The Dynamics of Electron Self-Exchange between Nanoparticles

Abstract

The rate of electron self-exchange reactions between discretely charged metal-like cores of nanoparticles has been measured in multilayer films of nanoparticles by an electrochemical method. The nanoparticles are Au monolayer-protected clusters with mixed monolayers of hexanethiolate and mercaptoundecanoic acid ligands, linked to each other and to the Au electrode surface with carboxylate-metal ion-carboxylate bridges. Cyclic voltammetry of the nanoparticle films exhibits a series of well-defined peaks for the sequential, single-electron, double-layer charging of the 1.6-nm-diameter Au cores. The electron self-exchange is measured as a diffusion-like electron-hopping process, much as in previous studies of redox polymer films on electrodes. The average electron diffusion coefficient is DE = 10(+/-5) x 10(-8) cm2/s, with no discernible dependence on the state of charge of the nanoparticles or on whether the reaction increases or decreases the core charge. This diffusion constant corresponds to an average first-order rate constant kHOP of 2(+/-1) x 10(6) s(-1) and an average self-exchange rate constant, kEX, of 2(+/-1) x 10(8) M(-1) x s(-1), using a cubic lattice hopping model. This is a very large rate constant, considering the nominally lengthy linking bridge between the Au cores.

Ion Limited Charging of Nanoparticle Thin Films

“…18 The validity of the assumption is dependent on both the thickness of the film and the diffusion coefficient of the species inside the film. 18 The electron diffusion coefficient is known to be as low as 10 -8 cm 2 /s, 19 which means that the onset of diffusion control would occur at a thickness of ca. 100-500 nm, the same scale as has been seen experimentally.…”

Dynamics of Electron Transfers between Electrodes and Monolayers of Nanoparticles

“…In one study, 8 the electron-transfer rate constant (ca. 10 6 s -1 ) between MPC nanoparticles (i.e., electron If the above hypothesis is correct, the following analysis shows that, in reference to Scheme 2, reactions of the MPC monolayer via the bonded pathway become more plausible.…”

Absolute Standard Redox Potential of Monolayer-Protected Gold Nanoclusters

“…[3][4][5][6] At ambient temperature, both freely diffusing and electrode-attached MPCs demonstrate the voltammetric responses featuring a series of evenly spaced current peaks. 4,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] This ensemble behavior is equivalent to a series of classical Coulomb staircase charging events or sequential electrochemical redox reactions, which occur as MPCs encompass an intermediate dimension between small molecules and bulk materials. Previously, the sequential electrontransferhasbeenobservedforfullerene(andderivatives) [22][23][24][25][26] and Pt-carbonyl nanoclusters [Pt n (CO) m ], [27][28][29] which led Weaver et al 30 to develop an electrostatic model to relate the electron transfer energetics of molecular capacitances in gas-and solution-phase systems.…”