The graphene formation via flash Joule heating: The effect of cooling rate

Conventional graphene synthesis encounter significant challenges in scalability, cost, and efficiency, which hinder their industrial applicability. Although flash Joule heating (FJH) enables the efficient and cost-effective production of high-quality graphene, its underlying mechanism, particularly the effect of cooling rate, has not been thoroughly investigated. In this work, ReaxFF molecular dynamics (ReaxFF MD) simulations were utilized to investigate the conversion of natural rubber into graphene via FJH. The results demonstrated that the rapid cooling process played a critical role in flash graphene formation. Radial distribution function analysis confirmed that the products obtained under cooling were high-quality graphene, with further improvements observed at slower cooling rates (0.22 K/ps and 0.44 K/ps). Moreover, potential energy assessments indicated that cyclization occurred more rapidly under ultrafast cooling, resulting in lower-quality graphene. Two crucial mechanisms were revealed to govern graphene formation via FJH. Firstly, the carbon source underwent rapid pyrolysis at transient high temperatures, during which tar and gases were released, leaving behind a char residue that condensed into graphene during the subsequent rapid cooling stage. Secondly, the reduction in system potential energy during the cooling process facilitated cyclization, with the reaction initiating once the potential energy reached approximately 75000 kcal/mol.