Electrochemical Actuators Based on Two-Dimensional Ti₃C₂T_x (MXene)

Abstract

Electrochemical actuators are devices that convert electrical energy into mechanical energy via electrochemical processes. They are used in soft robotics, artificial muscles, micropumps, sensors and other fields. The design of flexible and stable electrode materials remains a major challenge. MXenes, an emerging family of 2D materials, have found applications in energy storage. Here, we report an actuator device using MXene (Ti3C2Tx) as a flexible electrode material. The electrode in 1 M H2SO4 electrolyte exhibits a curvature's change up to 0.083 mm-1 and strain of 0.29%. Meanwhile, the MXene-based actuator with a symmetric configuration separated by gel electrolyte (PVA-H2SO4) has curvature and strain changes up to 0.038 mm-1 and 0.26% with excellent retention after 10,000 cycles. In-situ X-ray diffraction analysis demonstrates that the actuation mechanism is due to the expansion and shrinkage of the interlayer spacing of MXenes. This research shows promise of this new family of materials for electrochemical actuators.

Stimuli‐Responsive MXene‐Based Actuators

“…While many materials, including graphene, MoS 2 , CNT, and conducting polymers have been intensively used in electrochemical actuators, MXenes are newcomers in this field. [21,26,33,45,46,79,80,120,121] The mechanism for such actuators is straightforward. For many conducting polymers, oxidative and reductive reactions occur, converting these polymers into polyions.…”

“…[21,45,46,79,120] However, if the middle layer in the trilayer structure is a polymer electrolyte membrane, the corresponding actuators can work in air (Figure 12d). [26,123] Building on the benefits of the previous study, Yu Gao et al first reported Ti 3 C 2 T x -based electrochemical actuators, both bilayer and trilayer structures (Figure 12a,d). [26] These two structures were made of Ti 3 C 2 T x flexible freestanding films, which were prepared by vacuum filtering the MXene suspension.…”

“…It has been proved via in situ atomic force microscopy (AFM), topography, and x-ray diffraction (XRD) that MXenes enable many cations to be electrochemically intercalated among layers, thereby changing the volume, which can be good for actuators using electrical stimulants (Figure 2). [26,27,57,71,72] Reasons for intercalation could be the negatively charged surfaces (zeta potential of the colloidal solution: −39.5 mV) and polar functional groups of Ti 3 C 2 T x MXene. [73,74] While theoretical calculations via density functional theory (DFT) initially anticipated that lithium cation could diffuse on the surfaces of Ti 3 C 2 T x , most practical MXene synthesis processes now require intercalation with small cations or polar organic solvents as a key synthetic step to enlarge the interlayer spacing and weaken the interaction among MXene layers.…”

“…[21,46,[78][79][80] Although MXenes are relatively new in the field of actuators and there has been only one report applying these materials to wet-type actuators, their intercalation property with volume change, and the fact that increasingly more types of MXenes are being synthesized, could advance in soft actuators with increase in bending deformations. [6,26] While cation intercalation is limited to electroactive wet-type actuators, ionic liquid intercalation could extend to dry-type counterparts that can operate in open-air atmosphere. [37,[81][82][83] Figure 2.…”

Recent Advances in Photoactuators and Their Applications in Intelligent Bionic Movements

“…Owing to the advances in natural smart systems, numerous responsive materials that can transform dynamic and reversible shape deformations into locomotions have emerged under various external stimuli such as light, [1][2][3][4][5] humidity, [6][7][8][9][10][11][12] electric field, [13][14][15][16][17][18] organic solvents, [19][20][21] heat, [22] magnetism, [23][24][25] or a combination of multiple types of stimuli thereof. [26][27][28][29][30][31][32][33][34] Such materials exhibit the potential for applications in soft robotics, artificial muscles, and smart devices.…”