Efficient Charge Transport through a Metal Oxide Semiconductor in the Nanocomposite Film with Tris(2,2‘-bipyridine)ruthenium(II)

A nanocomposite film of tungsten trioxide (WO 3 ) and [Ru(bpy) 3 ] 2+ (bpy = 2,2‘-bipyridine) (denoted as Ru−WO 3 ) was prepared from an aqueous colloidal triad solution containing peroxotungstic acid, [Ru(bpy) 3 ] 2+, and poly(sodium 4-styrenesulfonate) by an electrodeposition technique. The electrochemical features of the Ru−WO 3 film were investigated using cyclic voltammetry (CV) and potential-step chronoamperospectrometry (PSCAS) techniques, compared with those in a [Ru(bpy) 3 ] 2+ /Nafion (Ru−Nf) film. PSCAS data spectrophotometrically showed that Ru II is completely oxidized for 0.3 s in the Ru−WO 3 film, in contrast to the corresponding reaction completed for 30 s in the Ru−Nf film. The apparent diffusion coefficient ( D app = (0.1−1.1) × 10 -7 cm 2 s -1 ) for charge transport (CT) by a Ru II /Ru III redox in the Ru−WO 3 film was higher than that (2.4 × 10 -10 cm 2 s -1 ) in the Ru−Nf film by 2 or 3 orders of magnitude. Activation energy ( E a ) for CT (14.1 kJ mol -1 ) for the Ru−WO 3 film was 3.5 times lower than that ( E a = 49.8 kJ mol -1 ) for the Ru−Nf film. The lower E a could be responsible for the faster CT in the Ru−WO 3 film than the Ru−Nf film. D app in the Ru−WO 3 film increased linearly with an increase of the final applied potential ( E f ) for PSCAS from 1.2 to 1.5 V vs SCE and saturated above E f = 1.5 V. The mechanism for CT in the Ru−WO 3 film is proposed, in which electrons are injected from [Ru(bpy) 3 ] 2+ into the conduction band (CB) of WO 3 and go through there to a collector electrode.