Gradient p-Polyanion/n-Polycation Heterojunction Endows Ionic Diodes with Vastly Boosted Output Voltage, Power Density and Sensitivity

Ionic diode-based generators show great superiority in harvesting low-frequency mechanical energy from human motions for various wearable applications. The major challenge is to improve their extremely limited output voltage for the miniaturization/simplicity of ionic diode-based self-powered devices as well as further improvement of mechanoelectric conversion performance. Herein, the construction of gradient polycation/polyanion heterojunction is demonstrated to vastly boost the output voltage, energy-harvesting efficiency, and sensing performance of ionic diode. Besides an inherent potential at the polyanion/polycation heterojunction interface, the additional transmembrane potentials can be generated across gradient polyanion and polycation conductors of ionic diodes due to their gradient charge distribution. Consequently, the gradient ionic diode-based generators produce much higher output voltage (306.53 mV) than previously reported homogeneous ones (4.1–135 mV). Meanwhile, the high output voltage imparts gradient ionic diode-based generator with ultrahigh power density (50.16 µW cm − 2 or 250.8 µW cm −3 ) and pressure-perception sensitivity (43582 mV/MPa), which are dramatically increased by 162.76% and 128.71%, respectively, compare to those of homogeneous one. Impressively, the resulting diode-based generators can generate ultralarge current density (≈0.52 mA cm −2 ) with ultralong discharge time (>400 s), thus enabling the continuous power generation under the low-frequency pressure for various wearable and implantable applications.