High-performance cellulose nanofibers-based actuators with multi-stimulus responses and energy storage

Smart actuating materials have received tremendous attention due to their promising applications in miniaturized robots, integrated electronics and wearable devices. However, simultaneously achieving sensitive multi-stimuli responsiveness, preferable energy storage capability and adequate mechanical properties by one material in a simple yet efficient way remains a considerable challenge. Herein, we propose a novel multi-responsive nanocomposite film actuator consisting of negatively charged cellulose nanofibers (CNF), polydopamine-chelated MXene-Fe 3 O 4 nanohybrids (PMF) and positively charged carbon nanotubes (CCNT) via a cost-efficient electrostatic self-assembly approach. Benefiting from the laminated porous structure and compositional superiorities, including the water-induced swelling effect of CNF and PMF, conductive CCNT with countless interior hydrophobic channels and magneto-conductive properties of PMF, the optimized nanocomposite film actuator presents a high bending speed (100.5°/s), ultrashort actuation time (2.0 s), long-term stability (1005 cycles) and good magnetic response. These actuators can be assembled into a supercapacitor exhibiting an areal capacitance of 33.5 mF/cm 2 at 0.5 mA/cm 2 and good cycling stability with a capacitance retention of 80.5 % after 5000 cycles. Furthermore, the actuators are designed as soft robots with different motion modes, mechanical grippers for performing consecutive actions and an integrated circuit system to monitor surrounding humidity changes. This work provides inspiration to develop advanced nanocomposite materials for smart devices that require multifunction integration.