Abstract
Electrochemical exfoliation is a promising bulk method for producing graphene from graphite; in this method, an applied voltage drives ionic species to intercalate into graphite where they form gaseous species that expand and exfoliate individual graphene sheets. However, a number of obstacles have prevented this approach from becoming a feasible production route; the disintegration of the graphite electrode as the method progresses is the chief difficulty. Here we show that if graphite powders are contained and compressed within a permeable and expandable containment system, the graphite powders can be continuously intercalated, expanded, and exfoliated to produce graphene. Our data indicate both high yield (65%) and extraordinarily large lateral size (>30 μm) in the as-produced graphene. We also show that this process is scalable and that graphene yield efficiency depends solely on reactor geometry, graphite compression, and electrolyte transport.
Highlights
Graphene, i.e., a single layer of sp2-hybridized carbon, is rightly touted for its superlative material properties and has been demonstrated both as a novel building block and as an additive for a wide range of multifunctional materials[1,2]
Graphene oxide may be thermally or chemically reduced to yield “reduced graphene oxide” nanosheets that retain some of their defects and oxygen-containing functional groups17–20. (ii) In contrast, pristine graphene is typically mechanically exfoliated from graphite, often in a liquid medium with sonication or shear mixing, but the actual product is a mixture of pristine graphene and unexfoliated graphite[16,21,22,23,24,25,26,27,28,29,30,31]
In ammonium sulfate, the sulfate ions and water molecules migrate into the interstitial regions of the graphite and locally form gas bubbles, which forces adjacent sheets apart (Fig. 1a)[1]. Despite these advances in electrochemical exfoliation, there are a number of major challenges facing the field: (i) Only graphite monoliths may be used as a source for electrochemical exfoliation because the graphite electrode must be continuous, electrically conductive, and connected to the external power supply. (ii) Most importantly, if electrochemical exfoliation occurs and the monolith is expanded to form graphene, the monolith disintegrates and the electrochemical exfoliation process stops
Summary
I.e., a single layer of sp2-hybridized carbon, is rightly touted for its superlative material properties and has been demonstrated both as a novel building block and as an additive for a wide range of multifunctional materials[1,2]. Several recent reports have described advances in scalable (better than linear) methods for production of few-layer pristine graphene from graphite[21] This analysis invariably neglects the problem of separating the as-produced graphene from the unexfoliated graphite; such separation techniques are notoriously difficult to scale up[32]. In ammonium sulfate, the sulfate ions and water molecules migrate into the interstitial regions of the graphite and locally form gas bubbles (such as SO2, O2), which forces adjacent sheets apart (Fig. 1a)[1] Despite these advances in electrochemical exfoliation, there are a number of major challenges facing the field: (i) Only graphite monoliths (as opposed to loose graphite powders) may be used as a source for electrochemical exfoliation because the graphite electrode must be continuous, electrically conductive, and connected to the external power supply. We discuss the “yield” of these processes in further detail below
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