Maximizing Performance of a Hybrid MnO2/Ni Electrochemical Actuator through Tailoring Lattice Tunnels and Cation Vacancies

Electrochemical actuators play a key role in converting electrical energy to mechanical energy. However, a low actuation stress and an unsatisfied strain response rate strongly limit the extensive applications of the actuators. Here, we report hybrid manganese dioxide (MnO2) fabricated by introducing ramsdellite (R-MnO2) and Mn vacancies into birnessite (delta-MnO2) nanosheets, which in situ grew on the surface of a nickel (Ni) film, forming a hybrid MnO2/Ni actuator. The actuator demonstrated a rapid strain response of 0.88% s(-1) (5.3% intrinsic strain in 6 s) and a large actuation stress of 244 MPa owing to the special R-MnO2 with a high density of sodium ion (Na+)-accessible lattice tunnels, Mn vacancies, and also a high Young's modulus of the hybrid MnO2/Ni composite. Besides, the cyclic stability of the actuator was realized after 1.2 x 10(4) cycles of electric stimulation under a frequency of 0.05 Hz. The finding of the novel hybrid MnO2/Ni actuator may provide a new strategy to maximize the actuating performance evidently through tailoring the lattice tunnel structure and introducing cation vacancies into electrochemical electrode materials.