Electrochemical kinetic energy harvesting mediated by ion solvation switching in two-immiscible liquid electrolyte

Kinetic energy harvesting has significant potential, but current methods, such as friction and deformation-based systems, require high-frequency inputs and highly durable materials. We report an electrochemical system using a two-phase immiscible liquid electrolyte and Prussian blue analogue electrodes for harvesting low-frequency kinetic energy. This system converts translational kinetic energy from the displacement of electrodes between electrolyte phases into electrical energy, achieving a peak power of 6.4 ± 0.08 μW cm^-2, with a peak voltage of 96 mV and peak current density of 183 μA cm^-2 using a 300 Ω load. This load is several thousand times smaller than those typically employed in conventional methods. The charge density reaches 2.73 mC cm^-2, while the energy density is 116 μJ cm^-2 during a harvesting cycle. Also, the system provides a continuous current flow of approximately 5 μA cm^-2 at 0.005 Hz for 23 cycles without performance decay. The driving force behind voltage generation is the difference in solvation Gibbs free energy between the two electrolyte phases. Additionally, we demonstrate the system's functionality in a microfluidic harvester, generating a maximum power density of 200 nW cm^-2 by converting the kinetic energy to propel the electrolyte through the microfluidic channel into electricity.