Effect of Displacement Deposition on Platinum Deposition within Nanoporous Silicon

In the use of nanoporous electrode, the control of mass transfer within nanopores is crucially important to elicit their best performance. However, mass-transfer rate for ionic species through electrolyte solution within nanopores tends to be very low, so that only a limited proportion of the whole specific surface area contributes to electrochemical reactions. In the case of the metal filling within the porous silicon by electrodeposition, poor supply of metal precursor into the nanopores also causes a problem to induce a plugging at the pore opening. We have investigated the pore filling with platinum in an aqueous solution with tuning the hydration property of the surface of pore wall and platinum complex anions [1-3]. The important insight we have found is the surface-induced phase transition (SIFT: the concentration of the hydrophobic solutes near the hydrophobic surface becomes orders of magnitude higher than that in the bulk) in the nanopores plays an important role in electrodeposition of platinum within the nanoporous silicon. Our previous reports, however, focused only on the presence of platinum deposits in the porous layer corresponding to the various experimental conditions and didn’t elucidate the dynamic aspects of the penetration of platinum complex anions into the nanopores. We adopted the time developments of the mixed-potential measured during the displacement deposition of platinum within the porous silicon to find the peculiar penetration dynamics that could not be understood within the framework of simple diffusion. One of the typical observations shows the penetration is faster when the pore diameter is smaller and the anion size is larger. In this paper, we also discuss the effect of the pore depth on the penetration dynamics.

[1] K. Fukami, R. Koda, T. Sakka, T. Urata, K. Amano, H. Takaya, M. Nakamura, Y. Ogata, and M. Kinoshita, Chem. Phys. Lett., 2012, 542, 99-105.

[2] K. Fukami, R. Koda, T. Sakka, Y. Ogata, and M. Kinoshita, J. Chem. Phys., 2013, 138, 094702.

[3] R. Koda, A. Koyama, K. Fukami, N. Nishi, T. Sakka, T. Abe, A. Kitada, K. Murase, and M. Kinoshita, J. Chem. Phys., 2014, 141, 074701.