Charge-controlled compositional/microstructural regulations and electrochemical actuation performance of bulk nanoporous Ni-Pd alloys

Bulk nanoporous (np) metallic actuators have attracted increasing attention due to their large strain and low stimulation voltage. However, studies focusing upon the combined effect of composition and structure on the actuation performance of metallic actuators are relatively scarce, and its underlying mechanism needs to be clarified. Herein, a series of bulk np-NiPd samples with different compositions and microstructures were fabricated using a dealloying-coarsening-dealloying strategy and charge-controlled electrochemical dealloying, and the process involves only one component of precursor alloy. It has been found that the np-NiPd cubes show a composition/structure-dependent mechanical property and electrochemical actuation performance. Specially, the np-Ni₇₀Pd₃₀ sample with a homogeneously porous structure and good network connectivity exhibits significantly larger strain amplitude and faster strain rate than other hierarchically porous NiPd samples (np-Ni₅₀Pd₅₀ and np-Ni₂₀Pd₈₀). Moreover, the np-Ni₇₀Pd₃₀ sample demonstrates good actuation stability with high strain retention after hundreds of cycles. Notably, the maximum strain amplitude (1.17%) is even comparable to that of advanced lead-free piezoceramic, and the maximum strain rate exceeds those of many reported metallic actuator materials. Our work indicates that good network connectivity plays a vital role in facilitating large/fast strain response in metallic actuators.