Hydrogen sorption and desorption related properties of Pd-alloys determined by cyclic voltammetry

• CV is utilized to determine H content of different Pd-alloys.
• Different phases are identified with potentiostatic loading curves and XRD.
• Total hydrogen uptake for low H contents in Pd-alloys is determined by kinetics.
• For long loading times the total H content is determined by thermodynamics.
• The peak potential may indicate interaction strength of H with the surface.

In this research we present a fast and quantitative electrochemical method – based on cyclic voltammetry (CV) – to screen the hydrogen (H) sorption (adsorption and/or absorption) and desorption behavior of Pd-based alloys. The method consists of a first step in which specimens are potentiostatically loaded with H, followed by a second step in which a CV experiment is performed with a wide-range potential sweep. During the second step, oxidation of H occurs as well as the formation of oxides and their consequent reduction. The H-loading and the CV start potential are the same so that H oxidation is not influenced by other surface reactions as it is the first process to take place. The method is applied to different Pd-alloys (Pd–Au, Pd–Mo–Cu) and it enabled to elucidate the differences in H-sorption/desorption properties of the alloys. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to investigate changes in the structure as a function of the H-loading times. It was shown with this work that (i) the phases present in the microstructure have a significant effect on the amount of hydrogen absorbed and the kinetics of absorption, (ii) even very small amounts of desorbed hydrogen can be detected by CV and (iii) alloying elements affect hydrogen sorption/desorption behavior of Pd-based alloys and the interaction strength of H with the surface or the bulk.