(217a) CO2-Derived CNT and Hierarchical Porous Carbon for Electrochemical Catalysis and Energy Storage

Our research group have developed various routes for thermal conversion of gaseous carbon dioxide (CO₂) to various carbon materials such as porous carbon, graphene and CNT at ambient pressure. We introduced ammonia borane (AB) as a reduction agent for securing BN-doped graphene oxide (GO) from 20 bars of CO₂. Because the GO product yield is too low in an AB-route, we have searched suitable reduction agent to give feasible carbon yields from the reaction with CO₂-containing gas. We have mainly used NaBH₄ for the synthesis of porous carbons and CNTs. This talk addresses CO₂ conversion to hierarchical porous carbon and paper-form interlayer for designing high-performance lithium-sulfur batteries. The hierarchical porous carbon was synthesized by reducing CO₂ in the presence of NaBH₄ with a nano-template of CaCO₃ particles and it has hierarchical porosity with a surface area of 900 to 1200 m²/g and a pore volume around 3 cm³/g. This high porosity can afford to accommodate a high amount of active sulfur material in the cathode. The sheet interlayer was prepared by electrospinning a mixture of PAN (95wt%) + NaBH4 (5wt%) and the subsequent CO₂ conversion leads to a mixed paper form of porous carbon and graphitic layer. Dispersing Fe-based molecular catalysts and sulfur-based active materials into the porous carbon electrode can significantly suppress the shuttle phenomenon based on superior chemical interactions. We used single atom catalysts with coordination bonds in form of Fe-N2 and Fe-N4, and obtained significantly higher electrochemical performance compared to bare carbon materials. DFT simulations elucidated the thermodynamic effects of Fe-N4 and Fe-N2 in terms of reducing the energy change in the redox reaction step and the barrier energy required for lithium ion diffusion. At the end of this talk, CO₂ conversion to crystalline carbon materials (CNT, Graphitic fiber, Graphene) will be also introduced for electrochemical catalysis of ORR reaction and energy storage.