Abstract
This work reports a novel two-step process to fabricate nano-microstructured deposit films that contain vertically aligned graphene microsheets in perpendicular to substrate surface: (Step 1) a molecular engineering approach to controlling the interspacing of restacked graphene microsheets with surface grafted ligand molecules and (Step 2) an electric field approach to inducing re-orientation of the graphene microsheets during the particulate slurry deposition process to form films. Four different ligand molecules (e.g., 2,5-diamino-1,4-dihydroxylbenzene dihydrochloride (DDDC), octadecyltrichlorosilane, polyaniline, and p-phenylenediamine) were studied for grafting on the surfaces of graphene oxides (GOs). The molecular ligand-modified GOs (i.e., m-GOs) were then reduced (m-rGO). XRD data showed well controlled nanometer sized (up to 1 nm) interlayer spacings between the restacked m-rGO sheets. The direct current electric field rendered vertically aligned m-rGO flake sheets along the field direction in deposit films. In addition, the field further enlarged interlayer spacing in vertically structured films, which correlate to enhance diffusion and accessibility of electrolyte ions. Enhancement in electrochemical performance (i.e., higher specific capacitance and faster electron and ion transport kinetics) was demonstrated with the vertical graphene deposit films, relative to the baseline films without the field alignment step. For vertical sample of DDDC-rGO compared to those for baseline samples, up to ~1.6 times higher capacitance (the highest capacitance of 430 F/g at 0.5 A/g) and ~67 % reduced equivalent series resistance (ESR) were achieved. Vertical graphene alignment by electric field could be a new versatile fabrication technique to tailor the microscopic architecture of graphene based film deposits for high performance supercapacitor.
