Advanced Energy Conversion Materials

Impedance Spectroscopy for Electroceramics and Electrochemical System

Subrata Karmakar — 2024-12-12

This tutorial review focuses on the basic theoretical backgrounds, their working principles, and the implementation of impedance spectroscopy in both electroceramics and electrochemical research and technological applications. Various contributions to the impedance, admittance, dielectric, and conductivity characteristics of electroceramics materials can be disentangled and independently characterized with the help of impedance spectroscopy as a function of frequency and temperature. In polycrystalline materials, the impedance, charge transport/conduction mechanism, and the macroscopic dielectric properties, i.e., dielectric constant and loss are typically composed of many contributions, including the bulk or grain resistance/capacitance, grain boundary, and sample-electrode interface effect. Similarly, electrochemical impedance spectroscopy (EIS) endeavors to the charging kinetics, diffusion, and mechanical impact of various electrochemical systems widely used in energy storage (i.e., supercapacitor, battery), corrosion resistance, chemical and bio-sensing, diagnostics, etc., in electrolytes as a function of frequency. The understanding of various contributions in the EIS spectra, i.e., kinetic control, mass control, and diffusion control is essential for their practical implications. It is demonstrated that electrochemical and electroceramics impedance spectroscopy is an effective method to explain and simulate such behavior. Deconvolution these contributions obtains a detailed understanding of the functionality of polycrystalline electroceramic materials. This short review aims to provide the necessary background information for junior researchers working in these fields and allows readers to quickly comprehend the fundamental understanding in this field by saving their time and understanding, and applying impedance spectroscopy in their future projects.

Technical Competence of Nanodiamond Nanocomposites in Energy Sector (Solar Cells, Fuel Cells, Batteries, Supercapacitors)-State-of-the-Art

Ayesha Kausar — 2024-12-17

This state-of-the-art overview is designed to present indispensable features of nanodiamond nanocomposites and their utilization of advanced energy devices/systems including solar cells, fuel cells, batteries, and supercapacitors. For these systems, nanodiamond nanocomposites have been used in electrodes, electrolytes, membrane-electrode assembly, separators, and other components. Nanodiamond and related nanocomposites have high surface area and unique structural, microstructural, electrochemical, and physical properties to be utilized in efficient devices. Nanodiamond nanocomposites have been designed using sonication/solution preparation, layer-by-layer deposition, chemical vapor deposition, ink deposition, high temperature annealing, doping, solution casting, and in situ polymerization. In this context, various polymeric matrices have been reinforced with nanodiamond to attain the desired design/performance. Accordingly, polypyrrole/nanodiamond and graphene/nanodiamond nanomaterials have been documented for solar cells with photovoltage of ~ 99 mV. Direct methanol fuel cells with platinum/nanodiamond nanocomposites exhibited high electrochemical catalytic activity, high surface area of 80-90 m²·g^-1and power density of 55 mW·cm^-2. Silica/nanodiamond and polypyrrole/nanodiamond nanocomposite-based battery designs revealed high capacity of 600-650 mAh/g (1,000 cycles). For supercapacitor electrodes, polyaniline/nanodiamond systems depicted specific capacitance > 640 F·g^-1 and capacitance retention > 80%. Future progress in designing efficient nanodiamond nanomaterials may overcome microstructural, conductivity, compatibility, and long-time functioning challenges toward high-performance energy devices.

Graphite Composite Electrodes for Effective Charge Storage via Synergistically Improved Compositions Enriched with Kaolinite and Cement as Matrix Inducers

Pannilage M. H. Madhushanka — 2025-03-21

The present work demonstrates the correlations between substrate composition and active material morphology, which is responsible for effective energy storage. The binary and ternary composite electrodes, including graphite-kaolinite (GKCE) and graphite-kaolinite-cement (GKCeCE) were carefully fabricated using a simple economical process that employed only mechanical compression and thermal activation. The microstructure related to composite electrodes, as examined via X-ray powder diffraction, reveals that graphite layer are tightly arranged in both electrodes compared to raw graphite, exhibiting the largest crystallite size in GKCeCE, indicating a better matrix owned to synergy between raw materials. Aniline electropolymerization on both GKCeCE and GKCE accounted for an interwoven polyaniline (PANI) nanofiber network that is embellished with distinctive features. PANI on GKCeCE is quite distinctive as it exhibits net-like PANI structural elements together with overlapped PANI nanofibers, which are the only structural elements available in PANI network that deposited on GKCE. The emeraldine salt formation in excess is greatly enhanced by GKCeCE synergetic matrix, resulting in a PANI network that is highly effective in charge storage. The supercapacitor cell constructed using PANI-GKCeCE accounts for the highest specific capacitance in comparison with PANI-GKCE device, supported by both Galvanostatic charge-discharge (GCD) and solid-state cyclic voltammetry. The more accurate and reliable GCD method accounts for a specific capacitance, which is 1,143 F·g^-1 for PANI-GKCeCE device, exhibiting nearly 100% coulombic efficiency, better cycle stability, high energy and power density over PANI-GKCE device. The PANI high electroactive surface area that is mainly due to overlapped nanofibers and net-like arrangement account for better energy storage performance over PANI-GKCE, which composed by overlapped PANI nanofibers only. The electrode composition greatly dominates the aniline electropolymerization, producing significantly different PANI structures, which determine the energy storage efficiency.

Local Thermo-EMF and Nano-Limits of Efficiency

Stanislav Ordin — 2024-11-14

Thermoelectronics includes invariant elements of thermoelectricity, thermoemission and theory of p-n junction. And the local Nano-Thermo-Electromotive Forces (EMFs) discovered and used to build this unified theory of nano-scale, which are orders of magnitude superior to the seebeck EMF, are not only a diagnostic tool for any microelements, but can also be used to increase the Energy conversion efficiency of all traditional electronic devices. But most importantly, they prompted understanding that between the micro and marco-worlds, Physics missed a scale where their linear approximations do not work, but the Thermoelectronic Laws of the nano-scale work. Whereas the macroscopic response from nano-effects, in contrast to its acceptance as due from quantum effects, with reference to Thermodynamics, due to not taking into account prigogine’s production of Local Entropy, was generally considered forbidden. Thus, Thermoelectricity, which was initially included in the fundamentals of Nonequilibrium Thermodynamics, returned again to the Fundamental Science of the nano-scale missed by Physics and actually expanded Electronics to thermoelectronics. Taking into account the thermoelectronic effects allowed us to identify previously unaccounted aspects of increasing the efficiency of energy conversion of the scale missed in theories. In addition, the refinement and expansion of the theory of thermoelectricity became the background (basis) of all evidence-based fundamental physics.