Multi-scale, multi-physics modeling of electrochemical actuation of Ni nanohoneycomb in water

Abstract

Recent experiments have shown that a composite cantilever structure comprising a Ni nanohoneycomb active layer, backed by a solid constraining layer of Ni, can exhibit bending in an electrolyte environment when a voltage is applied across the cantilever and electrolyte. In this work, a multi-scale, multi-field simulation approach is used to model such an electrochemical actuation behavior. Specifically, molecular dynamics simulations with reactive force-field potentials and a modified charge-equilibrium (QEq) method are used to calculate the surface stress built up in Ni(100) surface in contact with water electrolyte due to a voltage applied across the interface, as a result of capacitive charging of the double layer in the contacting electrolyte as well as redox reaction of the Ni surface. The calculated surface stress is then used as input in a meso-scale finite-element (FE) model to compute the actuating stress set up in a single hexagonal unit cell of the Ni nanohoneycomb structure. The single-unit actuating stress is eventually used in a continuum FE model at a larger scale, to calculate the bending of an entire bilayered cantilever which replicates experimental conditions. The actuation deflection of the bilayered nanohoneycomb nickel is predicted to be 41.4μm at 0.43V vs the point of zero charge (PZC), which corresponds to ∼0.48V vs saturated calomel electrode (SCE), and this is in excellent agreement with the experimental value of 45–62μm at a similar voltage vs SCE. This is the first successful attempt to simulate the electrochemical actuation of a real-sized, nano-porous metallic structure in an electrolytic environment.