(412c) Size-Controlled, Surface Functionalized Graphene Sheet Deposit Films for Enhanced Performance of Supercapacitors

Size-controlled, Surface Functionalized Graphene Sheet Deposit Films for Enhanced Performance of Supercapacitors

Gyoung G. Jang and Michael Z. Hu

Energy and Transportation Science Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831

ABSTRACT

Sub-micron-sized graphene oxide flake particles were grafted with an aromatic amine and hydroxyl group molecule (2,5-diamino-1,4-dihydroxylbenzene dihydrochloride (DDDC)) and was then reduced to form DDDC ligand-grafted reduced nano-GOs (nano-DDDC-rGO). DDDC serves as an interlayer spacer prohibiting stacking/aggregation and provide hydrophilicity, resulting in well dispersed slurry that is suitable for deposit uniform thin films on a circular disc substrate of carbon fiber paper (as current collector). The surface-modified graphene sheets enhanced surface usability and diffusion and accessibility of electrolyte ions by shortening transport paths (compared with horizontally stacked tenth micron size graphene sheets). By controlling the graphene size and surface property, nano-DDDC-rGO film electrodes showed enhancement in electrochemical performance (i.e., higher specific capacitance, faster electron and ion transport kinetics, better contact between current collector and active material), compared to the baseline films with larger sized (tens of micrometers) graphene flake particles. With aqueous electrolytes (e.g., 1M H₂SO₄), up to ~2.4 times higher specific capacitance and ~67 % reduced equivalent series resistance compared to the micron-sized DDDC-rGO were achieved. With a large molecule sized organic electrolyte (e.g., 1M tetraethylammonium tetrafluoroborate in acetonitrile), the size control enhancement was more effectively achieved by ~4.2 times higher capacitance, 4.0 times lower IR drops and order of magnitude enhanced response time. Therefore, controlling the particle size in the graphene film deposits could be an effective technique to tailor the property of graphene film-based electrodes for high performance supercapacitor.

Keywords: Nano sized graphene, Ligand grafting, Reduced graphene oxide, Supercapacitor, Graphene functionalization