Effect of applied potentials on electron transfer in oxidation and reduction of the Ru(bpy)(3)(2+/3+) couple in Nafion film as studied by potential-step chronoamperospectrometry

Potential-step chronoamperospectrometry (PSCAS) was employed to investigate electron transport associated with redox reactions of the Ru(bpy)(3)(2+/3) couple in a Nafion film. The electron propagation within the Nafion was f ound to take place through an electron hopping mechanism for the oxidation of Ru(bpy)(3)(2+) to Ru(bpy)(3)(3+), but by a physical diffusion mechanism for the reduction of Ru(bpy)(3)(3+) to Ru(bpy)(3)(2+). In the oxidation of Ru(bpy)(3)(2+), the electron transfer distance for the electron hopping and the bounded motion was estimated by modified Poisson statistics. The elect ron transfer distance, which includes the bounded motion and electron hoppi ng distance, become longer on increasing the applied potential from 1.1 to 1.5 V (SCE) due to the increase of electron hopping distance (increase of t he center-to-center distance from 1.13 to 1.47 nm). The bounded motion dist ance (0.25-0.31 nm) remained almost unchanged. The bimolecular rate constan t for an electron transfer step also increased with increasing the applied potential. The apparent diffusion coefficient (D-app) for electron propagat ion during the reduction of Ru(bpy)(3)(3+) was 1.2 similar to 8 times large r than that measured for the oxidation of Ru(bpy)(3)(2+) under the same con ditions. (C) 1999 Elsevier Science Ltd. All rights reserved.