Exfoliation of Graphite into Graphene in Aqueous Solutions of Inorganic Salts

TLDR

Mass production of high‑quality graphene sheets is essential for their practical application in electronics, optoelectronics, composite materials, and energy‑storage devices. Here we report a prompt electrochemical exfoliation of graphene sheets into aqueous solutions of different inorganic salts ((NH4)2SO4, Na2SO4, K2SO4, etc.). Highly conductive graphene films (11 Ω sq⁻¹) are readily fabricated on A4‑size paper by brush‑painting a concentrated graphene ink (10 mg mL⁻¹ in N,N′‑dimethylformamide). The exfoliation yields >85 % graphene with ≤3 layers, lateral sizes up to 44 µm, C/O ratio 17.2, and hole mobility 310 cm² V⁻¹ s⁻¹; the films enable flexible supercapacitors with 11.3 mF cm⁻² capacitance and 5000 mV s⁻¹ rate, demonstrating industrial‑scale potential.

Abstract

Mass production of high-quality graphene sheets is essential for their practical application in electronics, optoelectronics, composite materials, and energy-storage devices. Here we report a prompt electrochemical exfoliation of graphene sheets into aqueous solutions of different inorganic salts ((NH4)2SO4, Na2SO4, K2SO4, etc.). Exfoliation in these electrolytes leads to graphene with a high yield (>85%, ≤3 layers), large lateral size (up to 44 μm), low oxidation degree (a C/O ratio of 17.2), and a remarkable hole mobility of 310 cm2 V–1 s–1. Further, highly conductive graphene films (11 Ω sq–1) are readily fabricated on an A4-size paper by applying brush painting of a concentrated graphene ink (10 mg mL–1, in N,N′-dimethylformamide). All-solid-state flexible supercapacitors manufactured on the basis of such graphene films deliver a high area capacitance of 11.3 mF cm–2 and an excellent rate capability of 5000 mV s–1. The described electrochemical exfoliation shows great promise for the industrial-scale synthesis of high-quality graphene for numerous advanced applications.