Design And Preparation Of Ionic Diode-based Self-powered Ionic Skin For Multifunctional Application

With the development of bionics,artificial electronic/ionic skin which can imitate human skin to perceive the external environment and monitor human physiological activities,has attracted extensive research and attention.Among them,biomimetic ionic skin exhibits better compatibility due to its mechanical properties similar to biological tissues and the same signal transmission carrier（ions）as living organisms.Ionic diodes consisting of a pair of polycation and polyanion ionic conductors that can efficiently harvest electricity from low-frequency mechanical stimuli/human motions,have emerged as promising materials for self-powered I-skins.However,there exist several barriers towards their practical applications.Firstly,the mechanoelectric conversion mechanism of the ionic diode-based self-powered devices is not well understood.Secondly,the transparency and stretchability of devices are limited.Thirdly,the reported diode-based devices present the singular function of pressure perception.In order to solve the above problems,this paper designed ionic diode-based self-powered I-skins for the perception of multiple stimuli and revealed its mechanoelectric conversion mechanism.The main research results are listed as follows:1.In this paper,highly transparent and stretchable（>500%）ionic diode-based self-powered I-skins were prepared,using sodium alginate（SA）,chitosan（CS）and acrylamide（AM）.The self-powered I-skins can be assembled with two stretchable ionic hydrogel electrodes and a sandwiched hydrogel-based ionic diode,which can quickly respond to pressure and strain stimuli with high sensitivity and wide detection range.Besides,the self-powered I-skin can detect ionic concentration(10^-5M-10 M),and p H with high sensitivity,based on the potential variations induced by salinity gradient.Furthermore,based on experimental results and theoretical exploration,we demonstrate that the mechanoelectrical conversion of our I-skins lie on the thickness-dependent self-induced potentials of ionic diodes（Mechanism I）and varying potential losses at the diode/electrode interfaces under mechanical stimulation（Mechanism II）,providing a certain theoretical basis for the development of ionic diode-based self-powered devices.2.In order to explore the application of ionic diodes in the field of low-frequency mechanical energy harvesting,gradient polyanion/polycation hydrogel films wereprepared by copolymerization of sodium 2-acrylamide-2-methylpropane sulfonate（AMPS）and acryloyloxyethyltrimethylammonium chloride（ATAC）with acrylamide（AM）under an external electric field（1.5 V）to assemble ionic diodes.The ionic diode exhibits high output voltage（>300 m V）and high rectification ratio（13.2）,and its output power density reaches up to 5.22μW·cm^-2under 0.25 MPa pressure stimulation with an low-frequency of 0.5 Hz.In addition,the ionic diode has high compression sensitivity（336.45 m V/MPa）and excellent cycling stability（>500 cycles）when used as a pressure sensor.It can respond quickly when pressure is applied/released,and can sense static stimuli.3.In order to overcome the defects of dehydration at high temperature and freezing at low temperature of hydrogel,polyanion（P（SPAK-co-AM））and polycation（P（APTQ-co-AM））eutectogels were prepared to construct eutectogel ionic diode by solvent replacement method,using potassium 3-sulfopropyl acrylate（SPAK）,（3-acrylamidopropyl）trimethylammonium chloride（APTQ）and acrylamide（AM）.The eutectogel ionic diode is soft and stretchable（～900%）,showing excellent drying resistance（200℃）and frost resistance（-60℃）.Besides,it can be used as a self-powered sensor to accurately sense different pressures ranging from 0.25 to 25 k Pa and different strains ranging from 10%to 300%.Moreover,its sensing sensitivity has high stability at different temperatures（50℃,room temperature,-20℃）,promoting the long-term stable operation of ionic diode-based self-powered bionic skins in harsh environments.