Halogen (iodide, I À ) added aqueous electrolyte facilitates the capacitive behaviour of biomass derived activated carbon based electric double layer capacitors. To produce economically viable electrodes in large scale for supercapacitors (SCs), the activated carbons (ACs) prepared from Eichhornia crassipes (common water hyacinth) by ZnCl 2 activation. The prepared ACs were characterized by XRD, Raman, FT-IR and surface area, pore size and pore volume analysis. The electrochemical properties of the SCs were studied using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS) and cycling stability. The 3I À /I 3 À , 2I À / I 2 , 2I 3 À /3I 2 and I 2 /IO 3 À pairs produce redox peaks in CV and a large Faradaic plateau in charge-discharge curves. Similarly, I À ions improves the good ionic conductivity (lower charge transfer resistance) at the electrode/electrolyte interface which was identified through EIS studies. The calculated specific capacitance and energy density was 472 F g À1 and 9.5 W h kg À1 in aqueous solution of 1 M H 2 SO 4 . Interestingly, nearly two-fold improved specific capacitance and energy density of 912 F g À1 and 19.04 W h kg À1 were achieved when 0.08 M KI was added in 1 M H 2 SO 4 electrolyte with excellent cycle stability over 4000 cycles. Subsequently, this improved specific capacitance and energy density was compared with 0.08 M KBr added to 1 M H 2 SO 4(572 F g À1 , 11.6 W h kg À1 ) and 0.08 M KI added to 1 M Na 2 SO 4 (604 F g À1 , 12.3 W h kg À1 ) as electrolytes.

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A polyethylene oxide-based composite solid polymer electrolyte filled with one-dimensional ceramic Li0.33La0.557TiO3 nanofibers was designed and prepared.

Functionalizing nanostructured carbon nanofibers (CNFs) with bimetallic phosphides enables the material to become an active electrode for multifunctional applications. A facile electrospinning technique is utilized for the first time to develop NiCoP nanoparticles encapsulated CNFs that are used as an energy storage system of supercapattery, and as an electrocatalyst for oxygen reduction, oxygen evolution, and hydrogen evolution reaction in KOH electrolyte. Evolving from the inclusion of bimetallic phosphide nanoparticles, the NiCoP/CNF electrode unveils superior‐specific capacitance (333 Fg−1 at 2 Ag−1) and rate capability (87%). The fabricated supercapattery device offers a voltage of 1.6 V that supplies a remarkable energy density (36 Wh kg−1) along with an improved power density (4000 W kg−1) and unwavering cyclic stability (25 000 cycles). Meanwhile, the NiCoP/CNF electrode has simultaneously performed well as a multifunctional electrocatalyst for oxygen reduction reaction at a half‐wave potential of 0.82 V versus reversible hydrogen electrode and can attain a current density of 10 mA cm−2 at a very low overpotential of 268 and 130 mV for the oxygen evolution reaction and hydrogen evolution reaction, respectively. Thus, the NiCoP/CNF with all its inimitable electrode properties has profoundly proved its proficiency at handling multifunctional challenges in terms of both storage and conversion.

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To realize a suitable supercapacitor nanomaterial, the recently developed technique of reaction under autogenic pressure at elevated temperature has been employed by us to synthesize SnO 2 hexagonal nanocrystals and SnO 2 @C nanocomposites. The synthesis at different temperatures (viz. 500, 600, and 700 °C) yields three different composites. Characterization of these composites by various methods confirms the structural (XRD, Raman, FT-IR) and nanoparticulate (TEM, HRTEM) nature of the synthesized materials. TEM studies including HRTEM reveal that all the synthesized SnO 2 and SnO 2 @C nanomaterials are highly crystalline with hexagonal shape. Cyclic voltammetric studies carried out to examine the capacitance of SnO 2 @C in 1 M H 2 SO 4 show that the nanocomposite prepared at 700 °C has a maximum specific capacitance of 37.8 F/g at a scan rate of 5 mV/s.

The activated carbon was derived from tamarind fruit shell and utilized as electrodes in a solid state electrochemical double layer capacitor (SSEDLC). The fabricated SSEDLC with PVA (polyvinyl alcohol)/H2SO4 gel electrolyte delivered high specific capacitance and energy density of 412 F g(-1) and 9.166 W h kg(-1), respectively, at 1.56 A g(-1). Subsequently, Na2MoO4 (sodium molybdate) added PVA/H2SO4 gel electrolyte was also prepared and applied for SSEDLC, to improve the performance. Surprisingly, 57.2% of specific capacitance (648 F g(-1)) and of energy density (14.4 Wh kg(-1)) was increased while introducing Na2MoO4 as the redox mediator in PVA/H2SO4 gel electrolyte. This improved performance is owed to the redox reaction between Mo(VI)/Mo(V) and Mo(VI)/Mo(IV) redox couples in Na2MoO4/PVA/H2SO4 gel electrolyte. Similarly, the fabricated device shows the excellent capacitance retention of 93% for over 3000 cycles. The present work suggests that the Na2MoO4 added PVA/H2SO4 gel is a potential electrolyte to improve the performance instead of pristine PVA/H2SO4 gel electrolyte. Based on the overall performance, it is strongly believed that the combination of tamarind fruit shell derived activated carbon and Na2MoO4/PVA/H2SO4 gel electrolyte is more attractive in the near future for high performance SSEDLCs.

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