Pseudocapacitors

Fluctuation in the demand for electrical power and the intermittent nature of the supply of energy from renewable sources like solar and wind have made the need for energy storage a dire necessity. Current storage technologies like batteries and supercapacitors fall short either in terms of power output or in their ability to store sufficient energy. Pseudocapacitors combine features of both and offer an alternative to stabilize the power supply. They possess high rates of charge and discharge and are capable of storing much more energy in comparison to a supercapacitor. In the quest for solutions that are economical and feasible, we have investigated Prussian Blue in aqueous electrolytes for its use as a pseudocapacitor. Two different active materials based on Prussian Blue were prepared; one that has just Prussian Blue and the other that contains a mixture of Prussian Blue and carbon nanotubes (CNTs). Four electrolytes differing in the valence of the cation were employed for the study. Cyclic voltammetry and galvanostatic charge-discharge were used to characterize the electrodes. Our experiments have shown specific capacitances of Prussian Blue electrodes in the range of 140-720 F/g and that of Prussian Blue-CNT electrodes in the range of ~52 F/g. The remarkable capacity of charge storage in Prussian Blue electrodes is attributed to its electrochemical activity ensuring surface redox and its tunnel-like structure allowing ease of entry and exit for ions like Potassium. Simple methods of synthesis have yielded specific capacitances of the order of hundreds of Farads per gram showing that Prussian Blue has promise as an electrode material for applications needing high rates of charge-discharge.

The present study investigates the complex multi-scale coupled transport and electrochemical phenomena involved in charge storage in pseudocapacitors. It presents rigorously developed models for simulating pseudocapacitive electrodes in both hybrid pseudocapacitors and in three-electrode systems under cyclic voltammetry. The models account for (i) charge transport in the electrodes and electrolyte, (ii) formation and dissolution of the electric double layer (EDL) at the electrode/electrolyte interface, (iii) steric repulsions due to finite ion size, (iv) redox reactions at the pseudocapacitive electrode/electrolyte interface, and (v) insertion and deinsertion of the reaction product in the pseudocapacitive electrode. They were used to study the behavior of electrochemical pseudocapacitors and provide physical interpretation of experimentally obtained measurements. First, this study determined the respective contributions of faradaic reactions and EDL formation to charge storage in hybrid pseudocapacitors. It demonstrated the existence of two regimes for hybrid pseudocapacitors. First, a faradaic regime dominated by redox reaction and limited by the diffusion of Li in the pseudocapacitive electrode. Second, a capacitive regime dominated by the formation and dissolution of the EDL. A b-value of unity was shown to be associated with both regimes. The dip in b-value often observed experimentally was attributed to the transition between the two regimes. Second, this study presented an extensive parametric study for the design of the pseudocapacitive electrode in a hybrid pseudocapacitor. Increasing the fraction of the potential window dominated by faradaic current was found to increase the performance of the device. Indeed, the faradaic reactions resulted in a significantly larger current magnitude than the EDL charge storage. The effect of the electrode thickness and Li diffusion coefficient on this fraction were investigated for different scan rates. To study the interplay between these parameters, a scaling analysis was performed to identify the relevant dimensionless similarity parameters governing Li transport and intercalation in the pseudocapacitive electrode. A dimensionless parameters was derived accounting for the respective contributions of the thickness, diffusion coefficient and scan rate. Furthermore, above a critical value, the device was found to operate under a diffusion-independent regime. Finally, this study presented a model for simulating individual pseudocapacitive electrodes in three-electrode experiments. Notably, this model accounted for the variation of the redox reaction equilibrium potential with the oxidation state of the electrode. It was found to agree qualitatively with experimental measurements well and was used to provide physical interpretation to experimental measurements for Nb2O5 electrodes. These models and results could help in the design of pseudocapacitive electrodes to achieve maximum energy and power density.

Solid state power sources have developed remarkably in the last three decades owing to improvements in technology and a greater understanding of the underlying basic sciences. In particular, a greater impetus has recently been placed in developing and commercializing small, lightweight, and highly energetic solid state power sources driven by demands from portable consumer electronics, medical technology, sensors, and electric vehicles. This comprehensive handbook features contributions by forerunners in the field of solid state power source technology from universities, research organizations, and industry. It is directed at the physicist, chemist, materials scientist, electrochemist, electrical engineer, science students, battery and capacitor technologists, and evaluators of present and future generations of power sources, as a reference text providing state-of-the-art reviews on solid state battery and capacitor technologies, and also insights into likely future developments in the field. The volume covers a comprehensive series of articles that deal with the fundamental aspects and experimental aspects of solid state power sources, an in-depth discussion on the state of the various technologies, and applications of these technologies. A description of the recent developments on solid state capacitor technology, and a comprehensive list of references in each and every article will help the reader with an encyclopedia of hidden information. The organization of the material has been carefully divided into thirty-one chapters to ensure that the handbook is thoroughly comprehensive and authoritative on the subject for the reader.

This book satisfies the interest and curiosity of beginners in thin film electrode preparations, characterizations, and device making, while providing insight into the area for experts. The considerable literature on ‘metal chalcogenides based carbon composites and their versatile applications’ reflect its importance for research and demonstrate how it’s now reached a level where the timely review is necessary to understand the current progress and recent trends and future opportunities. In the book, the authors examine recent advances in the state-of-the-art fabrication techniques of metal sulfide based carbon composites along with their working mechanisms, associated issues/solutions, and possible future are discussed. In addition, detailed insight into the properties and various applications including principles, design, fabrication, and engineering aspects are further discussed.

Electrochemical capacitors are most important for the development of future energy storage systems and sustainable power sources. New superior hybrid supercapacitors are based on binary and ternary thin film nanocomposites involving carbon, metal oxides and polymeric materials. The synthesis of materials and fabrication of electrodes for supercapacitor applications is discussed in detail. The book also presents the fundamental theory and a thorough literature review of supercapacitors. Energy Storage, Electrochemical Capacitors, Nanocomposites, Hybrid Supercapacitors, Carbon/Metal Oxide Composites, Metal Oxides/Hydroxides Composites, Polymer Type Capacitors, Nanoscience, Hydrothermal Synthesis, Graphene-based Composites, Ultrasonic Assisted Synthesis

Making innovative products for energy generation that decrease carbon footprints are the need of the hour. This book describes innovations in porous materials for energy generation and storage applications that can have applications in developed as well as developing countries. It provides a comprehensive account of porous materials for potential new applications, such as catalysts for gas storage and energy efficient transformations, which engineers and scientists working in the areas of solar cells, batteries, supercapacitors, fuel cells, etc. will find to be of immense interest.

Nanomaterials are being incorporated into products all around us, having an incredible impact on durability, strength, functionality, and other material properties. There are a vast number of nanomaterials presently available, and new formulations and chemistries are being announced daily. Nanomaterials: A Guide to Fabrication and Applications provides product developers, researchers, and materials scientists with a handy resource for understanding the range of options and materials currently available. Covering a variety of nanomaterials and their applications, this practical reference: Discusses the scale of nanomaterials and nanomachines, focusing on integrated circuits (ICs) and microelectromechanical systems (MEMS) Offers insight into different nanomaterials’ interactions with chemical reactions, biological processes, and the environment Examines the mechanical properties of nanomaterials and potential treatments to enhance the nanomaterials’ performance Details recent accomplishments in the use of nanomaterials to create new forms of electronic devices Explores the optical properties of certain nanomaterials and the nanomaterials’ use in optimizing lasers and optical absorbers Describes an energy storage application as well as how nanomaterials from waste products may be used to improve capacitors Featuring contributions from experts around the globe, Nanomaterials: A Guide to Fabrication and Applications serves as a springboard for the discovery of new applications of nanomaterials.

Experts and key personnel straddling academia and related agencies and industries provide critical data for further exploration and research.