| The factors that govern the electrochemical reduction of CO2 on Sn and Bi electrodes were studied. Chapter 1 discusses the relevant literature, the merits of reducing CO2 electrochemically, the ways in which CO2 reduction systems are characterized, and the outstanding challenges. Chapter 2 describes the design and construction of a differential electrochemical mass spectrometry (DEMS) system that can be used to probe the products of electrochemical reactions in situ and in real time.;In Chapter 3, the role of surface oxides and hydroxides in the reduction of CO2 on Sn electrodes is discussed. in situ attenuated total reflectance infrared (ATR-IR) spectroscopy is the main analytical technique by which the system was studied. Peaks that are attributed to a surface-bound Sn carbonate are present under conditions that are suitable for CO2 reduction. A strong correlation between the presence of these peaks and catalytic activity exists with respect to the applied potential, the pH of the electrolyte, and the surface condition of the electrode. X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and electrochemical analysis were also used characterize the catalysts. Based on these data, a mechanism for the reduction of CO2 on Sn cathodes is proposed.;The roles of morphology and surface oxide presence in the reduction of CO2 on Bi cathodes are discussed in Chapter 4. ATR-IR spectroscopy, XPS, EDX, SEM, cyclic voltammetry, and preparative electrolysis are used to demonstrate that, unlike Sn, Bi electrodes do not possess oxide-dependent catalytic behavior. Instead, it is shown that Bi electrodes are highly sensitive to morphological changes in surface structure, and that surface roughness is detrimental to HCOO-- production from CO2. Finally, it is shown that oxide-derived Bi, formed by the in situ reduction of Bi2O3 nanoparticles at cathodic potentials, can reduce CO2 to HCOO-- at near unit efficiencies at --1.55 V vs. Ag/AgCl. |
