Electrocatalysis electrode

Understanding the activity and selectivity properties of electrocatalysts requires the characterization of catalyst surfaces, determination of adsorption characteristics, identification of surface intermediates and of all reaction products and paths, and mechanistic deliberation for complex as well as model reactions. Electrochemical and classical methods for adsorption studies are well documented in the literature (5, 7-9, 25, 24, 373. Here, we shall outline briefly some prominent electrochemical methods and some nonelectrochemical techniques that can provide new insight into electrocatalysis. Electrode kinetic parameters can be determined by potentionstatic methods using the methodology of Section II1,D,3. 

DMFC research at LANE in FY 2002 has focused primarily on fundamental issues relevant to potential portable and transportation applications of direct methanol fuel cells, such as cathode and anode electrocatalysis, electrode composition and structure, membrane properties and MEA design. Substantial progress has been achieved in cathode research. 

One factor contributing to the inefficiency of a fuel ceU is poor performance of the positive electrode. This accounts for overpotentials of 300—400 mV in low temperature fuel ceUs. An electrocatalyst that is capable of oxygen reduction at lower overpotentials would benefit the overall efficiency of the fuel ceU. Despite extensive efforts expended on electrocatalysis studies of oxygen reduction in fuel ceU electrolytes, platinum-based metals are stiU the best electrocatalysts for low temperature fuel ceUs. 

Electrodes. At least three factors need to be considered ia electrode selection as the technical development of an electroorganic reaction moves from the laboratory cell to the commercial system. First is the selection of the lowest cost form of the conductive material that both produces the desired electrode reactions and possesses stmctural iategrity. Second is the preservation of the active life of the electrodes. The final factor is the conductivity of the electrode material within the context of cell design. An ia-depth discussion of electrode materials for electroorganic synthesis as well as a detailed discussion of the influence of electrode materials on reaction path (electrocatalysis) are available (25,26). A general account of electrodes for iadustrial processes is also available (27). 

EC mechanism, 34, 42, 113 E. Coli, 186 Edge effect, 129 Edge orientation, 114 Electrical communication, 178 Electrical double layer, 18, 19 Electrical wiring, 178 Electrocapillary, 22 Electrocatalysis, 121 Electrochemical quartz crystal, microbalance, 52 Electrochemihuiiinescence, 44 Electrodes, 1, 107... 

Theoretical aspects of mediation and electrocatalysis by polymer-coated electrodes have most recently been reviewed by Lyons.12 In order for electrochemistry of the solution species (substrate) to occur, it must either diffuse through the polymer film to the underlying electrode, or there must be some mechanism for electron transport across the film (Fig. 20). Depending on the relative rates of these processes, the mediated reaction can occur at the polymer/electrode interface (a), at the poly-mer/solution interface (b), or in a zone within the polymer film (c). The equations governing the reaction depend on its location,12 which is therefore an important issue. Studies of mediation also provide information on the rate and mechanism of electron transport in the film, and on its permeability. 

Like other ion-exchange polymers, conducting polymers have been used to immobilize electroactive ions at electrode surfaces. Often the goal is electrocatalysis, and conducting polymers have the potential advantage of providing a fast mechanism for electron transport to and from the electrocatalytic ions. 

Electrocatalysis Again by definition, an electrocatalyst is a solid, in fact an electrode, which can accelerate a process involving a net charge transfer, such as e.g. the anodic oxidation of H2 or the cathodic reduction of 02 in solid electrolyte cells utilizing YSZ ... 

In the case of electrochemically promoted (NEMCA) catalysts we concentrate on the adsorption on the gas-exposed electrode surface and not at the three-phase-boundaries (tpb). The surface area, Ntpb, of the three-phase-boundaries is usually at least a factor of 100 smaller than the gas-exposed catalyst-electrode surface area Nq. Adsorption at the tpb plays an important role in the electrocatalysis at the tpb, which can affect indirectly the NEMCA behaviour of the electrode. But it contributes little directly to the measured catalytic rate and thus can be neglected. Its effect is built in UWr and [Pg.306]

The reason is that the backspillover ions desorb to the gas phase directly from the three-phase-boundaries or react directly at the three-phase-boundaries (electrocatalysis, A=l) before they can migrate on the gas-exposed electrode surface and promote the catalytic reaction. The limits of NEMCA are set by the limits of stability of the effective double layer at the metal/gas interface. 

In the first part of the present review, new techniques of preparation of modified electrodes and their electrochemical properties are presented. The second part is devoted to applications based on electrochemical reactions of solute species at modified electrodes. Special focus is given to the general requirements for the use of modified electrodes in synthetic and analytical organic electrochemistry. The subject has been reviewed several times Besides the latest general review by Murray a number of more recent overview articles have specialized on certain aspects macro-molecular electronics theoretical aspects of electrocatalysis organic applicationssensor electrodes and applications in biological and medicinal chemistry. 

Electrocatalysis with mediators located in coatings at the electrode surface is one... 

The first In situ MBS Investigation of molecules adsorbed on electrode surfaces was aimed primarily at assessing the feasibility of such measurements In systems of Interest to electrocatalysis (18). Iron phthalocyanlne, FePc, was chosen as a model system because of the availability of previous situ Mossbauer studies and Its Importance as a catalyst for O2 reduction. The results obtained have provided considerable Insight Into some of the factors which control the activity of FePc and perhaps other transition metal macrocycles for O2 reduction. These can be summarized as follows ... 

Potentials of Zero Charge of Electrodes Nonequilibrium Fluctuations in the Corrosion Process Electrocatalysis... 

The science of electrocatalysis provides the connection between the rates of electrochemical reactions and the bulk and surface properties of the electrodes on which these reactions proceed. 

In electrocatalysis, the major subject are redox reactions occurring on inert, nonconsumable electrodes and involving substances dissolved in the electrolyte while there is no stoichiometric involvement of the electrode material. Electrocatalytic processes and phenomena are basically studied in aqueous solutions at temperatures not exceeding 120 to 150°C. Yet electrocatalytic problems sometimes emerge as well in high-temperature systems at interfaces with solid or molten electrolytes. 

In electrocatalysis, in contrast to electrochemical kinetics, the rate of an electrochemical reaction is examined at constant external control parameters so as to reveal the influence of the catalytic electrode (its nature, its surface state) on the rate constants in the kinetic equations. 

Noguchi, H Okada, T. and Uosaki, K. (2008) Molecular structure at electrode/ electrolyte solution interfaces related to electrocatalysis. Faraday Discussion, 140, 125-137. 

Kohei Uosaki received his B.Eng. and M.Eng. degrees from Osaka University and his Ph.D. in Physical Chemistry from flinders University of South Australia. He vas a Research Chemist at Mitsubishi Petrochemical Co. Ltd. from 1971 to 1978 and a Research Officer at Inorganic Chemistry Laboratory, Oxford University, U.K. bet veen 1978 and 1980 before joining Hokkaido University in 1980 as Assistant Professor in the Department of Chemistry. He vas promoted to Associate Professor in 1981 and Professor in 1990. He is also a Principal Investigator of International Center for Materials Nanoarchitectonics (MANA) Satellite, National Institute for Materials Science (NIMS) since 2008. His scientific interests include photoelectrochemistry of semiconductor electrodes, surface electrochemistry of single crystalline metal electrodes, electrocatalysis, modification of solid surfaces by molecular layers, and non-linear optical spectroscopy at interfaces. 

Another electro-oxidation example catalyzed by bimetallic nanoparticles was reported by D Souza and Sam-path [206]. They prepared Pd-core/Pt-shell bimetallic nanoparticles in a single step in the form of sols, gels, and monoliths, using organically modified silicates, and demonstrated electrocatalysis of ascorbic acid oxidation. Steady-state response of Pd/Pt bimetallic nanoparticles-modified glassy-carbon electrode for ascorbic acid oxidation was rather fast, of the order of a few tens of seconds, and the linearity was observed between the electric current and the concentration of ascorbic acid. 

In electrocatalysis, the reactants are in contact with the electrode, and electronic interactions are strong. Therefore, the one-electron approximation is no longer justified at least two spin states on a valence orbital must be considered. Further, the form of the bond Hamiltonian (2.12) is not satisfactory, since it simply switches between two electronic states. This approach becomes impractical with two spin states in one orbital also, it has an ad hoc nature, which is not satisfactory. 

Outside of the double-layer region, water itself may be oxidized or reduced, leaving stable hydride, hydroxyl, or oxide layers on the electrode surface. These species may adsorb strongly and block sites from participating in electrocatalysis, as for example, hydroxyl species present at the polymer electrolyte membrane fuel cell... 

Lamy C, Leger JM, Claviher J, Parsons R. 1983. Structural effects in electrocatalysis A comparative study of the oxidation of CO, HCOOH and CH3OH on single crystal Pt electrodes. J Electroanal Chem 150 71-77. 

Lebedeva NP, Rodes A, Feliu JM, Koper MTM, van Santen RA. 2002b. Role of crystalline defects in electrocatalysis CO adsorption and oxidation on stepped platinum electrodes as studied by in situ infrared spectroscopy. J Phys Chem B 106 9863-9872. 

Nishimura K, Kunimatsu K, Enyo M. 1989. Electrocatalysis on Pd + An alloy electrodes Part III. IR spectroscopic studies on the surface species derived from CO and CH3OH in NaOH solution. J Electroanal Chem 260 167. 

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