Electrochemical actuation of nickel hydroxide/oxyhydroxide at sub-volt voltages

•Bilayered Ni and Ni(OH)2/NiOOH electrochemical actuator that functioned in NaOH solution bath and powered by sub-volt voltages is introduced.•The actuator can be actuated to 70% device strain.•The fabrication mainly involves two electrodepositions that can be accomplished in less than an hour.•A compact assembly of the actuators that can be actuated in air is demonstrated.•Actuators of various shapes and actuation performance are demonstrated.

The development of materials capable of actuating at low triggering voltages is crucial for applications such as compact prime movers for soft, micro robots. In this paper, the electrochemical actuation of Ni(OH)2/NiOOH in alkaline environment at low voltages is demonstrated and studied for the first time. Specifically, sub-micron layers of Ni(OH)2/NiOOH deposited on Ni films a few microns thick by anodic electrodeposition were found to undergo reversible contraction by ∼0.1% in an alkaline solution under a low voltage of only ∼0.4 V, causing a 5-mm long bi-layer actuator to bend by ∼3.5 mm at its end, giving a large device strain of ∼70%. The actuation mechanism is found to be due to a redox reaction in the Ni(OH)2/NiOOH couple. By masked electrodeposition, successful fabrication of actuators of various shapes and actuation performance was also demonstrated. The required electrolyte can be packaged with the actuating material to achieve a stand-alone actuating device.