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 (107–846.2 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.