Temperature-modulated synthesis of vertically oriented atomic bilayer graphene nanowalls grown on stainless steel by inductively coupled plasma chemical vapour deposition

Abstract

It is now clear that growing flat graphene nanostructures from the gas phase on planar substrates is possible. One of the keys to success —particularly in producing a very large specific surface in a reduced space— is the use of 3D carbon nanostructures (i.e., vertical graphene nanowalls, VGNWs) over a planar substrate as a growth template for the deposition of electrochemically active materials (as, for example, transition metal oxides (TMO)). Vertical graphene nanowalls, also known as petal-like, vertical graphene flakes or vertical graphene, can achieve a very large specific surface area of 1100 m2/g, which is comparable to or greater than that of carbon nanotubes —the reference material for its use in high-performance supercapacitors or in other energy-related applications requiring a large active surface area. Vertical graphene nanowalls also exhibit high vertical and in-plane electrical conductivity when grown on metal electrodes, which benefits their use in electrochemical applications. Here, we focus on the growth of VGNWs on flexible stainless-steel substrates (SS310), in principle suitable for applications to electrodes of electrochemical systems (batteries, supercapacitors, catalysts), by inductively coupled plasma chemical vapour deposition (ICP-CVD), from methane as a carbon precursor, in a wide range of temperatures (575 to 900 °C). We will discuss the effect of growth temperature on morphological and structural characteristics of VGNWs based on the results of Raman spectroscopy and field emission scanning electron microscopy (FE-SEM) analysis. Because the nanostructures of graphene nanowalls reported to date are, for the most part, based on multi-layered graphene, here we seek to highlight the effect of temperature on the number of atomic layers of VGNW. In the 700–750 °C range, and under the plasma conditions explored, vertical graphene nanowalls are bilayer, which is foreseen to directly affect the magnitude of the VGNW specific surface.