Orbital Overlap Effects in Electron Transfer Reactions across a Metal Nanowire/Electrolyte Solution Interface

In this paper, we report on calculations of the orbital overlap between Fe(III) and Cr(III) aquacomplexes and different electrode surfaces: Cu(111), Ag (111), Au(111), Pt(111), and corresponding monatomic wires. The electronic structure of the rnonocrystalline surfaces and nanowires are described in terms of the electronic spillover and density of electronic states at the Fermi level obtained from periodic density functional theory (DFT) calculations. The transmission coefficients (kappa) characterizing the first stage of outer-sphere electron transfer for the reduction of aquacomplexes are calculated on the basis of Landau-Zener theory as a function of electrode-reactant separation; the electronic transmission coefficients for the [Cr(H2O)(6)](3+/2+) redox couple were found to be smaller than those for [Fe(H2O)(6)](3+/2+). Two different intervals can be clearly distinguished for Cu, Au and Pt: a catalytic region, where kappa(wire) > kappa(Me slab) and an inhibition region, where kappa(wire) < kappa(Me slab). A similar behavior exhibits the coupling constant estimated for a hydrogen atom adsorbed at the Au(111) surface and the Au monatomic wire. These effects originate from some specific features of electronic density profile for metal nanowires: at short distances the electronic density of nanowires is higher compared with the (111) metal surfaces, while at larger separations it decreases more sharply.