Embedding Fe-Nx Structure in Porous Carbon Nanospheres for Enhanced CO2 Electroreduction to CO

Abstract

Electrochemical reduction of carbon dioxide (CO2ER) reaction has become an attractive and promising approach to convert CO2 into fuels and high-value-added chemicals. However, the electrochemical reduction of CO2 suffers from sluggish reaction kinetics and poor product selectivity. Therefore, the development of efficient catalysts with high electrochemical catalytic ability and selectivity is in high demand. To this regard, this thesis aims to develop a novel embedded Fe-Nx structure in porous carbon nanospheres as catalysts for efficient CO2ER, and to disclose the relationship between enhanced for efficiency and structural regulation.

In Chapter 1, current catalysts for electrochemical reduction CO2 have been systematically reviewed including metallic-based materials, metal oxides, transition-metal dichalcogenides, single-atom confined materials, and metal-free carbon-based materials. The conversions from CO2 into diversities of products were also discussed according to the relevant catalytic process. Chapter 2 gives the experimental details for this research project, including the chemicals, devices, fabrications of the catalysts and the testing protocols for physical characterizations and electrochemical performance of the as-prepared materials. Chapter 3 develops a novel catalyst for CO2 conversion into CO. 5,10,15,20-Tetraphenyl-21H,23H-porphine iron (III) chloride (Fe-TPP precursor) was embedded into zeolitic imidazolate framework-8 (ZIF-8) and finally obtained a Fe-Nx structure onto porous carbon nanosphere. The porous carbon nanospheres were prepared by a silica-protected strategy. The content of active sites Fe-Nx exposed for efficient catalysis is quite limited, which hinder the performance of catalysts. The hierarchical porous structures expose more Fe-Nx sites, which would enhance the properties of Fe-Nx-C catalysts. The local pH change near the catalyst surface and the influence of mesoporosity are also investigated. The results indicate that the mesoporosity can boost CO2 and proton diffusion and improve CO current density for CO2ER. Chapter 4 summarises the research findings and also offers several perspectives for enhancing CO2ER in the future.