Characterization of ZrC-V-Ti-ZrC multilayer hydrogen storage thin films prepared by e-beam evaporator

Abstract

In this study, a physical deposition method was used to prepare a ZrC–V–Ti–ZrC multi-layered stack film that was deposited on Ti and borosilicate glass substrates. The hydrogenation was achieved by thermal annealing of samples at temperatures of 200, 300, 400, and 550 °C in a pure hydrogen environment with a flow rate of 100 sccm for 30 min. RBS revealed that the multilayers are thermally stable, showing no sign of intermixing of layers up to 600 °C. It revealed the presence of oxygen in all the layers with a significant amount. ERDA revealed that a significant amount of H was near the surface and dropped towards the bulk of the samples, which is the middle layers (V and Ti layers) location. The probing towards the inner last layer (buried ZrC layer) of the multilayer stack showed an increase in the H amount detected. H amount decreased as the oxygen amount was increased in the layers indicating the negative impact of oxygen in the system, such that the total H amount in the samples with the TiO (1:1) and VO (1:1) was 99.122 at.% at 200 °C while that of Ti₂O₃ (2:3) and V₂O₃ (2:3) was 60.016 at.% at 300 °C indicating a significant change. The optimum temperature for the highest H amount observed was found to be between 200 °C and 300 °C. The as-deposited sample only showed the surface H, which is normally due to the atmosphere's hydrocarbons. The Raman spectroscopy results indicated that there was a significant decrease in the intensity of the D and G peaks due to annealing in a hydrogen environment. This suggests that the extent of hydrogen absorption, which occurs predominantly in the temperature range of 200–300 °C, is inversely related to the intensity of the D and G peaks. There was more formation of the sp3 at temperatures between 200 °C and 400 °C in the samples as seen by the decrease in the sp²/sp³ ratio from 0.13 to 0.003. XRD revealed the presence of diffraction phases, i.e., ZrC (111), ZrC (400), V₂O₅ (001), Ti (100), Ti (101), and Ti (103) in addition to the TiH₂ and the broadening of peaks for the system annealed at 200 °C and 300 °C due the high H amount, which is consistent with ERDA results. These results indicate the suitability of this system in hydrogen storage applications, provided it is optimized by eliminating oxygen contamination.