In Situ Stress Measurement During Hydrogen Sorption on Ultrathin (111)-Textured Pd Films in Alkaline Electrolyte

Abstract

The stress behavior of hydrogen adsorption/absorption into Pd layers electrodeposited on (111)-textured gold has been examined in alkaline solution. Although the kinetics are much slower than in acidic solution, the stress induced by H adsorption and absorption is very similar. Hydrogen adsorption causes a −0.46 N/m change in the surface stress. Compressive stress generation is consistent with first principle calculations as well as experimental data for hydrogen on Pt. Hydrogen absorption causes GPa-level compressive stress in the Pd due to the large volume expansion associated with the α–PdH to β–PdH phase transition. Although some indication of plastic deformation during hydride formation was observed, the large tensile coherency stress due to the + 4.9% lattice misfit between Pd and Au keeps the hydride cycle in the elastic regime. The stress measurement probes only those processes concerned with adsorption and absorption. Since the wafer curvature measurement responds directly to the volumetric strain induced by hydrogen incorporation and is insensitive to parasitic reactions, it serves as a nice complement to the more traditional electroanalytical techniques for studying hydrogen absorption kinetics.