Electric Field-Induced Dual-Gradient Heterojunction Diodes Toward Ultrasensitive Self-Powered Ionic Skin

The hydrogel ionic diode is regarded as a promising self-powered sensor, capable of harvesting energy from low-frequency stimuli human motions and converting it into electrical signals. However, the sensitivity of the reported conventional bilayer hydrogel ionic diodes are relatively low, due to the single heterojunction interface and high interface resistance, making it challenging to meet the demands of high-precision sensing. Here, a universal method for fabricating dual-gradient hydrogel ionic diodes without bilayer structure through the induction of anionic and cationic polymer gradient distribution via a direct current electric field is developed. Due to the dual-gradient distribution, numerous heterogeneous microstructures (i.e., microdiodes) with low interface resistance are formed in the bulk phase of hydrogel, and these series-connected microdiodes demonstrate a significantly increase in open circuit voltage in response to mechanical pressure. The dual-gradient hydrogel ionic diode exhibits ultra-high sensitivity (1247.3 mV/MPa) and ultralow detection limit (0.8 Pa), enabling the smart prosthetic hand to non-destructive grasp ultrasoft tofu. This work is expected to pave the way for novel high-precision self-powered sensors in intelligent wearable electronics.