Sustainable and Scalable Synthesis of 2D Ultrathin Hierarchical Porous Carbon Nanosheets for High-Performance Supercapacitor

2D carbon nanomaterials such as graphene, carbon nanosheets, and their derivatives, representing the emerging class of advanced multifunctional materials, have gained great research interest because of their extensive applications ranging from electrochemistry to catalysis. However, sustainable and scalable synthesis of 2D carbon nanosheets (CNs) with hierarchical architecture and irregular structure via a green and low-cost strategy remains a great challenge. Herein, prehydrolysis liquor (PHL), an industrial byproduct of the pulping industry, is first employed to synthesize CNs via a simple hydrothermal carbonization technique. After mild activation with NH₄Cl and FeCl₃, the as-prepared activated CNs (A-CN@NFe) display an ultrathin structure (≈3 nm) and a desirable specific surface area (1021 m² g⁻¹) with hierarchical porous structure, which enables it to be both electroactive materials and structural support materials in nanofibrillated cellulose/A-CN@NFe/polypyrrole (NCP) nanocomposite, and thus endowing nanocomposite with impressive capacitance properties of 2546.3 mF cm⁻² at 1 mA cm⁻². Furthermore, the resultant all-solid-state symmetric supercapacitor delivers a satisfactory energy storage ability of 90.1 µWh cm⁻² at 250.0 µW cm⁻². Thus, this work not only opens a new window for sustainable and scalable synthesis of CNs, but also offers a double profits strategy for energy storage and biorefinery industry.     

Enhanced Phosphorescence of Carbon Nanodots via Double Confinement for 3D Artworks with Long Emission Lifetimes

Phosphorescent materials as block elements to build artwork incorporating the time and emission, enable them with spectacular lighting effects. In this work, enhanced phosphorescence of carbon nanodots (CNDs) is demonstrated via double confinement strategy, which silica and epoxy resin are used as the first and the second order confinement layer. The multi-confined CNDs show an enhanced phosphorescence quantum yield up to 16.4%, with enduring emission lifetime up to 1.44 s. Delicately, the plasticity of the epoxy resin enables them easily to be designed for 3D artworks with long emission lifetimes in different shapes. The efficient and eco-friendly phosphorescent CNDs may arouse intense interest both in the academic community and markets.     

Laser‐Assisted Lattice Recovery of Graphene by Carbon Nanodot Incorporation

Producing highly oriented graphene is a major challenge that constrains graphene from fulfilling its full potential in technological applications. The exciting properties of graphene are impeded in practical bulk materials due to lattice imperfections that hinder charge mobility. A simple method to improve the structural integrity of graphene by utilizing laser irradiation on a composite of carbon nanodots (CNDs) and 3D graphene is presented. The CNDs attach themselves to defect sites in the graphene sheets and, upon laser‐assisted reduction, patch defects in the carbon lattice. Spectroscopic experiments reveal graphitic structural recovery of up to 43% and electrical conductivity four times larger than the original graphene. The composites are tested as electrodes in electrochemical capacitors and demonstrate extremely fast RC time constant as low as 0.57 ms. Due to their low defect concentrations, the reduced graphene oxide‐carbon nanodot (rGO‐CND) composites frequency response is sufficiently fast to operate as AC line filters, potentially replacing today's electrolytic capacitors. Using this methodology, demonstrated is a novel line filter with one of the fastest capacitive responses ever reported, and an aerial capacitance of 68.8 mF cm^?2. This result emphasizes the decisive role of structural integrity for optimizing graphene in electronic applications.     

Ultra‐light Hierarchical Graphene Electrode for Binder‐Free Supercapacitors and Lithium‐Ion Battery Anodes

A mild and environmental‐friendly method is developed for fabricating a 3D interconnected graphene electrode with large‐scale continuity. Such material has interlayer pores between reduced graphene oxide nanosheets and in‐plane pores. Hence, a specific surface area up to 835 m² g⁻¹ and a high powder conductivity up to 400 S m⁻¹ are achieved. For electrochemical applications, the interlayer pores can serve as “ion‐buffering reservoirs” while in‐plane ones act as “channels” for shortening the mass cross‐plane diffusion length, reducing the ion response time, and prevent the interlayer restacking. As binder‐free supercapacitor electrode, it delivers a specific capacitance up to 169 F g⁻¹ with surface‐normalized capacitance close to 21 μF cm⁻² (intrinsic capacitance) and power density up to 7.5 kW kg⁻¹, in 6 m KOH aqueous electrolyte. In the case of lithium‐ion battery anode, it shows remarkable advantages in terms of the initiate reversible Coulombic efficiency (61.3%), high specific capacity (932 mAh g⁻¹ at 100 mA g⁻¹), and robust long‐term retention (93.5% after 600 cycles at 2000 mAh g⁻¹).     

High Mass-Loading Biomass-Based Porous Carbon Electrodes for Supercapacitors: Review and Perspectives

Biomass-based porous carbon (BPC) with renewability and flexible nano/microstructure tunability has attracted increasing attention as efficient and cheap electrode materials for supercapacitors. To meet commercial needs, high mass-loading electrodes with high areal capacitance are preferred when designing supercapacitors. The increased mass percentage of active materials can effectively improve the energy density of supercapacitors. However, as the thickness of the electrode increases, it will face the following challenges including severely blocked ion transport channels, poor charging dynamics, poor electrode structural stability, and complex preparation processes. A bridge between theoretical research and practical applications of BPC electrodes for supercapacitors needs to be established. In this review, the advances of high mass-loading BPC electrodes for supercapacitors are summarized based on different biomass precursors. The key performance evaluation parameters of the high mass-loading electrodes are analyzed, and the performance influencing factors are systematically discussed, including specific surface area, pore structure, electrical conductivity, and surface functional groups. Subsequently, the promising optimization strategies for high mass-loading electrodes are summarized, including the structure regulation of electrode materials and the optimization of other supercapacitor components. Finally, the major challenges and opportunities of high mass-loading BPC electrodes in the future are discussed and outlined.     

Recent Advances in 3D Graphene Architectures and Their Composites for Energy Storage Applications

Graphene is widely applied as an electrode material in energy storage fields. However, the strong π–π interaction between graphene layers and the stacking issues lead to a great loss of electrochemically active surface area, damaging the performance of graphene electrodes. Developing 3D graphene architectures that are constructed of graphene sheet subunits is an effective strategy to solve this problem. The graphene architectures can be directly utilized as binder‐free electrodes for energy storage devices. Furthermore, they can be used as a matrix to support active materials and further improve their electrochemical performance. Here, recent advances in synthesizing 3D graphene architectures and their composites as well as their application in different energy storage devices, including various battery systems and supercapacitors are reviewed. In addition, their challenges for application at the current stage are discussed and future development prospects are indicated.     

Dual-Silica Template-Mediated Synthesis of Nitrogen-Doped Mesoporous Carbon Nanotubes for Supercapacitor Applications

1D carbon nanotubes have been widely applied in many fields, such as catalysis, sensing and energy storage. However, the long tunnel-like pores and relatively low specific surface area of carbon nanotubes often restrict their performance in certain applications. Herein, a dual-silica template-mediated method to prepare nitrogen-doped mesoporous carbon nanotubes (NMCTs) through co-depositing polydopamine (both carbon and nitrogen precursors) and silica nanoparticles (the porogen for mesopore formation) on a silica nanowire template is proposed. The obtained NMCTs have a hierarchical pore structure of large open mesopores and tubular macropores, a high specific surface area (1037 m² g⁻¹), and homogeneous nitrogen doping. The NMCT-45 (prepared at an interval time of 45 min) shows excellent performance in supercapacitor applications with a high capacitance (373.6 F g⁻¹ at 1.0 A g−¹), excellent rate capability, high energy density (11.6 W h kg⁻¹ at a power density of 313 W kg⁻¹), and outstanding cycling stability (98.2% capacity retention after 10 000 cycles at 10 A g⁻¹). Owing to the unique tubular morphology, hierarchical porosity and homogeneous N-doping, the NMCT also has tremendous potential in electrochemical catalysis and sensing applications.     

超级电容器电极用N-掺杂多孔碳材料的研究进展

多孔碳材料作为双电层电容器的主要电极材料,已成功应用于商业化超级电容器。但作为电极材料,纯碳材料表面疏水、内阻较大、电容较低等缺点使其进一步发展受到制约。近年来,随着超级电容器的迅速发展,氮掺杂多孔碳材料作为其电极材料引起研究人员的广泛关注,并采用不同的制备方法成功合成了一系列结构不同、性能优异的氮掺杂碳材料。基于超级电容器氮掺杂多孔碳电极材料的最新研究进展,首先介绍了氮在碳材料中的基本存在形式及对碳电极材料性能的影响,然后重点评述了氮掺杂碳电极材料的制备,最后总结了超级电容器氮掺杂碳材料的发展趋势。     

Disassembly–Reassembly Approach to RuO2/Graphene Composites for Ultrahigh Volumetric Capacitance Supercapacitor

A porous, yet compact, RuO₂/graphene hybrid is successfully prepared by using a disassembly–reassembly strategy, achieving effective and uniform loading of RuO₂ nanoparticles inside compact graphene monolith. The disassembly process ensures the uniform loading of RuO₂ nanoparticles into graphene monolith, while the reassembly process guarantees a high density yet simultaneously unimpeded ion transport channel in the composite. The resulting RuO₂/graphene hybrid possesses a density of 2.63 g cm⁻³, leading to a record high volumetric capacitance of 1485 F cm⁻³ at the current density of 0.1 A g⁻¹. When the current density is increased to 20 A g⁻¹, it remains a high volumetric capacitance of 1188 F cm⁻³. More importantly, when the single electrode mass loading is increased to 12 mg cm⁻², it still delivers a high volumetric capacitance of 1415 F cm⁻³ at the current density of 0.1 A g⁻¹, demonstrating the promise of this disassembly–reassembly approach to create high volumetric performance materials for energy storage applications.     

Porous Hybrid Composites of Few‐Layer MoS2 Nanosheets Embedded in a Carbon Matrix with an Excellent Supercapacitor Electrode Performance

Porous hierarchical architectures of few‐layer MoS₂ nanosheets dispersed in carbon matrix are prepared by a microwave‐hydrothermal method followed by annealing treatment via using glucose as C source and structure‐directing agent and (NH₄)₂MoS₄ as both Mo and S sources. It is found that the morphology and size of the secondary building units (SBUs), the size and layer number of MoS₂ nanosheets as well as the distribution of MoS₂ nanosheets in carbon matrix, can be effectively controlled by simply adjusting the molar ratio of (NH₄)₂MoS₄ to glucose, leading to the materials with a low charge–transfer resistance, many electrochemical active sites and a robust structure for an outstanding energy storage performance including a high specific capacitance (589 F g⁻¹ at 0.5 A g⁻¹), a good rate capability (364 F g⁻¹ at 20 A g⁻¹), and an excellent cycling stability (retention 104% after 2000 cycles) for application in supercapacitors. The exceptional rate capability endows the electrode with a high energy density of 72.7 Wh kg⁻¹ and a high power density of 12.0 kW kg⁻¹ simultaneously. This work presents a facile and scalable approach for synthesizing novel heterostructures of MoS₂‐based electrode materials with an enhanced rate capability and cyclability for potential application in supercapacitor.     

组氨酸功能化碳点/石墨烯气凝胶的制备及超级电容器性能

通过一步水热法制备组氨酸功能化碳点/石墨烯气凝胶(His-CDs/GA)。该材料具有独特的三维多孔结构、丰富的含氮和含氧官能团, 有利于电解液离子的快速扩散和提供更多的活性位点。当GO与His-CDs的质量比为2 : 1时, His-CDs/GA-2在1 A·g ^-1电流密度下比电容达到304 F·g ^{- 1}, 比GA(172 F·g ^-1)提高了76.7%; 当电流密度从1 A·g ^-1增加到50 A·g ^-1, 其比电容保持率为71.4%; 在电流密度10 A·g ^-1下, 循环充放电30000次后, 比电容仍保留93.5%。由His-CDs/GA组装的对称超级电容器展现出高能量密度(在功率密度为250 W/kg时, 能量密度达到10.14 Wh/kg)和良好的循环性能(在5 A·g ^-1下循环充放电20000次后, 比电容保持率为88.4%)。结果表明, His-CDs/GA是一种应用前景广阔的超级电容器电极材料。