Assessing Thermodynamic Selectivity of Solid-State Reactions for the Predictive Synthesis of Inorganic Materials.

Synthesis is a major challenge in the discovery of new inorganic materials. Currently, there is limited theoretical guidance for identifying optimal solid-state synthesis procedures. We introduce two selectivity metrics, primary and secondary competition, to assess the favorability of target/impurity phase formation in solid-state reactions. We used these metrics to analyze 3520 solid-state reactions in the literature, ranking existing approaches to popular target materials. Additionally, we implemented these metrics in a data-driven synthesis planning workflow and demonstrated its application in the synthesis of barium titanate (BaTiO3). Using an 18-element chemical reaction network with first-principles thermodynamic data from the Materials Project, we identified 82985 possible BaTiO3 synthesis reactions and selected 9 for experimental testing. Characterization of reaction pathways via synchrotron powder X-ray diffraction reveals that our selectivity metrics correlate with observed target/impurity formation. We discovered two efficient reactions using unconventional precursors (BaS/BaCl2 and Na2TiO3) that produce BaTiO3 faster and with fewer impurities than conventional methods, highlighting the importance of considering complex chemistries with additional elements during precursor selection. Our framework provides a foundation for predictive inorganic synthesis, facilitating the optimization of existing recipes and the discovery of new materials, including those not easily attainable with conventional precursors.

Synthesis of flexible Co nanowires from bulk precursors.

This work reports a method of producing flexible cobalt nanowires (NWs) directly from the chemical conversion of bulk precursors at room temperature. Chemical reduction of Li6CoCl8 produces a nanocomposite of Co and LiCl, of which the salt is subsequently removed. The dilute concentration of Co in the precursor combined with the anisotropic crystal structure of the hcp phase leads to 1D growth in the absence of any templates or additives. The Co NWs are shown to have high saturation magnetization (130.6 emu g-1). Our understanding of the NW formation mechanism points to new directions of scalable nanostructure generation.

Fast Diagnosis of Failure Mechanisms and Lifetime Prediction of Li Metal Batteries.

Lithium (Li) metal serving as an anode has the potential to double or triple stored energies in rechargeable Li batteries. However, they typically have short cycling lifetimes due to parasitic reactions between the Li metal and electrolyte. It is critically required to develop early fault-detection methods for different failure mechanisms and quick lifetime-prediction methods to ensure rapid development. Prior efforts to determine the dominant failure mechanisms have typically required destructive cell disassembly. In this study, non-destructive diagnostic method based on rest voltages and coulombic efficiency are used to easily distinguish the different failure mechanisms-from loss of Li inventory, electrolyte depletion, and increased cell impedance-which are deeply understood and well validated by experiments and modeling. Using this new diagnostic method, the maximum lifetime of a Li metal cell can be quickly predicted from tests of corresponding anode-free cells, which is important for the screenings of electrolytes, anode stabilization, optimization of operating conditions, and rational battery design.

Selectivity in Yttrium Manganese Oxide Synthesis via Local Chemical Potentials in Hyperdimensional Phase Space.

In sharp contrast to molecular synthesis, materials synthesis is generally presumed to lack selectivity. The few known methods of designing selectivity in solid-state reactions have limited scope, such as topotactic reactions or strain stabilization. This contribution describes a general approach for searching large chemical spaces to identify selective reactions. This novel approach explains the ability of a nominally "innocent" Na2CO3 precursor to enable the metathesis synthesis of single-phase Y2Mn2O7: an outcome that was previously only accomplished at extreme pressures and which cannot be achieved with closely related precursors of Li2CO3 and K2CO3 under identical conditions. By calculating the required change in chemical potential across all possible reactant-product interfaces in an expanded chemical space including Y, Mn, O, alkali metals, and halogens, using thermodynamic parameters obtained from density functional theory calculations, we identify reactions that minimize the thermodynamic competition from intermediates. In this manner, only the Na-based intermediates minimize the distance in the hyperdimensional chemical potential space to Y2Mn2O7, thus providing selective access to a phase which was previously thought to be metastable. Experimental evidence validating this mechanism for pathway-dependent selectivity is provided by intermediates identified from in situ synchrotron-based crystallographic analysis. This approach of calculating chemical potential distances in hyperdimensional compositional spaces provides a general method for designing selective solid-state syntheses that will be useful for gaining access to metastable phases and for identifying reaction pathways that can reduce the synthesis temperature, and cost, of technological materials.

Anisotropic nanoporous morphology of ZnO-supported Co that enhances catalytic activity.

A novel conversion reaction synthesis (CRS) method is used to synthesize ZnO-supported Co nanoporous metal hybrid structures from a co-precipitated nanocomposite precursor of ZnO and Co3O4. After removal of Li2O with water, the resulting material consists of ZnO-supported Co nanoparticles that are interconnected to form anisotropic micro-particles. Additionally, individual ZnO nanoparticles have an anisotropic morphology, as revealed by synchrotron XRD analysis. Microscopy and surface area studies show these materials have an average pore size of 10-30 nm and specific surface areas up to 28 m2 g-1. The hybrid structure also has increased heat resistance compared to that of pure nanoporous metals; the Co phase within the ZnO-Co hybrid exhibits much less coarsening than the analogous nanoporous metal without ZnO at temperatures of 400 °C and above. These ZnO-Co hybrid materials were tested as heterogeneous catalysts for the steam reformation of ethanol at 400 °C. The nanoporous ZnO-Co hybrid material exhibits complete conversion of ethanol and high hydrogen selectivity, producing H2 with a molar yield of approximately 70%.