Bilayer-favored intercalation induced low-voltage electrochemical production of nano-graphene oxide in neutral phosphate

Graphene oxide (GO) exhibits great potential in various fields such as catalysis, wastewater treatment, and energy storage. However, traditional top-down GO preparation methods based on graphite exfoliation often suffer from high energy consumption and inevitably environmental pollution. In this work, an environmentally benign and low-voltage electrochemical exfoliation approach to fabricate nanoscale GO employing carbon fiber-based materials as the precursor using phosphate was proposed. Under neutral phosphate electrolyte, bilayer graphene oxide with a lateral size of ∼500 nm, thickness of ∼1.5 nm, and C/O ratio of 2.96 could be obtained via a constant potential process. By adjusting the pH to 12 to intensify the exfoliation reaction, the lateral size of the graphene oxide was controllable, decreasing to ∼50 nm, while the C/O ratio decreased to 0.9. Due to the further decrease in C/O ratio, the thickness increased slightly to 2–3 nm. The exfoliation potential (1.6–2.5 V vs. Ag/AgCl) and electrolyte concentration (50–500 mM) had an obvious impact on the yield of graphene oxide. Through electrochemical analysis such as linear sweep voltammetry, as well as density functional theory calculations, the exfoliation mechanism of phosphate is elucidated in detail, demonstrating that the stepwise ionized phosphate anions possess more robust intercalation capability than sulfate, thus enabling efficient exfoliation to the intertwined nanocrystalline graphite structure of carbon fibers. The DFT results revealed the bilayer-favored intercalation of phosphate, which accords well with experiments. This work provides a new controllable and green approach for GO synthesis, demonstrated by life cycle assessment. It could assist subsequent studies exploring the size effects of GO and its applications in environmental remediation and energy storage.