Penetration of Platinum Complex Anions into Porous Silicon: Anomalous Behavior Caused by Surface-Induced Phase Transition

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• 作者：Akira Koyama ; Kazuhiro Fukami ; Tetsuo Sakka ; Takeshi Abe ; Atsushi Kitada ; Kuniaki Murase ; Masahiro Kinoshita
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：August 20, 2015
• 年：2015
• 卷：119
• 期：33
• 页码：19105-19116
• 全文大小：580K
• ISSN：1932-7455

文摘

We investigate the dynamics of the penetration of platinum complex anions into nanopores during platinum deposition within a nanoporous silicon electrode. The pore-wall surface is hydrophobic and the anions are large enough to behave like hydrophobic solutes. Some of the observations are anomalous in the sense that they cannot be understood in terms of the phenomenological theory for diffusion based on Fick鈥檚 law. For example, the penetration is faster when the pore diameter is smaller and the anion size is larger. The penetration rate remains unexpectedly fast even when the pores become deeper. The penetration can be made faster using large coexisting cations with sufficiently high hydrophobicity. We show that these results can be interpreted only by statistical mechanics of confined molecular liquids. When the manipulated variables (pore diameter, anion concentration, sizes of platinum complex anions and coexisting cations, etc.) are chosen so that the surface-induced phase transition (SIFT) can take place, the penetration is drastically accelerated. Under the condition with the SIFT occurrence, a strongly attractive, long-ranged effective surface鈥揳nion interaction comes into play, leading to the anomalous behavior. The experimental result is in qualitatively good accord with the theoretical argument. The outcome is of vital importance in controlling the mass transfer within nanoporous media and designing next-generation electrochemical devices.