Simultaneous enhancement of actuation strain and mechanical strength of nanoporous Ni–Mn actuators

Metallic 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.