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

Abstract

Pseudocapacitance-induced electrochemical actuators (EC-actuators) have attracted great attention in robots and artificial intelligence technologies.Despite major efforts to design such EC-actuators, a molecular-level understanding of the deformation mechanism is still lacking. Here, a reversible deformation of a freestanding MnO 2 /Ni bilayer film is demonstrated and in situ electrochemical atomic force microscopy, in situ Raman spectroscopy, and density functional theory simulation are used to study the origin of the deformation. The results show that the electrochemical actuation of the MnO 2 /Ni film is highly related with the redox pseudocapacitive behavior of MnO 2 layer. Valence state variation of Mn element, shortening and lengthening of MnO bond, and insertion and extraction of Na + ions, which all result from the redox pseudocapacitance of MnO 2 during charging and discharging, eventually lead to the reversible contraction and expansion of MnO 2 morphology. Such action counters with the nonactive Ni layer, finally inducing the reversible deformation of the MnO 2 /Ni bilayer film. It is believed that the study can provide useful guidance to design better EC-actuators in the future.hope our study could provide useful guidance to design better EC-actuators in the future.

The Mechanical Effect of MnO2 Layers on Electrochemical Actuation Performance of Nanoporous Gold

“…The corresponding samples after electrochemical deposition was named as npg + x MnO 2 ( x is the cycles of MnO 2 deposition). The X-ray diffraction (XRD) pattern revealed that the obtained MnO 2 material in an electrochemical deposition manner was -MnO 2 (see Figure 1 a), consistent with the previous reports [ 37 ]. The crystal structure did not change after applying the electrochemical potentials.…”

“…The charge can be stored in the MnO 2 layer by the reversible redox reaction in a neutral electrolyte (Na 2 SO 4 ) during the electrochemical charge and discharge process according to Equation (2) [ 37 ]: …”

“…Liu et al [ 37 ] investigated a reversible deformation of a freestanding MnO 2 /Ni bilayer film by in situ electrochemical atomic force microscopy. They found that the valence state variation of Mn element, shortening and lengthening of the Mn–O bond, and insertion and extraction of Na + ions, led to the reversible contraction and expansion of MnO 2 morphology.…”

“…They found that the valence state variation of Mn element, shortening and lengthening of the Mn–O bond, and insertion and extraction of Na + ions, led to the reversible contraction and expansion of MnO 2 morphology. The change in distance between MnO 2 micrometer particles at the surface was evaluated as ~2% within a 1 V potential window from the Atomic Force Microscope (AFM) data by Liu et al [ 37 ]. The potential-induced expansion or contraction of the MnO 2 layer results from the change in surface stress.…”

Directed Printing and Reconfiguration of Thermoresponsive Silica‐pNIPAM Nanocomposites

“…This principle has been used to synthesize a large variety of functional materials that undergo reversible change in their size, shape, and corresponding physical properties . A pre‐requisite for fabricating such shape changing materials is physical or chemical binding of two (or more) layers of materials with dissimilar stimuli‐induced strains . Fabricating such anisotropic materials requires complex synthetic approaches, such as lithography, which limits the large scale applicability of these adaptive and responsive materials.…”