Fast and Reversible Actuation of Metallic Muscles Composed of Nickel Nanowire‐Forest

Abstract

Surface-charge-induced reversible and millimeter-scale deflection is found in a bilayered Ni cantilever upon cyclic potential triggering. The nanowire-forest structure, in which unidirectional primary nanowires are evenly separated by cross-linking subnanowires, ensures fast ion transport leading to a record-high strain response time ≈0.1 s. The actuation is sustainable beyond 800 cycles; the strain energy is compatible with human skeletal muscles.

The Origin of Electrochemical Actuation of MnO2/Ni Bilayer Film Derived by Redox Pseudocapacitive Process

“…They are all Faradaic in nature, and owing to this mechanism, pseudocapacitive materials are generally capable of a greater deformation compared with carbon materials. Thus, pseudocapacitance‐induced EC‐actuators are getting more and more attention in recent years . Specifically, underpotential deposition refers to the monolayer adsorption of metal ions (or protons) and hydroxyl ions on the surface of metals when the deposition potential is less negative than the equilibrium potential.…”

“…Compared to conductive polymers, metal oxides have higher Young's modulus, which is expected to achieve a greater deformation. Nickel based oxide or hydroxide bilayer structures obtained by multistep electrochemical deposition are reported in EC‐actuator with sub‐volt deformation voltages . Nickel based materials usually exhibit battery‐like charge and discharge (a pair of obvious redox peaks appears at a specific voltage) rather than capacitive behavior, and this lower kinetic performance may limit their actuation performance.…”

Dealloying at High Homologous Temperature: Morphology Diagrams

“…Morphology evolution was studied under conditions of fixed dealloying potential and fixed current density and our results are summarized by the introduction of dealloying morphology diagrams that reveal the electrochemical conditions for the evolution of the various morphologies. Today electrochemical dealloying processes are used to design nanostructures for a variety of functions encompassing electrocatalysis 1-3 and biosensors 4-7 with additional applications being explored such as actuation [8][9][10][11] and structural composites. 12-14 To date, the targeted nanoscale morphologies include bi-continuous structures such as nanoporous gold (NPG) formed by a percolation dissolution mechanism 15-18 and so-called skin or core-shell nanoparticle structures, formed by a passivation-like process.…”

Nanoporous Metals with Structural Hierarchy: A Review

“…[102] The strain amplitude may be amplified in microstructures with multiple length-scales. [164] Yet, the switching time for actuation with larger nanoporous metal bodies is limited by the time required for the electrical migration of ions into the pore space. [122] Thin films of nanoporous metal can actuate with switching times well below one second.…”

“…[122] Thin films of nanoporous metal can actuate with switching times well below one second. [164] Yet, the switching time for actuation with larger nanoporous metal bodies is limited by the time required for the electrical migration of ions into the pore space. This is another instance where hierarchical structuring may be beneficial, since small pores at the lower hierarchy level may afford the required large specific surface area while larger pores at an upper hierarchy level may accelerate the transport.…”