Characterization and Analysis of Self-Assembly of a Highly Active Colloidal Catalyst for Water Oxidation onto Transparent Conducting Oxide Substrates
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- 作者：Takayuki Kuwabara ; Emi Tomita ; Sayaka Sakita ; Daisuke Hasegawa ; Koji Sone ; Masayuki Yagi
- 刊名：Journal of Physical Chemistry C
- 出版年：2008
- 出版时间：March 13, 2008
- 年：2008
- 卷：112
- 期：10
- 页码：3774 - 3779
- 全文大小：249K
- 年卷期：v.112,no.10(March 13, 2008)
- ISSN：1932-7455
文摘
An IrO2 colloid stabilized by citrate ions was self-assembled on an indium tin oxide (ITO) electrode when itwas immersed in the colloid solution at pH 3.5. The IrO2 colloid on the ITO surface was characterized usingelectrochemical, inductively coupled plasma mass spectroscopic, X-ray diffraction spectroscopic, scanningelectron microscopic, and atomic force microscopic techniques. The self-assembly was promoted steeply atpH 3.5 to 4.1, although it hardly occurred at pH 5.3 to 9.7. It is considered to be caused by chemical interactionbetween carboxylic groups on the citrate stabilizer and hydroxyl groups of the ITO surface. The adsorptionisotherm of the IrO2 colloid onto the ITO surface was analyzed by a Langmuir adsorption isotherm to providethe maximum coverage and an adsorption equilibrium constant 
max = 1.1 × 10-8 mol cm-2 and Kads = 1.8× 104 M-1 at 25 
C, respectively. The Kads value increased from 6.7 × 103 to 1.8 × 104 M-1 with a temperatureincrease from 5 to 25 C. The temperature dependence of Kads gave 
H = 36.5 kJ mol-1, G = -24.4 kJmol-1, and S = 204 J mol-1 K-1 at 25 C. The positive H and S values are explained by therearrangement of solvating water molecules and counter cations surrounding the IrO2 colloid that is involvedin its assembly on the ITO surface. In electrocatalytic water oxidation, the maximum turnover frequency ofthe IrO2 catalyst was 23 600 h-1 under potential static conditions at 1.3 V versus Ag/AgCl.
max = 1.1 × 10-8 mol cm-2 and Kads = 1.8× 104 M-1 at 25 C, respectively. The Kads value increased from 6.7 × 103 to 1.8 × 104 M-1 with a temperatureincrease from 5 to 25 C. The temperature dependence of Kads gave H = 36.5 kJ mol-1, G = -24.4 kJmol-1, and S = 204 J mol-1 K-1 at 25 C. The positive H and S values are explained by therearrangement of solvating water molecules and counter cations surrounding the IrO2 colloid that is involvedin its assembly on the ITO surface. In electrocatalytic water oxidation, the maximum turnover frequency ofthe IrO2 catalyst was 23 600 h-1 under potential static conditions at 1.3 V versus Ag/AgCl.