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

Abstract

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.

The Electrochemical Actuation Performances of Nanoporous Ternary AlCoCu Alloy with a Unique Nanosheet Structure

“…where Y s is the Young's modulus of solid metal and ρ np and ρ s are the densities of NPmetal/alloy and solid metal [10], respectively. ρ NP /ρ s is the solid phase fraction (ϕ) of NP-metal in this paper, and it can be obtained from the porosity (ϕ p ) (67.1%) [8]. For simplicity, we consider the Young's modulus (bulk modulus) of an NP alloy as the sum of the product of the Young's modulus (bulk modulus) of each metal and its relative proportion in the alloy [12].…”

“…NP-metals thus become a potential substitute for commercial actuators. Later, using a more convenient binary alloy dealloying method, a series of precious metal actuators, such as NP-Au [4][5][6], NP-Pd [7,8], and NP-Ag [9], were first designed. However, the raw materials of precious metal actuators are expensive and have limited reserves, making them unlikely to be put into mass production.…”