N/O Co-doped Porous Carbon with Controllable Porosity Synthesized via an All-in-One Step Method for a High-Rate-Performance Supercapacitor

A green and economical methodology to fabricate carbon-based materials with suitable pore size distributions is needed to achieve rapid electrolyte diffusion and improve the performance of supercapacitors. Here, a method combining in situ templates with self-activation and self-doping is proposed. By variation of the molar ratio of magnesium folate and potassium folate, the pore size distribution was effectively adjusted. The optimal carbon materials (Kx) have a high specific surface area (1021-1676 m2 g-1) and hierarchical pore structure, which significantly promotes its excellent capacitive properties. Notably, K2 shows an excellent mass specific capacitance of 233 F g-1 at 0.1 A g-1. It still retained 113 F g-1 at 55 A g-1. The assembled symmetric supercapacitor exhibited an outstanding cyclic stability. It maintains 100% capacitance after 100 000 cycles at 10 A g-1. The symmetric supercapacitor demonstrated a maximum power density of 99.8 kW kg-1. This study focuses on the preparation of layered pore structures to provide insights into the sustainable design of carbon materials.

High Rate Performance Supercapacitors Based on N, O Co-Doped Hierarchical Porous Carbon Foams Synthesized via Chemical Blowing and Dual Templates

N, O Co-Doped porous carbon materials are promising electrode materials for supercapacitors. However, it is still a challenge to prepare high capacitance performance N, O Co-Doped porous carbon materials with balanced pore structure. In this work, a simple chemical blowing method was developed to produce hierarchal porous carbon materials with Zn(NO3)2·6H2O and Fe(NO3)3·9H2O as the foaming agents and precursors of dual templates. Soybean protein isolate served as a self-doping carbon source. The amount of Fe(NO3)3·9H2O influenced the microstructure, element content and capacitance performance of the obtained porous carbon materials. The optimized sample CZnFe-5 with the addition of 5% Fe(NO3)3·9H2O displayed the best capacitance performance. The specific capacitance reached 271 F g-1 at 0.2 A g-1 and retained 133 F g-1 at 100 A g-1. The CZnFe-5//CZnFe-5 symmetric supercapacitors delivered a maximum energy density of 16.83 Wh kg-1 and good stability with capacitance retention of 86.33% after 40,000 cycles tests at 50 A g-1. The symmetric supercapacitors exhibited potential applications in lighting LED bulbs with a voltage of 3 V. This work provides a new strategy for the synthesis of hierarchical porous carbon materials for supercapacitors from low-cost biomass products.

Recent Breakthroughs in Supercapacitors Boosted by Macrocycles

Supercapacitors are essential for electrochemical energy storage because of their high-power density, good cycle stability, fast charging and discharging rates, and low maintenance cost. Macrocycles, including cucurbiturils, calixarene, and cyclodextrins, are cage-like organic compounds (with a nanocavity that contains O and N heteroatoms) with unique potential in supercapacitors. Here, we review the applications of macrocycles in supercapacitor systems, and we illustrate the merits of organic macrocycles in electrodes and electrolytes for improving the electrochemical double-layer capacitors and pseudocapacitance via supramolecular strategies. Then, the observed relationships between electrochemical performance and macrocyclic structures are introduced. This comprehensive review describes recent progress on macrocycle-block supercapacitors for researchers.

The Influence of Physical Mixing and Impregnation on the Physicochemical Properties of Pine Wood Activated Carbon Produced by One-Step ZnCl2 Activation

In this study, two different sample preparation methods to synthesize activated carbon from pine wood were compared. The pine wood activated carbon was prepared by mixing ZnCl₂ by physical mixing, i.e., "dry mixing" and impregnation, i.e., "wet mixing" before high temperature carbonization. The influence of these methods on the physicochemical properties of activated carbons was examined. The activated carbon was analyzed using nitrogen sorption (surface area, pore volume and pore size distribution), XPS, density, Raman spectroscopy, and electrochemistry. Physical mixing led to a slightly higher density carbon (1.83 g/cm³) than wet impregnation (1.78 g/cm³). Raman spectroscopy analysis also showed that impregnation led to activated carbon with a much higher degree of defects than physical mixing, i.e., I_D/I_G = 0.86 and 0.89, respectively. The wet impregnated samples also had better overall textural properties. For example, for samples activated with 1:1 ratio, the total pore volume was 0.664 vs. 0.637 cm³/g and the surface area was 1191 vs. 1263 m²/g for dry and wet mixed samples, respectively. In the electrochemical application, specifically in supercapacitors, impregnated samples showed a much better capacitance at low current densities, i.e., 247 vs. 146 F/g at the current density of 0.1 A/g. However, the physically mixed samples were more stable after 5000 cycles: 97.8% versus 94.4% capacitance retention for the wet impregnated samples.

Hierarchical NiMn-LDH Hollow Spheres as a Promising Pseudocapacitive Electrode for Supercapacitor Application

Layered double hydroxides (LDH) are regarded as attractive pseudocapacitive materials due to their impressive capacitive qualities that may be adjustable to their morphological features. However, the layered structure of LDH renders them susceptible to structural aggregation, which inhibits effective electrolyte transport and limits their practical applicability after limited exposure to active areas. Herein, we propose a simple template-free strategy to synthesize hierarchical hollow sphere NiMn-LDH material with high surface area and exposed active as anode material for supercapacitor application. The template-free approach enables the natural nucleation of Ni-Mn ions resulting in thin sheets that self-assemble into a hollow sphere, offering expended interlayer spaces and abundant redox-active active sites. The optimal NiMn-LDH-12 achieved a specific capacitance of 1010.4 F g-1 at a current density of 0.2 A g-1 with capacitance retention of 70% at 5 A g-1 after 5000 cycles with lower charge transfer impedance. When configured into an asymmetric supercapacitors (ASC) device as NiMn-LDH//AC, the material realized a specific capacitance of 192.4 F g-1 at a current density of 0.2 A g-1 with a good energy density of 47.9 Wh kg-1 and a power density of 196.8 W kg-1. The proposed morphological-tuning route is promising for designing template-free NiMn-LDHs spheres with practical pseudocapacitive characteristics.

Renovation of Agro-Waste for Sustainable Food Packaging: A Review

Waste management in the agricultural sector has become a major concern. Increased food production to satisfy the surge in population has resulted in the generation of large volumes of solid waste. Agro-waste is a rich source of biocompounds with high potential as a raw material for food packaging. Utilization of agro-waste supports the goal of sustainable development in a circular economy. This paper reviews recent trends and the development of agro-wastes from plant and animal sources into eco-friendly food packaging systems. Different plant and animal sources and their potential development into packaging are discussed, including crop residues, process residues, vegetable and fruit wastes, and animal-derived wastes. A comprehensive analysis of the properties and production methods of these packages is presented. Future aspects of agro-waste packaging systems and the inherent production problems are addressed.

Active carbon based supercapacitors with Au colloids: the case of placing the colloids in close proximity to the electrode interface

Supercapacitors (SCs) are short-term energy storage elements that find many applications, e.g., electronic charging devices and suppressors of power fluctuations in grids that are interfaced with sustainable sources. The capacitance of an ordinary capacitor increases when dispersing metallic colloids in its dielectric. A similar strategy for SCs means deployment of nano-scale metal colloids (in our case, Au nanoparticles, or AuNPs) at the very narrow interface between an electrolyte and a porous electrode (here, active carbon film, AC, on a grafoil current collector). Unlike previous studies, here we placed AuNPs at a small distance from the electrode. This was achieved by coating the AuNPs with a negatively charged ligand that also enables strong adhesion to the electrode. A very large specific capacitance amplification was demonstrated: for example, C-V data at a scan rate of 20 mV s-1 indicated a specific capacitance amplification of more than 10 when 30 μg of AuNPs was incorporated with 200 mg of active carbon while using a 1 M Na2SO4 electrolyte and a 5% cellulose acetate butyrate binder. Upon replacing the 1 M Na2SO4 electrolyte with 1 M KOH, and keeping the same set of electrodes, the amplification factor decreased but remained large, ∼3, as determined using C-V traces at the same scan rate. This proves that the AuNPs adhered well to the AC electrodes. Simulations indicated the importance of keeping the AuNPs in close proximity to the electrodes, but not in direct contact with them, in order to maintain a substantial amplified polarization effect. Unlike semiconductor embedded electrodes, optical effects were found to be minimal.

Recent Advances in Adsorptive Nanocomposite Membranes for Heavy Metals Ion Removal from Contaminated Water: A Comprehensive Review

Water contamination is one of the most urgent concerns confronting the world today. Heavy metal poisoning of aquatic systems has piqued the interest of various researchers due to the high toxicity and carcinogenic consequences it has on living organisms. Due to their exceptional attributes such as strong reactivity, huge surface area, and outstanding mechanical properties, nanomaterials are being produced and employed in water treatment. In this review, recent advances in the use of nanomaterials in nanoadsorptive membrane systems for wastewater treatment and heavy metal removal are extensively discussed. These materials include carbon-based nanostructures, metal nanoparticles, metal oxide nanoparticles, nanocomposites, and layered double hydroxide-based compounds. Furthermore, the relevant properties of the nanostructures and the implications on their performance for water treatment and contamination removal are highlighted. The hydrophilicity, pore size, skin thickness, porosity, and surface roughness of these nanostructures can help the water permeability of the nanoadsorptive membrane. Other properties such as surface charge modification and mechanical strength can improve the metal adsorption effectiveness of nanoadsorptive membranes during wastewater treatment. Various nanocomposite membrane fabrication techniques are also reviewed. This study is important because it gives important information on the roles of nanomaterials and nanostructures in heavy metal removal and wastewater treatment.

Synergetic Effect of Polyaniline and Graphene in Their Composite Supercapacitor Electrodes: Impact of Components and Parameters of Chemical Oxidative Polymerization

The current development of clean and high efficiency energy sources such as solar or wind energy sources has to be supported by the design and fabrication of energy storage systems. Electrochemical capacitors (or supercapacitors (SCs)) are promising devices for energy storage thanks to their highly efficient power management and possible small size. However, in comparison to commercial batteries, SCs do not have very high energy densities that significantly limit their applications. The value of energy density directly depends on the capacitance of full SCs and their cell voltage. Thus, an increase of SCs electrode specific capacitance together with the use of the wide potential window electrolyte can result in high performance SCs. Conductive polymer polyaniline (PANI) as well as carbonaceous materials graphene (G) or reduced graphene oxide (RGO) have been widely studied for usage in electrodes of SCs. Although pristine PANI electrodes have shown low cycling stability and graphene sheets can have low specific capacitance due to agglomeration during their preparation without a spacer, their synergetic effect can lead to high electrochemical properties of G/PANI composites. This review points out the best results for G/PANI composite in comparison to that of pristine PANI or graphene (or RGO). Various factors, such as the ratio between graphene and PANI, oxidants, time, and the temperature of chemical oxidative polymerization, which have been determined to influence the morphology, capacitance, cycling stability, etc. of the composite electrode materials measured in three-electrode system are discussed. Consequently, we provide an in-depth summary on diverse promising approaches of significant breakthroughs in recent years and provide strategies to choose suitable electrodes based on PANI and graphene.