Bioinspired multifunctional self-powered ionic receptors derived by gradient polyelectrolyte hydrogels

Emerging ionic diode-based self-powered ionic devices are intriguing in mimicking human perceptual systems. However, challenges remain for their applications such as undesired delamination between diode components, single function of press perception, and limited stretchability and transparency caused by metal/carbonous electrodes. Herein, we demonstrate a versatile strategy for constructing multifunctional self-powered ionic receptors/sensors. The gradient polyelectrolyte hydrogel has been firstly demonstrated to hold a pressure-sensitive built-in potential analogous to ionic diodes, but can avoid their defect of delamination. The receptor is assembled by two stretchable ionic hydrogel electrodes and a sandwiched gradient polyelectrolyte hydrogel, resembling the structure of electrolyte/cell membrane/electrolyte of human receptors. Benefitting from such sandwich structure, the as-prepared self-powered receptors are highly transparent, stretchable, and multifunctional. They not only can sensitively perceive tiny pressure change based on the thickness-dependent potentials of gradient hydrogels, but temperature, salinity and pH stimuli according to the potential variations induced by thermodiffusion and salinity gradient. The strategy can inspire the design and fabrication of high-performance self-powered sensors consisting entirely of ionic conductors, contributing to the development of complex humanlike sensing systems in the future.