Actuation of Dealloyed, Nanoporous Palladium upon Electrochemical Hydrogenation: Effects of Strain Rate and Type of Electrolyte

Description

The palladium-hydrogen system has been an extensively studied model system for hydrogen absorption in bulk metals over many decades. With nanoporous palladium structures (np-Pd), e.g. prepared via selective etching by electrochemical dealloying, extraordinarily fast hydrogen sorption can be achieved due to the high surface to volume ratio. Modern technological application potentials of np-Pd range from hydrogen storage and sensing to (electro-)catalysis and low-voltage actuation.
In previous studies, an extraordinarily strong expansion of more than 5% was achieved for np-Pd upon electrochemical hydrogen absorption [1]. Here we present a systematic dilatometric investigation of actuation under different hydrogenation conditions. The nanoporous samples, which are prepared by dealloying Co-Pd master alloys [2], are charged at different potentials (and thus sorption rates) in a variety of electrolytes covering a broad spectrum of pH values from strongly acidic to strongly alkaline.
The dilatometric data allow a clear distinction between hydrogen adsorption at the surface and hydrogen absorption into the bulk, which leads to strong actuation. The severe, continuous degradation of np-Pd, which was observed recently upon charging in acidic media [3], can be explained based on dilatometric data recorded in different electrochemical regimes. Aqueous KOH solution is shown to be an ideal electrolyte for efficient charging while avoiding degradation or dissolution.
A spontaneous material failure under the pressure of the dilatometer pushrod is observed during charging-induced actuation at very high strain rates. The underlying mechanisms will be discussed with regards to hydrogen sorption mechanisms, H-concentration profiles as well as a possible strain-rate dependence of the yield strength.

[1] E.-M. Steyskal et al., Beillstein J. Nanotechnol. 7 (2016) 1197
[2] M. Hakamada et al., J. Alloy. Compd. 479 (2009) 326
[3] J. Zhang et al., Electrochim. Acta 220 (2016) 91

Period	16 Sep 2017 → 21 Sep 2017
Event title	European Congress and Exhibition on Advanced Materials and Processes: Euromat 2017
Event type	Conference
Location	Thessaloniki, GreeceShow on map