Mass production of functionalized graphene nanoplatelets and their application as aqueous-based conductive inks

Abstract

Graphene nanoplatelets possess exceptional physical and chemical properties; however, the absence of efficient large-scale production methods and their poor dispersion in solvents significantly hinder their practical applications. Chemical exfoliation enables the large-scale production of graphene nanoplatelets; nonetheless, these processes involve strong acids, potent oxidizing agents, and hazardous chemicals, raising environmental and scalability concerns. In this study, we propose an environmentally friendly, scalable, and sustainable one-pot approach for the large-scale production of phosphate-functionalized graphene nanoplatelets (G-POH) via anodic exfoliation at a rate of 3.5 g/(h·L). Key innovations include temperature control (25 °C), continuous extraction of exfoliated-functionalized nanoplatelets using a peristaltic pump, and electrolyte recirculation. Using a 1 M H₃PO₄ aqueous solution as both the electrolyte and the source of phosphate functional groups, we successfully obtained G-POH with a thickness of 3.6 ± 0.22 nm (∼2–3 layers per stack), and a specific surface area of 175 m²/g (BET). ³¹P NMR confirmed the presence of phosphate monoester species chemically bound to graphene nanoplatelets. Moreover, G-POH exhibited good dispersion in polar solvents, enabling the formulation of an aqueous-based conductive ink. This ink was effectively applied to various surfaces (cotton lab coats, ceramic tiles, glass, drywall, biaxially oriented polypropylene (BOPP), and polyester films), using multiple application methods (fountain pen, brush, and film coater). The resulting conductive patterns successfully illuminated multiple LEDs. The conductive film on a flexible BOPP substrate demonstrated excellent electrical conductivity (1.183 × 10⁴ S/m, 16 ± 1.4 Ω/sq) over 100 bending cycles, highlighting its potential for flexible electronics and sustainable conductive coatings.