Electrodes iridium oxide

To detect CO2 in ambient air, the sensor is utilized as a novel design Severinghaus sensor. A sputtered thin film of iridium oxide is used as the pH sensing electrode. Iridium oxide, as well as several other metal oxides, has been shown to be pH sensitive [26], although the mechanism of this effect is not understood in detail. It is believed that the pH dependence is related to one of the redox couples of iridium oxide, such as... 

Metal oxide film coated metal electrodes can provide reliable potentiometric pH response. The miniaturized version of them gained application in potentiometric SECM. For example, a microdisc antimony pH electrode was used by Toth et al. [47] for investigating measuring function of silver iodide based ion selective cyanide electrode. Iridium oxide based microelectrode was applied by Wipf and coworkers [48] for pH imaging. 

Iridium as an electrode material has received considerable attention in the last decade not only because of its excellent catalytic properties but also in relation to the electrochromic effect observed for anodic iridium oxide films (AIROF). Electrochromism of iridium was thought to be of technical relevance for display applications and triggered several studies of the electrochemical and optical properties of AlROFs [67, 85-88],... 

Thick anodic iridium oxide films are formed by repetitive potential cycling between properly chosen anodic and cathodic limits [89]. The coloration (bleaching) transition is reflected in the cyclic voltammogram by a significant increase (decrease) of the electrode pseudo-capacity at a potential around 0.7 Vsce in acid electrolytes. At potentials above 0.7 V the thick film appears dark blue, while below 0.7 V the film is almost clear. 

The number of protons extracted from the film during coloration depends on the width of the potential step under consideration. As can be seen in the formulation of Fig. 26 an additional valence state change occurs at 1.25 Vsce giving rise to another proton extraction. The second proton exchange may explain the observation by Michell et al. [91] who determined a transfer of two electrons (protons) during coloration. Equation (5) is well supported by XPS measurements of the Ir4/ and Ols levels of thick anodic iridium oxide films emersed at different electrode potentials in the bleached and coloured state. Deconyolution of the Ols level of an AIROF into the contribution of oxide (O2-, 529.6 eV) hydroxide, (OH, 531.2 eV) and probably water (533.1 eV) indicates that oxide species are formed during anodization (coloration) on the expense of hydroxide species. The bleached film appears to be pure hydroxide (Fig. 27). 

In order to explain the changing optical properties of AIROFs several models were proposed. The UPS investigations of the valence band of the emersed film support band theory models by Gottesfeld [94] and by Mozota and Conway [79, 88]. The assumption of nonstoichiometry and electron hopping in the model proposed by Burke et al. [87] is not necessary. Recent electroreflectance measurements on anodic iridium oxide films performed by Gutierrez et al. [95] showed a shift of optical absorption bands to lower photon energies with increasing anodic electrode potentials, which is probably due to a shift of the Fermi level with respect to the t2g band [67]. 

S.A.M. Marzouk, S. Ufer, R.P. Buck, T.A. Johnson, L.A. Dunlap, and W.E. Cascio, Electrodeposited iridium oxide pH electrode for measurement of extracellular myocardial acidosis during acute... 

Depending on the fabrication techniques and deposition parameters, the pH sensitive slope of IrOx electrodes varies from near-Nemstian (about 59 mV/pH) to super-Nemstian (about 70mV/pH or higher). Since the compounds in the oxide layers are possibly mixed in stoichiometry and oxidation states, most reported iridium oxide reactions use x, y in the chemical formulas, such as lr203 xH20 and IrOx(OH)y. Such mixed oxidation states in IrOx compounds may induce more H+ ion transfer per electron, which has been attributed to causing super-Nerstian pH responses [41],... 

Considering the H+ dependent redox reaction between two oxidation states of the iridium oxide as the basis of the pH sensing mechanism, the electrode potential changes to the hydrogen ion concentration are expressed by Nemstian equation ... 

FIGURE 10.8 Two-dimensional pH distribution measured by an iridium oxide-based planar micro-pH electrode array after stimulation for only one minute. The electrode site in dark color is the Pt stimulating electrode. All other 15 electrodes are iridium oxide pH sensing electrodes. (Reproduced from [19], with permission from the Electrochemical Society, Inc.)... 

Simultaneous and continuous measurements of extracellular pH, potassium K+, and lactate in an ischemic heart were carried out to study lactic acid production, intracellular acidification, and cellular K+ loss and their quantitative relationships [6, 7], The pH sensor was fabricated on a flexible kapton substrate and the pH sensitive iridium oxide layer was electrodeposited on a planar platinum electrode. Antimony-based pH electrodes have also been used for the measurement of myocardial pH in addition to their application in esophageal acid reflux detection. 

K.G. Kreider, M.J. Tarlov, and J.P. Cline, Sputtered thin-film pH electrodes of platinum, palladium, ruthenium, and iridium oxides. Sens. Actuators B. 28, 167-172 (1995). 

M.L. Hitchman and S. Ramanathan, Evaluation of iridium oxide electrodes formed by potential cycling as pH probes. Analyst 113, 35-39 (1988). 

Various metal oxides including Pt02, Ir02, Ru02, 0s02, etc., have been used to prepare solid-state pH electrodes. In particular, the iridium oxide (mainly Ir02) pH electrodes exhibit important advantages... 

Redox potential pH Ionic activities Inert redox electrodes (Pt, Au, glassy carbon, etc.) pH-glass electrode pH-ISFET iridium oxide pH-sensor Electrodes of the first land and M" /M(Hg) electrodes) univalent cation-sensitive glass electrode (alkali metal ions, NHJ) solid membrane ion-selective electrodes (F, halide ions, heavy metal ions) polymer membrane electrodes (F, CN", alkali metal ions, alkaline earth metal ions)... 

Ir Ir02 electrodes (commercially available from Cypress Systems, Lawrence, KS) can measure pH in harsh environments or microscopic spaces [S. A. M. Marzouk, Improved Electrodeposited Iridium Oxide pH Sensor Fabricated on Etched Titanium Substrates, Anal. Chem. 2003, 75, 1258 A. N. Bezbaruah and T. C. Zhang, Fabrication of Anodically Electrodeposited Iridium Oxide Film pH Microelectrodes for Microenvironmental Studies, Anal. Chem. 2002, 74. 5726 D. O. Wipf. F. Ge, T. W. Spaine, and J. E. Baur, Microscopic Measurement of pH with Ir02 Microelectrodes, Anal. Chem. 2000, 72, 4921]. For pH measurement in nanoscopic spaces, see X. Zhang,... 

Iridium oxide, Ir02, is used in the fabrication of thin films for stable electrochromic materials and as an electrode material. Iridium metal is used in the manufacture of fountain pen points, airplane spark plugs, and hypodermic needles, see also Inorganic Chemistry. 

Fdti, G. and ComnineUis, Ch. (2004) Electrochemical oxidation of organics on iridium oxide and synthetic diamond based electrodes. In R.E. White, B.E. Conway, C.G. Vayenas and M.E. Gamboa-Adelco (Eds.), Modern Aspects of Electrochemistry, Vol. 37. Plenum, New York, NY, pp. 87-130. 

Iridium dioxide — Iridium oxide crystallizes in the rutile structure and is the best conductor among the transition metal oxides, exhibiting metallic conductivity at room temperature. This material has established itself as a well-known - pH sensing [i] and electrochromic [ii] material (- electrochromism) as well as a catalytic electrode in the production of chlorine and caustic [iii]. The oxide may be prepared thermally [iv] (e.g., by thermal decomposition of suitable precursors at temperatures between 300 and 500 °C to form a film on a substrate such as titanium) or by anodic electrodeposition [v]. 

The properties of sllane-derlvatlzed Iridium and anodic Iridium oxide (AIROF) electrodes have been studied by cyclic voltammetry In tetraethylammonlum perchlorate/acetonitrile solutions. Both electrodes react with silanes such as dlchlorosilylferrocene (DCSF) to give persistently bonded silylferrocene monolayers based on geometric area. This contrasts with the behavior of anodized platinum (Pt/PtO), which gives considerable polymerization with DCSF, resulting in layers of variable and unpredictable thickness. 

In a previous communication, we gave a detailed description of the electrochemical properties of silylferrocene on iridium (6). In this paper we briefly review this work, and compare deriva-tized iridium, Pt/PtO, and anodic iridium oxide electrodes. We show that the results of derivatization can give useful and sometimes unexpected information about the nature of the oxides on these electrodes. 

Petrii, O.A. and Vitins, A., Adsorption properties of the iridium oxide electrode Thermodynamic approach, Elektrokhimiya, 27, 461, 1991. 

Other pH-sensing transducers used in biosensors are metal oxide electrodes. Beside the common antimony oxide electrode, palladium oxide and iridium oxide probes have been coupled with immobilized enzymes. These sensors may be miniaturized by using chemical vapor deposition technology. Moreover, they are mechanically more stable than glass electrodes. Unfortunately the measuring signal of metal oxide electrodes is affected by redox active substances. 

Another urea microbiosensor, based on an iridium oxide electrode,... 

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