Changes in structure and surface properties of Si-based agent during hydrogen generation reaction

Abstract

Si-based agent which can generate a high amount of hydrogen by the reaction with weak alkaline solutions (e.g., pH8.3) has been investigated using SEM, XRD, DLS, XPS and FT-IR. Si-based agent consists of crystalline Si with the average crystallite size of ~20 nm, and Si nanocrystals form agglomerate with ~150 nm average size. The size of agglomerate slightly decreases from ~150 nm to ~130 nm during the initial hydrogen generation reaction stage up to 500 min in pH8.3 solutions at 36 °C and then the agglomerate size stays constant. The observed curve of the generated hydrogen volume vs. the reaction time is reasonably well expressed by the observed size change of Si crystallites, and also by the thickness of the silicon oxide layer. Before the hydrogen generation reaction, hydrogen atoms are present at the Si/silicon oxide interface as SiH, SiH2, and SiH3, and also at the surface and in the silicon oxide layer, as HSiO, HSiO2, and HSiO3. The concentrations of all hydrogen-containing species increase in the initial reaction stage, and then, decrease with the hydrogen generation reaction time, indicating that generated hydrogen atoms attack SiH bonds, leading to desorption as H2.