Structure−Performance Relationships of Copper and Post−Transition Metals in Electrochemical CO2 Reduction

This PhD thesis delves into electrochemical CO2 reduction reactions (eCO2RR), aiming to convert CO2 into valuable chemicals and fuels for environmental sustainability. Chapter 1 introduces the motivation and challenges of eCO2RR, highlighting the low product selectivity and limited understanding of electrocatalyst design. Transition metal Cu is capable of producing C2+ products, but often with low product selectivity and high hydrogen production, while post-transition metals exhibit high selectivity for formic acid production and good hydrogen suppression ability. The thesis combines Cu with post-transition metals as electrocatalysts in eCO2RR and employs multiscale in situ characterization techniques to investigate the structure-performance relationship involved. In Chapter 2, CuxPby electrocatalysts are synthesized from industrial residue Fayalitic slags, with Cu to Pb ratios varied. This tuning improves CO selectivity, revealing a volcano-shaped relationship with the Cu/Pb ratio. Cu9.20Pb0.80 demonstrates a two-fold increase in CO selectivity compared to pure Cu, while excessive Pb hinders CO production. In situ Raman Spectroscopy underscores the importance of the reducibility of Cu+ and Pb2+ in enhancing CO selectivity. Chapter 3 focuses on Sn-doped CuO electrocatalysts, showing enhanced CO2 to CO formation compared to pure CuO. CuO−0.4%Sn achieves 98.0% CO selectivity at -0.75 V vs. RHE, suppressing H2 production to 2.0%. In situ Raman Spectroscopy and in situ XRD reveal catalyst activation, indicating Sn-doping inhibits the Hydrogen Evolution Reaction (HER) and enhances CO generation. Chapter 4 explores Bi-based electrocatalysts, specifically layered Bi oxyhalides (BiOX). BiOBr achieves 91.0% formic acid Faradaic Efficiency (FE) at -1.05 V vs. RHE, with in situ characterization uncovering structural transformations during catalysis. Different halides influence facet exposure, with the Bi(003) facet in BiOBr being more selective for formic acid formation. In situ X-ray Absorption Spectroscopy (XAS) measurements highlight the tunability of the reconstruction rate by the halogen type. Chapters 2 and 3 showcase the potential of combining transition metal Cu with post-transition metals to enhance eCO2RR product selectivity. Chapter 4 provides insights into the active sites of in situ activated Bi-based electrocatalysts, laying the foundation for rational design in renewable chemical and fuel production. In summary, this PhD thesis addresses challenges in eCO2RR, utilizing innovative electrocatalyst designs to enhance product selectivity and stability, and in situ characterization techniques to reveal the reaction mechanism. The findings contribute to the development of sustainable solutions for converting CO2 into valuable resources, demonstrating the feasibility of mitigating selectivity issues in eCO2RR through tailored electrocatalyst combinations.