Electrochemistry with Metallic Nanoparticles

Studies of the interaction of colloidal metal particles with macroelectrodes are essential for an understanding of properties such as the redox potential of the nanometallic particles in the presence of a particular environment. This information will be useful in extending the conventional electrochemical treatment to colloidal systems. 

Bard and co-workers have reported on the attainment of equilibrium between the nanosized particles and an electrode in the presence of a redox mediator [25a]. The study refers to the production of a mediator (methyl viologen radical cation) that reduces water in the presence of colloidal gold and platinum metal catalyst. An electrochemical model based on the assumption that the kinetic properties are controlled by the half-cell reactions is proposed to understand the catalytic properties of the colloidal metals. The same authors have used 15 nm electrodes to detect single molecules using scanning electrochemical microscopy (SECM) [25b]. A Pt-Ir tip of nm size diameter is used along with a ferrocene derivative in a positive feedback mode of SECM. The response has been found to be stochastic and Ear-adaic currents of the order of pA are observed. 

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This includes two classes of materials namely, semiconductors and metals. There have been excellent reviews on electrochemistry with semiconductor nanoparticles [18-20]. Here, we confine ourselves to electrochemical studies with metallic nanoparticles. 

Most of the electrochemical phenomena occur in size regimes that are very small. The effects of size on diffusion kinetics, electrical double layer at the interface, elementary act of charge transfer and phase formation have recently been reviewed by Petrri and Tsirlina [12]. Mulvaney has given an excellent account of the double layers, optical and electrochemical properties associated with metal colloids [11]. Special emphasis has been given to the stability and charge transfer phenomenon in metal colloid systems. Willner has reviewed the area of nanoparticle-based functionalization of surfaces and their applications [6-8]. This chapter is devoted to electrochemistry with nanoparticles. One of the essential requirements for electrochemical studies is that the material should exhibit good conductivity. 

Enzyme sensors are another important application of metal nanoparticles in CMEs besides nonenzyme sensors. Many enzymes can keep their activity when anchored onto gold nanoparticles. A novel method for fabrication of a biosensor based on the combination of sol-gel and self-assembled techniques has been introduced very recently. For example, the gold nanoparticles and enzyme horseradish peroxidase (HRP) can be successfully immobilized on gold electrode by the help of sol-gel with thiol groups, and the direct electrochemistry of HRP has been achieved and the biosensor thus prepared exhibits fast response, good reproducibility, and long-term stability. 

Ionic liquid (IL) possesses tunable behaviors based on asymmetric ion-pair combinations. Along with its tmique characteristics, such as high conductivity and wide potential window, it will be desirable to applying IL into the fields of bio-electrochemistry [29]. Incorporating IL with nanomaterials (metallic nanoparticles and carbon materials) into the development of modified... 

Besides the electrochemistry route, wet chemistry methods of shape-control synthesis have also been developed in some Chinese laboratories, and the synthesized metal nanoparticles with high-energy surface were apphed mainly as electrocatalysts for alcohol oxidations. 

Niu, P., Femandez-Sanchez, C., Gich, M., Ayora, C., and Roig, A. (2015) Electroanalytical Assessment of Heavy Metals in Polluted Waters with Bismuth Nanoparticle-Porous Carbon Paste Electrodes, submitted to Electrochemistry Acta. 

Microelectrodes, due to their unique properties, such as small size, non-planar diffusion, small capacitance, and small current, have provided a major breakthrough in electrochemistry. Taking advantage of the superior properties of diamond, the diamond microelectrode is a promising new device for several applications in electrochemistry. Furthermore, modification of the diamond microelectrode with appropriate metal nanoparticles increases the quality of the measurements, in the terms of sensitivity, stability, and selectivity. 

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. 

Catalysis and Electrocatalysis at Nanoparticle Surfaces reflects many of the new developments of catalysis, surface science, and electrochemistry. The first three chapters indicate the sophistication of the theory in simulating catalytic processes that occur at the solid-liquid and solid-gas interface in the presence of external potential. The first chapter, by Koper and colleagues, discusses the theory of modeling of catalytic and electrocatalytic reactions. This is followed by studies of simulations of reaction kinetics on nanometer-sized supported catalytic particles by Zhdanov and Kasemo. The final theoretical chapter, by Pacchioni and Illas, deals with the electronic structure and chemisorption properties of supported metal clusters. 

Although it does not exhaust the entire range of porous materials, the list attempts to cover those that can be described in terms of extended porous structures and whose electrochemistry has been extensively studied. In addition, since 1990 there has been a growing interest in the preparation of nanostructures of metal and metal oxides with controlled interior nanospace, whereas a variety of nanoscopic poro-gens such as dendrimers, cross-linked and core-corona nanoparticles, hybrid copolymers, and cage supramolecules are currently under intensive research (Zhao, 2006). Several of such nanostructured systems will be treated along the text, although, for reasons of extension, the study in extenso of their electrochemistry should be treated elsewhere. 

Exploring various phenomena at metal/solution interfaces relates directly to heterogeneous catalysis and its applications to fuel cell catalysis. By the late 1980s, electrochemical nuclear magnetic resonance spectroscopy (EC-NMR) was introduced as a new technique for electrochemical smface science. (See also recent reviews and some representative references covering NMR efforts in gas phase surface science. ) It has been demonstrated that electrochemical nuclear magnetic resonance (EC-NMR) is a local surface and bulk nanoparticle probe that combines solid-state, or frequently metal NMR with electrochemistry. Experiments can be performed either under direct in situ potentiostatic control, or with samples prepared in a separate electrochemical cell, where the potential is both known and constant. Among several virtues, EC-NMR provides an electron-density level description of electrochemical interfaces based on the Eermi level local densities of states (Ef-LDOS). Work to date has been predominantly conducted with C and PtNMR, since these nuclei... 

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