Electrochemically Derived Monolayer Graphene with CVD-Comparable Optoelectrical Properties and High Capacitive Performance

Harnessing the exceptional properties of monolayer graphene (MG) requires scalable, cost-effective synthesis free from multi-layer graphene. While liquid-phase methods are inexpensive, they often produce oxidized, layer-polydisperse graphene with small flakes. Here, we present a liquid-phase method that synthesizes layermonodisperse MG via engineered electrochemical exfoliation. Using a 98% H2SO4 electrolyte, graphite was intercalated to stage-I Graphite bisulfate (GB) and subsequently exfoliated, followed by tuned ultrasonic agitation in NMP, achieving a high MG yield of ∼ 93.3%. This process results in large MG flakes (∼ 136 μm2) with low defect density (ID/IG < 0.1) and oxygen content of 2.8%. The MG also exhibits outstanding optoelectrical properties, including ∼ 96.86% transparency and high conductivity (∼ 2.45 ×106 S m-1), comparable to CVD-synthesized graphene. Additionally, MG films demonstrate superior supercapacitive energy storage with a specific capacitance of ∼ 1363 F g-1 at 1 A g-1, surpassing thicker graphene and reduced graphene oxide films.