Download or read book Analysis of Reaction and Transport Processes in Zinc Air Batteries written by Daniel Schröder and published by Springer. This book was released on 2016-01-22 with total page 259 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains a novel combination of experimental and model-based investigations, elucidating the complex processes inside zinc air batteries. The work presented helps to answer which battery composition and which air-composition should be adjusted to maintain stable and efficient charge/discharge cycling. In detail, electrochemical investigations and X-ray transmission tomography are applied on button cell zinc air batteries and in-house set-ups. Moreover, model-based investigations of the battery anode and the impact of relative humidity, active operation, carbon dioxide and oxygen on zinc air battery operation are presented. The techniques used in this work complement each other well and yield an unprecedented understanding of zinc air batteries. The methods applied are adaptable and can potentially be applied to gain further understanding of other metal air batteries.
Download or read book Zinc Air Batteries written by Zongping Shao and published by John Wiley & Sons. This book was released on 2023-01-04 with total page 309 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zinc–Air Batteries Authoritative and comprehensive resource covering foundational knowledge of zinc–air batteries as well as their practical applications Zinc–Air Batteries provides a comprehensive understanding of the history and development of Zn–air batteries, with a systematic overview of components, design, and device innovation, along with recent advances in the field, especially with regards to the cathode catalyst design made by cutting-edge materials, engineering processes, and technologies. In particular, design principles regarding the key components of Zn–air batteries, ranging from air cathode, to zinc anode, and to electrolyte, are emphasized. Furthermore, industrial developments of Zn–air batteries are discussed and emerging new designs of Zn–air batteries are also introduced. The authors argue that designing advanced Zn–air battery technologies is important to the realization of efficient energy storage and conversion—and, going further, eventually holds the key to a sustainable energy future and a carbon-neutral goal. Edited and contributed to by leading professionals and researchers in the field, Zinc–Air Batteries also contains information regarding: Design of oxygen reduction catalysts in primary zinc–air batteries, including precious metals, single-atoms, carbons, and transition metal oxides Design of bifunctional oxygen catalysts in rechargeable zinc–air batteries, covering specific oxygen redox reactions and catalyst candidates Design of three-dimensional air cathode in zinc–air batteries, covering loading of carbon-based and transition metal catalysts, plus design of the three-phase interface Design of electrolyte for zinc–air batteries, including liquid electrolytes (e.g., alkaline) and gel polymer electrolytes (e.g., PVA hydrogel) For students, researchers, and instructors working in battery technologies, materials science, and electrochemistry, and for industry and government representatives for decision making associated with energy and transportation, Zinc–Air Batteries summarizes the research results on Zn–air batteries and thereby helps researchers and developers to implement the technology in practice.
Download or read book Recent progress of in situ operando characterization approaches of zinc air batteries written by Jian-Feng Xiong and published by OAE Publishing Inc.. This book was released on 2024-01-01 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zinc-air batteries (ZABs) belong to the category of metal-air batteries, with high theoretical energy density, safety, and low cost. Nevertheless, there are still many challenges that need to be solved for the practical application of ZABs, including high overpotential, poor cycle life, and so on. This article first briefly introduced the principle of ZABs, covering the key components, functions of each element, and challenges faced by the system. Subsequently, seven methods for studying ZABs in-situ or operando were introduced, including X-ray computed tomography (XCT), optical microscopy imaging (OMI), transmission electron microscopy (TEM), nuclear magnetic resonance imaging (MRI), X-ray diffraction (XRD), Raman spectroscopy, and X-ray absorption spectroscopy (XAS), accompanied by specific research examples. The future perspectives of ZAB characterization have also been discussed.
Download or read book Electrochemical Energy Storage written by Reinhart Job and published by Walter de Gruyter GmbH & Co KG. This book was released on 2020-09-21 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt: Starting from physical and electrochemical foundations, this textbook explains working principles of energy storage devices. After a history of galvanic cells, different types of primary, secondary and flow cells as well as fuel cells and supercapacitors are covered. An emphasis lies on the general setup and mechanisms behind those devices to enable easy understanding for students from all technical and natural science disciplines.
Download or read book Investigation of the Transport and Reaction Processes Occurring Within Silver Oxide zinc Batteries written by Thedford Preston Dirkse and published by . This book was released on 1966 with total page 53 pages. Available in PDF, EPUB and Kindle. Book excerpt: The decomposition of Ag2O dissolved in KOH solutions was studied; effects of temperature, light, KOH concentration, Ag2O concentration, and additives on this decomposition were measured. At least two mechanisms are involved but the precise nature of these mechanisms is still unknown. Overvoltages for anodic and cathodic zinc electrode processes were measured by different methods. The presence of additives in the electrolyte had little effect on these overvoltages but overvoltages were markedly affected by KOH concentration and temperature. Amalgamation improved performance of the Zn electrode but this effect decreased with decreasing temperature. Ag contamination adversely affected cathodic Zn electrode processes. It appears that the beneficial effects of additives to the electrolyte are related to the presence of carboxyl groups and that the beneficial effects of additives to the Zn electrode are related to their wetting ability. (Author).
Download or read book Zinc Batteries written by Rajender Boddula and published by John Wiley & Sons. This book was released on 2020-05-05 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt: Battery technology is constantly changing, and the concepts and applications of these changes are rapidly becoming increasingly more important as more and more industries and individuals continue to make “greener” choices in their energy sources. As global dependence on fossil fuels slowly wanes, there is a heavier and heavier importance placed on cleaner power sources and methods for storing and transporting that power. Battery technology is a huge part of this global energy revolution. Zinc batteries are an advantageous choice over lithium-based batteries, which have dominated the market for years in multiple areas, most specifically in electric vehicles and other battery-powered devices. Zinc is the fourth most abundant metal in the world, which is influential in its lower cost, making it a very attractive material for use in batteries. Zinc-based batteries have been around since the 1930s, but only now are they taking center stage in the energy, automotive, and other industries. Zinc Batteries: Basics, Developments, and Applicationsis intended as a discussion of the different zinc batteries for energy storage applications. It also provides an in-depth description of various energy storage materials for Zinc (Zn) batteries. This book is an invaluable reference guide for electrochemists, chemical engineers, students, faculty, and R&D professionals in energy storage science, material science, and renewable energy.
Download or read book Metal Air Batteries written by Xin-bo Zhang and published by John Wiley & Sons. This book was released on 2019-02-11 with total page 432 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive overview of the research developments in the burgeoning field of metal-air batteries An innovation in battery science and technology is necessary to build better power sources for our modern lifestyle needs. One of the main fields being explored for the possible breakthrough is the development of metal-air batteries. Metal-Air Batteries: Fundamentals and Applications offers a systematic summary of the fundamentals of the technology and explores the most recent advances in the applications of metal-air batteries. Comprehensive in scope, the text explains the basics in electrochemical batteries and introduces various species of metal-air batteries. The author-a noted expert in the field-explores the development of metal-air batteries in the order of Li-air battery, sodium-air battery, zinc-air battery and Mg-O2 battery, with the focus on the Li-air battery. The text also addresses topics such as metallic anode, discharge products, parasitic reactions, electrocatalysts, mediator, and X-ray diffraction study in Li-air battery. Metal-Air Batteries provides a summary of future perspectives in the field of the metal-air batteries. This important resource: -Covers various species of metal-air batteries and their components as well as system designation -Contains groundbreaking content that reviews recent advances in the field of metal-air batteries -Focuses on the battery systems which have the greatest potential for renewable energy storage Written for electrochemists, physical chemists, materials scientists, professionals in the electrotechnical industry, engineers in power technology, Metal-Air Batteries offers a review of the fundamentals and the most recent developments in the area of metal-air batteries.
Download or read book Material Design and Engineering for Polymer Electrolyte Membrane Zinc air Batteries written by Jing Fu and published by . This book was released on 2018 with total page 147 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zinc-air batteries, whose advantages include relatively high energy density (1218 Wh kg-1), abundance of zinc in earth's crust, and very safe operational characteristics, are promising for applications in consumer electronics, electrified transportation, grid storage, and other fields. At the moment, primary zinc-air batteries are produced for low-drain electronic gadgets such as hearing aids. However, secondary (i.e., electrically rechargeable) zinc-air batteries have eluded widespread adoption due mainly to the slow reaction kinetics of oxygen evolution at the air electrode during recharge. A bifunctional oxygen electrocatalyst that can recharge the batteries more efficiently is required. Moreover, in the presence of aqueous alkaline electrolytes, zinc-air batteries suffer from low durability and performance loss due mainly to the formation of zinc dendrites during charging, the loss of aqueous electrolytes, the detachment of the catalyst layer and the precipitation of carbonates at the air electrode. These persistent issues have motivated a shift in electrolyte design towards efficient hydroxide ion-conductive polymeric electrolytes. A combination of efficient bifunctional oxygen electrocatalysts and polymeric electrolyte improvements may enable zinc-air batteries to be implemented in widespread applications in flexible/lightweight electronic devices and electric vehicles. In this work, I present a feasible strategy combining material innovations with engineering methods to develop a new type of zinc-air battery, i.e., a flexible, rechargeable polymer electrolyte membrane zinc-air battery (PEMZAB). In the first study, a proof of concept of a film-shaped, rechargeable PEMZAB was conducted by using a KOH-doped poly(vinyl alcohol) (PVA) gel electrolyte, porous zinc electrode and bifunctional air electrode comprising a commercial Co3O4 nanoparticles-loaded carbon cloth. Then, a novel hydroxide ion-conductive polymeric electrolyte membrane and an efficient bifunctional oxygen zinc-air battery performance. Specifically, highly quaternaized cellulose nanofibers were synthesized to produce a hydroxide ion-conductive electrolyte membrane (referred to as QAFC). The QAFC membrane shows advantages of a high ionic conductivity of 21.2 mS cm-1, good chemical stability, mechanical robustness and flexibility, and inhibition of zinc dendrites and carbonations. In addition to the QAFC electrolyte membrane development, a hybrid bifunctional oxygen electrocatalyst, consisting of cobalt oxysulfide nanoparticles and nitrogen-doped graphene nanomeshes (CoO0.87S0.13/GN), was prepared. The defect chemistries of both oxygen-vacancy-rich cobalt oxysulfides and edge-nitrogen-rich graphene nanomeshes lead to a remarkable improvement in electrocatalytic performance, where CoO0.87S0.13/GN exhibits strongly comparable catalytic activity and much better stability than the best-known benchmark noble metal catalysts. A simple, water-based filtration method for a direct assembly of the QAFC membrane and the CoO0.87S0.13/GN catalyst film was demonstrated with the PEMZAB. Such a fabrication approach enables intimate contact between the solid-solid catalyst-electrolyte interfaces for facile charge transfer. Moreover, benefiting from the performance improvement of the QAFC electrolyte membrane and the CoO0.87S0.13/GN bifunctional catalyst, the resulting battery possesses a higher energy density of 857.9 Wh kg-1 and a more stable cycling performance, over 300 hours of operation at 20 mA cm-2 under ambient conditions, than those of a battery using PVA-KOH gel electrolyte and commercial Co3O4 bifunctional catalysts. In the last study, the knowledge gained from the hybrid CoO0.87S0.13/GN bifunctional catalyst is transferred to the fabrication of a hybrid catalyst/current collector assembly for the bifunctional air electrode. In this assembly, a hair-like array of mesoporous cobalt oxide nanopetals in nitrogen-doped carbon nanotubes is grown directly on a stainless-steel mesh through chemical vapor deposition and electrodeposition methods. Such integrative design not only ensures a large number of catalytically active sites in a given electrode surface, but also increases the electron transfer between each individual catalyst and the conductive substrate. This advanced air electrode assembly further boosts the PEMZAB performance, with a high peak power density of 160.7 mW cm-2 at 250 mA cm-2 and a remarkable cycling durability: lasting over 600 hours of operation at 25 mA cm-2 under ambient conditions.
Download or read book Next generation Batteries with Sulfur Cathodes written by Krzysztof Jan Siczek and published by Academic Press. This book was released on 2019-03-06 with total page 259 pages. Available in PDF, EPUB and Kindle. Book excerpt: Next-Generation Batteries with Sulfur Cathodes provides a comprehensive review of a modern class of batteries with sulfur cathodes, particularly lithium-sulfur cathodes. The book covers recent trends, advantages and disadvantages in Li-S, Na-S, Al-S and Mg-S batteries and why these batteries are very promising for applications in hybrid and electric vehicles. Battery materials and modelling are also dealt with, as is their design, the physical phenomena existing in batteries, and a comparison of batteries between commonly used lithium-ion batteries and the new class of batteries with sulfur cathodes that are useful for devices like vehicles, wind power aggregates, computers and measurement units. Provides solutions for the recycling of batteries with sulfur cathodes Includes the effects of analysis and pro and cons of Li-S, Na-S, Al-S, Mg-S and Zn-S batteries Describes state-of-the-art technological developments and possible applications
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1994 with total page 1028 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Download or read book Hearings Reports and Prints of the Senate Committee on Public Works written by United States. Congress. Senate. Committee on Public Works and published by . This book was released on 1967 with total page 1726 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Non precious Cathode Electrocatalytic Materials for Zinc air Battery written by Baejung Kim and published by . This book was released on 2013 with total page 81 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the past decade, rechargeable batteries attracted the attention from the researchers in search for renewable and sustainable energy sources. Up to date, lithium-ion battery is the most commercialized and has been supplying power to electronic devices and hybrid and electric vehicles. Lithium-ion battery, however, does not satisfy the expectations of ever-increasing energy and power density, which of their limits owes to its intercalation chemistry and the safety.1-2 Therefore, metal-air battery drew much attention as an alternative for its high energy density and a simple cell configuration.1 There are several different types of metal-air batteries that convey different viable reaction mechanisms depending on the anode metals; such as Li, Al, Ca, Cd, and Zn. Redox reactions take place in a metal-air cell regardless of the anode metal; oxidation reaction at the anode and reduction reaction at the air electrode. Between the two reaction, the oxygen reduction reaction (ORR) at the air electrode is the relatively the limiting factor within the overall cell reactions. The sluggish ORR kinetics greatly affects the performance of the battery system in terms of power output, efficiency, and durability. Therefore, researchers have put tremendous efforts in developing highly efficient metal air batteries and fuel cells, especially for high capacity applications such as electric vehicles. Currently, the catalyst with platinum nanoparticles supported on carbon material (Pt-C) is considered to exhibit the best ORR activities. Despite of the admirable electrocatalytic performance, Pt-C suffers from its lack of practicality in commercialization due to their prohibitively high cost and scarcity as of being a precious metal. Thus, there is increasing demand for replacing Pt with more abundant metals due economic feasibility and sustainability of this noble metal.3-5 Two different attitudes are taken for solution. The first approach is by optimizing the platinum loading in the formulation, or the alternatively the platinum can be replaced with non-precious materials. The purpose of this work is to discover and synthesize alternative catalysts for metal-air battery applications through optimized method without addition of precious metals. Different non-precious metals are investigated as the replacement of the precious metal including transition metal alloys, transition metal or mixed metal oxides, and chalcogenides. These types of metals, alone, still exhibits unsatisfying, yet worse, kinetics in comparison to the precious metals. Nitrogen-doped carbon material is a recently well studied carbon based material that exhibits great potential towards the cathodic reaction.6 Nitrogen-doped carbon materials are found to exhibit higher catalytic activity compared to the mentioned types of metals for its improved conductivity. Benefits of the carbon based materials are in its abundance and minimal environmental footprints. However, the degradation of these materials has demonstrated loss of catalytic activity through destruction of active sites containing the transition metal centre, ultimately causing infeasible stability. To compensate for these drawbacks and other limits of the nitrogen-doped carbon based catalysts, nitrogen-doped carbon nanotubes (NCNT) are also investigated in the series of study. The first investigation focuses on a development of a simple method to thermally synthesize a non-precious metal based nitrogen-doped graphene (NG) electrocatalyst using exfoliated graphene (Ex-G) and urea with varying amounts of iron (Fe) precursor. The morphology and structural features of the synthesized electrocatalyst (Fe-NG) were characterized by SEM and TEM, revealing the existence of graphitic nanoshells that potentially contribute to the ORR activity by providing a higher degree of edge plane exposure. The surface elemental composition of the catalyst was analyzed through XPS, which showed high content of a total N species (~8 at.%) indicative of the effective N-doping, present mostly in the form of pyridinic nitrogen groups. The oxygen reduction reaction (ORR) performance of the catalyst was evaluated by rotating disk electrode voltammetry in alkaline electrolyte and in a zinc-air battery cell. Fe-NG demonstrated high onset and half-wave potentials of -0.023 V (vs. SCE) and -0.110 V (vs. SCE), respectively. This excellent ORR activity is translated into practical zinc-air battery performance capabilities approaching that of commercial platinum based catalyst. Another approach was made in the carbon materials to further improve the cost of the electrode. Popular carbon allotropes, CNT and graphene, are combined as a composite (GC) and heteroatoms, nitrogen and sulfur, are introduced in order to improve the charge distribution of the graphitic network. Dopants were doped through two step processes; nitrogen dopant was introduced into the graphitic framework followed by the sulfur dopant. The coexistence of the two heteroatoms as dopants demonstrated outstanding ORR performance to those of reported as metal free catalysts. Furthermore, effects of temperature were investigated through comparing ORR performances of the catalysts synthesized in two different temperatures (500 ??? and 900 ???) during the N-doping process (consistent temperature was used for S-doping). Through XPS analysis of the surface chemistry of catalysts produced with high temperature during the N-doping step showed absence of N-species after the subsequent S-doping process (GC-NHS). Thus, the synergetic effects of the two heteroatoms were not revealed during the half-cell testing. Meanwhile, the two heteroatoms were verified in the catalyst synthesized though using low temperature during the N-doping process followed by the S-doping step (GC-NLS). Consequently, ORR activity of the resulting material demonstrated promising onset and half-wave potentials of -0.117 V (vs. SCE) and -0.193 V (vs. SCE). In combination of these investigations, this document introduces thorough study of novel materials and their performance in its application as ORR catalyst in metal air batteries. Moreover, this report provides detailed fundamental insights of carbon allotropes, and their properties as potential elecrocatalysts and essential concepts in electrochemistry that lies behind zinc-air batteries. The outstanding performances of carbon based electrocatalyst are reviewed and used as the guides for further direction in the development of metal-air batteries as a promising sustainable energy resource in the future.
Download or read book Electric Power Reliability written by United States. Congress. Senate. Committee on Commerce. Subcommittee on Surface Transportation and published by . This book was released on 1967 with total page 1286 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Electrochemical Oxygen Technology written by Dr. Kim Kinoshita and published by John Wiley & Sons. This book was released on 1992-08-04 with total page 462 pages. Available in PDF, EPUB and Kindle. Book excerpt: Explores both electrochemistry fundamentals and the applications of oxygen in electrochemical systems. Much of the information is summarized in tables which are accompanied by a list of references to consult for details. Emphasizes fuel cells and metal/air batteries.
Download or read book Physical Chemistry of Ionic Materials written by Joachim Maier and published by John Wiley & Sons. This book was released on 2023-04-03 with total page 581 pages. Available in PDF, EPUB and Kindle. Book excerpt: Discover the physical chemistry of charge carriers in the second edition of this popular textbook Ionic and electronic charge carriers are critical to the kinetic and electrochemical properties of ionic solids. These charge carriers are point defects and are decisive for electrical conductivity, mass transport, and storage phenomena. Generally, defects are deviations from the perfect structure, and if higher-dimensional, also crucial for the mechanical properties. The study of materials science and energy research therefore requires a thorough understanding of defects, in particular the charged point defects, their mobilities, and formation mechanisms. Physical Chemistry of Ionic Materials is a comprehensive introduction to these charge carrier particles and the processes that produce, move, and activate them. Covering both core principles and practical applications, it discusses subjects ranging from chemical bonding and thermodynamics to solid-state kinetics and electrochemical techniques. Now in an updated edition with numerous added features, it promises to be the essential textbook on this subject for a new generation of materials scientists. Readers of the 2nd Edition of Physical Chemistry of Ionic Materials will also find: Two new chapters on solid state electrochemistry and another on nanoionics Novel brief sections on photoelectrochemistry, bioelectrochemistry, and atomistic modelling put the treatment into a broader context Discussion of the working principles required to understand electrochemical devices like sensors, batteries, and fuel cells Real laboratory measurements to ground basic principles in practical experimentation Physical Chemistry of Ionic Materials is a valuable reference for chemists, physicists, and any working researchers or advanced students in the materials sciences.
Download or read book Electrochemical Power Sources Fundamentals Systems and Applications written by Hajime Arai and published by Elsevier. This book was released on 2020-10-29 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt: Metal-air is a promising battery system that uses inexpensive metals for its negative electrode while unlimited, free and non-toxic oxygen is used for its positive electrode, however, only primary systems have been commercialized so far. Electrochemical Power Sources: Fundamentals, Systems, and Applications - Metal-Air Batteries: Present and Perspectives offers a comprehensive understanding of metal-air batteries as well as the solutions to the issues for overcoming the related difficulties of the secondary (rechargeable) system. Although metal-air batteries are widely studied as low-cost high-energy systems, their commercialization is limited to primary ones due to currently limited cycle life and insufficient reliability. For realization of the secondary systems, this book offers comprehensive understanding of metal-air batteries, including the details of both electrodes, electrolyte, cell/system, modelling and applications. Electrochemical Power Sources: Fundamentals, Systems, and Applications - Metal-Air Batteries: Present and Perspectives provides researchers, instructors, and students in electrochemistry, material science and environmental science; industry workers in cell manufacturing; and government officials in energy, environmental, power supply, and transportation with a valuable resource covering the most important topics of metal-air batteries and their uses. Outlines the general characteristics of metal-air compared with conventional batteries Offers a comprehensive understanding of various metal-air, featuring zinc, and lithium Contains comparisons and issues among various metal-air batteries and research efforts to solve them Includes applications and market prospects
Download or read book Design and Engineering of Hierarchically Porous Transition Metal based Electrocatalysts for Rechargeable Zn air Batteries written by Moon Gyu Park and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the critical cathodic and anodic reactions, respectively, in electrically rechargeable Zn-air battery. With a variety of advantages including relatively high energy density (1218 Wh kg-1), the abundance of zinc in the earth, and secure handling and safe operation, electrically rechargeable (secondary) Zn-air battery technology has been regarded as highly promising energy applications in consumer electronics, electric vehicles, and smart grid storage. Zn-air batteries consist of not only zinc anode, polymer separator, and an alkaline electrolyte that are typical battery components, but also air-breathing cathode that makes Zn-"air" battery unique technology. Unlike other general battery systems such as lithium-ion batteries, there is no active material stored in cathode, but gaseous oxygen molecules in the air are used as the fuel for energy-generating reaction in the air cathode of Zn-air technology. The reactions occurring during battery discharge and charge are ORR and OER, respectively, which are mostly dominating the overall energy efficiency of the Zn-air battery system due to their intrinsically sluggish kinetics. The high energy barrier attributed to conversions between oxygen molecules diffused from the air and hydroxide ions in the electrolyte at the thin layer of the electrode leads to low charge/discharge energy efficiency and insufficient cycle stability hindering the commercialization of rechargeable Zn-air batteries to the market. Therefore, it is necessarily required to facilitate the slow kinetics of oxygen electrocatalytic reactions by using bifunctionally active and durable oxygen electrocatalyst materials to progress the reactions at practically viable and stable rates. With the use of bifunctional oxygen catalysts, kinetics of ORR and OER can be improved, leading to enhancement of Zn-air battery performances such as higher operating voltage and longer battery cycling life. The current best-known catalysts for ORR and OER are noble metals, including platinum (Pt) and iridium (Ir), respectively. However, high cost and scarcity of the precious metal-based catalysts hinder their employment in large scale energy applications. Furthermore, the electrochemical stability of these materials is well known to be very insufficient for long term usage even under typical device operating conditions. Therefore, the development of non-precious transition metal-based electrocatalysts has significantly been a momentous research field. Along with this movement, the facile synthesis and inexpensive preparation of highly active and durable electrocatalysts will take the top priority for the fulfillment of practically available rechargeable Zn-air battery technology in a variety of energy applications from portable electronics to electric vehicles and smart grid storage systems. In this work, novel design strategies of bifunctionally active and durable electrocatalysts possessing robust three-dimensional framework with hierarchical porosity are presented. A porous structure with a large surface area is essential to improve the oxygen electrocatalysis since the oxygen reactions take place at the surface of materials, where active sites reside, and thereby the large surface indicating plenty of catalytically active sites enhances kinetics of the reactions. Additionally, the porous architecture facilitates diffusion of oxygen gas molecules during the oxygen electrocatalysis, leading to enhanced mass transport of reactants and reduced overpotentials for ORR and OER polarizations, eventually resulting in improved activities. In addition to the improvement of activities, electrochemical stability is an essential fundamental property for the rational design of electrocatalysts. Thus, the 3D porous structure must have robust framework which can endure the highly oxidative environment in OER potential range. Therefore, the work presented in this thesis is aiming for the design and engineering of hierarchically porous transition metal-based electrocatalysts involving high porosity as well as electrocatalytically robust frameworks to improve the oxygen electrocatalytic activities and durability and thereby put the rechargeable Zn-air battery technology at a commercially viable level. In the first study, a facile polymer template-derived method has been used to synthesize three-dimensionally ordered meso/macro-porous (3DOM) spinel cobalt oxide as a bifunctional oxygen electrocatalyst. Physicochemical characterizations have revealed the morphology of the designed electrocatalyst to be a hierarchically meso/macro-porous metal oxide framework. As investigated by electrochemical characterizations, 3DOM Co3O4 shows far enhanced ORR and OER activities with improved kinetics compared to the bulk material. The enhancement is majorly attributed to the five times higher specific surface area and significantly greater pore volume, leading to the increased number of catalytic active sites and facilitated diffusion of oxygen molecules into and out of the structure, respectively. Moreover, the robust frameworks of 3DOM Co3O4 helps to withstand harsh cycling environments by exhibiting significantly small performance reduction and retaining the original morphology. The improved oxygen electrocatalytic activity and durability have been well demonstrated in the rechargeable Zn-air battery system. 3DOM Co3O4 presents remarkably enhanced rechargeability over 200 cycles while retaining quite comparable operating voltage gap in comparison with the precious benchmark catalyst. In the second study, palladium (Pd) nanoparticle is deposited on the surface of 3DOM Co3O4 via a simple chemical reduction process. The morphological advantages of the 3DOM framework, as confirmed in the previous study, are expected to facilitate diffusion of oxygen molecules into and out of the structure leading to the decreased overpotentials during ORR and OER. However, using metal oxides as electrocatalysts restricts fast electron transfer leading to limited activity for oxygen catalysis due to their intrinsically low electrical conductivity. Therefore, Pd nanoparticles are introduced into 3DOM Co3O4 by expecting synergy from the combination of the morphological advantage of 3DOM architecture and the significant thermodynamic stability as well as the excellent ORR activity of palladium metal. Electrochemical characterizations have revealed that the combination demonstrates synergistically improved bifunctional electrocatalytic activity and durability. Moreover, computational simulation via density-functional-theory (DFT) verifies Pd@Co3O4(3DOM) is superior in two ways; (i) Activity-wise: the d-band center of Pd deposited on 3DOM Co3O4 was found to decrease significantly, resulting in increased electron abundance at the Fermi level, which in turn enhanced the overall electrical conductivity; (ii) Durability-wise: synergistic hybrid of Pd and 3DOM Co3O4 resulted in a significantly improved corrosion resistance, due to the much higher carbon oxidation potential and bulk-like dissolution potential of Pd nanoparticles on 3DOM Co3O4. The remarkable electrochemical activities and stabilities of Pd@3DOM-Co3O4 obtained from the half-cell testing resulted in excellent rechargeability of a prototype Zn-air battery, demonstrating the synergistic introduction of Pd into 3DOM Co3O4. In the last study, a type of metal-organic-framework (MOF) is selected as a template to synthesize MOF-based electrocatalyst possessing robust framework with multi-level porosity. Typically, MOF materials consist of metal centers linked by functional organic ligands, which gives them unique material characteristics such as high porosity and surface area, morphological and compositional flexibility, and high crystallinity. Especially, transition metal-based Prussian blue analogue (PBA) nanocubes with a chemical formula MxII[MyIII(CN)6]z▪H2O, where MII and MIII are divalent and trivalent transition metal cations, respectively, are employed as the MOF precursors due to a several material advantages such as simple precipitation synthesis, various possible compositions, and robust structure with high porosity
