Materials nanoelectrode

Nano-electrode arrays can be formed through nano-structuring of the electrocatalyst on an inert electrode support. Indeed, if the current of the analyte reduction (oxidation) on a blank electrode is negligible compared to the activity of the electrocatalyst, the former can be considered as an insulator surface. Hence, for the synthesis of nanoelectrode arrays one has to carry out material nano-structuring. Recently, an elegant approach [140] for the electrosynthesis of mesoporous nano-structured surfaces by depositioning different metals (Pt, Pd, Co, Sn) through lyotropic liquid crystalline phases has been proposed [141-143],... 

A persistent problem with micro- and nanoelectrodes is the sealing of the conductive element to the insulating material that surrounds the element such that solution does not creep into this junction [25,68,75]. This solution creeping is undesirable because it causes the double layer charging currents... 

The acid-base properties of polyaniline can be utilized to produce solid-state pH sensors where polyaniline works both as the pH-sensitive material and as the ion-to-electron transducer. An excellent example is the electrodeposition of polyaniline on an ion-beam etched carbon fiber with a tip diameter of ca. 100-500 nm resulting in a solid-state pH nanoelectrode with a linear response (slope ca. — 60mV/pH unit) in the pH range of 2.0-12.5 and a working lifetime of 3 weeks [104]. The response time vary from ca. 10 s (around pH 7) to ca. 2 min (at pH 12.5). 

Since mesoporous materials contain pores from 2 nm upwards, these materials are not restricted to the catalysis of small molecules only, as is the case for zeolites. Therefore, mesoporous materials have great potential in catalytic/separation technology applications in the fine chemical and pharmaceutical industries. The first mesoporous materials were pure silicates and aluminosilicates. More recently, the addition of key metallic or molecular species into or onto the siliceous mesoporous framework, and the synthesis of various other mesoporous transition metal oxide materials, has extended their applications to very diverse areas of technology. Potential uses for mesoporous smart materials in sensors, solar cells, nanoelectrodes, optical devices, batteries, fuel cells and electrochromic devices, amongst other applications, have been suggested in the literature.11 51... 

With the help of surface modification, the catalytic activity and selectivity could be manipulated by tailoring the structure of the electrodes. The rapid development of nanotechnology and bioscience has been witnessed by a large number of recent literatures on novel electrodes such as BDD, nanoelectrodes, and biosensors. This trend is likely to remain so for the next decade when the hot research topics for electrochemistry will be in advanced materials, biochemical-related application, and environmental analysis and protection. 

Bulk nanostructured materials are soUds with nanosized microstructure. Their basic units are usually nanoparticles. Several properties of nanoparticles are useful for applications in electrochemical sensors [67], However, their catalytic behavior is one of the most important. The high ratio of surface atoms with free valences to the total atoms has led to the catalytic activity of nanostructured SEs being used in electrochemical reactions. The catalytic properties of nanoparticles could decrease the overpotential of electrochemical reactions and even provide reversibility of redox reactions, which are irreversible at the bulk metal SE [68], Multilayers of conductive nanoparticles assembled on electrode surfaces produce a high porous surface with a controlled microenviromnent. These structures could be thought of as assemblies of nanoelectrodes with controllable areas. 

It is clear that the material and geometry of the electrodes can influence gas sensor behavior. Many researchers are investigating the fabrication of gas sensors using nanoparticulate materials as the sensitive layer. While it is possible to use normal sized electrodes with widths and separations of several microns for these devices, it is of interest to examine the changes in response which are obtained when nanoelectrodes are used i.e. contacts of comparable dimensions to a single particle - around 5 nm. Potential advantages of nanoelectrodes include ... 

Figure 10.38 SEM image of a single nanowire between the nanoelectrodes. The inset, an SEM image of a device with incomplete nanowire growth, shows the two-nanowire approach to bridging the gap. (Reprinted with permission from Advanced Materials, Bridging the Gap Polymer Nanowire Devices by N. T. Kemp, D, McGrouther, j. W. Cochrane and R. Newbury, 19, 18, 2634-2638. Copyright (2007) Wiley-VCH)...

A general template method for preparing nanomaterials has been investigated by Martin and others for the formation of micro- and nanoelectrode arrays (140). The method entails synthesis of the desired metal (or polymer, protein, semiconductor, carbon nanowire) within the cylindrical and monodisperse pores of a membrane or another porous material (Figure 10.9) (see also Section 16.2 in Chapter 16). 

The first part of this section focuses on the main characteristics and fabrication techniques used for obtaining templating membranes and depositing metal nanostructures by suitable electroless and elecuochemical procedures. Methods such as sol-gel (10-12) or chemical vapor deposition (10, 13), which have been used primarily for the template deposition of carbon, oxides, or semiconducting-based materials, will not be considered here in detail. The second part of the section focuses on the electrochemical properties of the fabricated nanomaterials with emphasis on the characteristics and applications of nanoelectrode ensembles (NEEs). 

Template synthesis has made accessible to almost any electrochemical laboratory the fabrication of electrode systans with critical dimensions in the nanometer domain. Future research efforts will likely be devoted to fundamental studies aimed at better understanding the effects related to deoeasing the size of electrodes to dimensions comparable or smaller than the dimensions of the double- and diffusion layers. From a practical and application perspective, the next frontier will focus on the development of methods and materials that allow one to better control the size, spatial distribution, and addressability of the single nanoelectrode elements in rather complex arrays or ensembles. 

Since the early talks of Richard Feynman in its There s Plenty of Room at the Bottom in 1959, there have been always a concern on what nano means and applies to. Recently, the Royal Society tried to make order between the definitions of nanoscience and nanotechnology, both referring to, respectively, the study or the preparation of materials from 100 nm down to the atomic level (approximately 0.2 nm) [1], Later, the British Standard Institution defined nanomaterial as material having one or more external dimensions in the nanoscale or which is nanostructured. [2] Accordingly, Murray makes a noticeable attempt to apply these concepts to nanoelectrochemistry of nanoparticles, nanoelectrodes, and nanopores, referring them as a dimensional scale of electrodes and electrochemical events [3]. 

Single crystal nanowires (SNW) are one-dimensional single crystal nanopartides like fullerenes vs. carbon nanotubes. While retaining the properties of nanopartides, SNW have been made into functional devices such as transistors, nanoelectrode arrays, and probes for biological sensing. Depending on the materials type and diameter, SWN and devices can be made electrically, optically, or magnetically functional. 

It has been observed for silver nanoparticles that and a values are altered at nanoelectrodes from their values for the bulk material, as is the case for 4-nitrophenol reduction in water, as compared to the reaction at bulk silver (F.W. Campbell et al, ChemPhysChem. 11 (2010) 2820]. 

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