Highly efficient electrochemical kinetic energy harvesting using nanomaterials – KineHarvest

<General Objectives>
KineHarvest project aims to develop an electrochemical kinetic energy harvesting device that converts low frequency (0.1~10 Hz) mechanical energy from various kinetic movements such as the human body motions. We developed a new electrochemical energy harvesting cell with a hybrid structure (called hybrid cell) consisting of a supercapacitor electrode and a battery electrode. The kinetic to electrical energy conversion occurs by the selective ion sweeping effect on the supercapacitor electrodes when there is an electrolyte flow due to the kinetic input. Based on this novel design, we will investigate the application of nanomaterials to the electrolyte and the electrodes in order to enhance the ion sweeping efficiency and thus obtain the high output voltage of the hybrid cell. For this, we will study the fundamental principle of the flow-induced ion sweeping behavior by using the flow shear tomography technique that we recently developed.

<Challenges>
1. The current energy harvesting techniques based on triboelectricity or piezoelectricity are optimized for high frequency vibrations (20~500 Hz). However, the kinetic energies available in the life and environment (e.g. human movements, winds, ocean waves and tides, etc.) usually has a frequency lower than 10 Hz and non-continuous pulses. This low frequency range and irregular motions are poorly explored for energy harvesting, which is the target of the KineHarvest project.
2. The flow-induced ion sweeping phenomenon – the key principle of our energy harvesting system – is new and its mechanism is not yet understood. Technically, increasing the amount of sweeping ions effective to the kinetic input will improve the energy conversion efficiency. So far, there has been no experimental method to quantitatively assess the influence of ion sweeping on the electrochemical output. We will investigate this using the microfluidic shear profiling method that we recently invented. This technique is especially capable of a 3D flow shear tomography and a real-time monitoring of the fluctuating shear at the local site near the interface, which is highly suitable for correlating the hydrodynamic shear and the ion sweeping at the electrolyte-electrode interface. By understanding this fundamental principle, we will search for optimal nanomaterial components of electrolyte and the capacitive electrode design.
3. A key condition to achieve the maximum output voltage of the hybrid cell is the selectivity of the ion sweeping behavior only on the supercapacitor electrode. Therefore, at the opposite side of the supercapacitor electrode, it is essential to achieve a stable ion storage inside the ion hosting battery electrode during the flow. However, even ion hosting battery materials contain adsorbed ions on its surface which can be swept under the flow. It is thus necessary to understand how much portion of ion adsorption on the surface is contributing to the charge storage of the battery electrode materials and how to reduce its portion to diminish the ion sweeping effect on the battery electrode. We will do this study on the ion-hosting material of our choice (Prussian Blue Analogues, PBA) and reveal the optimal PBA particle morphology and its thin film electrode structure.

<Final goals>
Our target hybrid cell performance is the current density of 1 mA/cm2 under the human body kinetic input, which is one order of magnitude higher than that of the state of the art piezoelectric and triboelectric systems. The impedance for the maximum power output will be several tens of Ohm, which is also four to five orders of magnitude lower than the state of the art. Such a highly efficient kinetic energy harvesting principle will be applied to wearable self-powering devices and Internet of Things (IoTs) for portable gadgets by efficiently transforming the energy of all kinds of body motions and floating vibration to the electricity.