A Seamlessly Integrated Sandwich‐Structured Hydrogel for Supercapacitors and Multimodal Wearable Sensors Enabling Information Transmission

Abstract The sandwich‐structured hydrogel devices are emerging as promising candidates for flexible supercapacitors (SCs) and wearable sensors. However, their development is hindered by the interfacial challenges, including weak adhesion, high interface resistance and relative slippage phenomena. Herein, this study reports a robust sandwich‐structure polyaniline–polyvinyl alcohol (PVA) hydrogel fabricated via layer‐by‐layer in situ deposition technology. The strong interfacial bonding arises from the shared PVA component in each layer and dynamic interactions including reversible borate ester and hydrogen bonds. The integrated hydrogel demonstrates excellent mechanical performance with a tensile strength of 9.20 MPa and an elongation at break of 367%. As an all‐gel SC, the device exhibits a high areal capacitance of 1604 mF cm ⁻² and energy density of 142.60 µWh cm ⁻² , and retains 95% capacitance after 1000 GCD cycles. Moreover, the hydrogel‐based strain sensor can monitor a wide range of human motions in real time. Leveraging this capability, a medical nursing system is developed that uses Morse code signals from finger movements for real‐time communication and remote diagnosis, assisting both patients and healthcare providers. This work offers an effective strategy for fabricating robust, layered hydrogels for use in energy storage and smart wearable electronics, with potential applications in motion monitoring, data transmission, and telemedicine.