Synthesis and characterisation of hybrid Zn0-carbon nanostructures for potential applications in hydrogen storage
This work presents the synthesis of hybrid zinc oxide carbon nanofibers (ZnO-CNFs) using ZnO nanorods as template and to investigate if they can be used as the hydrogen storage materials. The synthesis of ZnO nanoparticles (ZnO NPs) was carried out using direct current (DC) reactive magnetron sputtering at different deposition times, pressure and temperature, and were used as a seeding in the synthesis of ZnO nanorods (NRs). Using the hydrothermal process, vertically aligned ZnO NRs were grown on different seed particles which resulted in the different sizes and distribution of nanorods. ZnO NRs were used as templates in the deposition of ZnO-CNFs at various temperatures (500, 600, 700 and 800 °C), using chemical vapour deposition (CVD). Acetylene (C2H2) was used as the source of carbon during the depositions of ZnO-CNFs. Scanning electron microscopy (SEM) was used to study the surface morphology of all samples (ZnO NPs, ZnO NRs and ZnO-CNFs). The results from SEM images showed that the size of ZnO NPs increased with deposition time and ZnO NRs morphology depended on the seeding particle sizes. The size of ZnO NPs which ranges from 6.73 to 19.60 nm was measured from SEM images and was confirmed by Scherrer equation. The vertically aligned ZnO NRs average diameter and the average length ranges from 55.64 to 78.93 nm and 106.92 to 129.15 nm, respectively. ZnO-CNFs retained the hexagonal structure of ZnO NRs when annealed at 500 to 700 °C. When the temperature was raised to 800 °C the ZnO-CNFs completely lost the hexagonal structure of a template material. Chemical compositions of all samples prepared were determined using energy dispersive x-rays spectroscopy (EDS). From EDS results, it was discovered that the content of carbon on ZnO-CNFs annealed at 500 °C to 700 °C increases but decrease for the sample annealed at 800 °C. Crystal structure was studied using X-rays diffraction (XRD). XRD results of ZnO NPs and ZnO NRs confirmed that ZnO was crystalline with a wurtzite hexagonal structure. The disorder in ZnO-CNFs was studied using Raman spectroscopy. Raman showed that ZnO-CNFs have both sp2 and sp3 hybridisation which is a result of disordered carbon materials. ZnO-CNFs samples were tested for hydrogen absorption/adsorption using elastic recoil detection analysis (ERDA). From the ERDA results it was shown that more hydrogen was absorbed/adsorbed when ZnO-CNFs was annealed at 700 °C, and less when annealed at 800 °C. These results on hydrogen profiling show that ZnO-CNFs can be good candidates for hydrogen storage applications.
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