Electrochemistry in bicontinuous microemulsions derived from two immiscible electrolyte solutions for a membrane-free redox flow battery.

HYPOTHESES: Bicontinuous microemulsions (BMEs) have attracted attention as unique heterogeneous mixture for electrochemistry. An interface between two immiscible electrolyte solutions (ITIES) is an electrochemical system that straddles the interface between a saline and an organic solvent with a lipophilic electrolyte. Although most BMEs have been reported with nonpolar oils, such as toluene and fatty acids, it should be possible to construct a sponge-like three-dimensionally expanded ITIES comprising a BME phase.

EXPERIMENTS: Dichloromethane (DCM)-water microemulsions stabilized by a surfactant were investigated in terms of the concentrations of co-surfactants and hydrophilic/lipophilic salts. A Winsor III microemulsion three-layer system, consisting of an upper saline phase, a middle BME phase, and a lower DCM phase, was prepared, and electrochemistry was conducted in each phase.

FINDINGS: We found the conditions for ITIES-BME phases. Regardless of where the three electrodes were placed in the macroscopically heterogeneous three-layer system, electrochemistry was possible, as in a homogeneous electrolyte solution. This indicates that the anodic and cathodic reactions can be divided into two immiscible solution phases. A redox flow battery comprising a three-layer system with a BME as the middle phase was demonstrated, paving the way for applications such as electrolysis synthesis and secondary batteries.