A multifunctional droplet energy harvester enabled by ionogel electrodes

Droplet energy harvesters (DEH) have been undergoing extensive structural design and composition innovation to enhance their performance. However, the rigidity or opacity of traditional electronic conductors has limited their practical application. Despite the well-established equivalent circuit models for qualitatively understanding device operation, a comprehensive in-situ quantitative analysis of the dynamic process remains lacking. Herein, we present an ionogel-based DEH (i-DEH) featuring high transparency, flexibility, scalability, robustness, and versatility to mount on various substrates in flat/curved states. Compared to a conventional aluminum-based device as the control, i-DEH with an identical configuration demonstrated a 1.2-fold output voltage and current and achieved a remarkable power density of 67.1 W/m² with a 40-µL droplet, representing a 2.24-fold enhancement. For the first time, static and dynamic electrochemical impedance spectroscopy was utilized to elucidate the underlying mechanism. Moreover, we demonstrated a potential application scenario of i-DEH in a smart farm, including hybrid energy harvesting and self-powered acid-rain monitoring. This study provides fundamental insights into the understanding of ionogel-based DEH systems.