thermal, electrical, and optical properties. [2] In particular, graphene exhibits extremely high mobility of charge carriers, enormously large specific surface area, and superior thermal conductivity, which allow graphene to be widely applied in the fields of energy conversion and storage, materials, environment, and biomedicine. [3] The huge demand for its application thus necessitates the development of large-scale, low-cost, and efficient synthesis of graphene. [4] So far, various methods have been developed to synthesize graphene, such as mechanical cleavage of graphite, chemical vapor deposition (CVD), epitaxial growth, reduction of exfoliated graphene oxide, chemical pyrolysis, and flash Joule heating. [5] The monolayer graphene was first obtained in 2004 with a tape-assisted mechanical exfoliation of graphite. [6] Similarly, KOH-assisted microwave exfoliation was also used to synthesize porous graphene oxide paper in 2011. [7] The simple mechanical cleavage operation is easy to follow, but its scalability, yield efficiency, and product quality need further improvement. Instead, CVD technique was adopted in the preparation of high-quality graphene but it suffered from high cost, low yield, and requirement of proper substrates that limited the wider application of graphene. [8] Alternatively, Sutter obtained epitaxially grown graphene on SiC in 2009 and this method is now capable of yielding continuous, uniform, and large-area graphene though isolating graphene from the substrate still remains a challenge. [9] Soon, reduction of exfoliated graphene oxide was also reported to obtain graphene, [10] followed by a chemical pyrolysis strategy demonstrated to synthesize graphene from sodium gluconate or sodium citrate in 2018. [11] These methods have their own merits of large-scale production but either their procedure complexity or environmental toxicity should be taken into further consideration. Recently, the flash Joule heating method to acquire graphene was proposed by Tour in 2020. [5f ] Such an economic, ultrafast, and scalable strategy was applied for the high-quality graphene production, but the flash graphene suffered from the lowest defect concentrations reported so far for graphene that severely limited the wider application (such as single atom catalysis). As such, it is of great significance to develop new methodology capable of providing freestanding graphene with merits of high-quality, high yield, low cost, and contamination-free to further boost its practical applications.Novel methods and mechanisms for graphene fabrication are of great importance in the development of materials science. Herein, a facile method to directly convert carbonaceous salts into high-quality freestanding graphene via a simple one-step redox reaction, is reported. The redox couple can be a combination of sodium borohydride (reductant) and sodium carbonate (oxidant), which can readily react with each other when evenly mixed/calcined and yield gram-scale, high-quality, contamination-free, micron-sized, freestanding gra...
