Nanoarchitectured graphene-based supercapacitors for next-generation energy-storage applications

Achieving High-Energy-Density Graphene/Single-Walled Carbon Nanotube Lithium-Ion Capacitors from Organic-Based Electrolytes

Developing electrode materials with high voltage and high specific capacity has always been an important strategy for increasing the energy density of lithium-ion capacitors (LICs). However, organic-based electrolytes with lithium salts limit their potential for application in LICs to voltages below 3.8 V in terms of polarization reactions. In this work, we introduce Li[N(C2F5SO2)2] (lithium Bis (pentafluoroethanesulfonyl)imide or LiBETI), an electrolyte with high conductivity and superior electrochemical and mechanical stability, to construct a three-electrode LIC system. After graphite anode pre-lithiation, the anode potential was stabilized in the three-electrode LIC system, and a stable solid electrolyte interface (SEI) film formed on the anode surface as expected. Meanwhile, the LIC device using LiBETI as the electrolyte, and a self-synthesized graphene/single-walled carbon nanotube (SWCNT) composite as the cathode, showed a high voltage window, allowing the LIC to achieve an operating voltage of 4.5 V. As a result, the LIC device has a high energy density of up to 182 Wh kg-1 and a 2678 W kg-1 power density at 4.5 V. At a current density of 2 A g-1, the capacity retention rate is 72.7% after 10,000 cycles.

Surface-modified CuO nanoparticles for photocatalysis and highly efficient energy storage devices

Herein we report multifunctional surface-modified CuO nanomaterials were used to fulfill escalating needs in the electrochemical energy storage system and to achieve efficient photocatalysts for the degradation of AR88 organic dye. Due to the atom economy, ease of synthesis, high capacitance, observable electrochemical responsiveness, and low bandgap in CuO-based nanomaterials, its active surface was modified through cationic surfactant CTAB. Surface-modified nanoparticles were characterized using various characterization techniques such as XRD, DRS, FESEM, and TEM. Intriguingly the synthesized materials demonstrated a capacitance of 133 F/g with a long-term charge-discharge cycle of 2000 cycles. In addition, at pH 11, the material also exhibited a superior dye degradation performance under the UV lamp by showing 94.8% AR88 degradation at a catalyst concentration of 1.0 g/L. Hence, we believe this concept would provide novel insights into the preparation of the simplest and cheaper multifunctional materials for next-generation energy storage and photocatalytic applications.

Research on Preparation Methods of Carbon Nanomaterials Based on Self-Assembly of Carbon Quantum Dots

Here, based on self-assembly of carbon quantum dots (CDs), an innovative method to prepare nanomaterials under the action of a metal catalyst was presented. CDs were synthesized by a one-step hydrothermal method with citric acid (CA) as the carbon source, ethylenediamine (EDA) as the passivator and FeSO₄•7H₂O as the pre-catalyst. In the experiment, it was found that the nano-carbon films with a graphene-like structure were formed on the surface of the solution. The structure of the films was studied by high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FT-IR), etc. The results demonstrated that the films were formed by the self-assembly of CDs under the action of the gas–liquid interface template and the metal catalyst. Meanwhile, the electrochemical performance of the films was evaluated by linear cyclic voltammetry (CV) and galvanostatic charge discharge (GOD) tests. In addition, the bulk solution could be further reacted and self-assembled by reflux to form a bifunctional magnetic–fluorescent composite material. Characterizations such as X-ray diffractometer (XRD), fluorescence spectra (FL), vibrating sample magnetometer (VSM), etc. revealed that it was a composite of superparamagnetic γ-Fe₂O₃ and CDs. The results showed that self-assembly of CDs is a novel and effective method for preparing new carbon nanomaterials.

Material Nanoarchitectonics of Functional Polymers and Inorganic Nanomaterials for Smart Supercapacitors

Smart supercapacitors are a promising energy storage solution due to their high power density, long cycle life, and low-maintenance requirements. Functional polymers (FPs) and inorganic nanomaterials are used in smart supercapacitors because of the favorable mechanical properties (flexibility and stretchability) of FPs and the energy storage properties of inorganic materials. The complementary properties of these materials facilitate commercial applications of smart supercapacitors in flexible smart wearables, displays, and self-generation, as well as energy storage. Here, an overview of strategies for the development of suitable materials for smart supercapacitors is presented, based on recent literature reports. A range of synthetic techniques are discussed and it is concluded that a combination of organic and inorganic hybrid materials is the best option for realizing smart supercapacitors. This perspective facilitates new strategies for the synthesis of hybrid materials, and the development of material technologies for smart energy storage applications.

A Freestanding Chitin-Derived Hierarchical Nanocomposite for Developing Electrodes in Future Supercapacitor Industry

Crustacean cuticles are receiving extensive attention for its potential in developing environmentally friendly and high energy density electrodes for supercapacitor applications. In the current work, the demineralized tergite cuticle of mantis shrimp was employed as a precursor for the fabrication porous biochar. The structural benefits of the cuticle, including the hierarchical nanofiber networks, and the interpenetrating pore systems were maximumly retained, providing a high carbon content and specific surface area scaffold. Graphene oxide sheets were deposited across the biochar through the pore canal systems to further increase the conductivity of the biochar, forming a novel freestanding carbon composite. Throughout the modification process, the material products were examined by a range of methods, which showed desired structural, chemical and functional properties. Our work demonstrates that high performance carbon materials can be manufactured using a simple and green process to realize the great potential in energy storage applications.

Transition metal dichalcogenide (TMDs) electrodes for supercapacitors: a comprehensive review

As globally, the main focus of the researchers is to develop novel electrode materials that exhibit high energy and power density for efficient performance energy storage devices. This review covers the up-to-date progress achieved in transition metal dichalcogenides (TMDs) (e.g. MoS₂, WS₂, MoSe_2,and WSe₂) as electrode material for supercapacitors (SCs). The TMDs have remarkable properties like large surface area, high electrical conductivity with variable oxidation states. These properties enable the TMDs as the most promising candidates to store electrical energy via hybrid charge storage mechanisms. Consequently, this review article provides a detailed study of TMDs structure, properties, and evolution. The characteristics technique and electrochemical performances of all the efficient TMDs are highlighted meticulously. In brief, the present review article shines a light on the structural and electrochemical properties of TMD electrodes. Furthermore, the latest fabricated TMDs based symmetric/asymmetric SCs have also been reported.

The synthesis of mechanically stable polybenzoxazine-based porous carbon and its application as high-performance supercapacitor electrodes

Nitrogen self-doped mesoporous carbon is synthesized from a novel polybenzoxazine and used as an electrode for supercapacitor applications.

New Limits for Stability of Supercapacitor Electrode Material Based on Graphene Derivative

Supercapacitors offer a promising alternative to batteries, especially due to their excellent power density and fast charging rate capability. However, the cycling stability and material synthesis reproducibility need to be significantly improved to enhance the reliability and durability of supercapacitors in practical applications. Graphene acid (GA) is a conductive graphene derivative dispersible in water that can be prepared on a large scale from fluorographene. Here, we report a synthesis protocol with high reproducibility for preparing GA. The charging/discharging rate stability and cycling stability of GA were tested in a two-electrode cell with a sulfuric acid electrolyte. The rate stability test revealed that GA could be repeatedly measured at current densities ranging from 1 to 20 A g-1 without any capacitance loss. The cycling stability experiment showed that even after 60,000 cycles, the material kept 95.3% of its specific capacitance at a high current density of 3 A g-1. The findings suggested that covalent graphene derivatives are lightweight electrode materials suitable for developing supercapacitors with extremely high durability.

Progress of electrospray and electrospinning in energy applications

In the promotion of energy strategies to address the global energy crisis, nanotechnology has been successfully used to generate novel energy materials with excellent characteristics, such as high specific surface area, good flexibility and large porosity. Among the various methods for fabricating nanoscale materials, electrospray and electrospinning technologies have unlocked low-cost, facile and industrial routes to nanotechnology over the past ten years. This review highlights research into the key parts and primary theory of these techniques and their application in preparing energy-related materials and devices: especially fuel cells, solar cells, lithium ion batteries, supercapacitors as well as hydrogen storage systems. The challenges and future prospects of the manufacturing technologies are also covered in this paper.

Superior supercapacitive performance of grass-like CuO thin films deposited by liquid phase deposition

First report on deposition and supercapacitive performance of grass-like CuO thin films by liquid phase deposition on flat and mesh stainless steel (SS). The maximum specific capacitances on flat and mesh SS are 552 and 849 F g⁻¹.

Graphitic Carbon Nitride Doped Copper-Manganese Alloy as High-Performance Electrode Material in Supercapacitor for Energy Storage

Here, we report the synthesis of copper-manganese alloy (CuMnO₂) using graphitic carbon nitride (gCN) as a novel support material. The successful formation of CuMnO₂-gCN was confirmed through spectroscopic, optical, and other characterization techniques. We have applied this catalyst as the energy storage material in the alkaline media and it has shown good catalytic behavior in supercapacitor applications. The CuMnO₂-gCN demonstrates outstanding electrocapacitive performance, having high capacitance (817.85 A·g^-1) and well-cycling stability (1000 cycles) when used as a working electrode material for supercapacitor applications. For comparison, we have also used the gCN and Cu₂O-gCN for supercapacitor applications. This study proposes a simple path for the extensive construction of self-attaining double metal alloy with control size and uniformity in high-performance energy-storing materials.

Rationally engineered 3D-dendritic cell-like morphologies of LDH nanostructures using graphene-based core-shell structures

Functionalization of graphene-based materials using chemical moieties not only modify the electronic structure of the underlying graphene but also enable in limited enhancement of targeted properties. Surface modification of graphene-based materials using other nanostructures enhances the effective properties by minimally modifying the properties of pristine graphene backbone. In this pursuit, we have synthesized bio-inspired hierarchical nanostructures based on Ni-Co layered double hydroxide on reduced graphene oxide core-shells using template based wet chemical approach. The material synthesized have been characterized structurally and electrochemically. The fabricated dendritic morphology of the composite delivers a high specific capacity of 1056 Cg^-1. A cost effective solid state hybrid supercapacitor device was also fabricated using the synthesized electrode material which shows excellent performance with high energy density and fast charging capability.

Carbons with Regular Pore Geometry Yield Fundamental Insights into Supercapacitor Charge Storage

We conduct molecular dynamics simulations of electrical double-layer capacitors (EDLCs) using a library of ordered, porous carbon electrode materials called zeolite templated carbons (ZTCs). The well-defined pore shapes of the ZTCs enable us to determine the influence of pore geometry on both charging dynamics and charge storage mechanisms in EDLCs, also referred to as supercapacitors. We show that charging dynamics are negatively correlated with the pore-limiting diameter of the electrode material and display signatures of both progressive charging and ion trapping. However, the equilibrium capacitance, unlike charging dynamics, is not strongly correlated to commonly used, purely geometric descriptors such as pore size. Instead, we find a strong correlation of capacitance to the charge compensation per carbon (CCpC), a descriptor we define in this work as the average charge of the electrode atoms within the coordination shell of a counterion. A high CCpC indicates efficient charge storage, as the strong partial charges of the electrode are able to screen counterion charge, enabling higher ion loading and thus more charge storage within the electrode at a fixed applied voltage. We determine that adsorption sites with a high CCpC tend to be found within pockets with a smaller radius of curvature, where the counterions are able to minimize their distance with multiple points on the electrode surface, and therefore induce stronger local partial charges.

Plasmonic Jackiw-Rebbi Modes in Graphene Waveguide Arrays

We investigate the topological bound modes of surface plasmon polaritons (SPPs) in a graphene pair waveguide array. The arrays are with uniform inter-layer and intra-layer spacings but the chemical potential of two graphene in each pair are different. The topological bound modes emerge when two arrays with opposite sequences of chemical potential are interfaced, which are analogous to Jackiw-Rebbi modes with opposite mass. We show the topological bound modes can be dynamically controlled by tuning the chemical potential, and the propagation loss of topological bound modes can be remarkably reduced by decreasing the chemical potential. Thanks to the strong confinement of graphene SPPs, the modal wavelength of topological bound modes can be squeezed as small as 1/70 of incident wavelength. The study provides a promising approach to realizing robust light transport beyond diffraction limit.

Ni(OH)2 Nanoflakes Supported on 3D Ni3 Se2 Nanowire Array as Highly Efficient Electrodes for Asymmetric Supercapacitor and Ni/MH Battery

Porous Ni(OH)₂ nanoflakes are directly grown on the surface of nickel foam supported Ni₃ Se₂ nanowire arrays using an in situ growth procedure to form 3D Ni₃ Se₂ @Ni(OH)₂ hybrid material. Owing to good conductivity of Ni₃ Se₂ , high specific capacitance of Ni(OH)₂ and its unique architecture, the obtained Ni₃ Se₂ @Ni(OH)₂ exhibits a high specific capacitance of 1689 µAh cm^-2 (281.5 mAh g^-1 ) at a discharge current of 3 mA cm^-2 and a superior rate capability. Both the high energy density of 59.47 Wh kg^-1 at a power density of 100.54 W kg^-1 and remarkable cycling stability with only a 16.4% capacity loss after 10 000 cycles are demonstrated in an asymmetric supercapacitor cell comprising Ni₃ Se₂ @Ni(OH)₂ as a positive electrode and activated carbon as a negative electrode. Furthermore, the cell achieved a high energy density of 50.9 Wh L^-1 at a power density of 83.62 W L^-1 in combination with an extraordinary coulombic efficiency of 97% and an energy efficiency of 88.36% at 5 mA cm^-2 when activated carbon is replaced by metal hydride from a commercial NiMH battery. Excellent electrochemical performance indicates that Ni₃ Se₂ @Ni(OH)₂ composite can become a promising electrode material for energy storage applications.

Preparation of Core-Shell CQD@PANI Nanoparticles and Their Electrochemical Properties

In recent years, carbon quantum dots (CQDs) have been extensively investigated in many fields because of their incomparable and unique properties. However, the application of CQDs in the electrochemical field meets a big challenge due to their low specific capacitance. It is very important to improve the electrochemical performance of CQDs. In this study, a facile synthesis method was developed to synthesize CQD@PANI nanoparticles. The CQD@PANI nanoparticles were prepared via a precise quantitative adsorption polymerization method. TEM results showed that the PANI shell thickness could be adjusted by controlling the additive amount of aniline. Cyclic voltammetry and galvanostatic charge/discharge results showed that the electrochemical properties of CQDs have been significantly improved by coating PANI.

Horizontally Aggregation of Monolayer Reduced Graphene Oxide Under Deep UV Irradiation in Solution

Graphene has been widely used in novel optoelectronic devices in decades. Nowadays, fabrication of large size monolayer graphene with spectral selectivity is highly demanded. Here, we report a simple method for synthesizing large size monolayer graphene with chemical functionalized groups in solution. The few layer nano-graphene can be exfoliated into monolayer nano-graphene under short time UV irradiation in protic solution. The exfoliated monolayer nano-graphene could experience deoxygenation during long time UV exposure. At the same time, the edge of nano-graphene could be activated under deep UV exposure and small size nano-graphene sheets further aggregate horizontally in solution. The size of aggregated rGO increase from 40 nm to a maximum of 1 μm. This approach could be one promising cheap method for synthesizing large size monolayer reduced graphene oxide in the future.

Temperature-Dependent Morphologies of Precursors: Metal-Organic Framework-Derived Porous Carbon for High-Performance Electrochemical Double-Layer Capacitors

In this work, three Cu metal-organic framework samples with tunable rhombic, squama, and trucated bipyramid morphologies have been synthesized at 0, 25, and 60 °C, respectively, and further employed as precursors to initially prepare Cu@C composites by the calcination-thermolysis procedure. Then Cu@C composites have been etched with HCl and subsequently activated with KOH to obtain activated porous carbon (APC-0, -25, and -60). Interestingly, APC-25 presents a loose multilevel morphology of cabbage and possesses the largest specific surface area (1880.4 m² g^-1) and pore volume (0.81 cm³ g^-1) among these APC materials. Consequently, APC-25 also exhibits the highest specific capacitance of 196 F g^-1 at 0.5 A g^-1, and the corresponding symmetric supercapacitor cell (SSC) achieves a remarkable energy density of 11.8 Wh kg^-1 at a power density of 350 W kg^-1. Furthermore, APC-25 shows excellent cycling stability, and the loss of capacitance is only 7.7% even after 10000 cycles at 1 A g^-1. Significantly, five light-emitting diodes can be lit by six SSCs, which proves that APC-25 can be used in energy storage devices.

Practical use of polymer brushes in sustainable energy applications: interfacial nanoarchitectonics for high-efficiency devices

The discovery and development of novel approaches, materials and manufacturing processes in the field of energy are compelling increasing recognition as a major challenge for contemporary societies. The performance and lifetime of energy devices are critically dependent on nanoscale interfacial phenomena. From the viewpoint of materials design, the improvement of current technologies inevitably relies on gaining control over the complex interface between dissimilar materials. In this sense, interfacial nanoarchitectonics with polymer brushes has seen growing interest due to its potential to overcome many of the limitations of energy storage and conversion devices. Polymer brushes offer a broad variety of resources to manipulate interfacial properties and gain molecular control over the synergistic combination of materials. Many recent examples show that the rational integration of polymer brushes in hybrid nanoarchitectures greatly improves the performance of energy devices in terms of power density, lifetime and stability. Seen in this light, polymer brushes provide a new perspective from which to consider the development of hybrid materials and devices with improved functionalities. The aim of this review is therefore to focus on what polymer brush-based solutions can offer and to show how the practical use of surface-grafted polymer layers can improve the performance and efficiency of fuel cells, lithium-ion batteries, organic radical batteries, supercapacitors, photoelectrochemical cells and photovoltaic devices.

Polarity-assisted formation of hollow-frame sheathed nitrogen-doped nanofibrous carbon for supercapacitors

Heteroatom-doped carbon nanostructures with uniform size and morphology, well-designed architectures, and minimized interfacial resistance have been recognized as promising electrode materials for energy storage, but remain a crucial challenge. Herein, we develop a general approach of polarity-induced decoration of a monolayer sheath of metal-organic framework (MOF) particles with excellent uniformity in size and morphology on electrospun polymer nanofibers. These hybrid nanofibers are facilely converted into nitrogen-doped nanofibrous carbon (denoted as N-NFC) during pyrolysis. The thus-obtained N-NFC features (1) a one-dimensional nanofibrous structure with a highly conductive core, (2) a monolayer sheath of hollow carbon-frames with uniform size and morphology, (3) plenty of micro/mesopores with a highly accessible surface area, and (4) a high N-doping level, all of which guarantee its good electrochemical performance with a high capacitance of 387.3 F g-1 at 1 A g-1. In a solid-state supercapacitor, it delivers excellent rate capability (78.0 F g-1 at 0.2 A g-1 and 64.0 F g-1 at 1 A g-1), an enhanced energy density of 7.9 W h kg-1 at a power density of 219 W kg-1, and outstanding cycling stability with 90% capacity retained over 10 000 cycles at 1 A g-1.

Rapid synthesis of Ni(OH)2/graphene nanosheets and NiO@Ni(OH)2/graphene nanosheets for supercapacitor applications

β-Ni(OH)₂ or NiO@Ni(OH)₂ grew on commercial graphene nanosheets with high specific capacitance and excellent rate capability.

Molecular interaction balanced one- and two-dimensional hybrid nanoarchitectures for high-performance supercapacitors

Stepwise ultrasonication and self-assembly process enables good separation between disequilibrium and equilibrium thermodynamic molecular interactions, which allow excellent electrochemical charge storage based on ratio-dependent 1D–2D hybridisation.

Engineering hydrogenated manganese dioxide nanostructures for high-performance supercapacitors

Improving the rate capability of transition metal oxides is of great important for the development of high-performance electrodes for supercapacitors. Here, a novel strategy of hydrogenation to enhance the electron transfer rate of manganese dioxide (MnO₂) is proposed. Detailed preparative parameters (i.e. hydrogenation temperature and time) are systematically investigated. The hydrogenated MnO₂ (H-MnO_x) exhibits modified crystal phase/surface structures and increased electrical conductivity. The prepared H-MnO_x exhibits high specific capacitance (640 mF cm^-2 at current density of 1 mA cm^-2), good rate capability (89.6% of capacitance retained from 1 to 10 mA cm^-2), and good cycling stability (84.6% retention after 1000 cycles). The high specific capacitance is ascribed to the unique interconnected ultrathin nanosheets structure, which could not only provide porous channels for electrolyte infiltration to offer sufficient electrode/electrolyte interface, but also shorten the ions diffusion distance inside the active material. The good rate capability could be attributed to the good conductivity of the H-MnO_x nanosheets, which was confirmed by the DFT calculation. These results highlight the importance of hydrogenation as a facile yet effective strategy to improve the rate capability of transition metal oxides for supercapacitors.