pH Responsive Hydrogels for Programmed Activation of Electrochemical Storage Systems

Bioinspired materials are often ideally suited for applications that are biologically integrated due to naturally evolved advantageous characteristics. One area where this is particularly important is in electrochemical storage materials that use aqueous electrolytes which are amenable for applications ranging from biomedical devices to grid-scale storage. Hygroscopic ionomer electrolytes permit fine control over the transport of cations using various mechanisms, thus smart bioinspired polymers could enable spontaneous control of electrochemical discharge for use in the active control of battery operation. Here we present the design, fabrication, and characterization of pH-sensitive hydrogels that are bioinspired as polymeric electrolytes that can control the discharge of aqueous sodium-ion batteries. Heparin-methacrylated and poly(acrylic acid)-based hydrogels are used as transport membranes for electrolytes in conjunction with activated carbon anodes and manganese oxide cathodes. These pH-sensitive hydrogels exhibit macroscropic swelling and deswelling responses as the pH is adjusted from 1.5 to 7. Chemical control of hydrogel mesostructure permits selective discharge of the electrochemical cell in the “off” and “on” configuration, respectively. We report ionic mobilities in these two states while operating in galvanostatic conditions at 0.1C. pH-dependent discharge of electrochemical storage systems composed of biocompatible materials could serve as a passive control mechanism for battery operation in biologically relevant applications including ingestible electronic devices.