Heterogeneous Capture and Release of Energy Metals Using Carborane-Tethered Electrodes

Abstract

Li and U are the only trace metals dissolved in seawater that are proposed to be economical to extract. Both are at very low concentrations (Li (0.17 ppm), U (3.3 ppb)); however, their total content are approximately 10,000 and 1,000 times higher than in land-based reserves, respectively, representing huge untapped resources which could be collected in an environmentally friendly manner. With surging demand for Li-ion batteries for energy storage, it is estimated that current production methods will soon not meet market demands. In addition, low-carbon nuclear energy production is also expected to increase dramatically in many major countries.Previous studies have shown that reduction of the substituted closo-carborane polyhedral cluster, 1,2-L2-C2B10H10, to the nido-carborane, [1,2-L2-C2B10H10]2-, resulted in the rupture of the C–C bond, cage opening, and an increased bite angle, Θ (Scheme). This talk will start by describing how we used this redox-controlled chelation for the selective electrochemical capture and release of UO2 2+ from mixed-metal mixtures mimicking spent nuclear fuel in monophasic and biphasic media (Scheme; M = UO2 2+; L = Ph2PO).1-2 We will then discuss our current efforts to target other metals of energy importance, in particular M = Li+, for seawater extraction by incorporating Li-selective donating groups, L (Scheme). This talk will then focus heavily on our current work on anchoring these carboranes onto electrode surfaces using anchoring groups – e.g., allyl, pyrene, or thiols – for heterogeneous capture and release using galvanostatic charge/discharge cycles. Recent, soon-to-be published results demonstrate the successful application of this redox-controlled chelation for heterogeneous, selective capture of UO2 2+ from mixed-metal mixtures. Keener, M.; Hunt, C.; Carroll, T. G.; Kampel, V.; Dobrovetsky, R.; Hayton, T. W.; Ménard, G. Redox-switchable carboranes for uranium capture and release. Nature 2020, 577, 652-655.Keener, M.; Mattejat, M.; Zheng, S.-L.; Wu, G.; Hayton, T. W.; Ménard, G. Selective electrochemical capture and release of uranyl from aqueous alkali, lanthanide, and actinide mixtures using redox-switchable carboranes. Chem. Sci. 2022, 13, 3369-3374. Figure 1