N-doped carbon layer coated thermally exfoliated graphene and its capacitive behavior in redox active electrolyte

A nitrogen-doped carbon layer coated thermally exfoliated graphene (NC-TEG) is prepared by in-situ polymerization of p-phenylene diamine (PD) with thermally exfoliated graphene (TEG) and subsequent high temperature pyrolysis (600 °C for 1 h in argon gas environment). Fourier transfer infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy confirm the formation of poly-(p-phenylene diamine) layers on the TEG surfaces with a nitrogen doping level of ~6.1%. Physisorption analysis indicates that NC-TEG not only has the enlarged surface area, but also forms hierarchical three dimensional structures with several micro and meso-pores compared to pristine TEG. Due to the synergic effect of nitrogen atoms in the carbon structures and augmented surface area, the capacitance measured from cyclic voltammetry and galvanic charge-discharge increases to 282.5 F g^-1 from the 95.1 F g^-1 of TEG. Moreover, the PD monomer acts as a reversible faradaic agent. The capacitive performance of the NC-TEG electrode is investigated in different mixed electrolytes. The specific capacitance is significantly increased to 635.6 F g^-1 in a mixed electrolyte of 0.025 M PD and 2 M KOH. After 10,000 cycles, the capacitive retention shows remarkable stability as high as 87.4%.