Electro-Responsive Breathing Transition of Conductive Hydrogel for Broadband Kinetic Energy Harvesting

Reclaiming kinetic energy from vibrating machines holds great promise for sustainable energy harvesting technologies. Nevertheless, the impulsive current induced by vibrations is incompatible with conventional energy storage devices. The energy-management system necessitates novel designs of soft materials for lightweight, miniaturized, and integrated high-frequency electrochemical devices. Here, this work develops a conductive hydrogel with an electro-responsive polymeric network. The electro-responsive breathing transition of the crosslinking points facilitates the expeditious formation of a localized electrolyte layer. This layer features an exceedingly high local charge density, surpassing that of a saturated electrolyte solution by an order of magnitude, and thus enabling rapid charge transport under the influence of an applied voltage. The micro-capacitor based on the gel exhibits record-high capacitance of ≈2 mF cm^-2 when the frequency of energy input reaches up to 10⁴  Hz. This work also demonstrates a prototype battery charger that harvests energy from a running car engine. This study presents a feasible strategy for waste energy recycling using integrated electrochemical devices, opening a new avenue for ambient energy management.