Metal Oxide-Based Nanostructured Electrocatalysts for Fuel Cells, Electrolyzers, and Metal-Air Batteries is a comprehensive book summarizing the recent overview of these new materials developed to date. The book is motivated by research that focuses on the reduction of noble metal content in catalysts to reduce the cost associated to the entire system. Metal oxides gained significant interest in heterogeneous catalysis for basic research and industrial deployment. Metal Oxide-Based Nanostructured Electrocatalysts for Fuel Cells, Electrolyzers, and Metal-Air Batteries puts these opportunities and challenges into a broad context, discusses the recent researches and technological advances, and finally provides several pathways and guidelines that could inspire the development of ground-breaking electrochemical devices for energy production or storage. Its primary focus is how materials development is an important approach to produce electricity for key applications such as automotive and industrial. The book is appropriate for those working in academia and R&D in the disciplines of materials science, chemistry, electrochemistry, and engineering. Includes key aspects of materials design to improve the performance of electrode materials for energy conversion and storage device applications Reviews emerging metal oxide materials for hydrogen production, hydrogen oxidation, oxygen reduction and oxygen evolution Discusses metal oxide electrocatalysts for water-splitting, metal-air batteries, electrolyzer, and fuel cell applications

Highly active, low cost and durable electrocatalysts are desired for the development and commercialization of fuel cells and metal-air batteries. The efficiency of these devices is significantly limited by the activation of oxygen-involved reactions, namely oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Precious metals (such as Pt) and metal oxides (such as RuO2) are traditional electrocatalysts for ORR and OER, respectively. However, the electrocatalytic performance of these precious metal-based nanomaterials is still hindered by their scarcity, high cost, insufficient activity and poor durability. Recently, developing cost-efficient and highly active electrocatalysts to replace the precious metals and oxides have obtained increasing attentions. To enhance the performance of ORR electrocatalysis, formation of PtM (M=Fe, Co, Ni, Cu) is one of most widely used strategies. The utilization of PtM can not only decrease the overall cost but improve the catalytic activity due to the synergistic effect between Pt and M. In addition, porous carbon-based nanomaterials, such as heteroatom-doped carbon, metal-nitrogen-carbon (M-N-C) nanostructures and carbon/nonprecious metal hybrids, have also been demonstrated to be promising candidates for ORR catalysis in alkaline media. These porous catalysts can effectively reduce the cost because of the absence of precious metals. Besides, the unique porous structures are favorable for mass transport and electron transfer, thus improving ORR catalytic performance. For OER electrocatalysis, a multitude of efforts have been devoted to investigate earth-abundant and highly active catalysts, such as transition metal-based nanomaterials (alloys, oxides, phosphides, phosphates, hydroxides, etc.). The corresponding OER catalytic performance can be effectively improved by tailoring the intrinsic nature of the catalysts as well as forming sufficient active sites, which can be achieved by tuning the elemental composition and increasing the surface area. Herein, a large variety of nanostructured electrocatalysts with different composition and morphology were designed and synthesized. Thanks to their compositional and morphological advances, these catalysts have been demonstrated to be active for ORR or OER.

This dissertation, "Nanostructure of Transition Metal and Metal Oxide for Electrocatalysis" by Yanjuan, Gu, 谷艳娟, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled NANOSTRUCTURE OF TRANSITION METAL AND METAL OXIDE FOR ELECTROCATALYSIS Submitted by Gu Yan Juan for the degree of Doctor of Philosophy at The University of Hong Kong in August 2006 Pd, Pt, and Ru nanoparticles that were uniformly dispersed on multi-walled carbon nanotubes (MWNTs) were synthesized by vacuum pyrolysis using metal acetylacetonate as metal precursor, and the nanocomposites were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X- ray diffraction (XRD). The size and distribution of the nanoparticles were strongly affected by the reaction time, temperature, and the initial mass ratio of the metal precursors to MWNTs. The higher temperature, the smaller Pd nanoparticles were formed at the range of 250 to 500 C. The average size of the Pd nanoparticles increased with the increase in mass ratio of the metal precursors to MWNTs. The particle size of Pt and Ru showed little change with the change in mass ratio. Pt and Ru nanoparticles had the mean diameters of 3.00.6 and 2.50.4 nm when the mass ratio of Pt(acac) and Ru(acac) to 2 3 MWNTs was both 2:1 at 500 C. The electrocatalytic activity of Pt/MWNTs and PtRu/MWNTs was investigated at room temperature by cyclic voltammetry and chronoamperometry. All of the electrochemical results showed that the PtRu/MWNTs catalyst exhibit high activity for methanol oxidation that resulted from the high surface area of carbon nanotubes and the platinum/ruthenium nanoparticles. Compared with Pt/MWNTs, the onset potential is much lower and the ratio of forward anodic peak current to reverse anodic peak current is much higher for methanol oxidation. Pt Ru /MWNTs displayed the best electrocatalytic 45 55 activities among all carbon nanotubes supported Pt and PtRu catalysts. Hyperbranched RuO nanostructures can be formed through the oxidation of Ru nanoparticles at relatively low temperatures in air, which is a very simple and low cost method. The morphology of the RuO nanostructure is closely associated with the dispersivity of the Ru nanoparticles on the MWNTs. Cu, Pt and Pd nanoparticles are very effective catalysts in the formation of RuO hyperbranched nanostructures. The electrochemical studies of these nanorods demonstrated that they display characteristic properties of RuO (110) surface. The successful attachment of Pt nanoparticles to RuO surface through a simple, two-step chemically controlled procedure is reported. The effect of the single crystal structure of RuO nanorods on the electrocatalytic activity of Pt nanoparticles was investigated, showing that the presence of the RuO nanorods greatly increases the electrochemical activity of electrodes toward methanol oxidation, not only increasing the current density but also shifting the onset potential of methanol electrooxidation to over 200 mV lower than that on the Pt nanoparticle electrode. The results described here also demonstrate the ability of metal oxide nanorods to serve as a conductive support for fuel cell applications. DOI: 10.5353/th_b3777439 Subjects: Electrocatalysis Transition metals Nanoparticles Nanostructured materials Methanol - Oxidation

"We heartily recommend this book to all readers who wish to gain a better understanding of nanostructured carbon materials surface properties and used in catalysis." An-Hui Lu, ChemCatChem There is great interest in using nanostructured carbon materials in catalysis, either as supports for immobilizing active species or as metal-free catalysts due to their unique structural, thermal, chemical, electronic and mechanical properties, and tailorable surface chemistry. This book looks at the structure and properties of different doped and undoped nanocarbons including graphene; fullerenes; nanodiamonds; carbon nanotubes and nanofibers; their synthesis and modification to produce catalysts. Special attention is paid to adsorption, as it impacts the application of these materials in various industrially relevant catalytic reactions discussed herein, in addition to photocatalysis and electrocatalysis. Written by leading experts in the area, this is the first book to provide a comprehensive view of the subject for the catalysis community.

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.

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