Switchable electrolyte properties and redox chemistry in aqueous media based on temperature-responsive polymers

Abstract: Macromolecular ionomer solutions exhibiting macroscopic properties that change in response to temperature are referred to as thermally responsive polymer electrolytes (RPEs). Such materials provide a means to control electrochemical systems using an external stimulus that affects the polymer phase behavior and electrolyte properties. RPEs were synthesized with N-isopropylacrylamide, which governs the thermal properties, and varying fractions of acrylic acid, which provides ionic properties. These polymers undergo a thermally activated phase separation in aqueous solutions at a given temperature, thereby altering the ionic strength, pH, and conductivity of the electrolyte solution. In this article, we demonstrate how the molecular properties of RPEs, specifically the ionic composition, influence the temperature-dependent electrolyte properties and the extent to which these electrolytes can control the activity of redox electrodes. Materials with high ionic content provide the highest room temperature ion conductivity and redox activity; however, RPEs with low ionic content provide the highest “on–off” ratio in electrochemical activity at elevated temperatures. Graphical Abstract: [Figure not available: see fulltext.]