Nitrogen-doped reduced graphene oxide-polyaniline composite materials: hydrothermal treatment, characterisation and supercapacitive properties

Abstract

Among other factors, the electrochemical capacitor (EC) properties of graphene oxide (GO) are limited by conductivity issues emanating from high oxygen concentrations. Hence, innovative GO modifications, such as derivatisation and synthesising composites with conducting polymers, are required to boost the EC properties. This allows the exploitation of the low material cost associated with carbonaceous materials. Herein, the effect of temperature (70, 130 and 190 °C) on the hydrothermal treatment of a GO/urea mixture (to form nitrogen-doped reduced GO samples U70, U130 and U190 (N-RGO), respectively) was investigated in order to study the resulting physicochemical and EC properties of N-RGO in a K₂SO₄ electrolyte. Subsequently, the EC properties of the N-RGO obtained from the optimum temperature were investigated in composites with polyaniline (PANI). The functionality of the composites in the electrolytes, namely, K₂SO₄ (SO₄²⁻ radius: 258 pm) versus KOH (OH⁻ radius: 133 pm), was compared. The nitrogen at% in GO and N-RGO (U190) was 0.39 and 6.74%, respectively, with corresponding conductivities of 4.61 × 10⁻⁷ and 4.17 × 10⁻¹ S cm⁻¹. Compared with GO, U130 achieved the highest increase in specific capacitance (C_s) of 200 times at 10 mV s⁻¹. The 5 wt% PANI composite displayed the highest enhancement of C_s of 14 032% at 50 mV s⁻¹ and 4749% at 5 mV s⁻¹ relative to N-RGO and PANI in K₂SO₄, respectively. The highest C_s values for NRGO-PANI composites in KOH were more than double those of K₂SO₄. This work demonstrates that the hydrothermal treatment temperature tailors the physicochemical properties of the doped GO and, together with the anion size of the electrolyte and PANI wt%, synergistically tunes the EC properties of the ultimate PANI-N-RGO composite.