3-Dimensional ordered reduced graphene oxide embedded with N-doped graphene quantum dots for high performance supercapacitors

Energy utilization of agricultural waste: Machine learning prediction and pyrolysis transformation

The rapid screening of agricultural waste materials for capacitor preparation holds significant importance in comprehending the relationship between material properties and enhancing experimental efficiency. In this study, we developed two machine learning models to predict electrode material characteristics using 2997 data points extracted from 235 articles. The identification and influence of key features on prediction indices provide a theoretical foundation for subsequent practical preparation. Through regression analysis and index evaluation, corn straw emerged as the optimal material for capacitor preparation, leading us to propose a one-step activation and two-step modification approach to convert corn straw into porous biochar. By modifying biochar with Co(NO3)2·6H2O, the maximum electrode capacitance of porous carbon reached 732.6 F/g. Furthermore, the electrode exhibited exceptional cycle stability with a remaining capacitance of 96 % after 5000 cycles. The prepared symmetric capacitor demonstrated pseudocapacitance behavior with a capacitance of 183.15 F/g at a current density of 1.0 A/g, power density of 22 kW/kg, and energy density of 9.03 Wh/kg. Considering the increasing annual output of corn straw and its superior industrial application prospects compared to acid-, base-, or precious metal-based alternatives due to their cost-effectiveness and environmental friendliness, these findings highlight the potential practical value in utilizing modified corn straw biochar as an efficient energy storage electrode material.

Prominent enhancement of stability under high current density of LiFePO4-based multidimensional nanocarbon composite as cathode for lithium-ion batteries

A facile method for synthesizing carbon-coated lithium iron phosphate (LiFePO4, LFP) and an LFP-based multidimensional nanocarbon composite to enhance the electrochemical performance of lithium-ion batteries is presented herein. Three types of cathode materials are prepared: carbon-coated LFP (LC), carbon-coated LFP with carbon nanotubes (LC@C), and carbon-coated LFP with carbon nanotubes/graphene quantum dots (LC@CG). The electrochemical performances of the LC-nanocarbon composites are compared, and both LC@C and LC@CG show improved electrochemical performance than LC. Compared with both the LC and LC@C electrodes, the LC@CG electrode exhibits the highest specific capacity of 107.1 mA h g-1 under 20C of current density, as well as higher capacities and greater stability over all measured current densities. Moreover, after 300 charge-discharge cycles, the LC@CG electrode exhibits the best stability than the LC and LC@C electrodes. This is attributable to the graphene quantum dots, which enhance the morphological stability of the LC@CG electrode during electrochemical measurements. Our findings suggest that LFP-nanocarbon composites are promising as cathode materials and highlight the potential of graphene quantum dots for improving the stability of cathodes.

Agricultural waste to real worth biochar as a sustainable material for supercapacitor

Biochar made from agricultural waste is gaining more attention in energy field due to its sustainability, low cost, apart from having high supercapacitance performance. Also, it has a wide range of environmental applications, including wastewater treatment, upgrading soil fertility, contaminant immobilization, and in situ carbon sequestration. The existing thermo-chemical methodologies for converting agricultural waste into a sustainable material i.e. biochar and the role of activation agents in enhancing the performance of these materials were critically analyzed and discussed. An overview of recent trends in agricultural waste-derived biochar for supercapacitor electrodes is highlighted in this review that emphasizes green circular economy for encouraging net-zero utility of agriculture waste biomass. The roles of various newly prepared "green" electrolytes in reducing the negative consequences of supercapacitor is also reviewed. The trashing of agricultural waste and the depletion of energy supplies has become a global concern, hurting the world's ecosystem and economy through pollution and a fuel crisis and hence the concept of a green circular economic model is also highlighted.

Erbium-Doped GQD-Embedded Coffee-Ground-Derived Porous Biochar for Highly Efficient Asymmetric Supercapacitor

A nanocomposite with erbium-doped graphene quantum dots embedded in highly porous coffee-ground-derived biochar (Er-GQD/HPB) was synthesized as a promising electrode material for a highly efficient supercapacitor. The HPB showed high porosity, with a large surface area of 1295 m2 g−1 and an average pore size of 2.8 nm. The 2–8-nanometer Er-GQD nanoparticles were uniformly decorated on the HPB, subsequently increasing its specific surface area and thermal stability. Furthermore, the intimate contact between the Er-GQDs and HPB significantly reduced the charge-transfer resistance and diffusion path, leading to the rapid migration of ions/electrons in the mesoporous channels of the HPB. By adding Er-GQDs, the specific capacitance was dramatically increased from 337 F g−1 for the pure HPB to 699 F g−1 for the Er-GQD/HPB at 1 A g−1. The Ragone plot of the Er-GQD/HPB exhibited an ultrahigh energy density of 94.5 Wh kg−1 and a power density of 1.3 kW kg−1 at 1 A g−1. Furthermore, the Er-GQD/HPB electrode displayed excellent cycling stability, and 81% of the initial capacitance remained after 5000 cycles. Our results provide further insights into a promising supercapacitance material that offers the benefits of both fast ion transport from highly porous carbons and electrocatalytic improvement due to the embedment of Er-doped GQDs to enhance energy density relative to conventional materials.

A poly-(L-serine)/reduced graphene oxide-Nafion supported on glassy carbon (PLS/rGO-Nafion/GCE) electrode for the detection of naproxen in aqueous solutions

A new electrode was constructed via the anodic electropolymerization of poly-(L-serine) (PLS) on an rGO-Nafion-modified glassy carbon electrode (GCE) for the detection of the emerging organic contaminant naproxen (NPX). The morphology, crystal phase, and surface elements of the electrode were investigated with SEM, TEM, XRD, Raman, ATR-FTIR, zeta potential, C-H-O, and XPS analyses. Results of the surface analysis showed a porous structure resembling graphene sheets inside the Nafion/GCE architecture. Various electrochemical parameters, including scan rate, pH, and NPX concentration, were studied to evaluate the performance of the electrode. The synergistic effect of PLS and rGO-Nafion greatly facilitated the catalytic oxidation of NPX on PLS/rGO-Nafion/GCE. Electrochemical NPX oxidation was a one-electron transfer and adsorption limited process. The optimal working potential was 0.92 V vs. Ag/AgCl. The oxidation current of NPX increased with the increase in the concentration of analyte and scan rate but decreased with pH. The modified electrode exhibited excellent linearity with respect to NPX concentration in the range of 4.3 to 87 μM and limit of detection of 0.23 μM (S/N = 3). The PLS/rGO-Nafion/GCE is a fast, sensitive, reliable, and economical electrode for the detection of NPX in water.

Shedding Light on Graphene Quantum Dots: Key Synthetic Strategies, Characterization Tools, and Cutting-Edge Applications

During the last 20 years, the scientific community has shown growing interest towards carbonaceous nanomaterials due to their appealing mechanical, thermal, and optical features, depending on the specific nanoforms. Among these, graphene quantum dots (GQDs) recently emerged as one of the most promising nanomaterials due to their outstanding electrical properties, chemical stability, and intense and tunable photoluminescence, as it is witnessed by a booming number of reported applications, ranging from the biological field to the photovoltaic market. To date, a plethora of synthetic protocols have been investigated to modulate the portfolio of features that GQDs possess and to facilitate the use of these materials for target applications. Considering the number of publications and the rapid evolution of this flourishing field of research, this review aims at providing a broad overview of the most widely established synthetic protocols and offering a detailed review of some specific applications that are attracting researchers’ interest.