Expanded Carbon Nanotube Fiber at the Liquid–Air Interface for High-Performance Fiber-Based Supercapacitors and Electrochemical Sensors

Carbon nanotube fibers (CNTFs) are widely utilized in flexible and wearable electronics due to their outstanding electrical and mechanical properties. However, the spinning process of CNTFs has limited the CNTs from exposure, leading to an ultralow usage efficiency of individual CNTs. Here, we propose an electrochemical expansion strategy of a single CNTF at the liquid–air interface, forming a macroscopic spindle-shaped CNTF (SS-CNTF) with an enlarged volume of up to 5000-fold upon the spindle. The obtained spindle-shaped structure endows CNTF with a high specific surface area together with excellent conductivity and good mechanical properties. Therefore, the SS-CNTF-based devices exhibit outstanding performances both in energy storage (electrical double-layer supercapacitor, energy density: 11.22 Wh kg–1, power density: 203.9 kW kg–1) and electrochemical sensing (ascorbic acid: 1.26 μA μM–1 cm–2; dopamine: 103.91 μA μM–1 cm–2; uric acid: 11.53 μA μM–1 cm–2). The novel architecture of SS-CNTF prepared by one-step electrochemical expansion at the liquid–air interface enabled its high performance in multiple applications, providing new insight into the development of CNTF-based devices.