Biocompatible and Flexible Hydrogel Diode-Based Mechanical Energy Harvesting

Energy harvesting devices which convert low frequency mechanical energy sources such as human motions and ocean waves into electricity are attractive for powering portable devices and for green-energy generation. To date the state-of-the-art mechanical energy harvesting devices can only work efficiently at high vibration frequencies. Here, a biocompatible and flexible mechanical energy harvesting device is reported utilizing ionic diode as the transducer. This device utilizes the redistribution of cations and anions at the two hydrogel electrodes under stress to convert mechanical energy to electricity. It is shown that the device can be operated at low frequencies with high output current, e.g., 13.5 µA cm⁻², owing to the high ion concentration and unique working mechanism of the device. Moreover, the output current density and power density can be improved further by employing a multilayer configuration. By stacking five units with parallel structure, the hydrogel diode device can generate an output current of 64.3 µA cm⁻² and power density of 0.48 µW cm⁻². Considering the very high electric energy density of ionic devices, the hydrogel energy harvesting device demonstrated herein paves a way for efficient mechanical energy harvesting from many common low frequency sources.