COPPER-BASED ELECTROCATALYSTS FOR ELECTROCHEMICAL REDUCTION OF CO2 TO C2 PRODUCTSThe electrochemical reduction of CO2 using copper-based electrocatalysts has emerged as a promising approach for sustainable chemical production, offering a pathway to mitigate the rising atmospheric CO2 levels while generating valuable fuels and chemicals. However, the selectivity and efficiency of copper-based catalysts towards specific C2 products remain a major challenge, hindering their commercial viability. This thesis focuses on the development, characterization, and mechanistic understanding of three promising electrocatalyst systems for multi-carbon product generation from CO2 reduction: copper-phosphide (Cu-P), copper-tin (Cu-Sn), and copper selenide (Cu2Se). A comprehensive investigation of the electrocatalysts was conducted using advanced characterization techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectrometry (ICP-OES). The electrochemical performance of the electrocatalysts was evaluated under various operating conditions in a zero-gap membrane electrode assembly (MEA) electrolyzer, which enables operation at industrially relevant current densities. The Cu-P0.065 electrocatalyst demonstrated a remarkable enhancement in ethylene selectivity, achieving a Faradaic efficiency (FE) of 52% at a current density of 150 mA cm-2 in 0.1 M KHCO3 electrolyte. The Cu-Sn0.03 electrocatalyst exhibited a notable shift in selectivity towards ethanol, with an FE of 48% at 350 mA cm-2 in 1 M KOH electrolyte. The Cu2Se electrocatalyst showcased a unique selectivity towards acetate production, achieving an FE of 32% at 350 mA cm-2 in 0.1 M KHCO3 electrolyte, surpassing the performance of the pure Cu electrode and previously reported Cu-Se electrocatalysts. Durability studies revealed the stability of the electrocatalysts under prolonged CO2 reduction conditions, with the Cu2Se electrocatalyst demonstrating exceptional structural integrity. Thermodynamic considerations based on Pourbaix diagrams highlighted the role of electronegative dopants in stabilizing the desired oxidation states of the electrocatalysts, contributing to their enhanced performance and stability. This thesis advances the understanding of CO2 reduction mechanisms for multi-carbon products on Cu-based electrocatalysts and provides valuable insights into the rational design of efficient and selective electrocatalysts. The development of the Cu-P0.065, Cu-Sn0.03, and Cu2Se electrocatalysts, with their remarkable selectivity, stability, and activity, represents a significant step forward in the field of electrochemical CO2 reduction.
Authors:   , Dauda Monsuru 
Published: June 2024

The electrochemical reduction of CO2 using copper-based electrocatalysts has emerged as a promising approach for sustainable chemical production, offering a pathway to mitigate the rising atmospheric CO2 levels while generating valuable fuels and chemicals. However, the selectivity and efficiency of copper-based catalysts towards specific C2 products remain a major challenge, hindering their commercial viability. This thesis focuses on the development, characterization, and mechanistic understanding of three promising electrocatalyst systems for multi-carbon product generation from CO2 reduction: copper-phosphide (Cu-P), copper-tin (Cu-Sn), and copper selenide (Cu2Se). A comprehensive investigation of the electrocatalysts was conducted using advanced characterization techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectrometry (ICP-OES). The electrochemical performance of the electrocatalysts was evaluated under various operating conditions in a zero-gap membrane electrode assembly (MEA) electrolyzer, which enables operation at industrially relevant current densities. The Cu-P0.065 electrocatalyst demonstrated a remarkable enhancement in ethylene selectivity, achieving a Faradaic efficiency (FE) of 52% at a current density of 150 mA cm-2 in 0.1 M KHCO3 electrolyte. The Cu-Sn0.03 electrocatalyst exhibited a notable shift in selectivity towards ethanol, with an FE of 48% at 350 mA cm-2 in 1 M KOH electrolyte. The Cu2Se electrocatalyst showcased a unique selectivity towards acetate production, achieving an FE of 32% at 350 mA cm-2 in 0.1 M KHCO3 electrolyte, surpassing the performance of the pure Cu electrode and previously reported Cu-Se electrocatalysts. Durability studies revealed the stability of the electrocatalysts under prolonged CO2 reduction conditions, with the Cu2Se electrocatalyst demonstrating exceptional structural integrity. Thermodynamic considerations based on Pourbaix diagrams highlighted the role of electronegative dopants in stabilizing the desired oxidation states of the electrocatalysts, contributing to their enhanced performance and stability. This thesis advances the understanding of CO2 reduction mechanisms for multi-carbon products on Cu-based electrocatalysts and provides valuable insights into the rational design of efficient and selective electrocatalysts. The development of the Cu-P0.065, Cu-Sn0.03, and Cu2Se electrocatalysts, with their remarkable selectivity, stability, and activity, represents a significant step forward in the field of electrochemical CO2 reduction.