Role of Ion Size and Valency in Mechano-Electrical Energy Conversion of Flexo-Ionic Polymers*

The increasing environmental concerns and global warming, attributed to conventional energy production, have motivated researchers to scout for clean energy harvesting (EH) strategy from pollutant-free and natural energy resources. Inspired by naturally occurring mechano-electroactive materials, flexo-ionic devices consisting of a flexible solid polymer electrolyte membrane (PEM), consisting of an ionic compound and a polymer matrix host, laminated between two compliant carbonaceous electrodes were developed. The laminated flexo-ionic PEMs can generate electrical potential and current via ion diffusion/polarization by subjecting the PEM assembly under mechanical deformation. By varying cation sizes and valencies of ionic compounds in the development of these PEMs, the effects of ion size and valency on flexoelectric properties (i.e. output voltage and current/polarization), ionic conductivity, viscoelastic and mechanical properties were investigated as a function of ion concentration and mode of mechanical stimuli involving intermittent square (low frequency) and dynamic oscillatory (high frequency) displacement. The synergic effect of these factors and their roles in mechano-electrical energy conversion will be discussed.