Solid-State Double-Network Hydrogel Redox Electrolytes for High-Performance Flexible Supercapacitors

Reversibly Stretchable Organohydrogel-Based Soft Electronics with Robust and Redox-Active Interfaces Enabled by Polyphenol-Incorporated Double Networks

Hydrogel electrolytes as soft ionic conductors have been extensively exploited to establish skinlike and biocompatible devices. However, in many common hydrogels, there exists irreversible elongation upon prolonged stretching cycles and poor interfacial contact, which have significantly hindered their practical applications where long-term operation at large deformations is needed. Herein, multifunctional soft electronic devices with reversible stretchability and improved electrode/electrolyte interfaces are demonstrated by employing polyacrylamide-based double-network organohydrogel electrolytes soaked with a high content of tannic acid (TA) that affords multiple noncovalent interactions and redox activity. Performances of the TA-rich gels are evaluated for the first time in realizing shape-recoverable stretchable devices against repeated deformations to 500% strain, with superior gel-electrode interfaces exhibiting both intimate adhesion and boosted electrochemical capacitance of >200 mF·cm^-2. A maximal 4-fold higher capacitance can be achieved by introducing TA and ethylene glycol (EG) into hydrogels. Moreover, a soft electronic system consisting of stretchable supercapacitors and gel-based microsensors was demonstrated, in which the electronic performance of these devices can be well preserved after >1000 repeated cycles at strains of up to 200%, without obvious residual strain or electrode delamination. This could pave a route to the design of multifunctional gel networks tackling both the mechanical and interfacial issues in soft and biocompatible devices.

Nitrogen-Doped Nanoporous Anodic Stainless Steel Foils towards Flexible Supercapacitors

In this work, we report the fabrication and enhanced supercapacitive performance of nitrogen-doped nanoporous stainless steel foils, which have been prepared by electrochemical anodization and subsequent thermal annealing in ammonia atmosphere. The nanoporous oxide layers are grown on type-304 stainless steel foil with optimal thickness ~11.9 μm. The N-doped sample exhibits high average areal capacitance of 321.3 mF·cm⁻² at a current density of 1.0 mA·cm⁻², 3.6 times of increment compared with untreated one. Structural and electrochemical characterizations indicate that the significant enhancement is correlated to the high charge transfer efficiency from nitriding nanosheet products Fe₃N. Our report here may provide new insight on the development of high-performance, low-cost and binder-free supercapacitor electrodes for flexible and portable electronic device applications with multiple anions.