Hierarchically Structured Nanoporous Palladium with Ordered/Disordered Channels for Ultrahigh and Fast Strain.

Metallic actuators have increasingly shown the potential to replace conventional piezoelectric ceramics and conducting polymers. However, it is still a great challenge to achieve strain amplitudes over 4% while maintaining fast strain responses. Herein, we fabricated bulk nanoporous palladium (NP-Pd) with microsheet-array-like hierarchically nanoporous (MAHNP) structure by dealloying a eutectic Al-Pd precursor. The hierarchical structure consists of array-like microsized channels/sheets and disordered nanosized networks. The locally ordered channels play a critical role in fast mass transport while nanoligaments accumulate a large surface area for hydrogen adsorption/absorption and desorption. Therefore, the MAHNP-Pd not only obtains a fast strain rate with the maximum value close to 1 × 10 -4 s -1 but also exhibits an ultrahigh strain amplitude of 4.68%, exceeding all reported values for bulk electrochemical metallic actuators to date. Additionally, the superiority of the MAHNP structure is demonstrated in transport kinetics as benchmarked with the scenario of unimodal NP-Pd.