Separator with high ionic conductivity and good stability prepared from keratin fibers for supercapacitor applications

• Keratin-based solution has good fiber-forming ability. • Post-functional strategy by glutaraldehyde (GTA) has two functions. • A novel keratin-based separator with high ionic conductivity and good stability. • Device with keratin-based separator exhibits outstanding electrochemical performance. Keratin is one of natural polymers with super wettability, which is an alternative sustainable polymer to fabric separators for high-performance supercapacitors (SCs). However, the extracted keratin has poor fiber-forming ability, and it remains challenging to prepare high performance keratin-based separators. In this study, to overcome the conflict between good mechanical strength and high ionic conductivity, keratin-based nanofiber membranes were prepared by electrospinning and glutaraldehyde (GTA) post-function strategy, which endow high mechanical strength (7.87 MPa) and high ionic conductivity (2.21 mS/cm) to keratin-based membranes (KMs-8). The FTIR and XRD approved that GTA treatment has two functions, i.e., cross-linking reaction and oxidation reaction, which endow the membranes with connected crosslinking sited structure and with hydrophilic groups in comparison with unfunctionalized membrane. As expected, the SCs with KMs-8 separator exhibit outstanding electrochemical performances with high specific capacitance (173.68F g −1 ) and good cyclic stability (98.1% at 8000 cycles). This research provides new insight into the design of keratin-based separator for SCs, which will broaden the application range of keratin and suggest a sustainable natural polymer for the utility for energy-related devices.