Enhanced Photocurrent of an ITO Electrode by the Photodeposition of Pt Nanoclusters onto a Monolayer TiO2-Ru Complex Hybrid Film

An indium tin oxide (ITO) electrode modified with mono-/multilayer TiO2/[Ru(phen)(2)-(dC18bpy)](2+) [phen = 1,10-phenanthroline, dC18bpy = 4,4'-dioctadecy1-2,2'-bipyridyl] hybrid film [denoted as ITO/(TiO2-Ru)(n)] has been prepared by a modified Langmuir-Blodgett (LB) method. The effects of Pt-photodeposition on the photocurrent of above ITO/(TiO2-Ru)(n) electrode were studied. Our experiments illustrated: (1) the single-layered hybrid film of TiO2/[Ru(phen)(2)(dC18bpy)(2+) (denoted as TiO2-Ru) was closely packed at a surface pressure of 25 mN.m(-1) and had a thickness of (3.60 +/- 0.5) nm; (2) under light irradiation (lambda>360 nm), Pt clusters with radii of 20 similar to 160 nm were authentically observed by the reduction of [Pt(NH3)(6)](4+) through the TiO2-Ru hybrid film; (3) the enhanced photocurrent was achieved by depositing the Pt nanocluster onto the surface of the ITO/(TiO2-Ru)(n) electrodes at the applied potential above 500 mV (vs. Ag vertical bar AgCl vertical bar KCl) under light irradiation (lambda>360 nm). For example, the photocurrent of ITO/TiO2-Ru/Pt was increased about 5 times in comparison with an ITO/TiO2-Ru electrode at the applied potential 900 mV when they were both in contact with 0.1 mol.L-1 NaClO4 solution. Such a result indicates that the Pt clusters are able to hamper the combination of electron hole pairs and reduce the counterwork of insulating long alkyl chains of amphiphilic Ru(II) complexes, and thus produce the enhanced photocurrent; (4) the photocurrent was strongly dependent on the number of TiO2-Ru hybrid films. With the increase in the number of layers from one, two to four, the photocurrent intensity was found to firstly increase and then decrease, suggesting that the electron transfer be directly through the electrochemically inactive TiO2 monolayer.