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Lithium storage capacities beyond the stoichiometric limit of conversion have been reported for the transition metal oxides MnO, CoO, NiO, CuO, and beyond the alloying limit for the main group metal oxide SnO. This work examines the molecular mechanisms responsible for this extra capacity using first principles plane wave density functional theory with periodic boundary conditions. Energies of the optimized structures were employed to construct first discharge curves. Analysis of lithiated structures of transition metal oxides with moderate lithium content revealed the formation of two different phases within the electrode material, namely bulk metal and lithium oxide, Li 2 O. At higher lithium content, the interfacial region between the two phases was found to expand, giving rise to "free volume" for additional lithium storage. MnO had the highest free volume in the interfacial region for lithium storage, followed by CoO, NiO, CuO, and SnO. Of particular interest was CuO, which upon lithiation, formed linear and branched chains of Cu atoms that percolated throughout a large portion of the system. This behavior suggests that CuO may better maintain conductivity through the anode material for more cycles than the other transition metal oxides examined. Lithium ion batteries (LiBs) are commonly used as sources of power in portable electronics because of their high gravimetric capacity and power density, owing to the lighter molecular weight of lithium.1 Commercially available LiBs typically use graphite as the anode, LiCoO 2 as the cathode, and LiPF 6 in alkyl carbonate solvents as the electrolyte.2 The choice of materials for different components of LiBs, such as electrodes, electrolyte, current collectors, and the interactions between them, determine the overall battery performance. Increased energy demands have intensified the efforts to improve commercially available LiBs, especially to power electric vehicles and for load leveling applications.3 Materials with higher capacities than that of graphite and LiCoO 2 have been studied as electrode materials to improve the energy density of LiBs. 4,5 Different classes of materials that have been synthesized and tested for their electrochemical performance as prospective anode materials can be broadly divided into three classes based on their reactivity with lithium: intercalation, alloying, and conversion materials.6 Apart from carbon-based compounds, oxides of titanium that store lithium by means of intercalation have been studied because of their stability, wide availability, low cost, and good reversible capacity at an operating potential of 1.5 V vs Li/Li + . 7 But their theoretical capacity, which is lower than that of graphite (372 mAh g -1 ), and poor electronic conductivity have limited their application in high energy density LiBs. Alloying anode materials such as Si, Sb, Sn, SiO, SnO 2 , and Ge have higher theoretical capacities than graphite, but are limited by high volume expansion and high irreversible capacity losses after first cycle. 8Research has be...

Using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations, we conclusively demonstrate that acetaldehyde (AcH) undergoes aldol condensation when flown over ceria octahedral nanoparticles, and the reaction is desorption-limited at ambient temperature. trans -Crotonaldehyde (CrH) is the predominant product whose coverage builds up on the catalyst with time on stream. The proposed mechanism on CeO 2 (111) proceeds via AcH enolization (i.e., α C–H bond scission), C–C coupling, and further enolization and dehydroxylation of the aldol adduct, 3-hydroxybutanal, to yield trans -CrH. The mechanism with its DFT-calculated parameters is consistent with reactivity at ambient temperature and with the kinetic behavior of the aldol condensation of AcH reported on other oxides. The slightly less stable cis -CrH can be produced by the same mechanism depending on how the enolate and AcH are positioned with respect to each other in C–C coupling. All vibrational modes in DRIFTS are identified with AcH or trans -CrH, except for a feature at 1620 cm –1 that is more intense relative to the other bands on the partially reduced ceria sample than on the oxidized sample. It is identified to be the C=C stretch mode of CH 3 CHOHCHCHO adsorbed on an oxygen vacancy. It constitutes a deep energy minimum, rendering oxygen vacancies an inactive site for CrH formation under given conditions.

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Using DFT calculations and acetamide as the main example, we show that ceria is a potential catalyst for the hydrolysis of amide and similar bonds. The overall reaction is endergonic in the gas phase, yielding acetic acid and ammonia, but is slightly exergonic in the aqueous phase, which facilitates ionization of the products (CH 3 COO – and NH 4 + ). Neighboring Ce and O sites on the CeO 2 (111), (110), and (100) facets are conducive to the formation of an activated metastable tetrahedral intermediate (TI) complex, followed by C–N bond scission. With van der Waals and solvation effects taken into account, the overall reaction energetics is found to be most favorable on the (111) facet as desorption of acetic acid is much more uphill energetically on (110) and (100). We further suggest that the Ce–O–Ce sites on ceria surfaces can activate X(=Y)–Z type bonds in amides, amidines, and carboxylate and phosphate esters, among many others that we term “generalized esters”. A Brønsted-Evans–Polanyi relationship is identified correlating the stability of the transition and final states of the X–Z generalized ester bond scission. A simple descriptor (ΣΔχ) based on the electronegativity of the atoms that constitute the bond (X, Y, Z) versus those of the catalytic site (O, Ce, Ce) captures the trend in the stability of the transition state of generalized ester bond scission and suggests a direction for modifying ceria for targeting specific organic substrates.

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