UC Santa Barbara

Global energy consumption continues to increase annually, leading to dangerous levels of atmospheric carbon dioxide. To avoid irreparable harm to our planet, we need to rapidly convert our grid from fossil fuel dependence to low carbon sources of energy such as nuclear, wind and solar power. These technologies, however, need further development before the full conversion of our grid can occur. In this dissertation, we present advancements in spent nuclear fuel recycling and redox flow batteries for energy storage.In the first half, we studied the use of electrochemically switchable carboranes (polyhedral boron-carbon cluster compounds) for selective actinide capture from simulated spent nuclear fuel. Initially utilizing a biphasic approach, an organic phase containing an electrochemically generated ortho-substituted nido-carborane anion, (POCb2-) was found to selectively extract uranyl (UO22+) from a mixed-metal alkali (Cs+), lanthanide (Nd3+, Sm3+), and actinide (Th4+, UO22+) aqueous solutions. Bulk electrolysis of the organic phase was used to re-generate the closo-carborane (POCb) and release the captured UO22+, which was later back-extracted into a fresh aqueous phase. In a follow up study, we heterogenized our molecular, electrochemically switchable carboranes onto carbon electrodes. These functionalized electrodes demonstrated carborane-based heterogeneous electrochemical behaviour enhanced by the inclusion of single-walled carbon nanotubes (CNTs). Charged functionalized electrodes selectively captured and released actinides (Th4+, UO22+) from a mixed solutions containing alkali (Cs+), lanthanide (Nd3+, Sm3+) and actinide (Th4+, UO22+) metal ions. In the second half of my thesis, we demonstrated the use of commercially available phthalocyanine metal complexes (PcM) as cheap charge carriers in RFBs for green energy storage. Our systems utilized slurries of conductive carbon Ketjenblack (KB) to create electronically conducting percolation networks that interfaced with undissolved PcM. We found no significant performance differences between the commercial unsubstituted PcM and 1,4,8,11,15,18,22,25-octaethoxyphthalocyanine metal complexes (EtOPcM) synthesized with peripheral solubilizing substituents despite their increased solubility. Electrochemical analyses of several commercial first-row variants (PcTiCl2, PcVO, PcMnCl, PcFe, PcCo, PcNi, and PcCu) as well as one heavy-metal analogue (PcPb) revealed most to be effective charge carriers for slurry-based PcM/KB RFB applications. Cells using PcCu proved to have the highest efficiencies, energy density (1.23 Wh/L), and stability (>99% capacity retention) of the series while also having the lowest cost by mass.