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Thermodynamic and dynamic investigat...

Elsen, Heather Alyssa.

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Thermodynamic and dynamic investigations of hydrated iridium oxide potentiometric pH micro-sensors.

紀錄類型:	書目-語言資料,印刷品 : Monograph/item
正題名/作者:	Thermodynamic and dynamic investigations of hydrated iridium oxide potentiometric pH micro-sensors./
作者:	Elsen, Heather Alyssa.
面頁冊數:	230 p.
附註:	Adviser: Marcin Majda.
Contained By:	Dissertation Abstracts International69-03B.
標題:	Chemistry, Analytical. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3306128
ISBN:	9780549528470

Thermodynamic and dynamic investigations of hydrated iridium oxide potentiometric pH micro-sensors.
Elsen, Heather Alyssa.

Thermodynamic and dynamic investigations of hydrated iridium oxide potentiometric pH micro-sensors. - 230 p.

Adviser: Marcin Majda.

Thesis (Ph.D.)--University of California, Berkeley, 2007.

Hydrated Anodic Iridium Oxide Films (AIROF's) were investigated using equilibrium and dynamic electrochemical methods. Analysis of standard calibration curves, long term open circuit potentials, cyclic voltammetry and Electrochemical Time of Flight (ETOF) offered insight into the mechanical, operational and mechanistic properties of iridium oxide films.

ISBN: 9780549528470Subjects--Topical Terms:

586156
Chemistry, Analytical.

Thermodynamic and dynamic investigations of hydrated iridium oxide potentiometric pH micro-sensors.
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100 1 $a Elsen, Heather Alyssa. $3 1285916
245 1 0 $a Thermodynamic and dynamic investigations of hydrated iridium oxide potentiometric pH micro-sensors.
300 $a 230 p.
500 $a Adviser: Marcin Majda.
500 $a Source: Dissertation Abstracts International, Volume: 69-03, Section: B, page: 1614.
502 $a Thesis (Ph.D.)--University of California, Berkeley, 2007.
520 $a Hydrated Anodic Iridium Oxide Films (AIROF's) were investigated using equilibrium and dynamic electrochemical methods. Analysis of standard calibration curves, long term open circuit potentials, cyclic voltammetry and Electrochemical Time of Flight (ETOF) offered insight into the mechanical, operational and mechanistic properties of iridium oxide films.
520 $a Solutions used for the anodic deposition of iridium oxide were made from various iridium salts, usually iridium (III) or (IV) chloride. They also contained variable amounts of oxalic acid or EDTA, and a base (carbonate, phosphate, and hydroxide). Four methods of depositing AIROF's were described: constant current, constant potential, pulsed potential and cyclic potential deposition. While each resulted in a functioning iridium oxide layer, the physical characteristics such as softness, thickness, and adhesion of the layer varied. It was shown that some methods such as constant current deposition create thick, rough layers, while other methods, pulsed potential or cyclic growth deposition, created smooth, strongly adhering, thin layers. The mechanism of deposition was concluded to initially involve oxidation of water coordinated to the iridium complex. It was followed by conversion to an insoluble iridium hydroxide complex with oxygen bridges between iridium centers that deposits onto the electrode surface.
520 $a The potential versus pH response of iridium oxide sensors was not a function of the deposition method used. All sensors responded with a slope of 78 +/- 2 mV/pH unit if stored in DI water. The characteristics of the solution in which the AIROF was stored had a strong effect on the potential versus pH response, however. The solvent, electrolyte composition, and pH of the storage medium all affected the potential versus pH response causing variation from 60--90 mV/pH unit. When stored in either non-aqueous solvents or concentrated (> 0.1 M) electrolyte solutions, the iridium oxide layer's response decreased below the standard &sim;78 mV/pH unit determined for sensors stored in DI water. Only when AIROF's were stored in basic aqueous solutions did they exhibit a response higher than that of a sensor stored in water. Through cyclic voltammetry investigations this change of the response can be attributed to changes in the oxidation state of the film, as discussed below.
520 $a Cyclic voltammetry was critical in characterization of the iridium oxide sensors. Depending on the pH and the buffer capacity of the solution in which the cyclic voltammetry was conducted, two or three sets of peaks were present. The redox phenomena associated with each of these peaks were investigated by varying the solvent, electrolyte, buffer capacity and pH. From most positive to most negative potentials, the peaks were related to the iridium oxide (IV)/(V) couple, the iridium oxide (III)/(IV) couple, and to anion interactions. Cyclic voltammetry also allowed the determination of the redox composition of the iridium oxide layer. When performed on AIROF's stored in solutions of various pH and electrolyte composition, the changes in the potential versus pH response of the AIROF were correlated with changes in the initial films oxidation state. For example, the higher the pH of the storage solution the more oxidized the iridium oxide layer became.
520 $a In the mechanistic studies, the question of proton or hydroxide injection/expulsion was also considered. Cyclic voltammetry in non-aqueous solutions showed clearly that protons were injected at pH 4 and lower. Above pH 4, hydroxide ions were ejected. In the absence of hydroxide ions, small anions could partially substitute into the iridium oxide layer. A comparison between cyclic voltammograms taken in buffered and unbuffered solutions showed that the primary peaks (iridium oxide (III)/(IV) couple) were reversible only when the proton/hydroxide ion supply was high. In the absence of buffers, these peaks disappeared as the pH neared neutral conditions. ^ The rate of response and the capacitance of the AIROF's were investigated through ETOF. ETOF involved monitoring the open circuit potential at one microband electrode and generating protons or hydroxide ions at a constant current at another microband electrode separated by 20--100 mum. The sensor electrode was coated with an iridium oxide layer typically 10--400 nm in thickness. The resulting potential-time transients allowed measurement of the rate of potential response of the AIROF and, through comparisons with simulated transients, the capacitance.
590 $a School code: 0028.
650 4 $a Chemistry, Analytical. $3 586156
650 4 $a Chemistry, Physical. $3 560527
690 $a 0486
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710 2 $a University of California, Berkeley. $3 687832
773 0 $t Dissertation Abstracts International $g 69-03B.
790 $a 0028
790 1 0 $a Majda, Marcin, $e advisor
791 $a Ph.D.
792 $a 2007
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