Structural criticality manifested by a polarized ionic layer on a MWCNT yarn surface under mechanical loading

Abstract

The electrochemical capacitance of an energy harvester based on a multiwalled carbon-nanotube yarn is proportional to the total strain and then rapidly decreases after the strain exceeds a critical value. Rigorous characterization of the nonlinearities in the distortion of the polarized ion layer under an external load is necessary to systematically optimize the performance of energy-harvesting fibers. In this study, we conducted electrochemical experiments and all-atom molecular dynamics simulations to elucidate the dynamics of an ionic polarization layer on a nanotube surface. The in-plane compressive strain exerted under the mechanical tension of the energy harvester induced the radial buckling of the nanotubes, which in turn became the driving force behind the repulsion between adjacent polar ion layers. Therefore, electrochemical stability was guaranteed only under structural stability and the resulting elastic deformation experienced by each nanotube. The proposed mechanism reveals the available mechanical range wherein the polarized ionic layers can substantially function in chemomechanical energy conversion.