Catalytic Cu2O/Cu Site Trades off the Coupling and Etching Reactions of Carbon Intermediates for CO2-Assisted Graphene Synthesis

Abstract

In the chemical vapor deposition (CVD) synthesis of graphene, the surficial chemical state of the metal substrate has exerted key roles in all elemental reaction steps determining the growth mechanism of graphene. Herein, a CO₂-participated annealing procedure is designed to construct catalytic Cu₂O/Cu sites on Cu foil for the graphene CVD synthesis with CO₂/CH₄ as carbon sources. These Cu₂O/Cu species can catalyze the CH₄ decomposition and subsequent C─C coupling to form C₂ intermediates for fast growth of monolayer hexagonal graphene domains with a diameter of ≈30 µm within 0.5 min. The graphene growth kinetics can be bidirectionally regulated merely with the variation of CO₂ flow rate during annealing and growth stages, in association with the Cu⁺/Cu⁰ ratio, enabling simultaneous control over the size and shape of graphene domains. Density functional theory (DFT) calculations indicate that the catalytic Cu₂O/Cu sites reduce the activation energy by ≈0.13 eV for the first dehydrogenation of CH₄, allowing the growing rate of graphene driven by coupling of C₂ intermediates faster than their etching rate by O-containing ^*O and ^*OH species. The work provides novel insights into heterostructured nano-catalyst consisting of zero valent metal and variably valent metal oxide that facilitate the controllable synthesis of graphene materials.