Determination of charge transfer distance by potential-step chronoamperospectrometry in a nafion ® film containing ru(bpy) 32+ complex

Abstract

New potential-step chronoamperospectrometry (PSCAS) was employed to investigate the charge transport distance for Ru(bpy) 3 2+ (bpy = 2,2′-bipyridine) complex dispersed in a Nafion ® film coated on an ITO electrode by a mixture casting method. It was found that the charge transfer distance was independent of the concentration of the redox species in the polymer film at a given sample time under the PSCAS measurement if it is assumed that the distribution of the redox centers in the polymer follows Poisson statistics. Meanwhile, the sample time for the measurement was an important factor in determining the charge transfer distance between the redox molecules within the polymer film. The charge transfer distance increased with prolonged sample time. At the beginning of the PSCAS measurement at 1.3 V (SCE), the charge transport in the polymer film was ascribed to charge hopping. On a longer time scale, the slow increase of the charge transfer distance was ascribed to charge hopping involving bounded motion. From the different response time of the charge hopping and the bounded motion, the charge hopping distance between the adjacent redox complexes was estimated at 1.3 nm. The saturated charge transfer distance on a longer time scale was 1.6 nm, indicating that the bounded motion distance is about 0.3 nm. The estimated diffusion-limited charge hopping rate constant for the Ru(bpy) 3 2+ complex in the Nafion ® film was about 2.5 × 10 5 M −1 s −1 when the longest charge transfer distance was employed.