Surface design and engineering of hierarchical hybrid nanostructures for asymmetric supercapacitors with improved electrochemical performance

Cation intercalated one-dimensional manganese hydroxide nanorods and hierarchical mesoporous activated carbon nanosheets with ultrahigh capacitance retention asymmetric supercapacitors

We have reported the electrochemical performance of K⁺ ion doped Mn(OH)₄ and MnO₂ nanorods as a positive electrode and a highly porous activated carbon nanosheet (AC) made from Prosopis Juliflora as negative electrode asymmetric supercapacitor (ASC) with high rate capability and capacity retention. The cation K⁺ doped Mn(OH)₄ and MnO₂ nanorods with large tunnel sizes allow the electrolyte to penetrate through a well-defined pathway and hence benefits from the intercalation pseudocapacitance and surface redox reactions. As a result, they exhibit good electrochemical performance in neutral aqueous electrolytes. More specifically, the K⁺-Mn(OH)₄ nanorods exhibit higher capacitance values than K⁺-MnO₂ nanorods due to the homogenous distribution of 1D nanorods and optimum amount of OH bonds. The fabricated K⁺-Mn(OH)₄ symmetric electrochemical Pseudocapacitor shows very high energy density of 10.11 Wh/kg and high-power density of 51.04 W/kg over the range of 1.0 V in aqueous electrolyte. The energy density of AC||K⁺-Mn(OH)₄ ASC is improved significantly compared to those of symmetric supercapacitors. The fabricated ASC exhibits a wide working voltage window (1.6 V), high power (143.37 W/kg) and energy densities (41.38 Wh/kg) at 0.2 A g^-1, and excellent cycling behavior with 107.3% capacitance retention after 6000 cycles at 2 A g^-1 indicating the promising practical applications in electrochemical supercapacitors.

Skeleton/skin structured (RGO/CNTs)@PANI composite fiber electrodes with excellent mechanical and electrochemical performance for all-solid-state symmetric supercapacitors

Polyaniline coated reduced graphene oxide/carbon nanotube composite fibers ((RGO/CNTs)@PANI, RCP) with skeleton/skin structure are designed as fiber-shaped electrodes for high performance all-solid-state symmetric supercapacitor. The one-dimensional reduced graphene oxide/carbon nanotube composite fibers (RGO/CNTs, RC) are prepared via a simple in-situ reduction of graphene oxide in presence of carbon nanotubes in quartz glass pipes, which exhibit excellent mechanical performance of >193.4 MPa of tensile strength. Then polyaniline is coated onto the RC fibers by electrodepositing technique. The electrochemical properties of the RCP fiber-shaped electrodes are optimized by adjusting the feeding ratio of carbon nanotubes. The optimized one exhibits good electrochemical characteristic such as highest volumetric specific capacitance of 193.1 F cm^-3 at 1 A cm^-3, as well as excellent cyclic retention of 92.60% after 2000 cyclic voltammetry cycles. Furthermore, the all-solid-state symmetric supercapacitor, fabricated by using the final composite fiber as both positive and negative electrodes pre-coated with the poly(vinyl alcohol)/H₂SO₄ gel polyelectrolyte, possesses volumetric capacitance of 36.7 F cm^-3 at 0.2 A cm^-3 and could light up a red light-emitting diode easily. The excellent mechanical and electrochemical performances make the designed supercapacitor as promising high performance wearable energy storage device.

CVD Polymers for Devices and Device Fabrication

Chemical vapor deposition (CVD) polymerization directly synthesizes organic thin films on a substrate from vapor phase reactants. Dielectric, semiconducting, electrically conducting, and ionically conducting CVD polymers have all been readily integrated into devices. The absence of solvent in the CVD process enables the growth of high-purity layers and avoids the potential of dewetting phenomena, which lead to pinhole defects. By limiting contaminants and defects, ultrathin (<10 nm) CVD polymeric device layers have been fabricated in multiple laboratories. The CVD method is particularly suitable for synthesizing insoluble conductive polymers, layers with high densities of organic functional groups, and robust crosslinked networks. Additionally, CVD polymers are prized for the ability to conformally cover rough surfaces, like those of paper and textile substrates, as well as the complex geometries of micro- and nanostructured devices. By employing low processing temperatures, CVD polymerization avoids damaging substrates and underlying device layers. This report discusses the mechanisms of the major CVD polymerization techniques and the recent progress of their applications in devices and device fabrication, with emphasis on initiated CVD (iCVD) and oxidative CVD (oCVD) polymerization.

Boron–manganese–carbon nanocomposites synthesized from CO2 for electrode applications in both supercapacitors and fuel cells

Boron–manganese–carbon nanocomposites were synthesized from CO₂ for electrode materials in supercapacitor and fuel cell.