electronics, transportation, and future robotic technologies, supercapacitors with higher energy densities without sacrificing high power densities and cycle stabilities are still challenged. Transition metal compounds (TMCs) possessing high theoretical capacitance are always used as electrode materials to improve the energy densities of supercapacitors. However, the power densities and cycle lives of such TMCs-based electrodes are still inferior due to their low intrinsic conductivity and large volume expansion during the charge/discharge process, which greatly impede their large-scale applications. Most recently, the ideal integrating of TMCs and conductive carbon skeletons is considered as an effective solution to solve the above challenges. Herein, we summarize the recent developments of TMCs/carbon hybrid electrodes which exhibit both high energy/power densities from the aspects of structural design strategies, including conductive carbon skeleton, interface engineering, and electronic structure. Furthermore, the remaining challenges and future perspectives are also highlighted so as to provide strategies for the high energy/power TMCs/carbon-based supercapacitors.
Nanocellulose has emerged as a sustainable and promising nanomaterial owing to its unique structures, superb properties, and natural abundance. Here, we present a comprehensive review of the current ...research activities that center on the development of nanocellulose for advanced electrochemical energy storage. We begin with a brief introduction of the structural features of cellulose nanofibers within the cell walls of cellulose resources. We then focus on a variety of processes that have been explored to fabricate nanocellulose with various structures and surface chemical properties. Next, we highlight a number of energy storage systems that utilize nanocellulose-derived materials, including supercapacitors, lithium-ion batteries, lithium-sulfur batteries, and sodium-ion batteries. In this section, the main focus is on the integration of nanocellulose with other active materials, developing films/aerogel as flexible substrates, and the pyrolyzation of nanocellulose to carbon materials and their functionalization by activation, heteroatom-doping, and hybridization with other active materials. Finally, we present our perspectives on several issues that need further exploration in this active research field in the future.
Nanocellulose from various kinds of sources and nanocellulose-derived materials have been developed for electrochemical energy storage, including supercapacitors, lithium-ion batteries, lithium-sulfur batteries, and sodium-ion batteries.
Three-dimensional flower-like and hierarchical porous carbon material (FHPC) has been fabricated through a simple and efficient carbonization method followed by chemical activation with flower-like ...ZnO as template and pitch as carbon precursor. The hierarchical porous structure is composed of numerous micropores and well-defined mesopores in the interconnected macroporous walls. The FHPC electrode can achieve a relatively high capacitance of 294Fg−1 at a scan rate of 2mVs−1 and excellent rate capability (71% retention at 500mVs−1) with superior cycle stability (only 2% loss after 5000 cycles) in 6molL−1 KOH electrolyte. The symmetric supercapacitor fabricated with FHPC electrodes delivers a high energy density of 15.9Whkg−1 at a power density of 317.5Wkg−1 operated in the voltage range of 0–1.8V in 1molL−1 Na2SO4 aqueous electrolyte.
Highly corrugated graphene sheets (HCGS) have been prepared by a rapid, low cost and scalable approach through the thermal reduction of graphite oxide at 900°C followed by rapid cooling using liquid ...nitrogen. The wrinkling of the graphene sheets can significantly prevent them from agglomerating and restacking with one another face to face and thus increase the electrolyte-accessible surface area. The maximum specific capacitance of 349Fg−1 at 2mVs−1 is obtained for the HCGS electrode in 6M KOH aqueous solution. Additionally, the electrode shows excellent electrochemical stability along with an approximately 8.0% increase of the initial specific capacitance after 5000 cycle tests. These features make the present HCGS material a quite promising alternative for next generation of high-performance supercapacitors.
We demonstrated the fabrication of functionalized graphene nanosheets via low temperature (300 °C) treatment of graphite oxide with a slow heating rate using Mg(OH)2 nanosheets as template. Because ...of its dented sheet with high surface area, a certain amount of oxygen-containing groups, and low pore volume, the as-obtained graphene delivers both ultrahigh specific gravimetric and volumetric capacitances of 456 F g–1 and 470 F cm–3, almost 3.7 times and 3.3 times higher than hydrazine reduced graphene, respectively. Especially, the obtained volumetric capacitance is the highest value so far reported for carbon materials in aqueous electrolytes. More importantly, the assembled supercapacitor exhibits an ultrahigh volumetric energy density of 27.2 Wh L–1, which is among the highest values for carbon materials in aqueous electrolytes, as well as excellent cycling stability with 134% of its initial capacitance after 10 000 cycles. Therefore, the present work holds a great promise for future design and large-scale production of high performance graphene electrodes for portable energy storage devices.
Porous carbon materials derived from various biomasses have aroused intense interest from the scientific community due to their low cost, abundant resources, eco-friendliness and easy fabrication. ...Herein, three-dimensional honeycomb-like hierarchical structured carbon (HSC) has been fabricated by one-step carbonization/activation of abundant and low cost bacterial cellulose for ultrahigh energy density supercapacitors. Benefitting from its interconnected honeycomb-like hierarchical and open structure with a high specific surface area, the prepared HSC exhibits a superhigh specific capacitance of 422 F g-1 at 2 mV s-1 with remarkable rate performance (73.7% at 500 mV s-1) in 6 M KOH aqueous electrolyte. Meanwhile, the symmetric supercapacitor could deliver a high energy density of 37.3 W h kg-1 in 1 M Na2SO4 aqueous electrolyte. To evaluate the practical application, an asymmetric supercapacitor fabricated with NiCoAl-layered double hydroxide as the positive electrode and HSC as the negative electrode achieves a conspicuously high energy density of 100 W h kg-1 and could still retain 33 W h kg-1 even at a high power density of 36.8 kW kg-1, which is highly comparable with or even higher than those of the previously reported asymmetric supercapacitors in aqueous electrolytes. Furthermore, our asymmetric supercapacitor exhibits excellent cycling stability along with 113% capacitance retention after 10 000 cycles. Such spectacular results will shed new light on biomass-derived carbon materials for the next generation of ultrafast energy storage devices with high energy density and excellent long cycle life.
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