Interfacial Electrocatalysis

If a catalytic reaction of electron or ion transfer takes place at the oil/water interface between reagents located in two different contacting phases, we have deal with an example of interfacial catalysis discovered by Volkov and Kharkats [4—7]. The interface itself can serve as a catalyst for heterogeneous charge-transfer reactions. If the interfacial catalysis requires an electrical field, the reaction can take place at the interface between two immiscible electrolyte solutions having a fixed interfacial potential, a process called interfacial electrocatalysis. 

G.-Q. Lu, and A. Wieckowski, Heterogeneous Electrocatalysis A Core field of Interfacial Science, Current opinion in Colloid and Interface Science 5, 95 (2000). 

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. 

The lure of new physical phenomena and new patterns of chemical reactivity has driven a tremendous surge in the study of nanoscale materials. This activity spans many areas of chemistry. In the specific field of electrochemistry, much of the activity has focused on several areas (a) electrocatalysis with nanoparticles (NPs) of metals supported on various substrates, for example, fuel-cell catalysts comprising Pt or Ag NPs supported on carbon [1,2], (b) the fundamental electrochemical behavior of NPs of noble metals, for example, quantized double-layer charging of thiol-capped Au NPs [3-5], (c) the electrochemical and photoelectrochemical behavior of semiconductor NPs [4, 6-8], and (d) biosensor applications of nanoparticles [9, 10]. These topics have received much attention, and relatively recent reviews of these areas are cited. Considerably less has been reported on the fundamental electrochemical behavior of electroactive NPs that do not fall within these categories. In particular, work is only beginning in the area of the electrochemistry of discrete, electroactive NPs. That is the topic of this review, which discusses the synthesis, interfacial immobilization and electrochemical behavior of electroactive NPs. The review is not intended to be an exhaustive treatment of the area, but rather to give a flavor of the types of systems that have been examined and the types of phenomena that can influence the electrochemical behavior of electroactive NPs. 

Trasatti, S. (1999) Interfacial electrochemistry of conductive metal oxides for electrocatalysis, in Interfacial Electrochemistry Theory, Practice, Applications (ed. A. Wieckowski), Marcel Dekker, New York. 

Several important energy-related applications, including hydrogen production, fuel cells, and CO2 reduction, have thrust electrocatalysis into the forefront of catalysis research recently. Electrocatalysis involves several physiochemical environmental dfects, which poses substantial challenges for the theoreticians. First, there is the electric potential which can aifect the thermodynamics of the system and the kinetics of the electron transfer reactions. The electrolyte, which is usually aqueous, contains water and ions that can interact directly with a surface and charged/polar adsorbates, and indirectly with the charge in the electrode to form the electrochemical double layer, which sets up an electric field at the interface that further affects interfacial reactivity. 

Erdey-Gruz, 1048, 1306 1474 Erschler, 1133, 1134, 1425 Ethylene oxidation, anodic, 1052 1258 Exchange current density, 1049, 1066 correction of, 1069 definition, 1053 electrocatalysis and, 1278 impedance and, 1136 interfacial reaction, 1047 and partly polarizable interface, 1056 Excited states, lifetime, 1478 Exothermic reaction, 1041 Ex situ techniques, 785, 788, 1146... 

The changes in the potential profile of the interfacial region because specific adsorption do indeed affect the electrode kinetics of charge transfer processes, particularly when these have an inner sphere character [13, 26] (see Fig. 1.12). When this influence leads to an improvement of the current response of these processes, the global effect is called electrocatalysis. ... 

Electrodes represent an unrivaled platform onto which interfacial supramolecular structures can be assembled. They can be fully characterized before assembly and offer a convenient means to both probe and control the properties of the film. The interest in this area has increased dramatically in recent years because adsorbed monolayers enable both the nature of the chemical functional groups and their topology to be controlled. This molecular-level control allows the effects of both chemical and geometric properties on electron transfer rates to be explored. Moreover, these assemblies underpin technologies ranging from electrocatalysis to redox-switchable non-linear optical 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). 

Refs. [i] Inzelt G (2005) / Solid State Electrochem 9 245 [ii] Horanyi G (1980) Electrochim Acta 25 45 [iii] Horanyi G (2004) In Horanyi G (ed) Radiotracer studies of interfaces. Elsevier, Amsterdam, chapters 1,2,4,6 [iv] Horanyi G (2002) State of art present knowledge and understanding. In Bard AJ, Stratmann M, Gileadi E, Urbakh M (eds) Thermodynamics and electrified interfaces. Encyclopedia of electrochemistry, vol. 1. Wiley-VCH, Weinheim, Chap. 3 [v] Horanyi G (1999) Radiotracer studies of adsorption/sorption phenomena at electrode surfaces. In Wieckowski A (ed) Interfacial electrochemistry. Marcel Dekker, New York, pp 477 [vi] Horanyi G, Inzelt G (1978) / Electroanal Chem 87 423 [vii] Horanyi G, Inzelt G, Szetey E (1977) / Electroanal Chem 81 395 [viii] Vertes G, Horanyi G (1974) / Electroanal Chem 52 47 [ix] Horanyi G (1994) Catal Today19 285 [x] Horanyi G (2003) Electrocatalysis - heterogeneous. In Horvath IT (ed) Encyclopedia of catalysis, vol. 3. Wiley Interscience, Hoboken, pp 115-155 [xi] Inzelt G, Horanyi G (2006) The nickel group (nickel, palladium, and platinum). In Bard AJ, Stratmann M, Scholz F, Pickett CJ (eds) Inorganic chemistry. Encyclopedia of electrochemistry, vol 7a. Wiley-VCH, Weinheim, chap. 18... 

On the experimental side, we expect NMR to remain an important tool in the analysis of the nanoscale metallic materials widely used in heterogeneous and electrocatalysis. Its unique molecular/electronic information will complement that from other techniques such as IR, x-ray, or STM, etc. This is particularly true in the field of interfacial electrochemistry, where many electron-based spectroscopies are technically inapplicable. 

The Chapter by R. Adzic, N. Marinkovic and M. Vukmirovic provides a lucid and authoritative treatment of the electrochemistry and electrocatalysis of Ruthenium, a key element for the development of efficient electrodes for polymer electrolyte (PEM) fuel cells. Starting from fundamental surface science studies and interfacial considerations, this up-to-date review by some of the pioneers in this field, provides a deep insight in the complex catalytic-electrocatalytic phenomena occurring at the interfaces of PEM fuel cell electrodes and a comprehensive treatment of recent developments in this extremely important field. 

Several recent breakthroughs in the design of solid oxide fuel cell (SOFC) anodes and cathodes are described in the Chapter of H. Uchida and M. Watanabe. The authors, who have pioneered several of these developments, provide a lucid presentation describing how careful fundamental investigations of interfacial electrocatalytic anode and cathode phenomena lead to novel electrode compositions and microstructures and to significant practical advances of SOFC anode and cathode stabihty and enhanced electrocatalysis. 

Details of the electronic structure of the metal electrode surface. Interfacial electrochemical electron transfer via adsorbate states and electrocatalysis. 

Phenomena that arise in these materials include conduction processes, mass transport by convection, potential field effects, electron or ion disorder, ion exchange, adsorption, interfacial and colloidal activity, sintering, dendrite growth, wetting, membrane transport, passivity, electrocatalysis, electrokinetic forces, bubble evolution, gaseous discharge (plasma) effects, and many others. 

Interfacial structure The role of electrochemical phenomena at interfaces between ionic, electronic, photonic, and dielectric materials is reviewed. Also reviewed are opportunities for research concerning microstructure of solid surfaces, the influence of the electric field on electrochemical processes, surface films including corrosion passivity, electrocatalysis and adsorption, the evolution of surface shape, and self-assembly in supramolecular domains. 

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