In-Situ Synergistic 2D/2D MXene/BCN Heterostructure for Superlative Energy Density Supercapacitor with Super-Long Life.

The 2D/2D layered materials are gaining much-needed attention owing to the unprecedented results in supercapacitors by their robust structural and electrochemical compatibility. Here, a facile scalable synthesis of 2D/2D MXene/boron carbon nitride (BCN) heterostructure through no residue direct pyrolysis is reported. The process allows the in-situ growth of BCN nanosheets unravelling the surfaces of MXene synergistically that provide an interconnected conductive network with wide potential window, augmented proportion of Ti sites at elevated temperature removing terminal groups enabling high pseudocapacitive activity and impressive stability. As a result, the as-assembled MXene/BCN electrode records a high specific capacitance of 1173 F g-1 (1876 C g-1 ) at 2 A g-1 and an energy density of 45 Wh kg-1 . Further, the fabricated solid-state device exhibits an ultra-high cyclability of 100% capacitive retention after 100 000 cycles. This will be an epitome for future 2D/2D heterostructures with commendable electrochemical properties as an expedient solution for energy storage applications.

Switching the solubility of electroactive ionic liquids for designing high energy supercapacitor and low potential biosensor.

Ionic liquids are regarded as one of the most prodigious materials for sustainable technological developments with superior performance and versatility. Hence, in this study, we have reported the design and synthesis of electroactive disubstituted ferrocenyl ionic liquids (Fc-ILs) with two different counter anions and demonstrated the significance of their anion tuneable physicochemical characteristics towards multifunctional electrochemical applications. The Fc-IL synthesized with chloride counter anion (Fc-Cl-IL) displays water-solubility and can be used as a redox additive in the fabrication of supercapacitor. Supercapacitor device with Fc-Cl-IL based redox electrolyte exhibits outstanding energy and power densities of 91 Wh kg-1 and 20.3 kW kg-1, respectively. Meanwhile, ferrocenyl IL synthesized with perchlorate anion (Fc-ClO4-IL) exhibits water-insolubility and can serve as a redox mediator towards construction of a glucose biosensor. The biosensor comprising Fc-ClO4-IL is able to detect glucose at an exceptionally lower potential of 0.2 V, with remarkable sensitivity and selectivity. This study implies that the introduction of electroactive ILs could afford supercapacitor devices with high energy and power densities and biosensors with less detection potential.

New Method for the Synthesis of 2D Vanadium Nitride (MXene) and Its Application as a Supercapacitor Electrode.

MXenes are the class of two-dimensional transition metal carbides and nitrides that exhibit unique properties and are used in a multitude of applications such as biosensors, water purification, electromagnetic interference shielding, electrocatalysis, supercapacitors, and so forth. Carbide-based MXenes are being widely explored, whereas investigations on nitride-based ones are seldom. Among the nitride-based MXenes obtained from their MAX phases, only Ti4N3 and Ti2N are reported so far. Herein, we report a novel synthesis of V2NT x (T x is the surface termination) obtained by the selective removal of "Al" from V2AlN by immersing powders of V2AlN in the LiF-HCl mixture (salt-acid etching) followed by sonication to obtain V2NT x (T x = -F, -O) MXene which is then delaminated using the dimethyl sulfoxide solvent. The V2NT x MXene is characterized by X-ray diffraction studies, field emission scanning electron microscope imaging, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscope imaging. Supercapacitor electrodes are prepared using V2NT x MXenes and their electrochemical performances are examined by cyclic voltammetry, galvanostatic charge/discharge measurement, and electrochemical impedance spectroscopy. The V2NT x MXene electrode exhibits a specific capacitance of 112.8 F/g at a current density of 1.85 mA/cm2 with an energy and power density of 15.66 W h/kg and 3748.4 W/kg, respectively, in 3.5 M KOH aqueous electrolyte. The electrode exhibits an excellent capacitance retention of 96% even after 10,000 charge/discharge cycles. An asymmetric supercapacitor fabricated with V2NT x as a negative electrode and Mn3O4 nanowalls as a positive electrode helps obtain a cell voltage of 1.8 V in aqueous KOH electrolyte.