Unveiling Ion Dynamics in the Electric-Double Layer Under Piezoionic Actuation of Chemo-Mechanical Energy Harvesters

Understanding the ion dynamics within the electric double layer (EDL) is crucial for maximizing the potential of chemo-mechanical energy harvesters. This study elucidates the electrochemical response of EDL to the compressive mechanical stimulation of carbon nanotube (CNT) yarns from the perspective of ion adsorption. The results revealed that H₃O⁺ contributed to the ionic capacitance of the EDL by forming a polarized layer with Cl⁻ on the outer Helmholtz plane. The unique molecular shape, compatible with sp^x hybridized orbitals of CNTs also enhance surface adsorption properties. In contrast, Cl⁻ provides a strong electrostatic potential to the electrode, which has electronic structures incompatible with the sp^x hybridized orbitals of CNTs. The differing dynamic behaviors of these two ions jointly induce delamination of the cationic and anionic layers, as well as unipolarization of the EDL under mechanical compression of the microstructure. The ion dynamics revealed by multiscale simulations satisfactorily explain the experimentally observed high ion capacitance and energy conversion process of the HCl-based EDL.