Electrocatalysts fundamental properties

Carbon supported Pt and Pt-alloy electrocatalysts form the cornerstone of the current state-of-the-art electrocatalysts for medium and low temperature fuel cells such as phosphoric and proton exchange membrane fuel cells (PEMECs). Electrocatalysis on these nanophase clusters are very different from bulk materials due to unique short-range atomic order and the electronic environment of these cluster interfaces. Studies of these fundamental properties, especially in the context of alloy formation and particle size are, therefore, of great interest. This chapter provides an overview of the structure and electronic nature of these supported... 

The main basic parameter of catalyst evaluation is the specific exchange current density which, by definition, is normalized to the unit surface area of the electrocatalyst. This property is the target of many fundamental studies in electrocatalysis, too numerous to be listed (Adzic et al., 2007 Debe, 2013 Gasteiger and Markovic, 2009 Kinoshita, 1992 Paulus et al., 2002 Stamenkovic et al., 2007a,b Tarasevich et al., 1983 Zhang et al., 2005, 2008). 

Electrocatalysis is, in the majority of cases, due to the chemical catalysis of the chemical steps in an electrochemical multi-electron reaction composed of a sequence of charge transfers and chemical reactions. Two factors determine the effective catalytic activity of a technical electrocatalysts its chemical nature, which decisively determines its absorptive and fundamental catalytic properties and its morphology, which determines mainly its utilization. A third issue of practical importance is long-term stability, for which catalytic properties and utilization must occasionally be sacrificed. 

The search for new electrode materials is expected to be guided by the fundamental understanding of the factors governing the activity. In electrochemistry, this branch of the discipline is known by the name of electrocatalysis . Strictly speaking, electrocatalysis is the science devoted to the relationship between the properties of materials and the electrode reaction rate. The scope of electrocatalysis as a science is to establish a predictive basis for the design and the optimization of electrocatalysts. 

In Chapter 3, to give some basic knowledge and concepts, some fundamentals about the catalyst activity and stability of ORR electrocatalysts, which are the targeted research systems by rotating electrode methods, are presented. A detailed description about the electrocatalysts and catalyst layers and their applications for ORR in terms of their types, structures, properties, catalytic activity/stability, as well as their research progress in the past several decades are also given. Furthermore, both the synthesis and characterization methods for ORR electrocatalysts, and the fabrication procedures for catalyst layers are also reviewed. 

Supported nanoparticles are the main catalysts used in current fuel cell devices. The combined DFT, single crystal, polycrystalline, and electrochemical experiments demonstrated that WC and Pt/WC have catalytic properties that are promising for use as anode DMFC electrocatalysts. These fundamental results still left questions unanswered as to how these materials could be incorporated into a realistic device. These questions led to studies of WC and Pt/WC nanoparticles in a fuel cell test station [23]. The WC nanoparticles were obtained from Japan New Metals Company. The Pt/WC nanoparticles were prepared with a 10 wt% Pt loading using incipient... 

As discussed above, the oxygen adsorption and reduction processes are often simulated either on small Pt clusters or flat surfaces. However, both experimental measurements [51, 52] and computational calculations [53, 54] indicate that nanosized electrocatalysts show a considerably different catalytic activity from extended flat surfaces. These investigations would suggest that effects observed with particle size reduction go well beyond the increase in surface area and involve fundamental physical and chemical changes in the reaction steps. Han and his coworkers [55] studied explicitly Pt nanoparticles with 1 and 2 nm sizes and compared their chemical adsorption properties to those of an extended flat Pt (111) surface. As atomic oxygen (O) and hydroxyl group (OH) are two species of considerable importance [56], they focused on effect of particle size and Pt coordination on the chemisorption energies of O and OH. 

Debe MK (2012) Nanostructured thin film electrocatalysts fOT PEM fuel cells - a tutorial on the fundamental characteristics and practical properties of NSTF catalysts. ECS Trans 45(2) 47-68... 

Chapters 7-12 focus on the electrocatalysis of carbon-based non-precious metal catalysts. The unique properties and fuel cell applications of various carbon based catalysts are intensively discussed in these chapters. Chapter 7 summarizes the fundamental studies on the electrocatalytic properties of metallomacrocyclic and other non-macrocyclic complexes. Chapter 8 and 9 review the progress made in the past 5 years of pyrolyzed carbon-supported nitrogen-coordinated transition metal complexes. Chapter 10 gives a comprehensive discussion on the role of transitional metals in the ORR electrocatalysts in acidic medium. Chapter 11 introduces modeling tools such as density functional theory (DPT) and ah initio molecular dynamics (AIMD) simulation for chemical reaction studies. It also presents a theoretical point of view of the ORR mechanisms on Pt-based catalysts, non-Pt metal catalysts, and non-precious metal catalysts. Chapter 12 presents an overview on recent progresses in the development of carbon-based metal-free ORR electrocatalysts, as well as the correlation between catalyst structure and their activities. 

Chapter 13 and 14 summarize the development of transitional metal oxides and transition metal chalcogenides for ORR, respectively. Chapter 15 is the only chapter in this book dedicated to the ORR catalysis of alkaline fuel cells. Electrocatalytic properties of various non-Pt catalysts including Ag, Pd, transition metal macrocycles, metal oxides, and multifunctional materials are presented. Fundamental issues related to the design of low-cost, high-performance electrocatalysts for alkaline fuel cells are discussed. Chapter 16 and 17 review the recent advances on the study of ORR on Au and Pd-based catalysts, respectively. 

The fundamental basis of corrosion has been elaborated with electrochemical thermodynamic and kinetics considerations. It has been shown that, in an aqueous environment, most metals derive stability from a nanoscale protective film formed at the surface of the material. It has been argued that corrosion loss before attainmerrt of equilibrium can have a profotmd effect on the properties and performance of a material. The importance of these aspects in nanolayers, nanocoatings and nanoscale electrocatalysts has been used as illustrative case studies. 

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