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Formation mechanism of graphite derived from CO2

Graphite is the most thermodynamically stable allotropic form under standard conditions. However, carbon with a low graphitization degree (amorphous carbon) is easy to produce in the carbonization of traditional carbon precursors due to the very high kinetic barrier for the formation of graphite. The graphitization of amorphous carbon at high temperatures is indispensable for synthesizing graphite. Our synthesis method is different from the above two-stage synthetic procedure. The conversion reaction from CO2 to graphite can occur without transition metal catalysts when the CO2‒LiAlH4 system is heated to as low as 126 °C, indicating a low kinetic barrier of the conversion reaction (1) for synthesizing graphite. The favorable thermodynamics and kinetics are responsible for the graphite being directly formed from CO2 at the temperature range of 126–876 °C within several seconds. The solid products of CO2 reacting with LiAH4 were heated at 880 °C for three h under argon. Few differences in graphitization degree are observed in the as-synthesized carbon with and without heat treatment at 880 °C, signifying that the amorphous carbon was not converted into graphite at 880 °C presence of LiAlO2, Li2CO3, and Al. For understanding the graphitization of amorphous carbon, first-principles calculation was employed to calculate the kinetic barriers. The activation energy is as high as 1.66 eV, supporting that amorphous carbon was not converted into graphite at 880 °C, and higher temperatures are needed for the graphitization of amorphous carbon. In other words, our graphite is directly synthesized by reacting CO2 with LiAlH4. The reaction kinetics for synthesizing graphite derived from CO2 is found to strongly depend on the CO2 pressure. The sudden changes in temperatures and gas pressure are also observed in the heating process when the initial gas pressure of CO2 was decreased to 35 bar, indicating an exothermic reaction of CO2 with LiAlH4. If you are looking for high quality, high purity, and cost-effective graphite or require the latest price, please email contact mis-asia.

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