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Title: Effect of cation species on surface-induced phase transition observed for platinum complex anions in platinum electrodeposition using nanoporous silicon.
Authors: Koda, Ryo
Koyama, Akira
Fukami, Kazuhiro  kyouindb  KAKEN_id
Nishi, Naoya
Sakka, Tetsuo  kyouindb  KAKEN_id
Abe, Takeshi
Kitada, Atsushi  kyouindb  KAKEN_id
Murase, Kuniaki  kyouindb  KAKEN_id
Kinoshita, Masahiro  kyouindb  KAKEN_id
Author's alias: 木下, 正弘
Issue Date: 21-Aug-2014
Publisher: AIP Publishing
Journal title: The Journal of chemical physics
Volume: 141
Issue: 7
Thesis number: 074701
Abstract: In an earlier work [K. Fukami et al., J. Chem. Phys. 138, 094702 (2013)], we reported a transition phenomenon observed for platinum complex anions in our platinum electrodeposition experiment using nanoporous silicon. The pore wall surface of the silicon electrode was made hydrophobic by covering it with organic molecules. The anions are only weakly hydrated due to their large size and excluded from the bulk aqueous solution to the hydrophobic surface. When the anion concentration in the bulk was gradually increased, at a threshold the deposition behavior exhibited a sudden change, leading to drastic acceleration of the electrochemical deposition. It was shown that this change originates from a surface-induced phase transition: The space within a nanopore is abruptly filled with the second phase in which the anion concentration is orders of magnitude higher than that in the bulk. Here we examine how the platinum electrodeposition behavior is affected by the cation species coexisting with the anions. We compare the experimental results obtained using three different cation species: K(+), (CH3)4N(+), and (C2H5)4N(+). One of the cation species coexists with platinum complex anions [PtCl4](2-). It is shown that the threshold concentration, beyond which the electrochemical deposition within nanopores is drastically accelerated, is considerably dependent on the cation species. The threshold concentration becomes lower as the cation size increases. Our theoretical analysis suggests that not only the anions but also the cations are remarkably enriched in the second phase. The remarkable enrichment of the anions alone would give rise to the energetic instability due to electrostatic repulsive interactions among the anions. We argue that the result obtained cannot be elucidated by the prevailing view based on classical electrochemistry. It is necessitated to consult a statistical-mechanical theory of confined aqueous solutions using a molecular model for water.
Rights: © 2014 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.
URI: http://hdl.handle.net/2433/189839
DOI(Published Version): 10.1063/1.4892596
PubMed ID: 25149800
Appears in Collections:Journal Articles

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