Design issues electrodes

The commonly used pretreatment protocols for activating solid electrodes are reviewed in this chapter. Specifically, the pietreatment of carbon, metal, and semiconductor electrodes (thin conducting oxides) is discussed. Details of how the different electrode materials are produced, how the particular pretreatment works, and what effect it has on electron-transfer kinetics and voltammetric background current are given, since these factors determine the electroanalytical utility of an electrode. Issues associated with cell design and electrode placement (Chapter 2), solvent and electrolyte purity (Chapter 3), and uncompensated ohmic resistance (Chapter 1) are discussed elsewhere in this book. This... 

PAFC cells can last to anywhere between 10,000 and 50,000 hr. However, there are various issues that can reduce the lifetime. The most important is the one related to acid management. Effective humidity control is the key way to control the acid concentration inside that also helps to prevent loss of phosphoric acid. The other aspects of acid management is the uniform distribution of the acid in the matrix. Occurrence of any undesirable distribution of acid can be prevented through a well designed matrix-electrode assembly, along with good distributed contact with the internal/extemal acid reservoirs. 

From Table 2, it is apparent that a single lead-free alloy does not exhibit the best performance in all the categories listed. As an example, among the alloys considered, Sn-8Bi-3Zn has a melting point closest to eutectic Sn-Pb however, it exhibits poor wettability. Therefore alloy selection is, as often occurs in design issues, a matter of optimizing benefits through tradeoffs. Physical characteristics such as panel size, types of moimted components, electrode finishes, temperature sensitivity of components, and so on all play a role in alloy selection. 

The work reported here was designed to address the issue of adsorbate surface coverage in the effect on SERS of UPD Pb on Ag electrodes in aqueous chloride and bromide media using interfacial H20 species as the probe molecule. No studies have been reported on the effect of UPD layers on the SERS of interfacial solvent molecules previously. However, the solvent is an ideal choice for such studies, because it will always remain in intimate contact with the electrode surface. Moreover, the SERS of interfacial H20 has been characterized quite extensively in aqueous halide media (18-29) and allows the possible influence of anion on the response of the system to be assessed. 

Any one of the three components in SOFC, the cathode, anode, or electrolyte, can provide the structural support for the cells. Traditionally, the electrolyte has been used as the support however, this approach requires the use of thick electrolytes, which in turn requires high operating temperatures. Electrode-supported cells allow the use of thin electrolytes. The Siemens—Westinghouse Corporation has developed a cathode-supported design,although this has required electrochemical vapor deposition of the YSZ electrolyte. Most other groups have focused on anode-supported cells. In all cases, it is important to maintain chemical compatibility of those parts that come in contact and to match the thermal expansion coefficients of the various components. A large amount of research has been devoted to these important issues, and we refer the interested reader to other reviews. 

When one considers a distance scale much smaller than 1 pm, surface roughness also is an issue to observed electrode behavior. The ratio of the microscopic surface area to the projected electrode area is usually designated the roughness factor, and can vary from 1.0 to 5 or so for typical solid electrodes, or much higher for porous electrodes. Capacitance, surface faradaic reactions, adsorption, and electrode kinetics all depend on microscopic area. For example, double-layer capacitance increases with roughness such that the apparent capacitance (C°bs) is larger than the value for a perfectly flat electrode (Cflat) as shown in Equation 10.1 ... 

In general, traditional electrode materials are substituted by electrode superstructures designed to facilitate a specific task. Thus, various modifiers have been attached to the electrode that lower the overall activation energy of the electron transfer for specific species, increase or decrease the mass transport, or selectively accumulate the analyte. These approaches are the key issues in the design of chemical selectivity of amperometric sensors. The long-term chemical and functional stability of the electrode, although important for chemical sensors as well, is typically focused on the use of modified electrodes in energy conversion devices. Examples of electroactive modifiers are shown in Table 7.2. 

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