Continuous production prototype for scaling up of graphene oxide/carbon nanotube composite synthesis towards efficient hydrogen storage†

A continuous production prototype for scaling up the synthesis of a graphene oxide/multi-walled carbon nanotubes (GO/MWCNTs) composite as a hydrogen storage material has been proposed in this study. This prototype consists of an automatic feeding and mixing step wherein KMnO₄ and graphite are individually fed into concentrated H₂SO₄ and then mixed to form a graphite/oxidant mixture. Following this, the oxidation step involves oxidizing the graphite/oxidant mixture through two-step oxidation to produce a graphene oxide dispersion. Then, the composite synthesis step includes mixing, sonicating, and stirring the graphene oxide dispersion with a sonicated dispersion of MWCNTs to obtain the final product. As a result, the morphology and structure of the GO/MWCNTs composite synthesized by the large-scale method exhibit high similarity to those of the gram-scale sample. The GO/MWCNTs exhibited a 3D nanostructure composed of MWCNTs linked to the graphene oxide layers. The hydrogen storage test results, simulated to practical hydrogen storage tanks with large amounts of adsorbents, indicated that the hydrogen storage capacity of GO/MWCNTs can reach 3.1 wt% at ambient temperature and 50 bar. The analysis of life cycle impacts in terms of energy consumption, carbon footprint, cost, and environmental impact indicated that the proposed large-scale continuous production prototype is greener compared to other methods. Therefore, this approach holds great potential for industrial applications, paving the way for commercialization and facilitating the development of small storage units to explore the properties of the new storage system.