Electrochemcial Reduction Of CO₂to Formate On Tin Oxide And Bismuth Based Catalysts

Development of industrialization and modern civilization changes patterns of human life and provides many convenience to us. However attendant negative effects are gradually exposed. In recent decades, more attention was paid to the sustainable development of the environment and energy due to a large amount of energy consumption and outbreaks of environmental issues. With the increase of global average temperatures rise and emergence of extreme weather, the "greenhouse effect" is being mentioned more and more. Carbon dioxide is also studied extensively as a major greenhouse gas.By using electricity generated from renewable energy, carbon dioxide can be electrochemical reduced into carbon monoxide, formic acid, alcohols and hydrocarbon. However, the electrochemical reduction of carbon dioxide faces many problems:(i) lowing the overpotential so that the reaction can occur more easily,(ii) accelerating the reaction rate, to improve the conversion rate of the CO2per unit of time,(iii) increasing the current efficiency of the reaction and the selectivity to the target product.For these reasons, we hope to improve the activity of some common catalysts through changing their component and structure. By studying the activity of tin oxide and Bi based catalysts for electrochemical reduction of CO2, we found that oxygen vacancy promoted formation of formate on tin oxide and nanostructure Bi reduced from BiOC1showed better activity than commercial Bi powder.In the second chapter, we discussed the effects of oxygen vacancies on the tin oxide for electro-reduction of carbon dioxide. We found that when the initial sample of tin oxide contains oxygen vacancies, its ability of electro-reduction of carbon dioxide could be improved. This is reflected in two aspects:(i) increasing the reaction rate of the reduction of carbon dioxide,(ii) improving the selectivity of the conversion of carbon dioxide to formate. This phenomenon can be observed in both hydrothermal synthesis and commercial tin oxide. By using electrochemical methods, we found that the presence of oxygen vacancy could accelerate electron transfer and resulted in increasing of the reaction rate. On the other hand, more CO2might be adsorbed in a way which was benefit for the formation of formate when more oxygen vacancy existed.In the third chapter, we studied the catalytic activity of five bismuth based catalysts, including Bi powder, Bi2O3, BiOC1, BiPO4and Bi2WO6. These materials showed good catalytic activity towards CO2reduction except Bi2WO6. BiOC1was the best among them. We found the activity of these materials for electro-reduction of carbon dioxide came from bismuth which was generated after electrolysis and further study of BiOC1 confirmed this conclusion. We found the bismuth reduced from BiOC1had nanostructure, such a structure may facilitated the electrochemical reduction of CO2on its surface.