Electrocatalysis electrode surface area

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]

In electrocatalysis, the activity of different electrocatalysts is usually expressed via the exchange current I0, and the specific activity, via the exchange current density, iQ (A cm-2), still often computed on the basis of the superficial electrode surface area. Only when the current is normalized using the true surface area of the electrode-electrolyte interface, the comparison between different electrocatalysts is truly meaningful. The determination of the true surface area of porous electrodes is discussed in Sect. 2.3.5. 

Figure 17.4 Cartoon representation of strategies for studying and exploiting enzymes on electrodes that have been used in electrocatalysis for fuel cells, (a) Attachment or physisorption of an enzyme on an electrode such that redox centers in the protein are in direct electronic contact with the surface, (b) Specific attachment of an enzyme to an electrode modified with a substrate, cofactor, or analog that contacts the protein close to a redox center. Examples include attachment of the modifier via a conductive linker, (c) Entrapment of an enzyme within a polymer containing redox mediator molecules that transfer electrons to/from centers in the protein, (d) Attachment of an enzyme onto carbon nanotubes prepared on an electrode, giving a large surface area conducting network with direct electron transfer to each enzyme molecule.

This series covers recent advances in electrocatalysis and electrochemistry and depicts prospects for their contribution into the present and future of the industrial world. It illustrates the transition of electrochemical sciences from a solid chapter of physical electrochemistry (covering mainly electron transfer reactions, concepts of electrode potentials and stmcture of the electrical double layer) to the field in which electrochemical reactivity is shown as a unique chapter of heterogeneous catalysis, is supported by high-level theory, connects to other areas of science, and includes focus on electrode surface structure, reaction environment, and interfacial spectroscopy. 

In addition, such redox-active organometallic dendrimers are interesting materials with which to modify electrode surfaces. Applications of these dendrimer modified electrodes in the fields of amperometric and potentiometric biosensors, molecular recognition, as well as in electrocatalysis and photoelectrochemistry, clearly represent interesting areas of future research. 

Ion implantation is often recommended as an efficient tool to enhance electrocatalysis either by disrupting the surface structure of the catalyst or by placing active atoms on an inactive (or less active) matrix. The latter possibility (which links this section with Section 3.3 devoted to adatoms) offers also a way to the use of extremely small amounts of active but expensive materials. In order to investigate the effect of surface damages, self-implantation or ion beam bombardment is the most appropriate approach. Implantation of Ni on Ni has led to a modest enhancement of the surface area, but not to electrocatalytic effects [279]. On the other hand, Pt bombarded with neutrons has shown an increase in the activity for hydrogen evolution [280]. However, it has been suggested that this is not related to the formation of surface defects, but rather to the effect of the radioactivity induced on the electrode and on the electrolyte. 

Joaquin Gonzalez is a Lecturer at the University of Murcia, Spain. He follows studies of Chemistry at this University and got his Ph.D. in 1997. He has been part of the Theoretical and Applied Electrochemistry group directed by Professor Molina since 1994. He is author of more than 80 research papers. Between 1997 and 1999, he also collaborated with Prof. Ms Luisa Abrantes of the University of Lisboa. He is the coauthor of four chapters, including Ultramicroelectrodes in Characterization of Materials second Ed (Kaufmann, Ed). He has taught in undergraduate and specialist postgraduate courses and has supervised three Ph.D. theses. His working areas are physical electrochemistry, the development of new electrochemical techniques, and the modelization, analytical treatment, and study of electrode processes at the solution and at the electrode surface (especially those related to electrocatalysis). 

An area currently very active in electrochemical research deals with the design, fabrication and applications of chemically modified electrodes (CME s). The attractiveness of CME s stems from their potential to replace precious metals such as Pt in electrocatalysis for energy production (1-9), energy storage (10-13), electrosynthesis (14-19), electroanalysis (20-28), and other purposes (29-31). One approach has been to "immobilize", either by covalent attachment, strong adsorption or incorporation into polymeric structures, electrochemically active molecules, called mediators, which act as electron transfer bridges between the electrode surface and the solution species. It has been... 

M. -J., Bethelot, S., Leger, J.M., Lamy, C., Srinivasan, S., Electrocatalysis of fuel cell reactions - a RDE investigation using high surface area dispersed electrocatalysts dispersed in recast proton conductive membrane. In Electrode Materials... 

The modification of electrode surfaces with electroactive polymer films provides a means to control interfacial characteristics. With such a capability, one can envisage numerous possible applications, in areas as diverse as electronic devices, sensors, electrocatalysis, energy conversion and storage, electronic displays, and reference electrode systems [1, 2]. With these applications in view, a wide variety of electroactive polymeric materials have been investigated. These include both redox polymers (by which we imply polymers with discrete redox entities distributed along the polymer spine) and conducting polymers (by which we imply polymers with delocalised charge centres on the polymer spine). 

In electrocatalysis there is great interest in increasing the real surface area of electrodes. In such cases porous electrodes are used. Because modehng of real electrodes is difficult, a simpler model is usually used in which it is assumed that pores have a cylindrical shape with a length / and a radius... 

Various modified polymers and functional polymers have been used to coat electrode surfaces either to promote electrocatalysis or to act as permselective barriers [115, 116] and thus increase selectivity. The work in this area has been... 

The practical aspects of electrocatalysis (fuel cell-oriented research) required data on the specific adsorption at electrodes with high real-surface area, while for theoretical considerations, results obtained with well-defined electrode surfaces (single-crystal surfaces) were of great importance. 

CPs and their composites are utilized in the fields ofelectrochemistiy, electroanalysis, electrocatalysis, batteries and capacitors, etc as electrode. In addition to the conductivity and electroactivity of CPs, small ions and molecules can diffuse into the CP matrices, providing further improvement compared to the conventional electrode materials. Efficiently using all the active sites and enhancing mass transport during the electrode process, the thickness of the CP film can be reduced to allow the ion diffusion in the CP matrices. By these properties CP nanomaterials exhibit better performances, due to their larger specific surface areas and small dimensions. Additionally, nanostructures of CPs may produce new surface properties and better functionalities. 

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