Degree

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

Document Type

Dissertation

Abstract

The electrochemical CO2 reduction reaction (eCO2RR) in membrane electrode assembly (MEA) electrolyzers offers a compelling pathway for the sustainable production of value-added fuels and chemicals at industrially relevant current densities. To translate this promise into practical implementation, ambiguities regarding long-term selectivity, catalyst degradation, carbonate precipitation, and interfacial dynamics need to be mechanistically elucidated. Understanding these challenges requires a systematic investigation of the dynamic structural and chemical changes that occur under reaction conditions. We address these challenges by using synchrotron-based X-ray characterization to resolve the spatio-temporal evolution of Cu-based electrocatalysts under eCO2RR operating conditions.

Ex-situ inspection of the catalyst surface, pre- and post-electrocatalysis, has been conducted for various electrocatalyst binder (or ionomer) combinations, including Cu-PTFE, Cu-PVDF, and Cu-Nafion. Energy-dispersive X-ray spectroscopy (EDX) and Cu L-edge X-ray absorption spectroscopy (XAS) demonstrate that PTFE maintains the highest electrocatalyst loading on the gas diffusion layer, indicating sustained active sites for eCO2RR. Complementary carbon K-edge and potassium L-edge XAS reveal the presence of carbonates in K2CO3, KHCO3, and malachite forms.

The dilute Sn-doped copper catalyst (CuSn0.03) exhibits superior activity and selectivity compared to pure Cu and is therefore interrogated by operando energy-dispersive X-ray diffraction (ED-XRD) and XAS to reveal the evolution of the catalyst and the formation of salt phases in the gas diffusion electrode during eCO2RR. Operando ED-XRD provides direct insight into the spatiotemporal evolution of salt precipitation within the cathode, revealing heterogeneous KHCO3 nucleation, growth, dissolution, and redistribution throughout the catalyst and gas diffusion layers. These dynamic salt processes are closely coupled with local reaction conditions, product selectivity, and electrode stability.

Time-resolved operando XAS was used to investigate Cu nanoparticles (NP) and Cu2Se electrocatalysts at low current density. The catalyst is rapidly reduced at industrially relevant current densities. Slowing the reduction kinetics enabled us to investigate the transformation of both electrocatalysts using XANES and EXAFS, revealing a substantially more complex restructuring of Cu2Se than of Cu NP. Although both electrocatalysts contained a similar quantity of oxides even under reducing conditions, Cu2Se undergoes a structural transformation that, in turn, contributes to the metallic Cu phase on the catalyst surface.

Date

7-13-2026

Committee Chair

Phillip Sprunger

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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