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

Abstract 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.