High Power-Density WO3-x–Grafted Corannulene-Modified graphene nanostructures for Micro-Supercapacitors

Abstract

• Micro-supercapacitors (MSCs) with reduced graphene oxide (rGO) were designed. • Restocking of rGO nanosheets was prevented with corannulene Bucky-bowls. • rGO nanosheets were modified by grafted intercalation WO 3 nanoparticles. • Double-layer capacitance of rGO nanosheets was augmented with WO 3 pseudocapacitance. • High energy-density and high power-density of MSCs were achieved. The emergence of nanotechnology and development of new methods of nanoengineering novel materials have enabled to design supercapacitors, new devices filling the niche between the high energy-density electrochemical batteries and the high power-density dry capacitors. Thanks to the nanoengineering, new devices combining the unique properties of electrochemical double-layer capacitance with high storage capability of pseudocapacitance materials could became a reality. A special niche in these applications is for micro-supercapacitors, which can drive miniature sensors and implantable biodevices, requiring fast remote charging and high energy density packed in a small volume. In this work, the micro-supercapacitors were fabricated using WO 3-x nanoparticles immobilized on rGO nanosheets to increase the carbon nanoform double-layer capacitance by adding very high pseudocapacitance of WO 3-x . To improve the attachment of WO 3 to the carbon support and enhance the graphene matrix conductance, grafting of WO 3 nuclei onto the GO defect sites was employed by electrochemical processing and nanoparticle growth, followed by the electroreduction of unprotected oxidation sites of GO to form a highly-conductive reduced graphene oxide (rGO) support. Further protection of rGO nanosheets from stacking interactions was also necessary. It was achieved by modifying graphene sheets with corannulene (CORA) which is a C 20 H 10 polyaromatic hydrocarbon (PAH) molecule forming a cup (or: Bucky bowl) structure. We have found that corannulene can efficiently separate the rGO nanosheets in more hydrophobic locations of rGO where WO 3-x nanoforms are missing. The chemical structure, morphology, and electrochemical properties of hybrid materials used for designing the micro-supercapacitor devices were characterized by Raman spectroscopy (RS), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), infra-red spectroscopy (FTIR), electrochemical quartz crystal nanogravimetry (EQCN), cyclic voltammetry (CV), as well as potential-pulse and current-pulse charging/discharging characteristics. The supercapacitor properties of the proposed WO 3 ,CORA/rGO devices were favorable compared with those for mono plate graphene (MPG) and laser-induced graphene (LIG) MSCs.