Oxidating Fresh Porous Graphene Networks toward Ultra‐Large Graphene Oxide with Electrical Conductivity

Abstract Ultra‐large graphene oxide (ULGO) is one of the most important graphene derivates because of its processability in constructing various macrostructures with unique properties. However, existing oxidation–exfoliation technologies are limited in the available size range, structure controllability, and preparation efficiency of ULGO by the slow oxidant diffusion among graphite interlayers. Herein, a highly efficient strategy to fabricate ULGO featuring the oxidation of porous graphene networks freshly derived from electrochemical delamination, which highlights the significance of not only creation but also keeping of the fast diffusion channels for oxidant, is proposed. Consuming only 40 min and ultralow oxidant dosage (1 wt equiv.), this economical oxidation realizes high‐yield preparation (≈99.5%) of ULGO with record‐large average size (188.3 µm) and unusual low‐defect structure. Unlike previous reports, free‐standing films assembled from the as‐prepared ULGO exhibit an unexpected electrical conductivity (305.3 S m⁻¹) alongside record‐breaking mechanical properties (21.2 GPa in Young's modulus, 392.1 MPa in tensile strength). Also, the advantage of ULGO in constructing commercially desirable thick graphene films with high thermal conductivity is demonstrated (≈100 µm, 1576.1±26.7 W m⁻¹ K⁻¹). This new strategy based on new findings in mechanism provides a highly efficient route to enlarge lateral size and expand physical properties of graphene oxide.