TY - THES

T1 - MOF-Derived Metal-Carbon Composite Materials as Bifunctional Catalyst for Zn-Air Battery

AU - Sanli, Artun

N1 - embargoed until null

PY - 2021

Y1 - 2021

N2 - Starting with the industrial revolution, global energy demand grew rapidly and fossil fuels began to be used to meet the energy demand. The consumption of fossil fuels increased rapidly with the improvement in technology and growth in population and thus became a threat to our environment. In order to replace fossil fuels with the green energy, alternative energy storage devices are necessary. Currently used Li-Ion batteries are far from satisfying the world’s needs and metal-air batteries are promising candidates due to to their high energy density (1084 Wh kg-1) while utilizing one of the most abundant elements in the world, zinc. However, the necessary reactions for metal-air batteries--Oxygen Reducing Reaction (ORR) and Oxygen Evolution Reaction (OER)--are highly sluggish, and this delays the industrialization of metal-air batteries. Catalysts are strictly needed to guide these reactions and change their paths. Although some noble catalysts like, Pt for ORR and IrO2 and RuO2 for OER possess established efficiencies, these materials are rare and expensive, and thus are not optimal for industrialization but rather used for research purposes. Metal organic frameworks (MOFs) derived materials are alternative to noble catalysts, thanks to their high tunability, high surface area and hierarchical porous structure. MOF-derived materials often need high pyrolyzing temperatures for graphitization and also removal of metal centers. As an alternative Cd based MOF derived material is offered because of the low boiling temperature of Cd (767 °C). Cd MOF’s were synthesized by various modulating ligand ratios and synthesis times which resulted in different morphologies and particle sizes. Zn- ZIF-8 with various modulating ligand ratios were also synthesized in order to obtain similar particle size for optimal comparison. Samples were pyrolyzed in different temperatures, temperatures that are higher and lower than Cd boiling temperature and characterized. ORR and OER measurements were executed to understand the catalytic performance of Cd and Zn samples. Pyrolyzed Cd samples have shown much smaller CV plot, which indicates lower double-layer capacitance thus much lower surface area. Despite having much lower surface areas, pyrolyzed Cd samples have shown better or similar catalytic performance in ORR and much smaller Tafel- slopes, which were on par with reference Pt/C catalyst. OER performances of both samples were not good. The promising results gained from Cd catalysts have shown that more investigation is necessary to increase the surface area in order to be used in metal-air battery applications.

AB - Starting with the industrial revolution, global energy demand grew rapidly and fossil fuels began to be used to meet the energy demand. The consumption of fossil fuels increased rapidly with the improvement in technology and growth in population and thus became a threat to our environment. In order to replace fossil fuels with the green energy, alternative energy storage devices are necessary. Currently used Li-Ion batteries are far from satisfying the world’s needs and metal-air batteries are promising candidates due to to their high energy density (1084 Wh kg-1) while utilizing one of the most abundant elements in the world, zinc. However, the necessary reactions for metal-air batteries--Oxygen Reducing Reaction (ORR) and Oxygen Evolution Reaction (OER)--are highly sluggish, and this delays the industrialization of metal-air batteries. Catalysts are strictly needed to guide these reactions and change their paths. Although some noble catalysts like, Pt for ORR and IrO2 and RuO2 for OER possess established efficiencies, these materials are rare and expensive, and thus are not optimal for industrialization but rather used for research purposes. Metal organic frameworks (MOFs) derived materials are alternative to noble catalysts, thanks to their high tunability, high surface area and hierarchical porous structure. MOF-derived materials often need high pyrolyzing temperatures for graphitization and also removal of metal centers. As an alternative Cd based MOF derived material is offered because of the low boiling temperature of Cd (767 °C). Cd MOF’s were synthesized by various modulating ligand ratios and synthesis times which resulted in different morphologies and particle sizes. Zn- ZIF-8 with various modulating ligand ratios were also synthesized in order to obtain similar particle size for optimal comparison. Samples were pyrolyzed in different temperatures, temperatures that are higher and lower than Cd boiling temperature and characterized. ORR and OER measurements were executed to understand the catalytic performance of Cd and Zn samples. Pyrolyzed Cd samples have shown much smaller CV plot, which indicates lower double-layer capacitance thus much lower surface area. Despite having much lower surface areas, pyrolyzed Cd samples have shown better or similar catalytic performance in ORR and much smaller Tafel- slopes, which were on par with reference Pt/C catalyst. OER performances of both samples were not good. The promising results gained from Cd catalysts have shown that more investigation is necessary to increase the surface area in order to be used in metal-air battery applications.

KW - MOF

KW - ZIF

KW - ORR

KW - bicatalyst

KW - MOF

KW - ZIF

KW - ORR

KW - bicatalyst

M3 - Master's Thesis

ER -