Analysis of infinite d-dimensional networks – Capacitance between two adjacent nodes

This work showed that infinite d-dimensional networks consisting of identical capacitors each of capacitance C can be analyzed using basic concepts of physics. In this work we have showed that the equivalent capacitance C_eq between any two adjacent nodes in the infinite d-dimensional networks consisting of identical capacitors, is equal to dC where d is the dimension of the infinite network (i.e., d = 1,2,3,…). The results obtained here are in an excellent agreement with previous studied carried out.     

A Surface Grafting of Carbon Allotropes with in‐situ Generated 3‐aryl Diazonium Chlorides: Electrochemical Kinetic Studies

In this work three different carbon allotropes: multi‐walled carbon nanotubes (MWCNT), graphene and carbon nanohorns (CNH) were covalently bound with in‐situ generated 3‐diazonium aryl chlorides. These species were attached to the carbon surface using an electrochemically‐initiated radical coupling, similar to the Gomberg‐Bachman type reaction. An electrochemical grafting of the extended π‐systems at the carbon surface was performed in aqueous media in a simple 3‐electrode system and its kinetics was investigated by a modified Butler‐Volmer approach. The analysis of Hammett constants demonstrated a strong influence of the type of electron donating‐/withdrawing substituents on the reduction potential peak position and the peak current. Moderately or strong electron withdrawing groups like ‐carboxy or ‐nitro tend to shift reduction potential towards more positive values, which facilitates an electron uptake. The deposition time varies for different carbon allotropes and depends on the carbon graphitization and the surface area. The best surface coverage was obtained at 90–150 sec of the deposition. Although, the surface functionalities are less conductive than the carbon, the electrodes showed a low internal resistance and thus a high rate of electron transfer (high exchange current density and the electron transfer rate constant), with the most promising observed for carbon nanohorns. The best performing carbon revealed also superior mass transport of the redox active species toward the electrode surface, owing to their unique particle shapes and its very porous structure. The Tafel analysis complemented by an impedance spectroscopy allowed selecting the best carbon substrate for the functionalization with a 3‐aminobenzoic acid.     

Functional nanocomposites for energy storage: chemistry and new horizons

Energy storage devices are one of the hot spots in recent years due to the environmental problems caused by the large consumption of unsustainable energy such as petroleum or coal. Capacitors are a common device for energy storage, especially electrical energy. A variety of types including electrolytic capacitors, mica capacitors, paper capacitors, ceramic capacitors, film capacitors, and non-polarized capacitors have been proposed. Their specific applications depend on their intrinsic properties. Dielectric capacitors have reasonable energy storage density, with current research focusing on the enhancement of energy density and making the materials more flexible as well as lightweight. Improvement strategies are based on the premise that use of two or more different materials (e.g. polymers and ceramics/metals) at an optimal formulation can result in properties that combine the advantages of the precursor materials. Different polymers especially fluoropolymers (e.g. PVDF and PVDF based co-polymer) are the main components in dielectric nanocomposites for capacitors with high energy storage performance. In this article, we have briefly summarized the recent advances in functional polymers nanocomposites for energy storage applications with a primary focus on polymers, surface engineering, functional groups and novel synthesis/manufacturing concepts applied to new materials. The article presents a unique integrated structure and approaches providing key knowledge for the design and development of novel, low-cost, multifunctional next-generation energy storage materials with improved efficiency.     

A ZIF-8 Host for Dendrite-Free Zinc Anodes and N,O Dual-doped Carbon Cathodes for High-Performance Zinc-Ion Hybrid Capacitors

Zn is a promising anode for aqueous energy storage owing to it intrinsic superior properties such as large capacity, abundant reserves, low potential and safety. But, the growth of dendrites during charge and discharge leads to a decrease in reversibility. In addition, further development of zinc-ion hybrid capacitors (ZICs) is seriously challenging because of the lack of an exceptional cathode. Herein, we use ZIF-8 annealed at 500 °C (annealed ZIF-8) as a host material for stable and dendrite-free Zn anodes. Utilization of annealed ZIF-8 results in dendrite-free Zn deposition and stripping as a result of its porous construction, which contains trace Zn. Furthermore, we firstly proposed innovative N,O dual-doped carbon which was designed by the derived ZIF-8 (ZIF-8 derived C) as cathode for high-energy and power-density ZICs. The new ZIC assembled by Zn@annealed ZIF-8 anode and ZIF-8 derived C cathode provides a capacity of 135.5 mAh g⁻¹ and an energy density of 108.4 Wh kg⁻¹ with a power density of 800 W kg⁻¹ at 1.0 A g⁻¹. In addition, it shows outstanding cycling stability of 91% capacity retention after 6000 cycles at 5.0 A g⁻¹. Moreover, the solid-state ZICs can drive LEDs and smart watches. This ZIC holds promise for the practical application of supercapacitors.     

Addendum to “On the exploitability of thermo-charged capacitors” [Physica A 390 (2011) 482–491]

In the article [Physica A 390 (2011) 482–491], an explicit discussion on contact potential (and its alleged consequences) arising between the inner metallic sphere of a thermo-charged spherical capacitor and its Ag–O–Cs coating is missing. This addendum aims to clarify this issue.     

Enhanced energy-storage performance and thermal stability in Bi0.5Na0.5TiO3-based ceramics through defect engineering and composition design

Dielectric ceramics have been widely used in advanced microelectronics systems due to their inherent rapid charging/discharging capabilities and superb power density. However, concurrently attaining high energy storage density (W_rec), superior efficiency (η), and excellent thermal stability are arduous tasks for actual applications in dielectric ceramics. Herein, the introduction of predictable defects A-site vacancies (V_A) and oxygen vacancies (V_O) into the morphotropic phase boundary (MPB) of (Bi_0.45La_0.05Na_0.5)_0.94Ba_0.06TiO₃ (BLNBT) ceramics leads to a pinning effect in the grain boundary to improve the breakdown strength and energy storage performance. According to this strategy, the novel Sr_0.8Bi_0.1□_0.1Ti_0.8Zr_0.2O_2.95 (SBTZ)-modified BLNBT ceramics are designed and manufactured, which include SBTZ with a high relaxation behavior gene and BLNBT with an inherently high maximum polarization gene. As a result, a large W_rec of 3.84 J/cm³ with an excellent η of 90.8%, and outstanding charge/discharge capabilities (C_D ～ 584.99 A/cm², P_D ～ 40.94 MW/cm³ and τ_0.9 ～ 95 ns) in the 0.75BLNBT-0.25SBTZ ceramic are achieved. Notably, the corresponding ceramic shows a slight degradation of W_rec with a variation of less than 8% (RT ～ 200 °C), while the η remains at over 90%. The predictable defect engineering strategy proposed in this work is an effective way to develop new Bi_0.5Na_0.5TiO₃-based systems with good energy storage performances.     

Coordination polymer template synthesis of hierarchical MnCo2O4.5 and MnNi6O8 nanoparticles for electrochemical capacitors electrode

Two types of ternary metal oxides, MnCo₂O_4.5 and MnNi₆O₈ nanoparticles have been separately synthesized through chemical transformation from the corresponding bimetallic coordination polymer particles precursor under high-heating conditions. Series of electrochemical measurements are performed to examine the MnCo₂O_4.5 and MnNi₆O₈ electrodes, and the result shows that MnCo₂O_4.5 structure, especially for Mn/Co-600, has much higher capacitance than that of MnNi₆O₈ nanoparticles, indicating MnCo₂O_4.5 electrode is more suitable for applying in neutral electrolyte system. The Mn/Co-600 electrode exhibits a specific capacitance of 158 F g⁻¹ at 5 mV s⁻¹, good rate capability of 53.8% with a 20 times current density increase, good cycle performance (92.9% capacitance retention after 1000 cycles) and high power density (a specific power of 5760 W kg⁻¹ at 4.0 A g⁻¹) with low charge transfer resistance value of 1.8 Ω.     

A novel nonaqueous route to V2O3 and Nb2O5 nanocrystals

The reaction between transition metal alkoxides and benzyl alcohol provides a novel soft chemistry route to metal oxide nanoparticles. The method allows the preparation of nanocrystals of two important transition metal oxides, namely V₂O₃ and Nb₂O₅. Although the reaction temperatures of 200–220 °C are comparably low, the obtained particles are highly crystalline. According to TEM investigations, the V₂O₃ crystals exhibit particle sizes between 20 and 50 nm, and the Nb₂O₅ crystals display platelet-like particle shapes with sizes of 50–80 nm, without any indications of amorphous character.