Actuation by hydrogen electrosorption in hierarchical nanoporous palladium

We report a strategy for preparing macroscopic samples of nanoporous (np-) Pd by electrochemical dealloying. Starting out with the master alloy Cu85Pd15, single-step dealloying in 1 M H2SO4 at 60 degrees C provides a hierarchical network structure with two well-defined ligament sizes, 35 and < 10 nm. The material is distinguished by its uniform microstructure and its excellent mechanical deformability. Thereby, it may provide an alternative to dealloying-made nanoporous gold as a model system for nanoscale functional materials. Our study exemplifies this by exploring actuation through electrochemically controlled hydrogen sorption. Hydrogen underpotential deposition, bulk sorption isotherms and the concentration strain coefficient are found to agree closely with previous studies of H adsorption on planar surfaces and of hydrogen absorption in bulk, respectively. The actuation strain reaches amplitudes up to 4.0%. Even though each strain cycle brings the np-Pd-H through the alpha <-> alpha' phase transformation, the strain amplitude remains stable during much more than 1000 cycles. Furthermore, in view of the macroscopic sample size in all three dimensions, the switching time for actuation is remarkably fast.