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The implementation of thermal energy storage (TES) can improve the efficiency of existing industrial processes, and enable new applications that require the uptake/release of heat on-demand. Among the myriad strategies for TES, thermochemical hydration/dehydration reactions are arguably the most promising due to their high energy densities, simplicity, cost effectiveness, and potential for reversibility at moderate temperatures. The present study uses first-principles calculations to identify TES materials that can out-perform known compounds. High-throughput density functional theory calculations were performed on metal halide hydrates and hydroxides mined from the Inorganic Crystal Structure Database. In total, 265 hydration reactions were characterized with respect to their thermodynamic properties, gravimetric and volumetric energy densities, and operating temperatures. Promising reactions were identified for three temperature ranges: low (<100 °C), medium (100−300 °C), and high (>300 °C). Several high-energy-density reactions were identified, including the dehydration of CrF 3 •9H 2 O, a compound that appears to be unexplored for TES. Correlations linking TES performance with dozens of chemical features for hydrates and hydroxides were quantified using a Pearson correlation matrix. These analyses reveal property− performance relationships involving energy densities and the thermodynamics of hydration. In salt hydrates, the thermodynamics depend strongly on the water capacity of the hydrate. In hydroxides, thermodynamic properties are largely determined by the ionicity of the cation−hydroxide bond, which is in turn influenced by the cation's electronegativity and polarizing power. Based on these correlations, design rules for hydration-based TES systems are proposed.

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Magnesium (Mg) metal is a promising anode material for use in next-generation batteries because of its high theoretical energy density, abundance, and its reduced tendency to form dendrites as compared to lithium metal. Nonetheless, the development of a practical Mg battery presents several challenges. Among these challenges is the decomposition of the electrolyte solvent, which can contribute to passivation of the anode surface, thereby preventing reversible plating/stripping of Mg during battery cycling. The present study examines the thermodynamics and kinetics of electrode-mediated solvent decomposition in Mg batteries using first-principles calculations. The initial steps in the reaction pathway associated with decomposition of a model solvent, dimethoxyethane (DME), on three relevant electrode surface compositionsMg(0001), MgO(100), and MgCl2(0001)are examined. The energetics of DME decomposition are highly dependent on the composition of the anode surface. On the pristine Mg surface, decomposition is predicted to be highly exothermic, to proceed via a pathway with a low kinetic barrier, and to result in the evolution of ethylene gas. The tendency for DME to decompose on the Mg(0001) surface is rationalized via a charge-transfer analysis: reductive charge transfer from the electrode minimizes reaction barriers and stabilizes decomposition products. Conversely, decomposition is unfavorable on the oxide and chloride surfaces, where thermoneutral reaction enthalpies and large reaction barriers are observed. These latter calculations support the hypothesis that a Mg–Cl “enhancement layer” on the anode surface can improve the performance.

Soot particles are a significant pollutant formed as the result of incomplete combustion. Particle nucleation significantly impacts the formation and morphology of soot particles, yet remains a key knowledge gap. To elucidate the process of nucleation, we have investigated the thermodynamic stability of dimers of polycyclic aromatic hydrocarbons (PAHs), towards developing a more comprehensive model for PAH clustering behavior. Using a computational methodology based on molecular dynamics and well-tempered Metadynamics, we quantified the impact of morphological parameters on homo-molecular dimerization, as well as the relative size of monomers on the stability of hetero-molecular dimers. The results illustrated the substantial impact of PAH mass and geometry on the stability of homo-molecular and hetero-molecular dimers at flame temperatures. In particular, dimer stability was found to depend most strongly on monomer mass, followed by solvent-accessible surface area. Additionally, heteromolecular dimer stability was found to be largely determined by the size of the smallest monomer. Identifying relationships between PAH morphology and thermodynamic stability is a significant step towards a more comprehensive understanding of the physical interactions between PAHs. Altogether, this work presents a framework for elucidating the clustering behavior of arbitrary PAHs and will greatly impact understanding and modeling of particle nucleation and growth.

Owing to their high theoretical capacities, batteries that employ lithium (Li) metal as the negative electrode are attractive technologies for next-generation energy storage. However, the successful implementation of lithium metal batteries is limited by several factors, many of which can be traced to an incomplete understanding of surface phenomena involving the Li anode. Here, first-principles calculations are used to characterize the native oxide layer on Li, including several properties associated with the Li/lithium oxide (Li 2 O) interface. Multiple interface models are examined; the models account for differing interface (chemical) terminations and degrees of atomic ordering (i.e., crystalline vs amorphous). The interfacial energy, formation energy, and strain energies are predicted for these models. The amorphous interface yields the lowest interfacial formation energy, suggesting that it is the most probable model under equilibrium conditions. The work of adhesion is evaluated for the crystalline interfaces, and it is found that the O-terminated interface exhibits a work of adhesion more than 30 times larger than that of the Li-terminated model, implying that Li will strongly wet an oxygen-rich Li 2 O surface. The electronic structure of the interfaces is characterized using Voronoi charge analysis and shifts in the Li 1s binding energies. The width of the Li/Li 2 O interface, as determined by deviations from bulklike charges and binding energies, extends beyond the region exhibiting interfacial structural distortions. Finally, the transport of Li ions through the amorphous oxide is quantified using ab initio molecular dynamics. Facile transport of Li + through the native oxide is observed. Thus, increasing the percentage of amorphous Li 2 O in the solid electrolyte interphase may be beneficial for battery performance. In total, the phenomena quantified here will aid in the optimization of batteries that employ high-capacity Li metal anodes.

The interaction between catalyst and support is well known to influence the reactivity and stability of heterogeneous catalysts, and electrochemical hydrogen evolution catalysts based on amorphous or nanocluster MoS x have shown enhanced reactivity when supported on Au disk electrodes. However, it has been synthetically challenging to create strong interactions between the MoS x catalyst layer and the metallic support material while maintaining high surface area and solution dispersibility for the composite catalyst. In this work, we utilize colloidal ligand-exchange methods to adsorb a single layer of tetrathiometallate complex (MoS4 2–, WS4 2–) onto colloidal Au nanoparticles and characterize the influence of the Au support on the electronic and geometric properties of the surface MS x monolayer. Utilizing spectroscopic and computational methods, we show that the Au surface templates cross-linked oligomers of MoS x to generate highly active bridging disulfide moieties and tunes the hydrogen atom binding energies through strong covalent Au–S interactions. These Au@MoS4 nanoparticles are easily incorporated into high surface area electrodes and are able to achieve 100 mA/cm2 of hydrogen evolution current density at 171 mV of overpotential.

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