Effect of Different Electrolytes on the Supercapacitor Behavior of Single and Multilayered Electrode Materials Based on Multiwalled Carbon Nanotube/Polyaniline Composite

Nanocomposite Perfluorosulfonic Acid/Montmorillonite-Na+ Polymer Membrane as Gel Electrolyte in Hybrid Supercapacitors

Solid-state supercapacitors with gel electrolytes have emerged as a promising field for various energy storage applications, including electronic devices, electric vehicles, and mobile phones. In this study, nanocomposite gel membranes were fabricated using the solution casting method with perfluorosulfonic acid (PFSA) ionomer dispersion, both with and without the incorporation of 10 wt.% montmorillonite (MMT). MMT, a natural clay known for its high surface area and layered structure, is expected to enhance the properties of supercapacitor systems. Manganese oxide, selected for its pseudocapacitive behavior in a neutral electrolyte, was synthesized via direct co-precipitation. The materials underwent structural and morphological characterization. For electrochemical evaluation, a two-electrode Swagelok cell was employed, featuring a carbon xerogel negative electrode, a manganese dioxide positive electrode, and a PFSA polymer membrane serving as both the electrolyte and separator. The membrane was immersed in a 1 M Na2SO4 solution before testing. A comprehensive electrochemical analysis of the hybrid cells was conducted and compared with a symmetric carbon/carbon supercapacitor. Cyclic voltammetric curves were recorded, and galvanostatic charge-discharge tests were conducted at various temperatures (20, 40, 60 °C). The hybrid cell with the PFSA/MMT 10 wt.% exhibited the highest specific capacitance and maintained its hybrid profile after prolonged cycling at elevated temperatures, highlighting the potential of the newly developed membrane.

Stereolithography-Derived Three-Dimensional Pyrolytic Carbon/Mn3O4 Nanostructures for Free-Standing Hybrid Supercapacitor Electrodes

The development of permeable three-dimensional (3D) macroporous carbon architectures loaded with active pseudocapacitive nanomaterials offers hybrid supercapacitor (SC) materials with higher energy density, shortened diffusion length for ions, and higher charge-discharge rate capability and thereby is highly relevant for electrical energy storage (EES). Herein, structurally complex and tailorable 3D pyrolytic carbon/Mn₃O₄ hybrid SC electrode materials are synthesized through the self-assembly of MnO₂ nanoflakes and nanoflowers onto the surface of stereolithography 3D-printed architectures via a facile wet chemical deposition route, followed by a single thermal treatment. Thermal annealing of the MnO₂ nanostructures concurrent with carbonization of the polymer precursor leads to the formation of a 3D hybrid SC electrode material with unique structural integrity and uniformity. The microstructural and chemical characterization of the hybrid electrode reveals the predominant formation of crystalline hausmannite-Mn₃O₄ after the pyrolysis/annealing process, which is a favorable pseudocapacitive material for EES. With the combination of the 3D free-standing carbon architecture and self-assembled binder-free Mn₃O₄ nanostructures, electrochemical capacitive charge storage with very good rate capability, gravimetric and areal capacitances (186 F g^-1 and 968 mF cm^-2, respectively), and a long lifespan (>92% after 5000 cycles) is demonstrated. It is worth noting that the gravimetric capacitance value is obtained by considering the full mass of the electrode including the carbon current collector. When only the mass of the pseudocapacitive nanomaterial is considered, a capacitance value of 457 F g^-1 is achieved, which is comparable to state-of-the-art Mn₃O₄-based SC electrode materials.

Polyaniline Nanotubes/Carbon Cloth Composite Electrode by Thermal Acid Doping for High-Performance Supercapacitors

Carbon materials have been widely used in designing supercapacitors (SCs) but the capacitance is not ideal. Herein, we synthesize polyaniline (PANI) nanotubes on the basis of a carbon cloth (CC) through a one-step self-degradation template method, and fabricate a CC@PANI NTs-H (CC@PANI nanotubes doping at high temperature) composite electrode by thermal acid doping. The CC@PANI NTs-H electrode obviously exhibits better electrochemical performance with a gravimetric capacitance of 438 F g⁻¹ and maintains 86.8% after 10,000 cycles than the CC@PANI NTs-R (CC@PANI nanotubes doping at room temperature) electrode. Furthermore, we assemble a flexible solid state supercapacitor (FSSC) device with the as-prepared CC@PANI NTs-H composite electrodes, showing good flexibility and outstanding electrochemical performances with a high gravimetric capacitance of 247 F g⁻¹, a large energy density of 21.9 Wh kg⁻¹, and a capacitance retention of 85.4% after 10,000 charge and discharge cycles. Our work proposes a novel and easy pathway to fabricate low-cost FSSCs for the development of energy storage devices.