Insights on electrochemical capacitor performance of transition metal-vertical graphene nanosheets hybrid electrodes

Vertical graphene nanosheets (VGN) is envisioned as supercapacitor (SC) electrode material due to its distinct geometry and remarkable properties. Oflate, the hybrid structures of graphene- transition metal (TM) or oxides found to exhibit enhanced charge storage capacity. Herein, we report the charge storage performance of VGN-transition metal nanoparticles (Au, Ag, Cu, and Ni) hybrid electrodes. Amogst, Ni decorated VGN exhibited the highest enhancement upto 3.04 mF/cm2 (121.6 F/g) compared to 0.16 mF/cm2 for as-grown VGN. Further it has been corroborated by improved electrical as well as ionic conductivity of metal decorated VGN structures. Additionally, the presence of metal-oxygen-carbon bonding ensued the contribution from pseudocapacitance. Ab-initio caluculations elucidated the extent as well as the nature of charge (e-) transfer in TM nanoparticles-VGN hybrid structures. These findings are well corroborated with the charge storage performance. A combined effect of charge transfer and pseudocapacitance on charge storage performance of TM nanoparticles-VGN hybrid electrodes is demonstrated. A symmetric coin-cell supercapacitor device using Ni/VGN electrodes is fabricated and tested their sustained performance over 10000 charge-discharge cycles.