Reversible electrochemical actuation of metallic nanohoneycombs induced by pseudocapacitive redox processes

Current metallic-based electrochemical actuators are limited to nanoporous gold/platinum with randomly distributed pores, where the charge-induced reversible strain is mainly due to the nonfaradic charging/discharging processes along the capacitive electrochemical double layer. Here, we report an electrochemical actuating property of nanohoneycomb-structured nickel, with the actuation mechanism mainly due to a pseudocapacitive behavior by means of reversible faradic redox reactions. By using a dual-template synthesis method, a bilayered cantilever, comprising a nanohoneycomb layer backed by a solid layer of the same metal, was fabricated. Reversible bending of the cantilever upon cyclic potential triggering was observed. The strain of the cantilever increases nonlinearly with both potential and charge due to redox reactions. The maximum strain that can be achieved under a certain scan rate complies with a linear relationship with the capacity. Benefiting from the stable Ni(II)/Ni(III) redox couples at the electrode surface, the reversible actuation is very stable in hydroxide solutions.