Electrochemical actuation behaviors of bulk nanoporous copper with a hierarchical structure

Nanoporous metals have been used as electrochemical metallic actuators to generate large charge-induced strain at the electrode/electrolyte interface for twenty years. However, the high material cost greatly limits the practical application of metallic actuators. Herein, we fabricated a low-cost and unique hierarchically structured nanoporous Cu (np-Cu) with a millimeter scale by chemical dealloying (CD) and electrochemical dealloying (ECD) of an Mn0.7Cu0.3 precursor with a two-phase dendrite microstructure. Compared to np-Cu (CD), np-Cu (ECD) achieves a larger strain amplitude in a 1 M NaOH solution. The strain amplitude of np-Cu (ECD) could reach 0.12 %, which is comparable to the reported value for noble np-Pt and the commercial ferroelectric ceramics. The finer nanoporous structure with a more curved electrode/electrolyte surface is essential to generate larger strain amplitude. Additionally, the strain amplitude is influenced by both the charging time and the fluid resistance, and the strain rate can be improved by the unique hierarchically porous structure. These findings indicate that the low-cost np-Cu has great potentials for the application of electrochemical actuators.