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

Abstract

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 (MnO 2 ) fabricated by introducing ramsdellite (R-MnO 2 ) and Mn vacancies into birnessite (δ-MnO 2 ) nanosheets, which in situ grew on the surface of a nickel (Ni) film, forming a hybrid MnO 2 /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-MnO 2 with a high density of sodium ion (Na + )-accessible lattice tunnels, Mn vacancies, and also a high Young's modulus of the hybrid MnO 2 /Ni composite. Besides, the cyclic stability of the actuator was realized after 1.2 × 10 4 cycles of electric stimulation under a frequency of 0.05 Hz. The finding of the novel hybrid MnO 2 /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.

Adjusting Competitive Reaction to Control Nucleation and Growth of MnO2 for a High-Stress Output Electrochemical Actuator

“…Values of the transient strains and the theoretical actuating stresses of the CRD-MnO 2 /Ni film were calculated and are shown in Figure c. The intrinsic strain reached 8.3% after 60 s of voltage stimulation, and the actuating stress tended to be 390.1 MPa, which is much larger than those of the MnO 2 -based actuators. − The comparison of the intrinsic strain and output stress with those reported electrochemical actuating materials − ,− in the literature is also shown in Figure d. It is worth mentioning that the energy density of the CRD-MnO 2 /Ni actuator is as high as 1.62 MJ m –3 when the power density is 27 kW m –3 (detailed in the Supporting Information), which is much larger than that of mammalian skeletal muscle (∼8 kJ m –3 ) and most of the electrochemical actuating materials ,,,, due to both the excellent strain and high Young’s modulus of CRD-MnO 2 .…”

“…Artificial muscle is a type of human-made actuation material or device that can generate force and cause motions, which is in great demand in the automation industry, drug delivery systems, rehabilitation devices, intelligent robots, etc. − MnO 2 has been proven to be one of the most promising electrochemical actuating materials with high-output stress, owing to its high Young’s modulus and large intrinsic strain during charging and discharging. The output stress remains far below the expectation for practical applications although some research concerning the electrochemical actuation behavior of the polymorphs of ε-MnO 2 , δ-MnO 2 , and R-MnO 2 has been reported recently. The maximum actuating stress of the MnO 2 -based electrochemical actuator was reported to be 244 MPa, whose improvement is due to introducing R-MnO 2 into δ-MnO 2 to generate an extra volume variation from cations insertion .…”

“…The Ni film was electrodeposited on the surface of the Ti plate in a two-electrode system as we reported previously. 6 As shown in Figures S1a−c in the Supporting Information, the Ti plate (working area of 30 × 15 mm 2 ) and a piece of Ni plate (20 × 20 mm 2 ) were used as the cathode and anode, respectively. The electrodeposition process was conducted in an aqueous solution containing NiCl 2 •6H 2 O (0.8 M), NH 4 Cl (0.7 M), and HBO 3 (1 M) at 60 °C under a current density of 30 mA cm −2 for 1200 s. Then, the surface of Ni was washed several times with deionized (DI) water to remove impurities, and the specimen was designated Ni/Ti (Figure S1c).…”

“…The maximum actuating stress of the MnO 2 -based electrochemical actuator was reported to be 244 MPa, whose improvement is due to introducing R-MnO 2 into δ-MnO 2 to generate an extra volume variation from cations insertion. 6 However, the actuation of MnO 2 mainly comes from the JT distortion of the [MnO 6 ] octahedrons. The unstable high-spin Mn 3+ in a degenerate electronic state undergoes geometrical distortion to form a system of lower symmetry, 7 leading to the elongation of the [MnO 6 ] octahedron along the z-axis and volume expansion.…”

Air‐Working Electrochemical Actuator and Ionic Sensor Based on Manganese Dioxide/Gelatin‐Glycerol Composites

“…Characterization by XRD and SAED reveals that the structure obtained had a low crystallinity similar to other MnO 2 actuating materials (Figure 1C). [24,27] The MnO 2 electrode itself can be actuated under a liquid electrolyte, and therefore can be regarded as an in-liquid actuator. By cyclic voltammetry (CV) (Figure 1D, under 0.5 m Na 2 SO 4 , 0 ↔1 V versus SCE, scan rate: 25 mV s −1 ), it actuated by curling when the potential was scanned toward 0.0 V to trigger the reduction reaction, where MnO 2 expands by MnO 2 + Na + + e − → MnOONa.…”