Electrode surfaces properties

Due to their small size and high surface area, nanoparticles can be applied to modify electrode surface property. Convenient and sensitive electrochemical sensors to various targets have been set up by using nanoparticle modification. The determination of acetaminophen in a commercial paracetamol oral solution was reported using a multiwall CNTs composite film-modified glassy carbon electrode with a detection limit of 50 nM (Li etal. 2006a). Heavy metal ions, such as ar-senite (Dai and Compton 2006 Majid et al. 2006) and lead ion (Cui et al. 2005),... 

During this ECL process, a powerful reductant (C02 ) was in situ generated due to the decomposition of intermediate (C204 ). The ECL can be achieved by two pathways (1) reaction between the C02 and Ru(bpy) (Eqn (10)), (2) ion annihilation reaction between Ru(bpy)3 and Ru(bpy)3 (Eqn (12)). The intermediate C204 can be formed upon oxidation by Ru(bpy)3 or be directly oxidized at the electrode surface (Eqn (8)). For example, in acetonitrile (MeCN) media, oxalate is easier to be oxidized than Ru(bpy)3 " complex and both the reactants are oxidized during the light emission. In addition, the applied potential, the concentration of C204 and the electrode surface properties influence the direct oxidation of oxalate to the overall ECL behaviour. ... 

T. Lee, H. Cai, and 1. Hsing, Effects of gold nanoparticles and electrode surface properties on electrocatalytic silver deposition for electrochemical DNA hybridization detection. The Analyst 130, 364-369 (2005). 

A second-order effect that contributes to the in situ IR spectra consists of change in the interfacial structure of solvent, including the coordination to the surface, solute, and self-organization. Correlation between the structure of solvent and the HL ionic composition and the electrode surface properties is a considerable objective not only in electrochemistry but also in other numerous areas of science and technology dealing with surface modification. A number of systems have been studied to date, including acetonitrile [110, 115, 159, 179], acetone [110, 179], methanol [110, 180], and benzene [110] at a Pt electrode. However, particularly interesting but yet little understood is the most common solvent, water. 

Techniques for establishing electrode surface properties. In situ techniques for characterizing the surface properties of electrodes are of critical importance and warrant a continuing effort. Of particular importance are efforts to detect and characterize O2 surface species which may be the precursors to the 0-0 bond breaking step during the O2 reduction. 

Electrocatalysis is the science exploring the rates of electrochemical reactions as a function of the electrode surface properties. In these heterogeneous reactiOTis, the electrode does not rally accepts or supplies electrons (electron transfer), as in simple redox reactirais, but affects the reaction rates interacting with reactants, intermediates, and reaction products, i.e., acts as a catalyst remaining unchanged upon its completion. 

Frequency analysis of NP collisions is not simple because the shape and frequency of the current transients are affected not only by the NPs but also by the material and nature of the surface of the measuring electrode. For example, the current transient frequency of citrate-stabilized IrO NPs differed by the electrode material current transients for IrO, NP collisions were frequent on bare An, rare on bare Pt, and not observed at all on carbon liber UMEs. The electrocatalytic redox recycling behavior also depends strongly on the electrode material. The current spikes are sensitive to the electrode surface, and we find that the current transient behavior can be modified with different surface treatments, for example, by immersing the Pt UME in a 10 mM aqueous NaBH4 solution for 5 min. The influence of the electrode surface properties on NP behavior is still not well understood, but the single NP collision detection techniques described here can be useful tools to study such phenomena. 

Tetrathiafulvalene (TTE) has also been used in electrochromic devices. TTE-based polymers spin-coated onto transparent electrode surfaces form stable thin films with reproducible electrochromic properties (100). The slow response of these devices has been attributed to the rate of ion movement through the polymer matrix. 

Electrochemical polymeriza tion of heterocycles is useful in the preparation of conducting composite materials. One technique employed involves the electro-polymerization of pyrrole into a swollen polymer previously deposited on the electrode surface (148—153). This method allows variation of the physical properties of the material by control of the amount of conducting polymer incorporated into the matrix film. If the matrix polymer is an ionomer such as Nation (154—158) it contributes the dopant ion for the oxidized conducting polymer and acts as an effective medium for ion transport during electrochemical switching of the material. 

Nonstoichiometric oxide phases are of great importance in semiconductor devices, in heterogeneous catalysis and in understanding photoelectric, thermoelectric, magnetic and diffusional properties of solids. They have been used in thermistors, photoelectric cells, rectifiers, transistors, phosphors, luminescent materials and computer components (ferrites, etc.). They are cmcially implicated in reactions at electrode surfaces, the performance of batteries, the tarnishing and corrosion of metals, and many other reactions of significance in catalysis. ... 

Another approach to molecular assembly involves siloxane chemistry [61]. In this method, the electrically or optically active oligomers are terminated with tii-chlorosilane. Layers are built up by successive cycles of dip, rinse, and cure to form hole transport, emissive, and electron transport layers of the desired thicknesses. Similar methods have also been used to deposit just a molecular monolayer on the electrode surface, in order to modify its injection properties. 

Film-forming chemical reactions and the chemical composition of the film formed on lithium in nonaqueous aprotic liquid electrolytes are reviewed by Dominey [7], SEI formation on carbon and graphite anodes in liquid electrolytes has been reviewed by Dahn et al. [8], In addition to the evolution of new systems, new techniques have recently been adapted to the study of the electrode surface and the chemical and physical properties of the SEI. The most important of these are X-ray photoelectron spectroscopy (XPS), SEM, X-ray diffraction (XRD), Raman spectroscopy, scanning tunneling microscopy (STM), energy-dispersive X-ray spectroscopy (EDS), FTIR, NMR, EPR, calorimetry, DSC, TGA, use of quartz-crystal microbalance (QCMB) and atomic force microscopy (AFM). 

It is now well established that in lithium batteries (including lithium-ion batteries) containing either liquid or polymer electrolytes, the anode is always covered by a passivating layer called the SEI. However, the chemical and electrochemical formation reactions and properties of this layer are as yet not well understood. In this section we discuss the electrode surface and SEI characterizations, film formation reactions (chemical and electrochemical), and other phenomena taking place at the lithium or lithium-alloy anode, and at the Li. C6 anode/electrolyte interface in both liquid and polymer-electrolyte batteries. We focus on the lithium anode but the theoretical considerations are common to all alkali-metal anodes. We address also the initial electrochemical formation steps of the SEI, the role of the solvated-electron rate constant in the selection of SEI-building materials (precursors), and the correlation between SEI properties and battery quality and performance. 

At the electrode surface there is competition among many reduction reactions, the rates of which depend on iQ and overpotential q for each process. Both /0 and q depend on the concentration of the electroactive materials (and on the catalytic properties of the carbon surface). However, the chemical composition of the SEI is also influenced by the solubility of the reduction products. As a result, the voltage at... 

The SEI is formed by parallel and competing reduction reactions and its composition thus depends on i0, t], and the concentrations of each of the electroactive materials. For carbon anodes, (0 also depends on the surface properties of the electrode (ash content, surface chemistry, and surface morphology). Thus, SEI composition on the basal plane is different from that on the cross—section planes. 

The capacitance is a readily measured interfacial property and it gives qualitative information on the adsorption of species at the electrode surface. Since the surface charge density, q, is a function of the potential and of coverage, the measured capacitance may be expressed as the sum of a true (high frequency) capacitance and an adsorption pseudocapacitance, i.e. q f(E,6) and hence... 

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