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Iridium Anodic Oxidation to Ir(III) and Ir(IV) Hydrous Oxides
Author(s) -
Juodkazytė Jurga,
Šebeka Benjaminas,
Valsiunas Ignas,
Juodkazis Kestutis
Publication year - 2005
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/elan.200403200
Subject(s) - iridium , cyclic voltammetry , inorganic chemistry , chemistry , metal , oxide , electrode , electrochemistry , standard electrode potential , titanium , analytical chemistry (journal) , catalysis , biochemistry , organic chemistry , chromatography
Iridium oxide films (IROFs) are known to have an enhanced or the so‐called super‐Nernstian (<59 mV/pH) pH‐sensitivity. The intention in the present study was to find out the reasons of such behavior and also to elucidate the nature of iridium anodic oxidation processes. The methods employed were combined cyclic voltammetry and chronopotentiometry. Iridium layers of 0.1 to 0.2 μm thickness, deposited thermally on titanium or gold‐plated titanium substrates, were used for investigations. IROFs on the surface of working electrodes were formed anodically by applying a constant potential in deaerated and oxygen‐containing solutions of 0.5 M H 2 SO 4 , 0.1 M KOH and 0.5 M H 3 PO 4 +KOH. Linear pH‐dependences of the stationary open‐circuit potential with the slopes close to 59 mV/pH were found for iridium electrode oxidized at 0.4 V–0.8 V (RHE) in deaerated and at 0.8 V–1.2 V (RHE) in O 2 ‐containing solutions. They were attributed to reversible Ir/Ir(OH) 3 and Ir/ IrO 2 ⋅ n H 2 O metal‐oxide electrodes, respectively. It has been suggested that the main current peaks seen in the voltammograms of iridium electrode in acid and alkaline solutions are of different nature. The difference between iridium electrode surface states in acid and alkaline solutions has been presumed to be the main reason of super‐Nernstian pH‐sensitivity of the IROFs. On the basis of the results obtained standard potential of Ir/Ir(OH) 3 electrode and the solubility product of Ir(OH) 3 have been evaluated: $\rm{E_{\rm Ir/Ir(OH)_3}^{\circ}}$ =0.78±0.02 V and K sp =3.3×10 −64 .