Engineering the edge-terminations and defect-density to enhance the electrochemical capacitance performance of vertical graphene nanosheets

Abstract Recently, the vertical graphene nanosheets (VGN) garnered a lot of attention, due to its unique morphology and remarkably high surface area. Herein, we engineered the edge-terminations of VGN by post-deposition plasma treatment under different gas environments (H2, N2 and O2), to realize VGN surfaces with desired functionalities (-H, -N and –O or -OH) to extend its potentiality. Furthermore, the plasma functionalization is found to manipulate the defect type (sp3 or vacancy) in VGN’s. Both, spin polarized first principle density functional theory based calculations and x-ray photoelectron spectroscopic (XPS) analysis substantiated the annihilation of vacancy defects in case of N2 plasma treatment and an enhancement in defect density incase of H2 and O2 plasma treatment. A significant enhancement in surface energy (107 to 846.2 mJ m-2) of plasma treated VGN is evident. This in-turn manipulates the intrinsic-hydrophobic VGN to super- hydrophilic. Further, the plasma treated VGN’s exhibits one order enhancement in electrochemical capacitance, which also corroborates with the wetting nature. Additionally, the higher capacitance retention of plasma-treated VGN’s signifies an improvement in their electro-chemical stability. The above facts emphasize the significant role of edge-terminations, defect density and defect type for enhancing the electrochemical capacitance performance of VGN with improved cycle stability.