Ultrathin Supercapacitor Electrode Based on Reduced Graphene Oxide Nanosheets Assembled with Photo-Cross-Linkable Polymer: Conversion of Electrochemical Kinetics in Ultrathin Films

An ultrathin supercapacitor electrode based on reduced graphene oxide (rGO) nanosheets is prepared using Layer-by-Layer (LbL) assembly. The rGO nanosheets functionalized with a conducting polymer, poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), were assembled using a photo-cross-linkable diazoresin (DR). The unique photo-cross-linking property of the DR polymer enabled the conversion of the ionic bonds in the LbL-assembled film to covalent bonds upon UV irradiation, significantly enhancing the overall electrochemical activity of the resulting ultrathin supercapacitor electrode. By UV/vis and Fourier transform infrared (FT-IR) spectroscopy measurements, we proved that decomposition of the diazonium group from DR, followed by covalent bond formation, contributed to the enhanced integrity of the adjacent interfaces within the multilayers. In particular, electrochemical measurements suggested that a charge transfer process is facilitated after cross-linking, which resulted in a considerable increase in the volumetric capacitance. The hybrid thin film of the rGO supercapacitor exhibited a capacitance of 354 F/cm³ at a scan rate of 20 mV/s and maintained a capacitance of 300 F/cm³ even at a high scan rate of 200 mV/s, thus outperforming many other thin film supercapacitors.