Graphene-Cellulose Nanocrystals Composite as Electrode Material for Electrochemical Double-Layer Capacitors

Abstract

It has been a constant challenge to develop more sustainable and better-performing supercapacitors that meet the large-scale demands of hybrid electric vehicles, wearable microelectronics, and grid storage in the future. They require green, facile, and efficient production methods to realise their prospective applications. In this work, graphene-nanocellulose crystals (G-CNC) composites were evaluated as electrode active materials for symmetric, electrochemical double-layer capacitors (EDLCs). The G-CNC electrodes were fabricated through manual spray-coating of the composites, prepared by a green and facile high-shear, liquid-phase exfoliation of natural graphite flakes. The obtained G-CNC composites of high graphene (>7 mg·mL-1) and CNC (11-32 % w/w) concentrations were identified to significantly reduce the composite’s electronic conductivity, along with presence of partially exfoliated graphite in several dispersions. The G-CNC electrodes display decent energy storage capabilities, with an average specific capacitance of up to ~40 F·g-1 in aqueous electrolyte solution (1.0 M NaClO4). The 2D stacking arrangement of the graphene flakes in the G-CNC electrodes was determined to impede ion transport needed for double-layer capacitance formation. Low energy efficiencies (<75 %) were obtained for these electrodes, which suggests that modifications in the G-CNC material, the electrode preparation, or the EDLC component materials are still needed for a better understanding of the G-CNC’s full “capacity” as a promising material for energy storage applications.