Synchronised regulation of the hydrophilicity and microstructure of CNT/PANI film electrodes ensure electrochemical ionic actuators with ultra-long cycle performance

Electrochemical ion actuators (ECIAs), a novel soft smart robotics technology, can effectively convert electrical energy into mechanical energy via electrochemically induced ion migration. The behaviors of ECIAs mainly depends on the electrochemical storage capacity of the electrodes, but the electrochemical instability of the electrodes directly result in poor lifetime of ECIAs. Herein, we successfully designed and prepared a novel flexible free-standing carbon nanotube/polyaniline (CNT/PANI) film via the in-situ electro-polymerization of PANI on CNT films for ultra-long cycle performance ECIAs. Unlike conventional CNT or PANI electrodes, the developed CNT/PANI composite film offers a unique synergistic effect combining the electric double-layer capacitance of CNTs and the pseudocapacitance of PANI. The in-situ electro-polymerization method enables uniform PANI deposition within the CNT network, forming a tightly bonded, three-dimensional structure with enhanced ion accessibility and interfacial contact. The CNT/PANI film electrodes have excellent hydrophilicity and affinity to ionic liquid, which enhances the adhesion between electrode and electrolyte layers and facilitates the migration of hydrophilic ions (EMI+ and BF4-). Meanwhile, the in-situ electropolymerized PANI materials can improve the ion storage capacity of the CNT/PANI film electrodes, which in turn enhances the actuation abilities of the ECIAs. Consequently, the ECIAs based on the A-CNT/PANI film electrodes not only perform excellent electromechanical performance (strain 0.97%, stress 7.07 MPa), but also give an ultra-high cycling stability of up to 100,000 cycles. Our findings demonstrate a robust, flexible electrode design that mitigates common challenges in the integration of pseudocapacitive materials, ensuring stability and superior long-term performance in ECIAs.