| AVS 58th Annual International Symposium and Exhibition | |
| Biomaterial Interfaces Division | Wednesday Sessions |
| Session BI+AS+NS+SS-WeA |
| Session: | Functionalization and Characterization of Nanostructures |
| Presenter: | Igor Zoric, Chalmers University of Technology, Sweden |
| Authors: | C.B. Langhammer, Chalmers University of Technology, Sweden E.M.K. Larsson, Chalmers University of Technology, Sweden I.L. Zoric, Chalmers University of Technology, Sweden V.P. Zhdanov, Boreskov Institute of Catalysis, Russian Federation |
| Correspondent: | Click to Email |
Nanostructured materials have been proposed as a solution for the development of efficient hydrogen storage systems. As the size of the system gets reduced in the nanometer range enthalpies and entropies of hydrogen dissolution in the metal (α-phase) and hydride formation (β-phase) as well as activation barriers for diffusion and desorption of hydrogen become size dependent thus influencing both thermodynamics (pressure-composition isotherms) and kinetics (loading/unloading kinetics). The pressure-composition isotherms for a H2/M system show a well-known behavior typical for an α-phase in the low pressure-composition range followed by a plateau signaling the onset of a hydride formation (β-phase) via a first order phase transition and a coexistence of the two over a wide composition range. At higher pressure a pure β-phase exists characterized by a pressure-composition curve with a steep slope. The plateau pressure of the H2/M system is determined by the requirement of equilibrium between the three phases in coexistence, thus primarily by the enthalpy and entropy of hydride formation. In case of more than one hydride type a coexistence region exhibits multiple plateaux determined by appropriate energetics as described above. In all known cases the same multiple plateaux features were observed both during the charging and discharging process, i.e. when hydrogen pressure was increased/decreased, accompanied of course by a perennial hysteresis.
In this work we report unusual pressure-composition isotherms for H2/Pd nanosized rings where a double plateau isotherms are observed during the charging process and a single plateau one during the hydrogen discharging. The Pd nanorings were fabricated using colloidal lithography. Hydrogen isotherms were followed by monitoring the shift in the ring Localized Surface Plasmon Resonance, LSPR, upon exposing the system to increasing/decreasing hydrogen pressure steps (and equilibrating the sample at each pressure step). The shift of the LSPR resonance was calibrated by preparing the same ring structure on a quartz crystal microbalance and ”weighing” directly absorbed hydrogen. A linear relation between the LSPR shift and QCM frequency shift (proportional to hydrogen concentration) was observed.
We present a simple model, based on the observed heterogeneity of the nanorings (as seen in TEM) and by taking into account the defect induced lattice strain, that accounts for the unusual behavior of the observed isotherms.