High-performing, linearly controllable electrochemical actuation of c-disordered δ-MnO2/Ni actuators

Abstract

Electrochemical actuating materials that can generate mechanical motions in response to low voltage stimuli are useful as artificial muscles in micro- or insect-scale robots. However, such materials tend to have small actuation strain and stress, slow actuation response rate, and poor motion controllability, and they often require alkaline electrolytes to operate. Here, we demonstrate and analyse the electrochemical actuation properties of c-disordered δ-MnO₂ due to a volume-changing pseudo-capacitive redox reaction, with outstanding actuation performance and maneuverability in the neutral electrolyte of Na₂SO₄. An electrochemo-mechanical model well describes quantitatively the intrinsic actuation properties of δ-MnO₂ and the bending motion of bilayered cantilever actuators comprising an active layer of δ-MnO₂ supported by a Ni thin-film substrate. Upon changing the potential between −0.2 and 0.8 V vs. SCE in Na₂SO₄, δ-MnO₂ exhibits an electrochemical driving force of (5.39 ± 0.40) × 10⁻²³ J and activation volume of (6.26 ± 0.40) × 10⁻³¹ m³ for the actuation at 298 K, and a maximum strain of 1.28%, an actuation stress of 71.5 MPa, and a maximum energy density of 2.76 MJ m⁻³, indicating its high potential to be utilized as a strong artificial muscle material in multi-functional miniaturized actuating devices.