Hydrous Ir Oxide Film Properties at Sol-Gel Derived Ir Nanoparticles

Abstract

There has been much interest in the practical applications of Ir oxide films in supercapacitive, 1-3 electrochromic, 4-6 and energy storage devices, 6 as interneural stimulating electrodes, 7,8 electrocatalysts, [9][10][11][12][13] and pH electrodes. 14-16 In many cases, Ir oxide films have been formed electrochemically, i.e., by cycling or pulsing the potential of an Ir metal electrode between critical limits in various aqueous solutions. [4][5][6][17][18][19][20][21][22][23][24][25][26][27] This can result in the formation of relatively thick films (up to several micrometers in thickness), which are hydrous in nature (coded as activated iridium oxide films (AIROFs) in the prior literature 2,15,28-30 ) and exhibit very rapid oxidation/ reduction kinetics when the films are switched between their conducting Ir(IV) and insulating Ir(III) states. However, this method of film growth is both time and energy intensive, requires a metallic Ir substrate (often not fully reacted), and also usually involves some simultaneous loss, through dissolution, of the Ir metal substrate.Other methods 2,15,28,29 which have been used to form Ir oxide films have involved the thermal oxidation of iridium salts, or the sputtering of Ir onto a conductive substrate in an oxidizing plasma environment. Sputtered iridium oxide films (SIROFs) are known to be less hydrous in nature, have a more featureless cyclic voltammetric (CV) response, and yield lower maximum charge densities than do AIROFs. 2,15,28,29 Ir oxide films have also been formed by induction heating 31 and by electrodeposition at constant anodic potentials from alkaline Ir-containing solutions, 32 although insufficient data are available for the properties of these films to be assessed relative to AIROFs and SIROFs.The present paper is a continuation of our previous work, 33 involving the use of the sol-gel (SG) technique for the preparation of Ir oxide films. The SG method has been employed before to prepare IrO 2 34 and mixed oxides such as IrO 2 -Ta 2 O 5 , 34 IrO2-SnO 2 , 35 and RuO 2 -IrO 2 , 36 in powdered form. IrO 2 coatings were also obtained by painting 37,38 and dip-coating 38 techniques, using substrates such as amorphous silica microbeds 37 and glass, 38 followed by drying at temperatures between 350 and 600ЊC. However, only compositional/structural studies of these materials were performed, 34-38 and no prior electrochemical characterization has been reported.In our previous paper, 33 it was shown that the Ir-containing films formed by the SG method actually consist of Ir metal nanoparticles. These can be transformed easily into the oxide by potential cycling within the limits normally used for the electrochemical growth of IrOx films at bulk Ir electrodes. The resulting films, which were not studied in detail previously by us, 33 were shown to exhibit the general properties of AIROFs. In the present work, SG-formed Ir oxide films are demonstrated to be electrochromic, to yield high charge densities, as well as to exhibit excellent (Ir(III)/(IV)) oxidation/ reducti...

Optimization of Synthesis Parameters Employed during Pt Nanoparticle Formation by in situ Reduction

“…Furthermore, the successful use of NaOC 2 H 5 for Ir 22,23 and Ru oxide nanoparticle formation [34][35][36] and our interest in developing a one-pot synthesis of mixed noble metal nanoparticles supports our interest in further optimization of Pt nanoparticle formation using this reducing agent.…”

Controlled activation of iridium film for AIROF microelectrodes

“…The figure 11 could be approximately identified as the relationship of the redox activity with the activation cycles. to increase until 500 activation cycles shown in figure 9(c), we could conclude that the quantity of the stable Ir(III)/Ir(IV) is larger due to the decomposition of the unstable high valence state of iridium [69][70][71]. What's more, the changes of redox activity in the first 100 activation cycles are the fastest, then those of second hundred activation cycles and the last 300 activation cycles are the slowest.…”

Microparticle-based iridium oxide ultramicroelectrodes for pH sensing and imaging

“…sputtering from a metallic iridium target in an oxygen plasma [17,[32][33][34], pulsed-laser ablation of iridium oxide targets [35], electrophoretic deposition [36], anodic or cathodic electrodeposition [19,24,37], induction heating [38], sol-gel processes [39], and electrochemical oxidation of iridium wires [9,16] or films [40].…”