| dc.description.abstract | With the ever-rising CO₂ levels in the atmosphere, it is paramount to cease reliance on fossil fuels to meet global energy demands. While the cost of electricity from renewable sources, such as solar and wind, continues to decrease and has even fallen below that of fossil fuels since 2014, these renewable energy sources suffer from intermittency, potentially causing shortages at peak demands. Thus, methods to store or economically use excess renewable energy are needed for full decarbonization. One promising avenue is to store the excess generated electrical energy in chemical bonds, creating molecules and materials with industrial or energy storage utility. In this proposed scheme, the renewable electricity would be used to electrochemically convert earth-abundant molecules into value-added chemical or fuels. These generated products could then be utilized as feedstocks in industrial applications or as a fuel source to generate electricity when needed by transforming back into their earth-abundant forms.
Central to transforming earth-abundant molecules into value-added chemicals or fuels is the oxygen evolution reaction (OER), which is found in nearly every process. The plentiful nature of OER’s main reactant, water, and moderate thermodynamic potential of 1.23 V vs. the reversible hydrogen electrode, make OER an ideal reaction to pair with other transformations. However, the slow kinetics of OER significant hinder the efficiency of these processes. As such, discovering new OER catalysts with high activity and stability would have wide-spread impacts. On the other hand, one of the most promising renewable fuel sources is methanol, which boasts about 3 times the energy density of hydrogen and can be used as an alternative to hydrogen in proton exchange membrane fuel cells. However, the sluggish kinetics of the methanol oxidation reaction (MOR), even with current state-of-the-art noble metal catalysts causes direct methanol fuel cells to reach an efficiency of <40%, limiting their practical usage. While significant research has been invested in discovering new MOR electrocatalysts, PtRu has reigned for 5 decades, highlighting the need for a true breakthrough.
In this thesis, electrocatalysts for OER and MOR are examined in depth. For OER, metal-hydroxide organic frameworks (MHOFs), a promising new class of hybrid organic-inorganic materials with potential to mimic the superior functionality of enzymes, are studied. Operando vibrational and absorption spectroscopy methods are used to characterize the degradation mechanisms and lattice oxygen exchange capacity as a function of the linkers. Using such knowledge, defects are engineered into the MHOF that increase both the activity and stability compared to the pristine material. Furthermore, the traditionally reported MOR mechanism is studied using isotope-labeled reactants and operando mass spectrometry. These experiments revealed that, in contradiction to typically accepted mechanisms, the C-O bond in methanol can be cleaved during MOR, with the resulting CO₂ molecule containing two water-derived oxygen atoms, opening a new paradigm for MOR catalyst design. Driven by the need to discover new materials at scale, a fluorescence-based OER catalyst screening method is developed that can screen an entire composition space simultaneously. In addition, an AI-driven, automated platform for screening a high-dimensional multimetallic space for MOR is presented. | |
