Electrodes early developments

Impedance Some of the errors arising from the use of linear polarisation resistance led to interest and development in a.c. systems.An early development used a fixed a.c. frequency and a commercial instrument was produced in the UK. Inaccuracies still occurred, however, and were due to the electrode impedance which is fequency dependent. Electrode reactions have a capacitance component, in addition to resistance, resulting in a requirement to measure the impedance. However, the total impedance comprises values for the reaction, solution, diffusion and capacitance. Measurements at different frequency are more reliable, particularly where high solution resistances occur. Simplifications for industrial monitoring have been developed consisting of two measurements, i.e. at a high (10 kHz) and low frequency (0-1 Hz). The high-frequency measurement can identify the... 

The most popular voltammetric technique is probably cyclic voltammetry (CV), partly because of its early development in theory and the availability of the corresponding commercial equipment. In this technique, the electrode potential is first scanned linearly with time from a starting potential, where no reaction occurs, passing E°, towards another potential, and then reversed back to the starting potential. In this case, the time variable can be conveniently represented by the scan rate, v. 

The physical properties of lithium metal were given in Table 4.4. Despite its obvious attractions as an electrode material, there are severe practical problems associated with its use in liquid form at high temperatures. These are mainly related to the corrosion of supporting materials and containers, pressure build-up and the consequent safety implications. Such difficulties were experienced in the early development of lithium high temperature cells and led to the replacement of pure lithium by lithium alloys, which despite their lower thermodynamic potential remained solid at the temperature of operation and were thus much easier to use. 

The ready availability of electricity following the invention by Alssandro Volta of his famous pile in 1800 prompted, from an early date, the study of its effects on condensed matter and, most particularly, the decomposition of water by electrolysis involving chemical reactions at the electrodes. Work developed to the point where, by the middle of the second half of the nineteenth century, well-established industrial processes for the manufacture of aluminium and chlorine gas operated by electrolysis. 

The employment of cell organelles has been limited to mitochondrial and microsomal fractions (Table 15). As early as 1976, Guilbault et al. coupled pig heart mitochondrial electron transfer particles (ETP) with an oxygen electrode. This development has been further pursued by Aizawa et al. (1980c). Decoupling of the electron transfer from oxidative phosphorylation makes ETP catalyze the following reactions ... 

At the early stage of the development of the heart-on-a-chip, a PDMS microfluidic network was combined with planar electrode array to measure the extracellular potential from individual adult cardiomyocytes [54]. Another microfluidic device with an array of electrodes was developed to electrically measure the metabolic profile of cardiomyocytes and optically measure cell contractility [55]. Grosberg et al. first introduced a tissue level heart-on-a-chip to measure the contractility of neonatal cardiac muscle tissue [52]. In the design, eight muscular thin films (MTF) were fabricated on a chip. A layer of poly(N-isopropylacrylamide) (PIPAAm) dissolved at below 35 °C is spin-coated on top of a glass slide (Fig. 5A). Subsequently, a PDMS layer was coated on top of the PIPAAM layer. The PDMS layer was used to seed neonatal rat ventricular cardiomyocytes. The substrate seeded with cells is placed in the bath and the film layers were manually cut to fabricate an array of two opposite rows of four rectangular film layers of MTFs. The MTFs are peeled off after PIPAAm is dissolved as a solution when kept below 35 °C. Finally, electrodes are placed on the top and the bottom of MTFs. 

Unfortunately, mechanisms of elementary steps, e.g., electron transfer, in electrode processes were not at all well understood during the period of early development of electro-organic chemistry, and the significance of the fundamental relation between overpotential ( polarization ) and current density was not appreciated until the work of Volmer, Gurney, Bowden,... 

In addition to the glass electrode responsive to hydrogen ions, other ion selective electrodes are now available. These electrodes were first developed around 1964, and E. Pungor was associated with some of the early developments. A great many ions can now be estimated in this way, and among the more widely used electrodes are those responsive to potassium, calcium, fluoride and nitrate ions. 

Early electrode systems. The first type of electrode used for calcium determination was an amalgam electrode which consisted of an amalgam of calcium oxalate and either lead or silver oxalate. Later, thin crystals of naturally occurring fluorite (calcium fluoride) were used as membranes for the potentiometric determination of calcium in pure aqueous solutions and in milk. Other early developments included a series of studies using membranes produced from pure paraffin containing calcium oxalate and a non-ionic detergent, and attempts to produce a glass electrode for calcium. ... 

Electrochemical-deposition Electrode. Vilambi-Reddy et al. [62] presented the early research on the electrochemical deposition electrode. They developed an electrochemical catalyzation (ECC) technique to deposit platinum catalyst particles selectively in the regions accessible to both ions and electrons. In the ECC technique, a hydrophobic porous carbon paper was first coated with dispersed carbon particles and PTFE to form a substrate. Then the Nafion ionomer was impregnated onto this carbon substrate. This substrate was then placed into a platinum acid-plating bath, along with a platinum counter electrode. One side of this substrate, without Nafion, was masked with a non-conducting film, which... 

Mixed metal oxide coated anodes, also called dimensionally stable anodes (DSA), are based on electrode technology developed in the early 1960s for the production of chlorine and caustic soda. The mixed metal oxide films are thermally applied to a noble metal such as titanium, niobium, and tantalum as substrate materials and are available in a variety of sizes and shapes. These oxide coatings have excellent conductivity, are resistant to acidic environments, are chemically stable, and have relatively low consumption rates. Groundbed installation in soils usually specifies that the anode be prepackaged in a canister with carbonaceous backfill material. 

Very substantial advances have been made in terms of improvements in electrode stmctures and increases in the Pt utili2ation as illustrated in Figure 1. It appears that Pt loadings of less than 0.2 mg Pt/cm are adequate to obtain acceptable performance in PEFCs using pure H2 as the fuel (see Thin films). Whereas early electrodes contained 4 mg Pt/cm, the most recent developments in electrode fabrication have permitted Pt loadings to be reduced to 0.13 mg Pt/cm in a thin-film stmcture, while maintaining high performance. 

Electric-Arc Furnace. The electric-arc furnace is by far the most popular electric steelmaking furnace. The carbon arc was discovered by Sir Humphry Davy in 1800, but it had no practical appHcation in steelmaking until Sir William Siemens of open-hearth fame constmcted, operated, and patented furnaces operating on both direct- and indirect-arc principles in 1878. At that early date, the avadabiHty of electric power was limited and very expensive. Furthermore, carbon electrodes of the quaHty to carry sufficient current for steel melting had not been developed (see Furnaces, electric). 

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