Precious metal electrodes

Important inherent characteristics of an enzyme that should be considered are the substrate affinity, characterized by the Michaelis constant the rate of turnover fecat> providing the catalytic efficiency fecat/ M. and the catalytic potential. Several attempts to compare enzyme catalysis with that of platinum have been published. Direct comparisons are difficult, because enzyme electrodes must be operated in aqueous electrolyte containing dissolved substrate, whereas precious metal electrodes aie often supplied with a humidified gaseous stream of fuel or oxidant, and produce water as steam. It is not straightforward to compare tme optimal turnover rates per active site, as it is often unclear how many active sites are being engaged in a film of enzyme on an electrode. 

Coated Electrodes and Carrier Materials Numerous interesting electrode materials are applicable exclusively in the form of a coating on a carrier material. Besides the electrocatalytic coatings hsted below the use of precious metal electrodes as a thin layer on a cheaper carrier material will be attractive. 

Investigations of other precious metal electrodes also showed increased cathodic currents in C02 saturated solutions. These studies include Ir, Pd, Pt, and Pt-Ru alloy in 0.2 m LiClOi and Pd, Pt, and Ru in 1.0 m Na2S0i+. Although the Ru metal electrode did not give any evidence for a new cathodic peak, there was an increase in cathodic current beginning near -0.7 V for the C02"Saturated solution. The Ru electrode was inactive with respect to reactions of NaCOOH (Table I), but the reduction of CO2 to CO, CH3OH, and even CH14 has been reported for this metal (6, 8). 

Studies are in progress to identify and quantify the products formed by the electrochemical reduction of CO2 on precious metal electrodes as well as on other electrodes such as Mo when nearly neutral electrolytes are used that minimize proton donor or acceptor reactions. A review of CO2 reduction on metal electrodes shows that CHi+ is produced on Ru and Cu (8, 9), CH3OH is a major product on Ru and Mo (6-8), carbon monoxide is formed on Ru, Pd, Pt, Co, Fe, Au, and Ag (7-9), HCOO is the main product on Cd, In, Sn, and Pb (, ), and a product more complex than formic acid is reported for Pt... 

The elevated operating temperatures enable the use of non-precious metal electrodes, and electrode reaction kinetics may also be faster at these elevated temperatures. 

Low temperature carbon monoxide sensors based on the reversible carbon monoxide adsorptive poisoning of precious metal electrodes are also being developed by Los Alamos National Laboratory. The addition of metals such as ruthenium to the platinum electrode material greatly improves the hydrogen oxidation kinetics in the presence of CO. An amperometric sensor that senses the CO inhibition of the hydrogen oxidation can be fabricated from a platinum electrode, a proton conductor and a platinum ruthenium alloy electrode. While the... 

A major challenge in the MLCC industry has been to replace the precious metal electrodes (usually a Pd-Ag alloy) with base metals such as Ni. The MLCC industry accounts for about 75% of the electronic industries use of palladium. 

Bennett, M. D. and Leo, D. J. (2003). Manufacture and characterization of ionic polymer transducers employing non-precious metal electrodes, Smart Materials and Structures 12, 3, p. 424. 

The Clark electrodes described above are not suitable for oxygen determination in dry gaseous samples such as air because the thin layer of electrolyte solution contained behind the membrane is prone to rapid drying. A different arrangement is therefore used for such applications. Amperometric gas sensors for oxygen (and sensors for other electroactive species in the vapor phase) usually consist of a porous PTFE membrane that bears a precious metal electrode deposited, also in porous form, directly on the backside. This keeps the diffusion length short while... 

Future trends will include a further decrease in capacitor size to keep up with the miniaturization of end-use equipment. This will necessitate layer counts as high as 300 to provide the capacitance values. Another trend is a move away from precious metal electrodes such as palladium to base metals such as nickel or copper in order to reduce the cost of the chip capacitors. 

Non-precious metal electrodes such as Ni, Zn, and A1 provide ohmic contact with PTC thermistor, which is n-type semiconductor ceramics. In-Ga alloy also makes ohmic contact, and is used for experimental samples. 

Electrode materials and scalable reactors - in different bioelectrochemical systems expensive electrode materials such as carbon nanotubes or precious metal electrodes are used. These materials are unconsolidated for large-scale MES. In terms of maximizing productivity and minimizing costs, cheap and reusable three-dimensional electrodes are needed. In a technical electrochemical reactor, the use of an expensive separator such as a membrane should be avoided. During the lab stage, the scalability of the reactor concept should receive attention as important parameter. 

In general, precious metal electrodes or precious metal coated electrodes are used in batteries, fuel cells. 

Precious metal electrodes are used either as reference electrodes or for making electrical contact in oxidation-reduction systems. Platinum, the more commonly used metal, may be used in the shiny form (oxidation-reduction electrodes), the black form (hydrogen electrode and conductance cells to reduce polarisation errors) or the grey form (conductance cells). 

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