Electrochemical and spectroscopic insights into the electroreduction of carbon dioxide to value added chemicals
The electroreduction of carbon dioxide to value-added chemicals, powered by renewable electricity, such as solar, wind, and geothermal energy, holds promise to enable the transition to carbon neutrality. This dissertation employs several methods to develop the porous and active catalysts for CO2 electroreduction and focuses on interrogating the electrocatalytic mechanisms for the CO2 conversion reaction through spectrochemical studies. Chapter 2 reports several high surface area Cu-based catalysts, prepared by the electro-deposition of Cu, Cu/Ag, and Cu/Sn alloy films with the addition of 3,5-diamino-1,2,4-triazole (DAT) as an electrodeposition inhibitor. All three Cu-based electrodes exhibit high Faradaic efficiency (FE) of CO2 reduction toward C2H4 production. The CuSn-DAT electrode exhibits the highest FE for CO (~90% at -0.4 V) and C2H4 (~60% at -0.8 V) production and high current density (~-225 mA/cm2). In situ Surface Enhanced Raman Spectroscopy (SERS) studies in a flow cell obtained from the three Cu-based samples show a correlation between the decreased oxide content on the Cu surface, increased presence of CO, and increased activity for CO and C2 production. The CuSn-DAT electrode has the lowest amount of Cu2O and exhibits the highest activity, whereas the Cu-DAT electrode has an increasing Cu2O content and exhibits lower activity as the potential is made negative. These results demonstrate that the incorporation of different well-mixed alloy materials provides a way to tune CO2 reduction speciation. Chapter 3 presents a copper-polyamine hybrid catalyst, developed through co-electroplating, that significantly increases the selectivity for ethylene production. The Faradaic efficiency for ethylene production is 87% ± 3% at -0.47 V versus reversible hydrogen electrode, with a full-cell energetic efficiency reaching 50% ± 2%. Raman measurements indicate that the polyamine entrained on the Cu electrode results in higher surface pH, higher CO content, and higher stabilization of intermediates relative to entrainment of additives containing little or no amine functionality. More broadly, this work shows that polymer incorporation can alter surface reactivity and lead to enhanced product selectivity at high current densities. Overall, studies reported in this dissertation provide both electrochemical and spectrochemical insights into the design of catalysts for the electroreduction of CO2 to the desired products, which guides the catalyst development for CO2RR and scale-up industry application.
CO2 electroreduction, Ethylene, Raman, Surface pH
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign