Electrodes Modified with Synthetic Clay Minerals: Electron Transfer between Adsorbed Tris(2,2‘-bipyridyl) Metal Cations and Electroactive Cobalt Centers in Synthetic Smectites

Abstract

Clay-modified electrodes (CMEs) were prepared with two synthetic cobalt smectites. Large increases in the peak currents were observed in the cyclic voltammograms of tris(2,2‘-bipyridyl) metal cations ([M(bpy)3]2+, M = Os, Fe, or Ru) adsorbed in these CMEs when the potential was scanned high enough to oxidize redox active cobalt centers in the lattices of the synthetic clays. The cathodic charges obtained in the cobalt clay were 18.6, 25.7, and 12.3 times larger than those obtained in electrodes modified with a natural montmorillonite for the osmium, ruthenium, and iron bipyridyl cations, respectively. These increases were attributed to electron transfer between the intercalated cations and the oxidized cobalt centers. The redox active cobalt centers in the clay lattices functioned as relays, transferring electrons between adsorbed cations that otherwise would be electrochemically inactive and the conductive substrate. In some cases, nearly 100% of the cations present in the cobalt CMEs participated in the...