Hydrogen-induced plasticity in nanoporous palladium

Abstract

The mechanical strain response of nanoporous palladium (npPd) upon electrochemical hydrogenation using an in situ dilatometric technique is investigated. NpPd with an average ligament diameter of approximately 20 nm is produced via electrochemical dealloying. A hydrogen-induced phase transition from PdHβ to PdHα is found to enable internal-stress plasticity (or transformation-mismatch plasticity) in nanoporous palladium, which leads to exceptionally high strains without fracture as a result of external forces. The high surface stress in the nanoporous structure in combination with the internal-stress plasticity mechanism leads to a peculiar strain response upon hydrogen sorption and desorption. Critical potentials for the formation of PdHα and PdHβ in npPd are determined. The theoretical concepts to assess the plastic strain response of nanoporous samples are elucidated, taking into account characteristics of structure and deformation mechanism.

Coherent Phase Change in Interstitial Solutions: A Hierarchy of Instabilities

“…For nanoporous Pd‐H—as a solid solution—a large and transient contraction is reported when the net hydrogen fraction moves into the miscibility gap. [ 80 ] The explanation in terms of hydrogen‐induced plasticity [ 80 ] may be challenged in view of the transient nature of the phenomenon. The spontaneous buckling of the ligaments would naturally explain the observation.…”

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

“…However, because the hydrogen evolution reaction will occur at a strongly negative potential (such as −1.4 V vs SCE) together with hydrogen adsorption/absorption, direct calculation from the amount of charge accumulated during hydrogen adsorption/absorption might overestimate the X H/Pd . 25,27 To minimize the effect of hydrogen evolution, we calculated the X H/Pd from the hydrogen desorption charge (Q HD ) according to previously reported literature. [24][25][26][27]52,53 Considering Figure 3b,d as an example, the hydrogen desorption peaks can be distinguished.…”

“…25,27 To minimize the effect of hydrogen evolution, we calculated the X H/Pd from the hydrogen desorption charge (Q HD ) according to previously reported literature. [24][25][26][27]52,53 Considering Figure 3b,d as an example, the hydrogen desorption peaks can be distinguished. Thus, a series of current curves for hydrogen desorption at different scan rates are plotted in Figure S5a, and Figure S5b shows the corresponding integration results.…”

“…In the initial stage (from −1.4 to −0.94 V vs SCE), the hydrogen adsorption/absorption results in the lattice expansion of Pd, inducing a significant increase in the strain. 18,19,27 During the subsequent forward scan (from −0.94 to 0.16 V vs SCE), continuous contraction can be observed. The strain decrease in this process is divided into two stages, namely, a slight contraction due to the hydrogen desorption from the ligament surface and a sharp contraction induced by hydrogen desorption from the surface/bulk of the ligaments.…”

“…Under electrochemical conditions, Pd can reach an atomic ratio of H/Pd more than 0.6, 24−26 which would lead to significant lattice expansion, thereby inducing a macroscopic volume change. 18,19,27 In order to attain desirable actuation performance, Pd is a preferred material. However, reaching a fast strain response is challenging due to the sluggish ion diffusion in fine channels of nanoporous Pd (NP-Pd).…”