Mechanistic investigation of the graphene functionalization using p-phenylenediamine and its application for supercapacitors

The p-phenylenediamine (PPD) modified graphene oxide (GO)/reduced graphene oxide (rGO) composite materials were synthesized by a facile solution processing with two different routes: 'Reaction first then Reduction' and 'Reduction first then Reaction', which are referred to as GPPDH and GHPPD, respectively. The two composites were employed as active supercapacitor electrode materials, their electrochemical properties were studied, and the mechanism how PPD improves the electrochemical performance is investigated systematically. GPPDH with the PPD molecules incorporated between the graphene sheets demonstrated a loose and crumpled microstructure. However, for GHPPD, the graphene sheets were stacked and cross-linked through PPD molecules. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) also provided quantitative information about the newly formed chemical constituents in the synthesized materials. The specific capacitance values of GPPDH and GHPPD are 316.54 and 249.24 F g(-1) at 10 mV s(-1), respectively. The synthesized materials also exhibited an excellent cycling stability as 93.66% (GPPDH) and 87.14% (GHPPD) retentions after 4000 cycles at current density of 2 A g(-1). The results revealed the role of amine-based organic additives in graphene supercapacitor materials and validated the GPPDH as the electrodes of supercapacitor with an excellent electrochemical performance. (C) 2015 Published by Elsevier Ltd.