Disproportionation Phenomenon at the Silica Interface of Propylene Carbonate-1,2-Dimethoxyethane Binary Solvent Containing Lithium Perchlorate

Solution structures at solid-liquid interfaces play important roles in electrochemical reaction systems. To gain insights into interactions between binary solutions and metal oxides, we used quantitative 1H NMR and resonance shear measurements to investigate the behavior of a mixed solvent of propylene carbonate (PC)-1,2-dimethoxyethane (DME) at the interface with SiO2. The PC-DME mixture formed a well-ordered structure at the SiO2 interface, with the viscosity increasing from 0.5 mPa s in the bulk to 105 mPa s at 25 nm from the SiO2 surface. This long-range structure resulted from the preferential concentration of DME on the SiO2 surface owing to the different absorptivities of the solvent molecules. LiClO4 addition reduced the distance from the SiO2 surface at which the solution structure formed to 10 nm at 1.0 mol L-1 and 7.5 nm at 2.0 or 3.0 mol L-1. This interfacial structure affected ionic conduction and was consistent with the distance from the SiO2 surface at which the activation energy of ionic conduction in solid-liquid systems became 10 kJ mol-1 greater than the bulk value. The disproportionation of the solvent mixture at the SiO2 interface was competitive with ion solvation but was suppressed when the [DME]/[Li+] ratio was <= 2.6.