Electrochemical CO2 reduction

• Main Author: Begum, Afroza, 1975-
• Other Authors: Memorial University of Newfoundland. Dept. of Chemistry
• Format: Thesis
• Language: English
• Published: 2011
• Subjects: Carbon dioxide mitigation; Carbon dioxide > Industrial applications; Electrolytic reduction; Electrocatalysis; Newfoundland studies; University of Newfoundland
• Online Access: http://collections.mun.ca/cdm/ref/collection/theses5/id/14718

Thesis (Ph.D.)--Memorial University of Newfoundland, 2011. Chemistry Bibliography: leaves 192-209. Electrochemical methods for CO2 reduction have been receiving continuous attention for the last few decades mainly for the conversion of CO2 to fuels as an alternative global energy source and the inexpensive production of carboxylated products for industrial applications. CO2 is considered as a greenhouse gas, whose increasing concentration in the atmosphere is a growing environmental concern. The main obstacle for the direct electrochemical reduction of CO2 is the requirements of very high negative standard potential as high as -2.21 V vs SCE. Several transition-metal based molecular catalysts, for example, ruthenium polypyridyl complexes, were reported to convert CO2 to fuels, such as methanol, formic acid, oxalic acid, methane etc., at a lower cathodic potential. On the other hand, electrocatalytic conversions of CO2 using aromatic ketones were also found to be useful in the syntheses of medicinally useful materials, such as 2-arylpropanoic acids and α-oxocarboxylic acids (as anti-inflammatory drugs), agricultural chemicals and perfumes. A number of monometallic and bimetallic ruthenium benzimidazole and benzothiazole based polypyridyl complexes were synthesized in this work that were found to be operate as electrocatalysts for CO2 reduction at reasonable cathodic potentials. These complexes were characterized by cyclic voltammetry (CV), electronic absorption (UV-Vis) and emission, X-ray diffraction (XRD) techniques. -- Electrolysis of the complexes was performed to reveal their electrocatalytic effect on CO2 reduction. Product analysis by high-performance liquid chromatography (HPLC)/UV-Vis methods revealed that formate and oxalate are detectable in addition to some other products. In this study, it was found that structural variations in the electrocatalyst could influence the activity, however all benzothiazole containing complexes exhibited much higher activities than those of the corresponding benzimidazole complexes. Formate and oxalate were produced and detected at moderately low cathodic overpotentials for [{(bpy)2Ru}2(py2tbtz)]4+ . This is an unprecedented result for benzothiazole complexes. In addition, the electrochemical reduction of CO2 by fluorenone-9-one was found to produce 9-hydroxyfluorene and 9-hydroxyfluorene-9-carboxylic acid, in addition to formate and oxalate at a low cathodic overpotential.