Hydrous RuO2‐Decorated MXene Coordinating with Silver Nanowire Inks Enabling Fully Printed Micro‐Supercapacitors with Extraordinary Volumetric Performance

The fabrication of fully printable, flexible micro‐supercapacitors (MSCs) with high energy and power density remains a significant technological hurdle. To overcome this grand challenge, the 2D material MXene has garnered significant attention for its application, among others, as a printable electrode material for high performing electrochemical energy storage devices. Herein, a facile and in situ process is proposed to homogeneously anchor hydrous ruthenium oxide (RuO₂) nanoparticles on Ti₃C₂T_x MXene nanosheets. The resulting RuO₂@MXene nanosheets can associate with silver nanowires (AgNWs) to serve as a printable electrode with micrometer‐scale resolution for high performing, fully printed MSCs. In this printed nanocomposite electrode, the RuO₂ nanoparticles contribute high pseudocapacitance while preventing the MXene nanosheets from restacking, ensuring an effective ion highway for electrolyte ions. The AgNWs coordinate with the RuO₂@MXene to guarantee the rheological property of the electrode ink, and provide a highly conductive network architecture for rapid charge transport. As a result, MSCs printed from the nanocomposite inks demonstrate volumetric capacitances of 864.2 F cm^?3 at 1 mV s^?1, long‐term cycling performance (90% retention after 10 000 cycles), good rate capability (304.0 F cm^?3 at 2000 mV s^?1), outstanding flexibility, remarkable energy (13.5 mWh cm^?3) and power density (48.5 W cm^?3).     

Interconnected Frameworks with a Sandwiched Porous Carbon Layer/Graphene Hybrids for Supercapacitors with High Gravimetric and Volumetric Performances

A facile approach to synthesize porous disordered carbon layers as energy storage units coating on graphene sheets to form interconnected frameworks by one‐step pyrolysis of the mixture of graphene oxide/polyaniline and KOH is presented. As effective energy storage units, these porous carbon layers play an important role in enhancing the electrochemical performances. The obtained porous carbon material exhibits a high specific surface area (2927 m² g^?1), hierarchical interconnected pores, moderate pore volume (1.78 cm³ g^?1), short ion diffusion paths, and a high nitrogen level (6 at%). It displays both unparalleled gravimetric (481 F g^?1) and outstanding volumetric capacitance (212 F cm^?3) in an aqueous electrolyte. More importantly, the assembled symmetrical supercapacitor delivers not only high gravimetric (25.7 Wh kg^?1 based on total mass of electroactive materials) but also high volumetric energy densities (11.3 Wh L^?1) in an aqueous electrolyte. Furthermore, the assembled asymmetric supercapacitor yields a maximum energy density up to 88 Wh kg^?1, which is, to the best of our knowledge, the highest value so far reported for carbon//MnO₂ asymmetric supercapacitors in aqueous electrolytes. Therefore, this novel carbon material holds great promise for potential applications in energy‐related technological fields.     

Stretchable Supercapacitors as Emergent Energy Storage Units for Health Monitoring Bioelectronics

Emerging health monitoring bioelectronics require energy storage units with improved stretchability, biocompatibility, and self‐charging capability. Stretchable supercapacitors hold great potential for such systems due to their superior specific capacitances, power densities, and tissue‐conforming properties, as compared to both batteries and conventional capacitors. Despite the rapid progress that has been made in supercapacitor research, practical applications in health monitoring bioelectronics have yet to be achieved, requiring innovations in materials, device configurations, and fabrications tailored for such applications. In this review, the progress in stretchable supercapacitor‐powered health monitoring bioelectronics is summarized and the required specifications of supercapacitors for different types of application settings with varying demands on biocompatibility are discussed, including nontouching wearables, skin‐touching wearables, skin‐conforming wearables, and implantables. The perspective of this review is then broadened to focus on integration of stretchable supercapacitors in bioelectronics and aspects of energy harvesting and sensing. Finally further insights on the existing challenges in this developing field and potential solutions are provided.     

Nanostructured Ternary Electrodes for Energy‐Storage Applications

A three‐component, flexible electrode is developed for supercapacitors over graphitized carbon fabric, utilizing γ‐MnO₂ nanoflowers anchored onto carbon nanotubes (γ‐MnO₂/CNT) as spacers for graphene nanosheets (GNs). The three‐component, composite electrode doubles the specific capacitance with respect to GN‐only electrodes, giving the highest‐reported specific capacitance (308 F g^?1) for symmetric supercapacitors containing MnO₂ and GNs using a two‐electrode configuration, at a scan rate of 20 mV s^?1. A maximum energy density of 43 W h kg^?1 is obtained for our symmetric supercapacitors at a constant discharge‐current density of 2.5 A g^?1 using GN–(γ‐MnO₂/CNT)‐nanocomposite electrodes. The fabricated supercapacitor device exhibits an excellent cycle life by retaining ≈90% of the initial specific capacitance after 5000 cycles.     

Antimonene Engineered Highly Deformable Freestanding Electrode with Extraordinarily Improved Energy Storage Performance

Advanced 2D materials have spurred great interest as a new paradigm in pursuing improved energy storage performance. Herein, for the first time, antimonene is utilized as an effective active component for constructing highly deformable and editable freestanding film electrodes, as the basis of a supercapacitor with record‐breaking electrode performance. The insertion of antimonene is able to improve the environmental stability of the antimonene/MXene composite electrode and remarkably enhance the energy storage capability in both protic and neutral electrolytes. Notably, an ultrahigh specific volumetric capacitance of 4255 F cm^?3 is achieved by the electrode tested in a1 m H₂SO₄ electrolyte, which represents the state‐of‐the‐art value reported to date for supercapacitor electrodes based on MXenes. The flexible supercapacitors constructed by the composite electrode, also demonstrate highly competitive energy and power densities: 459.75 mWh cm^?3 and 3.12 W cm^?3 for the asymmetrical one with a much widened potential window of 2 V in neutral electrolyte; 112.52 mWh cm^?3 and 1 W cm^?3 for the symmetrical configuration with an outstanding capacitance of 1265 F cm^?3 in acidic media. This work sheds new light on the fabrication of high‐performance supercapacitor electrodes with functionalities in different electrolyte media and various device configurations.     

Supercapacitor Electrodes Obtained by Directly Bonding 2D MoS2 on Reduced Graphene Oxide

Layered molybdenum disulfide (MoS₂) is deposited by microwave heating on a reduced graphene oxide (RGO). Three concentrations of MoS₂ are loaded on RGO, and the structure and morphology are characterized. The first layers of MoS₂ are detected as being directly bonded with the oxygen of the RGO by covalent chemical bonds (Mo‐O‐C). Electrochemical characterizations indicate that this electroactive material can be cycled reversibly between 0.25 and 0.8 V in 1 m HClO₄ solution for hybrids with low concentrations of MoS₂ layers (LCMoS₂/RGO) and between 0.25 and 0.65 V for medium (MCMoS₂/RGO) and high concentrations (HCMoS₂/RGO) of MoS₂ layers on graphene. The specific capacitance measured values at 10 mV s^?1 are 128, 265, and 148 Fg^?1 for the MoS₂/RGO with low, medium, and high concentrations of MoS₂, respectively, and the calculated energy density is 63 W h kg^?1 for the LCMoS₂/RGO hybrid. This supercapacitor electrode also exhibits superior cyclic stability with 92% of the specific capacitance retained after 1000 cycles.     

Facile Synthesis of 3D MnO2–Graphene and Carbon Nanotube–Graphene Composite Networks for High‐Performance,Flexible, All‐Solid‐State Asymmetric Supercapacitors

The integration of graphene nanosheets on the macroscopic level using a self‐assembly method has been recognized as one of the most effective strategies to realize the practical applications of graphene materials. Here, a facile and scalable method is developed to synthesis two types of graphene‐based networks, manganese dioxide (MnO₂)–graphene foam and carbon nanotube (CNT)–graphene foam, by solution casting and subsequent electrochemical methods. Their practical applications in flexible all‐solid‐state asymmetric supercapacitors are explored. The proposed method facilitates the structural integration of graphene foam and the electroactive material and offers several advantages including simplicity, efficiency, low‐temperature, and low‐cost. The as‐prepared MnO₂–graphene and CNT–graphene electrodes exhibit high specific capacitances and rate capability. By using polymer gel electrolytes, a flexible all‐solid‐state asymmetric supercapacitor was synthesized with MnO₂–graphene foam as the positive electrode and CNT‐graphene as the negative electrode. The asymmetric supercapacitors can be cycled reversibly in a high‐voltage region of 0 to 1.8 V and exhibit high energy density, remarkable rate capability, reasonable cycling performance, and excellent flexibility.