Catalytic methane technology for carbon nanotubes and graphene
Carbon nanomaterials, mainly carbon nanotubes (CNTs) and graphene, have received much attention in the past two decades. With the maturity of preparation technology and performance studies, they have been gradually applied in the industries of lithium-ion batteries (as conductive agents) and supercapacitors (as the main electrode materials). The large-scale production (up to thousands of tons per year) of CNTs has been realized, and the production cost has been greatly reduced. The production of graphene also exceeds one hundred tons per year, requiring the same improvement in performance/cost ratio. As one of the cheapest hydrocarbons, methane serves as a feedstock of both CNTs and graphene. The catalytic methane technology via the chemical vapor deposition method is advantageous for the controlled synthesis and mass production of carbon materials with high yield, high quality and at low cost, which are necessary requirements for any potential yet competitive commercial applications. Firstly, the methane deposition of CNTs is discussed, with a brief introduction on the preparation of CNTs, then the growth mechanism of CNTs, thermodynamics of methane decomposition in CNT synthesis, catalysts to decompose methane for CNT growth, and the synthesis of CNTs with different structures from methane. Secondly, the methane deposition of graphene is discussed, with a brief introduction on the preparation of graphene, then the growth kinetics of graphene, the quality estimation of graphene, and the synthesis of graphene with different structures from methane. Finally, the reactor technology for the enhanced production of CNTs and graphene is introduced, including the large-scale production of powder-like CNTs and graphene, ultralong CNTs, and graphene films, respectively. The review is useful for understanding the scientific and engineering challenges in this field and for the large-scale production of these important carbon nanomaterials from methane in the future.