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1. Ca ₂ Ga ₄ Ge ₆ and Ca ₃ Ga ₄ Ge ₆ : Synthesis, Structure, and Electronic Properties

   https://doi.org/10.1002/zaac.202100342  

   Hodge, Kelsey L; Davis, H Olivia; Koster, Karl G; Windl, Wolfgang; Moore, Curtis E; Goldberger, Joshua E (August 2022, Zeitschrift für anorganische und allgemeine Chemie)

   Abstract During the search for transition metal‐free alkyne hydrogenation catalysts, two new ternary Ca−Ga−Ge phases, Ca₂Ga₄Ge₆(Cmc2₁, a=4.1600(10) Å, b=23.283(5) Å, c=10.789(3) Å) and Ca₃Ga₄Ge₆(C2/m, a=24.063(2) Å, b=4.1987(4) Å, c=10.9794(9) Å, β=91.409(4)°), were discovered. These compounds are isostructural to the previously established Yb₂Ga₄Ge₆and Yb₃Ga₄Ge₆analogues, and according to Zintl‐Klemm counting rules, consist of anionic [Ga₄Ge₆]⁴⁻and [Ga₄Ge₆]⁶⁻frameworks in which every Ga and Ge atom would have a formal octet with no Ga−Ga or Ga−Ge π‐bonding. These compounds are metallic, based on temperature dependent electrical resistivity and thermopower measurements for Ca₃Ga₄Ge₆, along with density functional theory calculations for both phases. Unlike the highly active 13‐layer trigonal CaGaGe phase, these new compounds exhibit minimal activity in the semi/full alkyne hydrogenation of phenylacetylene, which is consistent with previous observations that the lack of a formal octet for framework atoms is essential for catalysis in these Zintl‐Klemm compounds. 

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2. Synergistic enhancement of chemical looping-based CO ₂ splitting with biomass cascade utilization using cyclic stabilized Ca ₂ Fe ₂ O ₅ aerogel

   https://doi.org/10.1039/C8TA10277E  

   Sun, Zhao; Wu, Xiaodong; Russell, Christopher K.; Dyar, M. Darby; Sklute, Elizabeth C.; Toan, Sam; Fan, Maohong; Duan, Lunbo; Xiang, Wenguo (January 2019, Journal of Materials Chemistry A)

   Thermochemical splitting of carbon dioxide to carbon-containing fuels or value-added chemicals is a promising method to reduce greenhouse effects. In this study, we propose a novel process for synchronous promotion of chemical looping-based CO 2 splitting with biomass cascade utilization. The superiority of the process is reflected in (1) a biomass fast pyrolysis process is carried out for syngas, phenolic-rich bio-oil, and biochar co-production with oxygen carrier reduction; (2) the reduced oxygen carrier and the biomass-derived biochar were both applied for CO 2 splitting during the oxygen carrier oxidation stage with carbon monoxide production as well as oxygen carrier re-oxidation; (3) the redox looping of the oxygen carrier was found to synchronously promote the comprehensive utilization of biomass and CO 2 splitting to CO. Various characterizations e.g. HRTEM- and SEM-EDX mapping, H 2 -TPR, CO 2 -TPO, XRD, XPS, N 2 nitrogen adsorption and desorption isotherm tests, Mössbauer, etc. were employed to elucidate the aerogels' microstructures, phase compositions, redox activity, and cyclic stability. Results indicate that the Ca 2 Fe 2 O 5 aerogel is a promising initiator of the proposed chemical looping process from the perspectives of biomass utilization efficiency, redox activity, and cyclic durability. 

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3. Unlocking the thermoelectric potential of the Ca ₁₄ AlSb ₁₁ structure type

   https://doi.org/10.1126/sciadv.abq3780  

   Justl, Andrew P.; Ricci, Francesco; Pike, Andrew; Cerretti, Giacomo; Bux, Sabah K.; Hautier, Geoffroy; Kauzlarich, Susan M. (September 2022, Science Advances)

   The interplay of synthesis, experiments, and theory in broadening the landscape of thermoelectric materials is reported. 

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4. Highly Surface-Active Ca(OH) ₂ Monolayer as a CO ₂ Capture Material

   https://doi.org/10.1021/acs.nanolett.7b04981  

   Özçelik, V. Ongun; Gong, Kai; White, Claire E. (March 2018, Nano Letters)

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5. Structure Effect on Pseudocapacitive Properties of A ₂ LaMn ₂ O ₇ (A = Ca, Sr)

   https://doi.org/10.1002/ente.202201249  

   Kananke-Gamage, Chandana C. W.; Ramezanipour, Farshid (January 2023, Energy Technology)

   Herein, the effect of structure on pseudocapacitive properties in alkaline conditions is demonstrated through the investigation of isoelectronic oxides Ca₂LaMn₂O₇and Sr₂LaMn₂O₇, where the difference in ionic radii of Ca²⁺and Sr²⁺leads to a change in structure and lattice symmetry, resulting in an orthorhombicCmcmstructure for the former and a tetragonalI4/mmmstructure for the latter. While calcium and strontium do not make a direct contribution to the near‐surface faradaic processes that are essential to the pseudocapacitive properties, their effect on the structure leads to a change in the oxygen intercalation process and the associated pseudocapacitive energy storage. It is shown that Sr₂LaMn₂O₇has a significantly greater specific capacitance than Ca₂LaMn₂O₇. In addition, the former shows a considerably higher‐energy density compared to the latter. Furthermore, these materials show highly stable energy‐storage properties, and retain their specific capacitance over 10 000 cycles of charge–discharge in a symmetric pseudocapacitive cell. Importantly, these findings show the structure–property relationships, where a change in the structure and lattice symmetry can result in a significant change in pseudocapacitive charge–discharge properties in isoelectronic systems. 

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