Catalytic Activity of Spherical Meso-Porous Pt Films-Deposited Fluorine-Doped Tin Oxide Substrate Covered By Multi-Walled Carbon Nanotube for Iodine Reduction

Platinum (Pt) is known to be one of the best catalysts for various electrochemical reactions although it is an expensive rare metal.  Therefore, a investigation on reducing consumption of Pt is of great interest by many researchers.  For this purpose, we recently focus our attention on a mesoporous Pt film which posses not only a large surface area but also extremely high catalytic activity for methanol oxidation [1].

To make most of the mesoporous Pt film effectively, we focus our attention to moderately small spherical configuration. Spherical configuration increase the active surface area for electrochemical reactions.  However, the interface between Pt particles and the substrate is considered to yield high interfacial resistance because of the limited point contacts.  Therefore, in this study, Multi-Walled Carbon Nanotube (MWCNT), which is superior in mechanical strength and electric conductivity, a specific thermal conductivity, and the large surface area, was deposited to bypass the spherical mesoporous Pt film and the substrate as depicted in Fig.1.  In this presentation, the redox reaction of the iodide ions will be mainly discussed for the application to dye-senstized solar cell.

  MWCNT/mesoporous Pt composite film was prepared by two steps.  At first, the mesoporous Pt was deposited on TiO₂/ Fluorine-doped Tin Oxide (FTO) substrates, and then the surface was wholly covered by MWCNT.  The electrodeposition was performed in a three-electrode cell by chronoamperometry: various FTO substrates are used for working electrode, platinum wire for counter electrode, and an Ag/AgCl electrode for reference electrode.  For the electrolyte, 20 mM K₂PtCl₄aqueous solution resolving 1.0 wt % Brij58 (Aldrich) was utilized.  10 mg/mL of CNT solution resolving sodium dodecylbenzenesulfonate was dropped on the mesoporous Pt film and dried at room temperature.

  The spherical mesoporous Pt film was demonstrated to deposit at the potential of -0.1 V when a TiO₂/FTO is used as substrate.  Cyclic voltamograms of the bare TiO₂/FTO substrate, and the TiO₂/FTO substrates modified with the composite film, the spherical mesoporous Pt film, and the MWCNT film, respectively were measured in an acetonitrile solution consisting of 0.1M TBAP, 1 mM I₂, and 0.1 M LiClO₄.  As shown in Fig.2, the reduction peak current corresponding to iodine reduction for the composite film showed approximately three times larger than that for the both substrates modified only with the spherical mesoporous Pt film and the MWCNT film.  These results revealed that the composite film can be the best catalyst for iodine reduction.

[1] H. Wang et al., Chem. Mater., 2012, 24, 1591-1598.