Moniruzzaman Sk

Synthesis of polyaniline nanotubes using the self-assembly behavior of vitamin C: a mechanistic study and application in electrochemical supercapacitors

Herein, we report the discovery of an unprecedented behavior of vitamin C to form a rod-like assembly through hydrogen-bonding in water, which, upon the addition of aniline monomer, produces polyaniline (PANI) nanotubes via the oxidative polymerization method. It was observed that tubular growth of PANI at the nanometer scale can be controlled by varying the molar ratio of vitamin C to aniline. At a molar ratio of 0.25 (i.e. [Vitamin C]/[Aniline] = 0.25), long and uniform nanotubes which extended to several micrometers with an outer diameter (OD) in the range of 80–120 nm were observed. We have also demonstrated the efficient electrochemical properties of novel PANI nanotube based electrodes which showed higher capacitance and energy density values of 714.68 and 99.34 W h kg−1 at 0.5 mA, respectively. The observed results were compared and justified with the theoretical capacitance value.

Facile growth of heparin-controlled porous polyaniline nanofiber networks and their application in supercapacitors

Herein, we present the synthesis of porous polyaniline (PANI) nanofiber networks by a chemical oxidative polymerization method using a biomolecule, heparin. Long uniform nanofibers were formed when the weight ratio of heparin to aniline was 0.25 (PANIH-0.25), where the average nanofiber diameter was about 80–110 nm. No such PANI nanofibers were formed at other weight ratios. A comparison of the morphology of PANIH-0.25 was made with the pure PANI which was synthesized without any template. We further studied the potential of PANIH-0.25 as a nanostructured electrode material for the supercapacitor applications. The PANIH-0.25 nanofiber electrode yielded a six-fold improvement in specific capacitance when compared with pure PANI. The PANIH-0.25 electrode exhibited a specific capacitance of 732.18 ± 24.1 F g−1 and a longer cycle life with the capacitance retention of 72.28% after 1000 cycles. The observed capacitance was elucidated and justified based on theoretical considerations.

Layer-by-layer (LBL) assembly of graphene with p-phenylenediamine (PPD) spacer for high performance supercapacitor applications

A novel route to perform the layer-by-layer (LBL) assembly of graphene sheets through the covalent functionalization of graphene oxide is reported. The two-dimensional (2D) graphene sheets have the tendency to aggregate or stack which reduces the available surface area and limits the ion transport during the electrochemical process. This makes it hard for the stacked graphene assembly to achieve optimum device performance. Herein, we report a strategy to solve these problems by transforming the aggregated graphene sheets into an open structure by introducing a spacer between the layers. In this study, a highly reliable, efficient and very simple modification route is reported, where p-phenylenediamine (PPD) is covalently functionalized onto graphene oxide (GO) nanosheets through the reaction between two amine groups of PPD and the epoxy groups on the basal plane of GO. The modified graphene sheet (GPPD) is capable of delivering a much higher specific capacitance and energy density of 282.33 F g−1 and 39.24 W h kg−1, respectively at a discharge current of 0.75 mA. The GPPD electrode also displays excellent electrochemical stability of 92.82% after 1000 charge–discharge cycles. A comparison is made with the existing electrochemical performance and it is found that the results obtained in our study using such a simple process are superior to most of the results reported in the literature.

Development of 3D Urchin-Shaped Coaxial Manganese Dioxide@Polyaniline (MnO2@PANI) Composite and Self-Assembled 3D Pillared Graphene Foam for Asymmetric All-Solid-State Flexible Supercapacitor Application

We have fabricated high-energy-density all-solid-state flexible asymmetric supercapacitor by using a facile novel 3D hollow urchin-shaped coaxial manganese dioxide@polyaniline (MnO2@PANI) composite as positive electrode and 3D graphene foam (GF) as negative electrode materials with polyvinyl alcohol (PVA)/KOH gel electrolyte. The coaxial MnO2@PANI composite was fabricated by hydrothermal route followed by oxidation without use of an external oxidant. The formation mechanism of the 3D hollow MnO2@PANI composite occurs first by nucleation and growth of the MnO2 crystal species via dissolution-recrystallization and oriented attachment mechanisms followed by the oxidation of aniline monomers on the MnO2 crystalline template. The self-assembled 3D graphene block was synthesized by hydrothermal route using vitamin C as a reducing agent. The microstructures of the composites are analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The morphology is characterized by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), which clearly showed the formation of urchin-shaped coaxial MnO2@PANI composite. The electrochemical studies are explored by cyclic voltammetry, electrochemical impedance spectrometry, and cyclic charge-discharge tests. The symmetric all-solid-state flexible MnO2@PANI//MnO2@PANI and GF//GF supercapacitors exhibit the specific capacitance of 129.2 and 82.1 F g-1 at 0.5 A/g current density, respectively. The solid-state asymmetric supercapacitor shows higher energy density (37 Wh kg-1) with respect to the solid-state symmetric supercapacitors MnO2@PANI//MnO2@PANI and GF//GF, where the obtained energy density are found to be 17.9 and 11.4 Wh kg-1, respectively, at 0.5 A/g current density. Surprisingly, the asymmetric supercapacitor shows a high energy density of 22.3 Wh kg-1 at a high current density of 5 A g-1. The solid-state asymmetric supercapacitor shows a good cyclic stability in which ∼11% capacitance loss was observed after 5000 cycles.

A novel high performance bismaleimide/diallyl bisphenol A (BMI/DBA)–epoxy interpenetrating network resin for rigid riser application

A new class of interpenetrating network (IPN) resin system was developed by mixing tetrafunctional epoxy resin (TGDDM) with diallyl bisphenol A (DBA) modified bismaleimide (BMI) for rigid riser applications at high temperatures of more than 280 °C. The curing kinetics of the resins were assessed by differential scanning calorimetry (DSC). Epoxy resin with DBA modified BMI (BMI/DBA–epoxy IPN) showed low activation energy which is due to the autocatalytic effect of DBA modified BMI in the curing process. The thermal stability of the cured resins as evaluated using thermogravimetric analysis (TGA) showed that they were stable up to 325 °C. Dynamic mechanical analysis (DMA) showed that the BMI/DBA–epoxy IPN resin had a glass transition temperature (Tg) equal to that of neat epoxy of around 280 °C. The incorporation of DBA modified BMI into the epoxy resin enhanced the mechanical properties such as tensile, flexural and impact strength by 25%, 30% and 45%, respectively compared to neat epoxy resin. Furthermore, the viscosity of the IPN was 0.3–1 Pa s which is within the filament winding range required for rigid risers. Prototype rigid risers were made using the BMI/DBA–epoxy IPN resin as matrix and carbon fiber as the reinforcement using the filament winding technique. The approach presented here represents a good approach to developing high performance high thermal stability resins for rigid risers in oil field applications.

Development of a 3D graphene aerogel and 3D porous graphene/MnO2@polyaniline hybrid film for all-solid-state flexible asymmetric supercapacitors

There is an increasing demand for safe, environmentally benign energy storage devices in portable electronic appliances, wearable gadgets, flexible displays, and other personal multimedia devices. In this study, we have fabricated an all-solid-state flexible asymmetric supercapacitor using a novel 3D porous reduced graphene oxide/manganese dioxide@polyaniline (RGO/MnO2@PANI) hybrid film as the positive electrode and a self-assembled 3D pillared graphene aerogel as the negative electrode material with a polyvinyl alcohol/potassium hydroxide (PVA/KOH) gel electrolyte. The flexible composite film was synthesized by vacuum filtration of GO and a MnO2@PANI mixture followed by chemical reduction of the resulting film in a hydrothermal autoclave. The 3D graphene aerogel was synthesized by a hydrothermal route using a solution of the nonionic triblock copolymer Pluronic F-68 as a soft template and vitamin C as a reducing agent. Herein, the Pluronic copolymer played dual roles: first, it enabled the effective dispersion of graphene oxide in water, and second, it assisted the formation of a stable 3D pillared hydrogel assembly. The RGO/MnO2@PANI-based symmetric supercapacitor shows a high energy density of 18.33 W h kg−1 at a power density of 0.388 kW kg−1. An asymmetric supercapacitor (graphene aerogel//RGO/MnO2@PANI), which was fabricated by optimizing the individual electrode materials, exhibited a very high energy density of 38.12 W h kg−1 at a power density of 1.191 kW kg−1 utilizing a large potential window of 1.5 V. Moreover, 3 cells connected in series successfully lit up a red LED for 45 s and displayed similar performance under bending conditions.