Vertically aligned epitaxial graphene nanowalls with dominated nitrogen doping for superior supercapacitors

For graphene-based electrode materials, N doping is one of the leading approaches for enhancing the performance of supercapacitors. However, such an outstanding performance is suppressed by the agglomeration of graphene and unspecified N incorporation. Here, we demonstrate a direct growth of vertically epitaxial graphene nanowalls (GNWs) on flexible carbon cloths (CCs) via microwave plasma-enhanced chemical vapor deposition, whereby predominantly N doping was sequentially achieved by introducing in situ NH3 plasma, to form N-doped GNWs (NGNWs). The vertically aligned three-dimensional (3D) architecture of epitaxial NGNWs and their unique selectivity to the specific N dopants make such electrodes an ideal platform, not only for enhancing the capacitive performance but also for studying the role of the CN bonding configuration in its performance. Remarkably, NGNW supercapacitors exhibit an excellent specific capacitance of 991.6 F/g (estimation based on the actively contributing component) and an apparent area-normalized capacitance of 1488.9 mF/cm2, at a specific current of 14.8 A/g. This approach allows us to achieve an energy density of 275.4 Wh/kg at a power density of 14.8 kW/kg (specific current of 14.8 A/g), and a power density of 74.1 kW/kg at an energy density of 232.6 Wh/kg (specific current of 74.1 A/g) in 1 M H2SO4.