High-performance flexible-film supercapacitors of layered hydrous RuO2/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) through vacuum filtration

Nanostructured Conducting Polymers and Their Applications in Energy Storage Devices

Due to the energy requirements for various human activities, and the need for a substantial change in the energy matrix, it is important to research and design new materials that allow the availability of appropriate technologies. In this sense, together with proposals that advocate a reduction in the conversion, storage, and feeding of clean energies, such as fuel cells and electrochemical capacitors energy consumption, there is an approach that is based on the development of better applications for and batteries. An alternative to commonly used inorganic materials is conducting polymers (CP). Strategies based on the formation of composite materials and nanostructures allow outstanding performances in electrochemical energy storage devices such as those mentioned. Particularly, the nanostructuring of CP stands out because, in the last two decades, there has been an important evolution in the design of various types of nanostructures, with a strong focus on their synergistic combination with other types of materials. This bibliographic compilation reviews state of the art in this area, with a special focus on how nanostructured CP would contribute to the search for new materials for the development of energy storage devices, based mainly on the morphology they present and on their versatility to be combined with other materials, which allows notable improvements in aspects such as reduction in ionic diffusion trajectories and electronic transport, optimization of spaces for ion penetration, a greater number of electrochemically active sites and better stability in charge/discharge cycles.

Rare Earth-Based Nanomaterials for Supercapacitors: Preparation, Structure Engineering and Application

Supercapacitors (SCs) can effectively alleviate problems such as energy shortage and serious greenhouse effect. The properties of electrode materials directly affect the performance of SCs. Rare earth (RE) is known as "modern industrial vitamins", and their functional materials have been listed as key strategic materials. In the past few years, the number of scientific reports on RE-based nanomaterials for SCs has increased rapidly, confirming that adding RE elements or compounds to the host electrode materials with various nanostructured morphologies can greatly enhance their electrochemical performance. Although RE-based nanomaterials have made rapid progress in SCs, there are very few works providing a comprehensive survey of this field. In view of this, a comprehensive overview of RE-based nanomaterials for SCs is provided here, including the preparation methods, nanostructure engineering, compounds, and composites, along with their capacitance performances. The structure-activity relationships are discussed and highlighted. Meanwhile, the future challenges and perspectives are also pointed out. This Review can not only provide guidance for the further development of SCs but also arouse great interest in RE-based nanomaterials in other research fields such as electrocatalysis, photovoltaic cells, and lithium batteries.

Interstitial boron-doped mesoporous semiconductor oxides for ultratransparent energy storage

Realizing transparent and energy-dense supercapacitor is highly challenging, as there is a trade-off between energy storing capability and transparency in the active material film. We report here that interstitial boron-doped mesoporous semiconductor oxide shows exceptional electrochemical capacitance which rivals other pseudocapacitive materials, while maintaining its transparent characteristic. This improvement is credited to the robust redox reactions at interstitial boron-associated defects that transform inert semiconductor oxides into an electrochemically active material without affecting its transparency. By precisely tuning the level of doping, the pseudocapacitive reactivity of these materials is optimized, resulting in a volumetric capacitance up to 1172 F cm-3. Attributing to such efficient charge storage utilization on the active film, the fabricated transparent supercapacitor delivers a maximum areal energy density of 1.36 × 10-3 mWh cm-2 that is close to those of conventional pseudocapacitive materials, with nearly 100% capacitance retention after 15000 cycles and ultrahigh transparency (up to 85% transmittance at 550 nm). In addition, this device shows excellent durability and flexibility with multiple optional outputs, demonstrating the potential as a transparent energy supply in planar electronics.

Application of Octanohydroxamic Acid for Salting out Liquid-Liquid Extraction of Materials for Energy Storage in Supercapacitors

The ability to achieve high areal capacitance for oxide-based supercapacitor electrodes with high active mass loadings is critical for practical applications. This paper reports the feasibility of the fabrication of Mn₃O₄-multiwalled carbon nanotube (MWCNT) composites by the new salting-out method, which allows direct particle transfer from an aqueous synthesis medium to a 2-propanol suspension for the fabrication of advanced Mn₃O₄-MWCNT electrodes for supercapacitors. The electrodes show enhanced capacitive performance at high active mass loading due to reduced particle agglomeration and enhanced mixing of the Mn₃O₄ particles and conductive MWCNT additives. The strategy is based on the multifunctional properties of octanohydroxamic acid, which is used as a capping and dispersing agent for Mn₃O₄ synthesis and an extractor for particle transfer to the electrode processing medium. Electrochemical studies show that high areal capacitance is achieved at low electrode resistance. The electrodes with an active mass of 40.1 mg cm^-2 show a capacitance of 4.3 F cm^-2 at a scan rate of 2 mV s^-1. Electron microscopy studies reveal changes in electrode microstructure during charge-discharge cycling, which can explain the increase in capacitance. The salting-out method is promising for the development of advanced nanocomposites for energy storage in supercapacitors.

Fused Heterocyclic Molecule-Functionalized N-Doped Reduced Graphene Oxide by Non-Covalent Bonds for High-Performance Supercapacitors

Indole molecules with fused heteroaromatic structures can be adsorbed on the N-doped graphene surface through the π-π interaction. Therefore, the indole-functionalized N-doped graphene (InFGN) with mesopores is successfully fabricated by a simple hydrothermal method and subsequent vacuum freeze-drying process. The microstructure, thickness, element composition, pore structure, and electrochemical performance of InFGN are analyzed via SEM, TEM, AFM, BET, UV-vis, FT-IR, XPS, Raman, XRD, and electrochemical technologies. Since the five-membered aromatic heterocycles are electron-rich, the indole molecules fixed on the N-doped graphene surface can repair the structural defects generated by N doping. Electrochemical measurements show that the InFGN electrode highlights an excellent capacitance of 622.3 F g^-1 at 2 A g^-1 and a durable cycling life of 100.5% after 5000 charging/discharging cycle times. For further practical application, a symmetric device has been assembled by using InFGN electrodes, which realizes high-power and energy densities (18.8-20.6 Wh kg^-1 at 800-8000 W kg^-1). This study provides a shortcut for building green supercapacitors with enhanced energy storage performance.

High performance flexible supercapacitors based on secondary doped PEDOT-PSS-graphene nanocomposite films for large area solid state devices

In this work, we propose the development of high performance and flexible supercapacitors using reduced graphene oxide (rGO) incorporated poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT-PSS) nanocomposites by secondary doping. The structural and morphological features of the composite film were analyzed in detail using SEM, AFM, FTIR, XPS and TGA. Secondary doping of ethylene glycol (EG) assisted by rGO incorporation significantly enhances the room temperature conductivity of PEDOT-PSS films from 3 S cm-1 to nearly 1225 S cm-1 for a 10 wt% composite. The secondary doped PEDOT-PSS:EG/rGO composite film demonstrated improved electrochemical performances with specific capacitance of 174 (F g-1) and energy density of 810 (W h kg-1) which is nearly 4 times greater than pristine PEDOT-PSS due to synergetic interactions between rGO and PEDOT-PSS. The prepared composite films show long term stability with capacitance retention of over 90% after 5000 cycles of charging-discharging. The nanocomposite films used in the present investigation demonstrates percolative behavior with a percolation threshold at 10 wt% of rGO in PEDOT-PSS. The assembled supercapacitor device could be bent and rolled-up without a decrease in electrochemical performance indicating the potential to be used in practical applications. To demonstrate the practical applicability, a rolled-up supercapacitor device was constructed that demonstrates operation of a red LED for 40 seconds when fully charged. This study will provide new dimensions towards designing cost effective, flexible and all solid-state supercapacitors with improved electrochemical performance using electrodes based on secondary doped PEDOT-PSS/rGO organic thin films.