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Classical capacitance studies have revealed that the first layer of water present at an aqueous metal-electrolyte interface has a die-lectric constant less than 1/10th that of bulk water. Modern theory indicates that under such solvent conditions the barrier for elec-tron transfer will decrease substantially, yet this important prediction has not been tested experimentally. Here we report interfa-cial electron transfer kinetics for molecules positioned at variable distanced within the electric double layer of a transparent con-ductive oxide as a function of the Gibbs free energy change. The data indicate that the solvent reorganization is indeed near zero and increases to bulk values only when the molecules are positioned greater than 15 Å from the conductive electrode. Consistent with this conclusion, lateral intermolecular electron transfer, parallel to a semiconducting oxide electrode, was shown to be more rapid when the molecules were within the electric double layer. The results provide much needed feedback for theoretical studies and also indicate a huge kinetic advantage for aqueous electron transfer and redox catalysis that takes place proximate to a solid interface.

Bangle, R. E.; Schneider, J.; Conroy, D. T.; Aramburu-Troselj, B. M.; Meyer, G. J. Kinetic Evidence that the Solvent Barrier for Electron Transfer is Absent in the Electric Double Later. J. Am. Chem. Soc. 2020, 142 (35), 14940-14946.

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