Atomically dispersed vanadium oxides on multiwalled carbon nanotubes via atomic layer deposition: A multiparameter optimization

Abstract

The focus of the present work is to investigate the bonding characteristics of vanadium oxide species to different oxygen functional groups on multiwalled carbon nanotubes (MWCNT). Atomic layer deposition (ALD) was used to deposit atomically dispersed vanadium oxide species on MWCNT. To generate atomically dispersed vanadium, only one ALD cycle was applied for the deposition of vanadium. The MWCNT functional groups that are involved in the deposition process were identified by thermal analysis and grafting experiments. A variety of ALD process parameters were tested, and revealed that purging times between dosing of vanadium precursor and dosing of water as coreactant had a strong influence on the ratio of vanadium species that are physisorbed or chemisorbed to the MWCNT. The ALD process parameters were optimized to focus on the immobilization of the vanadium due to a chemical bond between vanadium species and MWCNT. Because of the direct correlation between catalytic stability and immobility of the vanadium species, the importance of knowledge about the influence of the ALD parameter onto the bond formation is essential. Raman spectroscopy and high resolution scanning transmission electron microscopy images were used to prove the single site structure of the vanadium oxide.