Scalable and high-yield production of exfoliated graphene sheets in water and its application to an all-solid-state supercapacitor

One of the most critical issues in graphite exfoliation is realizing efficient, low-cost, eco-friendly, and scalable production of graphene for energy storage applications. The most promising strategies for exfoliating graphite to single-layer graphene sheets in scalable quantities with nearly non-oxidized content is the exfoliation of graphite by using an environmentally friendly solution. Herein, we demonstrate a universal exfoliation principle that uses imidazole, which has an anionic nature and pi-conjugated heterocyclic coplanar structure, as the exfoliant for the successful production of large quantities of graphene suspensions in water. The exfoliant interacts with both surfaces of the exfoliated graphene sheets and the aqueous solution, significantly improving graphene dispersion (1 mg/mL) in water. Exfoliation in aqueous solutions produced graphene in high yield (>90%, <= 3 layers), with a large lateral size (mu m) and high quality (I-D/I-G ratio approximate to 0.1). The electrical conductivity of the graphene paper is 131.7 S/cm, which is superior to the values reported from exfoliated graphene prepared using solution processes. An all-solid-state supercapacitor with a new design fabricated using the atomically thin and flat conductive exfoliated graphene sheets delivered an ultrahigh area capacitance (similar to 71.9 mF/cm(2)). Therefore, imidazole-assisted exfoliation has great potential for scalable preparation of graphene suspensions for supercapacitor applications. (C) 2015 Elsevier Ltd. All rights reserved.