Tuning flexoelectric effect in polymer electrolyte membranes via cation selection for potential energy harvesting applications

With increasing energy demands associated with portable electronics, routes to capture dissipated energy associated with everyday actions (energy harvesting) can be a key component in an integrated sustainable energy system. Exploiting the flexoelectric effect in an ion conductive, flexible, ionic polymer electrolyte membrane (PEM) provides one route to harvest energy through ion polarization across the PEM during bending. Here we demonstrate a facile route to manipulate the polarity switching (i.e., reversal of polarization direction) during the bending through the size of the cations in the PEM. The direction of the polarization is found to be primarily governed by the size disparity between the cation and anion. This ability to control the polarization state in flexoionic devices through selection of the ion pairs provides possibilities to simplify the design of energy harvesting where positive and negative curvatures would be expected to occur across a device.