3d Interface Engineered Transition Metal Oxide Carbon Hybrid Structures For Efficient Bifunctional Oxygen Electrocatalysis In Alkaline And Acidic Environments

Use of regenerative fuel cells requires efficient bifunctionality in oxygen electrocatalysis: oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Commonly used noble metals like Pt and its alloys (Pt/Ir or Pt/Ru) are often used for their catalytic activity, selectivity and stability in harsh environments. However, Pt can degrade during operation from catalyst agglomeration and poisoning. Therefore, researchers have used non-precious transition metal oxides (TMO) including Fe3O4, MnOx and Co3O4 and/or nanocarbon structures (NC) as potential catalyst. Composite structures where TMO nanoparticles are deposited onto a NC, derived from either graphene oxide (GO) or metal-organic frameworks (MOFs), have often been used. NCs have high surface area and excellent electronic conductivity, and while many studies assert these types of composite materials exhibiting synergistic effects in oxygen electrocatalysis, efforts to elucidate the origin of the synergy is lacking. This doctoral research explores how functional groups present on the surface of NCs affect synergy (reaction route and kinetics) of these electrocatalysis. To incur catalytically active sites between the metal oxides and carbon, the NCs basal plane were functionalized using acid treatments, after which various types of TMO/NC hybrids were synthesized using either wet process or vacuum deposition techniques. The hydroxylated CeO2/graphene hybrids showed the best ORR and OER performance in both alkaline and acidic media, in terms of onset/half-wave potential, electron transfer number, and current density when compared to the performance of benchmark catalysts: Pt/C (for ORR) and IrO2 (for OER). From a series of material and electrochemical analyses, it was determined that a strong tethering of TMOs on graphene's basal plane prohibited restacking and particle-carbon interfaces dictates the performance and reaction route, as indicated in density functional theory calculations. In addition, a hybrid catalyst of TiO2 nanodots, uniformly anchored on phosphorylated carbon by atomic layer deposition (ALD), showed even better ORR and OER performance in alkaline media when compared the aforementioned CeO2/graphene hybrid. Materials characterization emphasized a strong adhesion of TMOs on MOF structures; thus providing ample surface interactions for a favorable reaction route. Therefore, an activation of catalytic sites can be realized by proper engineering of interfaces in each hybrid system.

The Frontiers in Materials Editorial Office team are delighted to present the inaugural “Frontiers in Materials: Rising Stars” article collection, showcasing the high-quality work of internationally recognized researchers in the early stages of their independent careers. All Rising Star researchers featured within this collection were individually nominated by the Journal’s Chief Editors in recognition of their potential to influence the future directions in their respective fields. The work presented here highlights the diversity of research performed across the entire breadth of the materials science and engineering field, and presents advances in theory, experiment and methodology with applications to compelling problems. This Editorial features the corresponding author(s) of each paper published within this important collection, ordered by section alphabetically, highlighting them as the great researchers of the future. The Frontiers in Materials Editorial Office team would like to thank each researcher who contributed their work to this collection. We would also like to personally thank our Chief Editors for their exemplary leadership of this article collection; their strong support and passion for this important, community-driven collection has ensured its success and global impact. Laurent Mathey, PhD Journal Development Manager

Defects in Two-Dimensional Materials addresses the fundamental physics and chemistry of defects in 2D materials and their effects on physical, electrical and optical properties. The book explores 2D materials such as graphene, hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMD). This knowledge will enable scientists and engineers to tune 2D materials properties to meet specific application requirements. The book reviews the techniques to characterize 2D material defects and compares the defects present in the various 2D materials (e.g. graphene, h-BN, TMDs, phosphorene, silicene, etc.). As two-dimensional materials research and development is a fast-growing field that could lead to many industrial applications, the primary objective of this book is to review, discuss and present opportunities in controlling defects in these materials to improve device performance in general or use the defects in a controlled way for novel applications. Presents the theory, physics and chemistry of 2D materials Catalogues defects of 2D materials and their impacts on materials properties and performance Reviews methods to characterize, control and engineer defects in 2D materials

The book is a multi-author survey (in 15 chapters) of the current state of knowledge and recent developments in our understanding of oxide surfaces. The author list includes most of the acknowledged world experts in this field. The material covered includes fundamental theory and experimental studies of the geometrical, vibrational and electronic structure of such surfaces, but with a special emphasis on the chemical properties and associated reactivity. The main focus is on metal oxides but coverage extends from 'simple' rocksalt materials such as MgO through to complex transition metal oxides with different valencies.

Fuel cells are one of the most promising clean energy conversion devices that can solve the environmental and energy problems in our society. However, the high platinum loading of fuel cells - and thus their high cost - prevents their commercialization. Non- or low- platinum electrocatalysts are needed to lower the fuel cell cost. Electrocatalysis in Fuel Cells: A Non and Low Platinum Approach is a comprehensive book summarizing recent advances of electrocatalysis in oxygen reduction and alcohol oxidation, with a particular focus on non- and low-Pt electrocatalysts. All twenty four chapters were written by worldwide experts in their fields. The fundamentals and applications of novel electrocatalysts are discussed thoroughly in the book. The book is geared toward researchers in the field, postgraduate students and lecturers, and scientists and engineers at fuel cell and automotive companies. It can even be a reference book for those who are interested in this area.

This book presents a state-of-the-art overview of the research and development in designing electrode and electrolyte materials for Li-ion batteries and supercapacitors. Further, green energy production via the water splitting approach by the hydroelectric cell is also explored. Features include: • Provides details on the latest trends in design and optimization of electrode and electrolyte materials with key focus on enhancement of energy storage and conversion device performance • Focuses on existing nanostructured electrodes and polymer electrolytes for device fabrication, as well as new promising research routes toward the development of new materials for improving device performance • Features a dedicated chapter that explores electricity generation by dissociating water through hydroelectric cells, which are a nontoxic and green source of energy production • Describes challenges and offers a vision for next-generation devices This book is beneficial for advanced students and professionals working in energy storage across the disciplines of physics, materials science, chemistry, and chemical engineering. It is also a valuable reference for manufacturers of electrode/electrolyte materials for energy storage devices and hydroelectric cells.

It is well known that renewable energy, e.g., wind and solar power, are intermittent energy sources. This means that energy storage devices are needed to store the energy for when it is needed. Currently Li-ion batteries are used as these energy storage devices, not only for alternative energy plants but in vehicles and electronics. There are several drawbacks with using Li-ion batteries, such as low safety, harmful Li mining practices, and high material costs. Rechargeable zinc-air batteries (ZABs) have gained a lot of traction recently due to their low cost, high safety, low environmental impact, and high theoretical energy density. However, a major obstacle is the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air electrode, which have hindered practical applications of ZABs. Precious metal catalysts have been applied to help mitigate the slow reaction kinetics; however, these are expensive and complicate manufacturing practices since two different precious metals are needed to achieve a bifunctional catalyst. Therefore, a low-cost bifunctional catalyst is needed to improve the slow reaction kinetics at the air electrode. This work focuses on further investigating a previously developed impregnation technique for air electrode preparation using an array of transition metal (Zn, Ni, Mn, and Co) oxide combinations. Various electrochemical and microstructural characterization techniques, e.g., linear sweep voltammetry, electrochemical impedance spectroscopy, electron microscopy, and energy dispersive X-ray spectroscopy, are used to examine each sample. The first study involved fabricating several catalysts by decorating nitrogen doped carbon nanotubes (N-CNTs) with either tri-metallic (Ni-Mn-Co) or tetra-metallic (Zn-Ni-Mn-Co) oxides, through a simple impregnation method into carbon-based, gas diffusion layers (GDL). Metal oxide compositions were selected based on previous results, preliminary electrochemical testing, and statistical design of experiments (DOE). Microstructural characterization was done using electron microscopy and X-ray photoelectron spectroscopy (XPS), and determined that the oxides fabricated were spinel oxides. Samples were electrochemically tested and the best candidates were subjected to full cell testing and bifunctional cycling for 200 charge/discharge cycles at 10 mA/cm2. The overall bifunctional efficiency, after cycling, of the best NiMnCoOx/N-CNT and ZnNiMnCoOx/N-CNT catalysts was 53.3% and 56.4%, respectively; both outperformed Pt-Ru/C in both overall bifunctional efficiency (38%) and cycling stability. The maximum power density of one of the tetra-metallic oxides exceeded that of Pt-Ru/C (110 mW/cm2) at 134 mW/cm2. The addition of Zn with Ni-Mn-Co oxide particles showed improved cycling stability and overall bifunctional efficiency. The second study investigated the effect of co-doping of carbon nanotubes with nitrogen and sulfur (N,S-CNTs), combined with tri-metallic and tetra-metallic oxides, on the ORR and OER reaction kinetics at the air electrode. The best tri-metallic (Ni-Mn-Co) oxide and tetra-metallic (Zn-Ni-Mn-Co) oxide from the first study were used in this investigation. Microstructural characterization analysis revealed that the Co and Mn valences increased for the Ni-Mn-Co and Zn-Ni-Mn-Co oxides, respectively. Electrochemical testing revealed that the Ni-Mn-Co oxide was comparable to the Pt-Ru/C catalyst with a power density of ~95 mW/cm2 and Zn-Ni-Mn-Co oxide was comparable to the Pt-Ru/C catalyst with an efficiency of 56.0% at 20 mA/cm2. The addition of sulfur to the N-CNTs positively impacted the Ni-Mn-Co oxide, leading to a round trip bifunctional cycling efficiency of 55.1% for 200 charge-discharge cycles at 10 mA/cm2. The impact of sulfur did not have a positive impact on the Zn-Ni-Mn-Co oxide; the LSV results were significantly worse than the equivalent oxide on N-CNTs and the full cell testing was comparable to the N-CNT oxide. Both tri-metallic and tetra-metallic oxides outperformed Pt-Ru/C during bifunctional cycling.

Metal Oxide–Carbon Hybrid Materials: Synthesis, Properties and Applications reviews the advances in the fabrication and application of metal oxide–carbon-based nanocomposite materials. Their unique properties make them ideal materials for gas-sensing, photonics, catalysis, opto-electronic, and energy-storage applications. In the first section, the historical background to the hybrid materials based on metal oxide–carbon and the hybridized metal oxide composites is provided. It also highlights several popular methods for the preparation of metal oxide–carbon composites through solid-state or solution-phase reactions, and extensively discusses the materials’ properties. Fossil fuels and renewable energy sources cannot meet the ever-increasing energy demands of an industrialized and technology-driven global society. Therefore, the role of metal oxide–carbon composites in energy generation, hydrogen production, and storage devices, such as rechargeable batteries and supercapacitors, is of extreme importance. These problems are discussed in in the second section of the book. Rapid industrialization has resulted in serious environmental issues which in turn have caused serious health problems that require the immediate attention of researchers. In the third section, the use of metal oxide–carbon composites in water purification, photodegradation of industrial contaminants, and biomedical applications that can help to clean the environment and provide better healthcare solutions is described. The final section is devoted to the consideration of problems associated with the development of sensors for various applications. Numerous studies performed in this area have shown that the use of composites can significantly improve the operating parameters of such devices. Metal Oxide–Carbon Hybrid Materials: Synthesis, Properties and Applications presents a comprehensive review of the science related to metal oxide–carbon composites and how researchers are utilizing these materials to provide solutions to a large array of problems. Reviews the fundamental properties and fabrication methods of metal-oxide–carbon composites Discusses applications in energy, including energy generation, hydrogen production and storage, rechargeable batteries, and supercapacitors Includes current and emerging applications in environmental remediation and sensing

This book comprehensively describes the fundamentals of electrochemical water electrolysis as well as the latest materials and technological developments. It addresses a variety of topics such as electrochemical processes, materials, components, assembly and manufacturing, and degradation mechanisms, as well as challenges and strategies. It also includes an understanding of how materials and technologies for electrochemical water electrolysis have developed in recent years, and it describes the progress in improving performance and providing benefits to energy systems and applications. Features the most recent advances in electrochemical water electrolysis to produce hydrogen Discusses cutting-edge materials and technologies for electrochemical water electrolysis Includes both experimental and theoretical approaches that can be used to guide and promote materials as well as technological development for electrochemical water electrolysis Comprises work from international leading scientists active in electrochemical energy and environmental research and development Provides invaluable information that will benefit readers from both academia and industry With contributions from researchers at the top of their fields, the book includes in-depth discussions covering the engineering of components and applied devices, making this an essential read for scientists and engineers working in the development of electrochemical energy devices and related disciplines.