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Item type:Publication, Access status: with files , Robust metallic actuators based on nanoporous gold rapidly dealloyed from Gold–Nickel precursorsDealloyed nanoporous gold (np-Au) has applications as oxygen reduction catalysis in Li-air batteries and fuel cells, or as actuators to convert electricity into mechanical energy. However, it faces the challenges of coarsening-induced structure instability, mechanical weakness due to low relative densities, and slow dealloying rates. Here, monolithic np-Au is dealloyed from a single-phase Au25Ni75 solid-solution at a one-order faster dealloying rate, ultra-low residual Ni content, and importantly, one-third more relative density than np-Au dealloyed from conventional Au25Ag75. The small atomic radius and low dealloying potential of the sacrificing element Ni are intrinsically beneficial to fast produce high relative density np-Au, as predicted by a general model for dealloying of binary alloys and validated by experiments. Stable, durable, and reversible actuation of np-Au takes place under cyclic potential triggering in alkaline and acidic electrolytes with negligible coarsening-induced strain-shift. The thermal and mechanical robustness of bulk np-Au is confirmed by two-order slower ligament coarsening rates during annealing at 300 °C and 45 MPa macroscopic yielding strength distinctive from the typical early onset of plastic yielding. This article opens a rich direction to achieve high relative density np-Au which is essential for porous network connectivity, mechanical strength, and nanostructure robustness for electrochemical functionality.Publicationtype: Journal ArticleScopus© Citations 22 74 159 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Simultaneous enhancement of actuation strain and mechanical strength of nanoporous Ni–Mn actuatorsMetallic electrochemical actuators convert electrical energy into mechanical energy via charge-induced strain at the nanoporous metal/electrolyte interface. To enhance the actuation amplitude, a general choice is to increase the electrode surface area to elevate the charge capacity. However, a large surface area is detrimental to the actuation stability and mechanical strength of the actuator, such as irreversible volume shrinkage due to surface coarsening. Here, this critical issue can be mitigated by introducing a secondary actuation metal (Mn) into the network of a primary actuation metal (Ni). A nanoporous Ni–Mn actuator is synthesized by chemical dealloying with a controllable Mn content by adjusting dealloying conditions. Mn enriched nanowires are entangled with much larger sized Ni nanoligaments throughout the whole nanoporous network. Mn contributes a two-electron-transfer redox of Mn(OH)2/MnOOH/MnO2, which induces reversible volume change via H+ intercalation/deintercalation. It is more efficient for strain generation than a one-electron-transfer redox of Ni(OH)2/NiOOH in the host. A recorded high reversible strain of 1.94% is obtained. Simultaneously, the mechanical strength of the actuator exponentially increases with the relative density due to the introduction of the secondary actuation metal.Publicationtype: Journal ArticleScopus© Citations 14 98 142 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Electrochemical mechanics of metal thin films : charge-induced reversible surface stress for actuation(2020-01-01); ; The intrinsic charge-induced surface stress of Ni thin films during electrochemical reactions with an alkaline electrolyte is measured in situ. Surface stresses induced by H absorption/desorption, α-Ni(OH)2 formation, capacitive double-layer charging, the α- to β-Ni(OH)2 transformation, and β-Ni(OH)2/β-NiOOH redox reactions are identified, and each provided additive contributions to the overall stress state. Surface stresses are magnified in high-surface-area nanoporous Ni because local stress-relaxation mechanisms are restricted when compared to a smooth Ni film. Ni film reversible tensile/compressive surface stresses correlate with anodic/cathodic potential scanning but with an opposite trend to that of a less reactive Au film. Surface stresses in the Ni films are up to 40 times that of Au films and suggest the possibility of using controlled surface-stress generation for electrochemical actuation.Publicationtype: Journal ArticleScopus© Citations 14 194 219 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Semiordered hierarchical metallic network for fast and large charge-induced strain(American Chemical Society (ACS), 2017-07-27); ; ; ; Nanoporous metallic actuators for artificial muscle applications are distinguished by combining the low operating voltage, which is otherwise reserved for polymer-based actuators with interesting values of strain amplitude, strength, and stiffness that are comparable of those of piezoceramics. We report a nanoporous metal actuator with enhanced strain amplitude and accelerated switching. Our 3D macroscopic metallic muscle has semiordered and hierarchical nanoporous structure, in which μm-sized tubes align perpendicular with the sample surface, while nm-sized ligaments consist of the tube walls. This nanoarchitecture combines channels for fast ion transportation with large surface area for charge storage and strain generation. The result is a record reversible strain amplitude of 1.59% with a strain rate of 8.83 × 10-6 s-1 in the field of metallic based actuators. A passive hydroxide layer is self-grown on the metal surface, which not only contributes a supercapacitive layer, but also stabilizes the nanoporous structure against coarsening, which guarantees sustainable actuation beyond ten-thousand cycles.Publicationtype: Journal Article147 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Fast and reversible actuation of metallic muscles composed of nickel nanowire-forestA study is conducted to demonstrate fast and reversible actuation of metallic muscles composed of nickel nanowire-forest. The synthesis approach creates a mechanically strong 3D network with overall dimensions of centimeters. Energy dispersive X-ray spectroscopy shows that Ni is the dominate element within the bilayered Ni, with a slight amount of Co possibly due to the impurity of the electrodeposition solution, and O due to the formation of a passive film Ni(OH)2 on the Ni surface when template was selectively removed by 1 M NaOH solution. The electrochemical actuation has been characterized by an in situ experimental setup.Publicationtype: Journal Article124