Nano-micro-structured graphene film electrodes for enhanced performance of supercapacitors

The graphene structures at either nanoscale or microscale are important to the film electrode performance. At nanoscale, a molecular engineering approach (i.e., molecular ligand grafting) was used to control the interspacing between restacked graphene sheets. At microscale, this work applied an external field to align the graphene sheets along the field direction during the film deposition from liquid slurry of molecularly engineered graphene. Five different ligand molecules were effectively grafted on the surfaces of well-dispersed graphene oxides (GOs) in liquid suspension and the grafted GOs were chemically reduced to form molecules modified graphene or reduced GOs (m-rGOs). XRD data shows well controlled nanometer sized interlayer spacings between the re-stacked sheets of m-rGOs. Then, we investigated the effects of ligand grafting on the deposited film structure. Their baseline electrochemical cell performance was evaluated by different aqueous electrolytes (e.g., H₂SO₄ va. KOH) for the following external field alignment. Initially, the m-rGO film electrodes exhibited higher capacitance performance with H₂SO₄ electrolyte, compared with KOH. Also, the external field has rendered the graphene sheets to be oriented velrtically to the film surface, resulting in enhanced capacitance due to enhanced diffusion and accessibility of electrolyte ions into the graphene film structure. Aligning graphene nanosheets in film deposits via external field could be a novel versatile fabrication technique to tailor microscopic architecture of graphene coatings for high performance supercapacitor.