Photoelectrochemical and quenching studies of tris(2,2'-bipyridine)ruthenium(II) bound to Nafion- and clay-coated electrodes

Abstract

The photosensitizer [Ru(bipy)₃]²⁺(bipy = 2,2'-bipyridine) was adsorbed on Nafion(nf)- and bentonite clay(bt)-coated electrodes. Photoelectrochemical cells were constructed using Pt-nf-[Ru(bipy)₃]²⁺ and Pt-bt-[Ru(bipy)₃]²⁺ electrodes with cobalt(III) complexes and Fe³⁺ ion as electron relays. At appropriate applied potentials, anodic and cathodic photocurrents were induced when the electrodes were irradiated with visible light in solutions containing a mixture of a cobalt(III) complex and HClO₄. The photoresponse could be switched between anodic and cathodic by controlling the applied electrode potential. The origin of the photocurrent is explained by an oxidative quenching by the cobalt(III) complex of the photoexcited ^∗[Ru(bipy)₃]²⁺ complex confined at the electrode, followed by electrochemical reduction or oxidation of the resulting [Ru(bipy)₃]³⁺ and cobalt(II) complex respectively. The quenching rate constants, k_q, for the reaction of [Ru(bipy)₃]²⁺ with three different cobalt(III) complexes and Fe³⁺ion were determined by photoelectrochemical methods.