Indium oxide electrode

I. Taniguchi, K. Watanabe, M. Tominaga, and F.M. Hawkridge, Direct electron transfer of horse heart myoglobin at an indium oxide electrode. J. Electroanal. Chem. 333, 331-338 (1992). 

M. Tominaga, T. Kumagai, S. Takita, and I. Taniguchi, Effect of surface hydrophilicity of an indium oxide electrode on direct electron transfer of myoglobins. Chem. Lett. 10, 1771-1774 (1993). 

Use of modified gold electrodes is not the only approach to achieve cytochrome c electrochemistry. Indeed, a number of studies have been reported on a variety of electrode surfaces. In 1977, Yeh and Kuwana illustrated (23) well-behaved voltammetric response of cytochrome c at a tin-doped indium oxide electrode the electrode reaction was found to be diffusion-controlled up to a scan rate of 500 mV sec Metal oxide electrodes were further studied (24, 25) independently in Hawkridge and Hill s groups. The electrochemical response of cytochrome c at tin-doped indium oxide and fluoride-doped tin oxide was very sensitive to the pretreatment procedures of the electrode surface. At thin-film ruthenium dioxide electrodes, variation of the faradaic current with pH correlating with the acid-base protonation of the electrode surface was observed. 

First realization of reversible ET of cytochrome c employing tin-doped indium oxide electrodes... 

It has been reported that a reversible one-electron transformation of cytochrome c occurs on an indium oxide electrode. Cytochrome c yields quasi-reversible maxima at EhO 0. 25 V on a gold electrode in the presence of 4,4 -bipyridine. 

Yeh and Kuwana " were the first to report on the electrochemistry of cytochrome c at doped metal oxide semiconductor electrodes. A nearly reversible electrode reaction was indicated by the cyclic voltammetry and differential pulse voltammetry of cytochrome c at tin-doped indium oxide electrodes. Except for the calculated diffusion coefficient, all of the characteristics of the electrochemistry of cytochrome c at this electrode indicated that the electrode reaction was well-behaved. A value of 0.5 x 10" cmVs was determined for the diffusion coefficient which, like previously determined values at mercury, is lower than the value obtained by nonelectrochemical methods (i.e., 1.1 X 10 cm /s " " ). The electrochemical response of cytochrome c at tin oxide semiconductor electrodes was reported to be quasi-reversible, although no details were given. " ... 

With a discovery that was free of arguments concerning electron mediation, Yeh and Kuwana showed [53] that cytochrome c gave stable electrochemistry (CV and DPV) at a Sn-doped-indium oxide electrode. The cyclic voltammetry at pH 7 was diffusion-controlled and reversible up to a scan rate of 500 mVs . In this case we may now regard the electrode surface to be naturally functionalized through the presence of the stable oxide groups. 

However, Hawkridge and co-workers established also that cytochrome c undergoes strong adsorption at Sn-doped indium oxide electrodes with retention of native properties. They observed [54] that cyclic voltammetry could be obtained... 

Roller and Hawkridge used a tin-doped indium-oxide electrode and made measurements over the temperature range 5 to 75 °C at pH 7 using phosphate (I = 0.20 M) or Tris/cacodylate (I = 0.20 M) buffer media [86]. In further work they extended the pH range to 5.3 and 8.0 [87]. 

A.2.2 Solid electrodes (gold, carbon, metal oxide electrodes). Cytochrome c is also adsorbed irreversibly at solid electrodes, which mostly results in irreversible kinetices of the electrode reaction. A nearly reversible reaction of strongly adsorbed cytochrome c is, however, observed at electrodes of metal oxides (doped metal oxide semiconductor electrodes, tin-doped indium oxide electrode) [202, 203]. 

Martin LP, Glass RS (2005) Hydrogen sensor based on YSZ electrolyte and tin doped indium oxide electrode. J Electrochem Soc 152 H43-H47... 

Manzoli A, Steffens C, Paschoalin RT, Correa AA, Alves WF, Leite FL, Herrmann PSP (2011) Low-cost gas sensors produced by the graphite line-patterning technique applied to monitoring banana ripeness. Sensors 11 6425-6434 Martin LP, Glass RS (2005) Hydrogen sensor based on YSZ electrolyte and tin doped indium oxide electrode. J Electrochem Soc 152 H43-H47... 

An exception to the above could be the observed cyclic voltammograms recorded for HRP at a tin-doped indium oxide electrode [36], This contribution reports on a midpoint potential of the voltammograms equal to -270 mV vs. NHE, which agrees well with the expected E° of Fe /Fe redox conversion for HRP, however, any data on the bioelectrocatalytic reduction of H2O2 at these electrodes remain absent. 

A further refinement to provide a crystal of a potentially long lifetime is to trap a single wall as shown in fig. 30.29. A crystal of this configuration with indium oxide electrodes, has sustained >10 switching cycles successfully (Barkley et al., 1972). 

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