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Author: Budak, Ö. ×

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    Carbide-Derived Niobium Pentoxide with Enhanced Charge Storage Capacity for Use as a Lithium-Ion Battery Electrode
    (Washington, DC : ACS Publications, 2020) Budak, Ö.; Geißler, M.; Becker, D.; Kruth, A.; Quade, A.; Haberkorn, R.; Kickelbick, G.; Etzold, B. J. M.; Presser, V.
    Nb2O5 has been explored as a promising anode material for use as lithium-ion batteries (LIBs), but depending on the crystal structure, the specific capacity was always reported to be usually around or below 200 mAh/g. For the first time, we present coarse-grained Nb2O5 materials that significantly overcome this capacity limitation with the promise of enabling high power applications. Our work introduces coarse-grained carbide-derived Nb2O5 phases obtained either by a one-step or a two-step bulk conversion process. By in situ production of chlorine gas from metal chloride salt at ambient pressure, we obtain in just one step directly orthorhombic Nb2O5 alongside carbide-derived carbon (o-Nb2O5/CDC). In situ formation of chlorine gas from metal chloride salt under vacuum conditions yields CDC covering the remaining carbide core, which can be transformed into metal oxides covered by a carbon shell upon thermal treatment in CO2 gas. The two-step process yielded a mixed-phase tetragonal and monoclinic Nb2O5 with CDC (m-Nb2O5/CDC). Our combined diffraction and spectroscopic data confirm that carbide-derived Nb2O5 materials show disordering of the crystallographic planes caused by oxygen deficiency in the structural units and, in the case of m-Nb2O5/CDC, severe stacking faults. This defect engineering allows access to a very high specific capacity exceeding the two-electron transfer process of conventional Nb2O5. The charge storage capacities of the resulting m-Nb2O5/CDC and o-Nb2O5/CDC are, in both cases, around 300 mAh/g at a specific current of 10 mA/g, thereby, the values are significantly higher than that of the state-of-the-art for Nb2O5 as a LIB anode. Carbide-derived Nb2O5 materials also show robust cycling stability over 500 cycles with capacity fading only 24% for the sample m-Nb2O5/CDC and 28% for o-Nb2O5/CDC, suggesting low degree of expansion/compaction during lithiation and delithiation.
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    High-performance ion removal via zinc–air desalination
    (Amsterdam : Elsevier, 2020) Srimuk, P.; Wang, L.; Budak, Ö.; Presser, V.
    Electrochemical processes enable a new generation of energy-efficient desalination technologies. While ion electrosorption via capacitive deionization is only suitable for brackish water with low molar strength, the use of Faradaic materials capable of reversible ion intercalation or conversion reactions allows energy-efficient removal of ions from seawater. However, the limited charge transfer/storage capacity of Faradaic materials indicates an upper limit for their desalination applications. Therefore, a new electrochemical concept must be explored to exceed the current state-of-the-art results and to push the desalination capacity beyond 100–200 mgNaCl/gelectrode. In this proof-of-concept work, we introduce the new concept of using metal–air battery technology for desalination. We do so by presenting performance data for zinc–air desalination (ZAD) in 600 mM NaCl. The ZAD cell provides a desalination capacity of 0.9–1.0 mgNaCl/cm2 (normalized to the membrane area; corresponding to 1300 mgNaCl/gZn) with a charge efficiency of 70% when charging/discharging the cell at 1 mA/cm2. The energy consumption of ZAD is 68–92 kJ/mol.