Understanding heterogeneous growth mechanisms at graphene edges: a theoretical study on acetylene deposition and mechanistic analysis

This study aims to bridge significant knowledge gaps in the understanding of graphene growth mechanisms. We enhance current kinetic models through a detailed investigation of C2H2 deposition processes on solid graphene surfaces. These processes represent key elementary reaction steps in the complex heterogeneous network responsible for pyrocarbon formation during chemical vapor deposition and infiltration processes. Unlike previous methodologies that relied on analogies with gas-phase systems, our research meticulously explored the actual system, providing a comprehensive overview of the reactions involved in graphene growth at both armchair and zigzag edges. Utilizing transition state theory, we calculate accurate, temperature-dependent rate constants for all elementary reactions in graphene edge growth. This sheds light on the mechanisms and kinetics of pyrocarbon growth, including the potential for structural defect formation. Findings are compared with analogous gas-phase reactions responsible for soot particle formation, assessing the impact of surface interactions. A lumping technique is applied to reduce the complexity of species and reactions while preserving the accuracy of the chemical description. As such, this approach offers valuable insights into relevant pathways paving the way towards a deep understanding of the chemistry of the pyrolysis of hydrocarbons aiming to produce nanomaterials with targeted properties.DFT and CI-NEB are used to investigate potential energy surfaces and determine rate constants of C2H2 deposition on graphene edges. Chemical lumping enables implementation of the proposed rate constants in pyrocarbon deposition kinetic models.