Effect of voltage waveform on characteristics of electrochemically exfoliated graphene nanoplatelets

Abstract

Electrochemical synthesis of graphene is an established process with high consistency and scalable potential. However, information on the effect of types of waveform on the quality of graphene nanoplatelets (NPs) is scanty. In this study, different types of waveform, namely direct current (DC), pulsed direct current (PDC) and bipolar waveform (BP) were used for the electrochemical exfoliation of graphite. All experiments were performed keeping other process parameters constant, such as electrolyte concentration (0.05 M KOH solution), temperature (303 K), distance between electrodes (6 cm) and stirring speed (200 rpm). It is observed that the type of waveform plays a significant effect on the defect concentration and size of the as-synthesized graphene NPs. The size of graphene NPs synthesized using PDC, BP and DC waveforms was in the range of 1–5, 60–220 and 250–450 nm, respectively. Raman spectroscopic analysis confirmed that multilayer graphene consisting of 4–5 layers of C atoms was successfully synthesized irrespective of the type of waveform. Further, the calculated defect concentration of graphene synthesized using PDC waveform was 1.64 ± 0.41 × 10⁹ cm^–2, which is significantly less than those prepared by DC and BP waveforms. The X-ray photoelectron spectroscopic (XPS) analysis showed that the highest C/O ratio (i.e., less oxygen) was noted in graphene synthesized using the PDC waveform. A proof-of-concept study showed a 50% increase in the specific capacitance of Al-doped ZnO nanopowder using graphene quantum dots.