Synthesis and Supercapacitor Performance of Polyaniline/Nitrogen-Doped Ordered Mesoporous Carbon Composites

Proton is Essential or Not: A Fresh Look on Pseudocapacitive Energy Storage of PANI Composites

Protonation has been considered essential for the pseudocapacitive energy storage of polyaniline (PANI) for years, as proton doping in PANI chains not only activates electron transport pathways, but also promotes the proceeding of redox reactions. Rarely has the ability for PANI of storing energy without protonation been investigated, and it remains uncertain whether PANI has pseudocapacitive charge storage properties in an alkaline electrolyte. Here, this work first demonstrates the pseudocapacitive energy storage for PANI without protonation using a PANI/graphene composite as a model material in an alkaline electrolyte. Using in situ Raman spectroscopy coupled with electrochemical quartz crystal microbalance (EQCM) measurements, this work determines the formation of -N= group over potential on a PANI chain and demonstrates the direct contribution of OH- in the nonprotonation type of oxidation reactions. This work finds that the PANI/graphene composite in an alkaline electrolyte has excellent cycling stability with a wider operation voltage of 1 V as well as a slightly higher specific capacitance than that in an acidic electrolyte. The findings provide a new perspective on pseudocapacitive energy storage of PANI-based composites, which will influence the selection of electrolytes for PANI materials and expand their application in energy storage fields.

Efficient and sustainable extraction of uranium from aquatic solution using biowaste-derived active carbon

Efficient and cost-effective biosorbents derived from biowaste are highly demanding to handle various environmental challenges, and demonstrate the remarkable synergy between sustainability and innovation. In this study, the extraction of uranium U(VI) was investigated on biowaste activated carbon (BAC) obtained by chemical activation (phosphoric acid) using Albizia Lebbeck pods as biowaste. The biowaste powder (BP), biowaste charcoal (BC) and BAC were evaluated by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET) with nitrogen adsorption for thermal properties, chemical structures, porosity and surface area, respectively. The pHPZC for acidic or basic nature of the surface and X-ray diffraction (XRD) analysis were performed for BAC. The morphological and elemental analysis were performed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The extraction of uranium U(VI) ions from aqueous solutions using BAC as sorbent was investigated by using different variables such as pH, contact time, initial uranium U(VI) concentration and BAC dose. The highest adsorption (90.60% was achieved at 0.5 g BAC dose, 2 h contact time, pH 6, 10 ppm initial U(VI) concentration and with 200 rpm shaking speeds. The production of this efficient adsorbent from biowaste could be a potential step forward in adsorption of uranium to meet the high demand of uranium for nuclear energy applications.

The effects of different activating agents on the physical and electrochemical properties of activated carbon electrodes fabricated from wood-dust of Shorea robusta

This study focuses on the effects of activating agents on the physical and electrochemical properties of activated carbon (AC) electrodes, fabricated from wood dust of Shorea robusta. Three different activating agents namely H₃PO_4, KOH and Na₂CO₃ have been used to prepare ACs, which were named as: Sr–H₃PO₄, Sr–KOH and Sr–Na₂CO₃. The ACs were characterized by TGA/DSC, XRD, Raman, SEM, FTIR and BET. All the as prepared ACs were found to be amorphous in nature. The oxygen surface functionality was developed at the surface. The surface area of Sr–H₃PO₄, Sr–KOH and Sr–Na₂CO₃ were found to be 1269.5 m²/g, 280.6 m²/g and 58.9 m²/g respectively. The activated carbon-electrodes were then fabricated and supercapacitive performances were evaluated by “three electrode system” in aqueous 6M KOH using cyclic voltammetry (CV), galvanostatic charge discharge (GCD) and electrochemical impedance spectroscopy (EIS).The GCD performed at 1A/g revealed the specific capacitance values were 136.3 F/g, 42.2 F/g and 59.1 F/g for Sr–H₃PO₄, Sr–KOH and Sr–Na₂CO₃-electrodes, respectively. Energy density for Sr–H₃PO₄ electrode was found to be 3.0 Wh/kg at 99.6 W/kg power densities. Moreover, it also displayed imposing cyclic stability of about 96.9 %, 89.5 % and 78.5 % after 1000 cycles of charge/discharge respectively. The overall electrochemical performance of Sr–H₃PO₄ showed outstanding supercapacitive performances demonstrating the high possibility of this material to be used for the EDLC application in supercapacitive energy storage. The Nyquist plot also showed the lowest internal resistance of about 0.4 Ω for Sr–H₃PO₄ electrode.

One-Step Synthesis of Nitrogen-Doped Hydrophilic Mesoporous Carbons from Chitosan-Based Triconstituent System for Drug Release

In situ nitrogen-doped hydrophilic mesoporous carbon spheres with different carbon-to-silicon (C/Si) ratios (NMCs-x/3, x = 5, 6, 7, and 8) were prepared by one-step method coupled with a spray drying and carbonizing technique, in which triblock copolymer (F127) and tetraethyl orthosilicate (TEOS) were used as template agents, and biocompatible chitosan (CS) was used as the carbon source and nitrogen source. These carbon materials were characterized by TG, BET, XRD, Raman, FTIR, TEM, XPS, and contact angle measuring device. The adsorption and release properties of mesoporous carbon materials for the poorly soluble antitumor drug hydroxycamptothecin (HCPT) were investigated. Results showed that nanospherical mesoporous carbon materials were successfully prepared with high specific surface area (2061.6 m²/g), narrowly pore size distribution (2.01-3.65 nm), and high nitrogen content (4.75-6.04%). Those NMCs-x showed a satisfactory hydrophilicity, which gradually increased with the increasing of surface N content. And the better hydrophilicity of NMCs-x was, the larger adsorption capacity for HCPT. The absorption capacity of NMCs-x towards HCPT was in the following orders: q_NMCs-5/3 > q_NMCs-6/3 > q_NMCs-7/3 > q_NMCs-8/3. NMCs-5/3 had the largest saturated adsorption capacity of HCPT (1013.51 mg g^-1) and higher dissolution rate (93.75%).

One-Step In Situ Self-Assembly of Cypress Leaf-Like Cu(OH)2 Nanostructure/Graphene Nanosheets Composite with Excellent Cycling Stability for Supercapacitors

Transition metal hydroxides and graphene composite holds great promise to be the next generation of high performance electrode material for energy storage applications. Here we fabricate the cypress leaf-like Cu(OH)₂ nanostructure/graphene nanosheets composite through one-step in situ synthesis process, employed as a new type of electrode material for high efficiency electrochemical energy storage in supercapacitors. A solution-based two-electrode system is applied to synthesize Cu(OH)₂/graphene hybrid nanostructure, where anodic graphene nanosheets firmly anchor cathodic Cu(OH)₂ nanostructure due to the electrostatic interaction. The in situ self-assembly of Cu(OH)₂/graphene ensures good structural robustness and the cypress leaf-like Cu(OH)₂ nanostructure prompt to form the open and porous morphology. The hybrid structure would facilitate charge transport and effectively mitigate the volume changes during long-term charging/discharging cycles. As a consequence, the Cu(OH)₂/graphene composite exhibits the highest capacitance of 317 mF/cm² at the current density of 1 mA/cm² and superior cyclic stability with no capacitance decay over 20,000 cycles and remarkable rate capability at increased current densities.

Synthesis of nitrogen-doped mesoporous carbon for high-performance supercapacitors

A simple strategy to improve electrochemical performance is by in situ polymerization of monomers in a template.