Correlating electrochemical impedance with hierarchical structure for porous carbon-based supercapacitors using a truncated transmission line model

Nanostructured Thick Electrode Strategies toward Enhanced Electrode-Electrolyte Interfaces

This article addresses the issue of bulk electrode design and the factors limiting the performance of thick electrodes. Indeed, one of the challenges for achieving improved performance in electrochemical energy storage devices (batteries or supercapacitors) is the maximization of the ratio between active and non-active components while maintaining ionic and electronic conductivity of the assembly. In this study, we developed and compared supercapacitor thick electrodes using commercially available carbons and utilising conventional, easily scalable methods such as spray coating and freeze-casting. We also compared different binders and conductive carbons to develop thick electrodes and analysed factors that determine the performance of such thick electrodes, such as porosity and tortuosity. The spray-coated electrodes showed high areal capacitances of 1428 mF cm^-2 at 0.3 mm thickness and 2459 F cm^-2 at 0.6 mm thickness.

Phyllanthus emblica Seed-Derived Hierarchically Porous Carbon Materials for High-Performance Supercapacitor Applications

The electrical double-layer supercapacitance performance of the nanoporous carbons prepared from the Phyllanthus emblica (Amala) seed by chemical activation using the potassium hydroxide (KOH) activator is reported. KOH activation was carried out at different temperatures (700-1000 °C) under nitrogen gas atmosphere, and in a three-electrode cell set-up the electrochemical measurements were performed in an aqueous 1 M sulfuric acid (H₂SO₄) solution. Because of the hierarchical pore structures with well-defined micro- and mesopores, Phyllanthus emblica seed-derived carbon materials exhibit high specific surface areas in the range of 1360 to 1946 m² g^-1, and the total pore volumes range from 0.664 to 1.328 cm³ g^-1. The sample with the best surface area performed admirably as the supercapacitor electrode-material, achieving a high specific capacitance of 272 F g^-1 at 1 A g^-1. Furthermore, it sustained 60% capacitance at a high current density of 50 A g^-1, followed by a remarkably long cycle-life of 98% after 10,000 subsequent charging/discharging cycles, demonstrating the electrode's excellent rate-capability. These results show that the Phyllanthus emblica seed would have significant possibilities as a sustainable carbon-source for the preparing high-surface-area activated-carbons desired in high-energy-storage supercapacitors.

Role of Electrochemical Techniques for Photovoltaic and Supercapacitor Applications

Electrochemistry forms the base of large-scale production of various materials, encompassing numerous applications in metallurgical engineering, chemical engineering, electrical engineering, and material science. This field is important for energy harvesting applications, especially supercapacitors (SCs) and photovoltaic (PV) devices. This review examines various electrochemical techniques employed to fabricate and characterize PV devices and SCs. Fabricating these energy harvesting devices is carried out by electrochemical methods, including electroreduction, electrocoagulation, sol-gel process, hydrothermal growth, spray pyrolysis, template-assisted growth, and electrodeposition. The characterization techniques used are cyclic voltammetry, electrochemical impedance spectroscopy, photoelectrochemical characterization, galvanostatic charge-discharge, and I-V curve. A study on different recently reported materials is also presented to analyze their performance in various energy harvesting applications regarding their efficiency, fill factor, power density, and energy density. In addition, a comparative study of electrochemical fabrication techniques with others (including physical vapor deposition, mechanical milling, laser ablation, and centrifugal spinning) has been conducted. The various challenges of electrochemistry in PVs and SCs are also highlighted. This review also emphasizes the future perspectives of electrochemistry in energy harvesting applications.

Design of Porous Carbons for Supercapacitor Applications for Different Organic Solvent-Electrolytes

The challenge of optimizing the pore size distribution of porous electrodes for different electrolytes is encountered in supercapacitors, lithium-ion capacitors and hybridized battery-supercapacitor devices. A volume-averaged continuum model of ion transport, taking into account the pore size distribution, is employed for the design of porous electrodes for electrochemical double-layer capacitors (EDLCs) in this study. After validation against experimental data, computer simulations investigate two types of porous electrodes, an activated carbon coating and an activated carbon fabric, and three electrolytes: 1.5 M TEABF4 in acetonitrile (AN), 1.5 M TEABF4 in propylene carbonate (PC), and 1 M LiPF6 in ethylene carbonate:ethyl methyl carbonate (EC:EMC) 1:1 v/v. The design exercise concluded that it is important that the porous electrode has a large specific area in terms of micropores larger than the largest desolvated ion, to achieve high specific capacity, and a good proportion of mesopores larger than the largest solvated ion to ensure fast ion transport and accessibility of the micropores.

Porous Ni Photocathodes Obtained by Selective Corrosion of Ni-Cu Films: Synthesis and Photoelectrochemical Characterization

In this work, a dealloying technique is proposed as a synthesis method to obtain highly porous Nickel electrodes starting from Ni-Cu co-deposit: pulsed corrosion is applied adopting different corrosion and relaxation times. Different morphologies, pore size distribution and residual copper amount were obtained depending on the corrosion conditions. For the developed electrodes, the surface roughness factor, Rf, was evaluated by electrochemical impedance spectroscopy (EIS). The hydrogen evolution reaction (HER) on these electrodes was evaluated by means of steady-state polarization curves, and the related parameters were derived by Tafel analysis. Finally, a thin layer of NiO on the porous structures was obtained to exploit the semiconductor characteristic of the oxide, so that an extra-photopotential was obtained by the simulated solar light action. Results demonstrate greater apparent activity of the developed electrodes towards HER in comparison with commercial smooth Ni electrode, which can be mainly attributed to the large Rf obtained with the proposed technique.

Aligned Ionogel Electrolytes for High-Temperature Supercapacitors

Ionogels are a new class of promising materials for use in all-solid-state energy storage devices in which they can function as an integrated separator and electrolyte. However, their performance is limited by the presence of a crosslinking polymer, which is needed to improve the mechanical properties, but compromises their ionic conductivity. Here, directional freezing is used followed by a solvent replacement method to prepare aligned nanocomposite ionogels which exhibit enhanced ionic conductivity, good mechanical strength, and thermal stability simultaneously. The aligned ionogel based supercapacitor achieves a 29% higher specific capacitance (176 F g-1 at 25 °C and 1 A g-1) than an equivalent nonaligned form. Notably, this thermally stable aligned ionogel has a high ionic conductivity of 22.1 mS cm-1 and achieves a high specific capacitance of 167 F g-1 at 10 A g-1 and 200 °C. Furthermore, the diffusion simulations conducted on 3D reconstructed tomography images are employed to explain the improved conductivity in the relevant direction of the aligned structure compared to the nonaligned. This work demonstrates the synthesis, analysis, and use of aligned ionogels as supercapacitor separators and electrolytes, representing a promising direction for the development of wearable electronics coupled with image based process and simulations.