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The kinetics of aqueous outer-sphere electron-transfer (ET) reactions are determined in large part by noncovalent electrostatic interactions that originate from the surrounding electrolyte solution...

Data-driven approaches based on high-throughput capabilities and machine learning hold promise in revolutionizing human-centred materials discovery for sustainability and decarbonization. This Review examines the strengths and limitations of different traditional and emerging approaches to demonstrate their inherent connection and highlight the evolving paradigms of materials design., Breakthroughs in molecular and materials discovery require meaningful outliers to be identified in existing trends. As knowledge accumulates, the inherent bias of human intuition makes it harder to elucidate increasingly opaque chemical and physical principles. Moreover, given the limited manual and intellectual throughput of investigators, these principles cannot be efficiently applied to design new materials across a vast chemical space. Many data-driven approaches, following advances in high-throughput capabilities and machine learning, have tackled these limitations. In this Review, we compare traditional, human-centred methods with state-of-the-art, data-driven approaches to molecular and materials discovery. We first introduce the limitations of human-centred Edisonian, model-system and descriptor-based approaches. We then discuss how data-driven approaches can address these limitations by promoting throughput, reducing cognitive overload and biases, and establishing atomistic understanding that is transferable across a broad chemical space. We examine how high-throughput capabilities can be combined with active learning and inverse design to efficiently optimize materials out of millions or an intractable number of candidates. Lastly, we pinpoint challenges to accelerate future workflows and ultimately enable self-driving platforms, which automate and streamline the optimization of molecules and materials in iterative cycles.

Complex oxides, such as ABO3 perovskites, are an important class of functional materials that exhibit a wide range of physical, chemical, and electrochemical properties, including high oxygen electrocatalytic activity, tunable electronic/ionic conductivity, and ferroelectricity. When complex oxides are engineered as thin films, their chemical and physical properties can be modified to be markedly different from their bulk form, providing additional degrees of freedom in materials design. In this review, we survey the landscape of strain-induced design of complex oxides in the context of oxygen electrocatalysis and ferroelectricity. First, we identify the role of strain in influencing oxide electronic properties, driven by the combination of modification of Bsingle bondO bond length and octahedral distortion in perovskites. We describe electronic structure parameters, such as the O 2p-band center, that quantitatively capture these electronic changes, highlighting the broad influence of the O 2p-band center on surface reactivity (oxygen adsorption and dissociation energy) and bulk defect energetics (oxygen vacancy formation and migration energy). Motivated by the promise of the influence of strain on material properties relevant for oxygen electrocatalysis and ferroelectricity, we describe the advances in state-of-the-art thin-film fabrication and characterization that have enabled a high degree of experimental control in realizing strain effects in oxide thin-film systems. In oxygen electrocatalysis, leveraging strain has not only resulted in activity enhancements relative to bulk unstrained material systems but also revealed mechanistic influences of oxide phenomena, such as bulk defect chemistry and transfer kinetics, on electrochemical processes. Similarly for ferroelectric properties, strain engineering can both enhance polarization in known ferroelectrics and induce ferroelectricity in material systems that would be otherwise non-ferroelectric in bulk. Based on understanding of a diverse range of perovskite functionalities, we offer perspectives on how further coupling of strain, oxygen electrocatalysis, and ferroelectricity opens up pathways toward the emergence of novel device design features with dynamic control of increasing complex chemical and high-performance electronic processes. Ministry of Education (MOE) Nanyang Technological University Accepted version This work was supported in part by the Skoltech-MIT Center for Electrochemical Energy. Z. F. acknowledges startup funding from Oregon State University. X.R.W. acknowledges supports from the Nanyang Assistant Professorship grant from Nanyang Technological University and Academic Research Fund Tier 1 (RG108/17 and RG177/18) from Singapore Ministry of Education, Singapore. K.A.S. was supported in part by the Linus Pauling Distinguished Post-Doctoral Fellowship Pacific Northwest National Laboratory (PNNL, Laboratory Directed Research and Development Program 69319). PNNL is a multiprogram national laboratory operated for DOE by Battelle. D. L. was supported by Advanced Support Program for Innovative Research ExcellenceI funding (#15540-18-47811) provided by the Office of the Vice President for Research at the University of South Carolina. R.J. and D.M. were supported by the National Science Foundation (NSF) Software Infrastructure for Sustained Innovation (SI2) award No. 1148011.

The hydrogen adsorption energetics on the surface of inorganic compounds can be used to predict electrolyte stability in Li-ion batteries and catalytic activity for selective oxidation of small molecules such as H2 and CH4. Using first-principles density functional theory (DFT), the hydrogen adsorption was found to be unfavorable on high-band-gap insulators, which could be attributed to a lower energy level associated with adsorbed hydrogen relative to the bottom of the conduction band. In contrast, the hydrogen adsorption was shown to be the most favorable on metallic and semiconducting compounds, which results from an electron transfer from adsorbed hydrogen to the Fermi level or the bottom of the conduction band. Of significance, computed hydrogen adsorption energetics on insulating, semiconducting, and metallic oxides; phosphates; fluorides; and sulfides were decreased by lowering the ligand p band center, while the energy penalty for ligand vacancy formation was increased, indicative of decreased surface reducibility. A statistical regression analysis, where 16 structural and electronic parameters such as metal-ligand distance, electronegativity difference, Bader charges, bulk and surface metal and ligand band centers, band gap, ligand band width, and work function were examined, further showed that the surface ligand p band center is the most accurate single descriptor that governs the hydrogen adsorption tendency, and additional considerations of the band gap and average metal-ligand distance further reconcile the differences among compounds with different ligands/structures, whose ligand bands are different in shape and width. We discuss the implications of these findings for passivating coatings and design of catalysts and the need for novel theoretical methods to accurately estimate these quantities from first principles. These results establish a universal design principle for future high-throughput studies aiming to design electrode surfaces to minimize electrolyte oxidation by dehydrogenation in Li-ion batteries and enhance the H-H and C-H activation for selective oxidation catalysis.

Ion diffusion is important in a variety of applications, yet fundamental understanding of the diffusive process in solids is still missing, especially considering the interaction of lattice vibrations (phonons) and the mobile species. In this work, we introduce two formalisms that determine the individual contributions of normal modes of vibration (phonons) to the diffusion of ions through a solid, based on (i) Nudged Elastic Band (NEB) calculations and (ii) molecular dynamics (MD) simulations. The results for a model ion conductor of $\rm{Ge}$-substituted $\rm{Li_3PO_4}$ ($\rm{Li_{3.042}Ge_{0.042}P_{0.958}O_4}$) revealed that more than 87% of the $\rm{Li^+}$ ion diffusion in the lattice originated from a subset of less than 10% of the vibrational modes with frequencies between 8 and 20 THz. By deliberately exciting a small targeted subset of these contributing modes (less than 1%) to a higher temperature and still keeping the lattice at low temperature, we observed an increase in diffusivity by several orders of magnitude, consistent with what would be observed if the entire material (i.e., all modes) were excited to the same high temperature. This observation suggests that an entire material need not be heated to elevated temperatures to increase diffusivity, but instead only the modes that contribute to diffusion, or more generally a reaction/transition pathway, need to be excited to elevated temperatures. This new understanding identifies new avenues for increasing diffusivity by engineering the vibrations in a material, and/or increasing diffusivity by external stimuli/excitation of phonons (e.g., via photons or other interactions) without necessarily changing the compound chemistry., 50 pages, 17 figures

Recent work on superionic conductors has demonstrated the influence of lattice dynamics and the softness of the lattice on ionic transport. When examining either the changes in the acoustic phonon spectrum or the whole phonon density of states, both a decreasing activation barrier of migration and a decreasing entropy of migration have been observed, highlighting that the paradigm of “the softer the lattice, the better” does not always hold true. However, both approaches to monitor the changing lattice dynamics probe different frequency ranges of the phonon spectrum, and thus, it is unclear if they are complementary. In this work, we investigate the lattice dynamics of the superionic conductor Na3PS4–xSex by probing the optical phonon modes and the acoustic phonon modes, as well as the phonon density of states via inelastic neutron scattering. Notably, Raman spectroscopy shows the evolution of multiple local symmetry reduced polyhedral species, which likely affect the local diffusion pathways. Meanwhile, ...

The ionic conductivity and activation energy of lithium in the Li3PO4-Li3VO4-Li4GeO4 system was systematically investigated. The sharp decrease in activation energy upon Ge substitution in Li3PO4 and Li3VO4 was attributed to the reduction in the defect formation energy while the variation in activation energy upon increasing Ge content was rationalized in term of the inductive effect. We also found a correlation between the pre-exponential factors and the activation energies in agreement with the well-known Meyer-Neldel rule. The series of compound with and without partial lithium occupancy were shown to fall into two distinct lines. The slope of the line was found to be related to the inverse of the energy scale associated with phonons in the system, which agrees with the multiexcitation entropy theory. The intercept of the line was found to be related to the Gibbs free energy of defect formation. Compiled data of pre-exponential factor and activation energy for commonly studied lithium-ion conductors shows that this correlation is very general, implying an unfavorable trade-off between high pre-exponential factor and low activation energy needed to achieve high ionic conductivity. Understanding the circumstances under which this correlation can be violated might provide a new opportunity to further increase the ionic conductivity in lithium-ion conductors.

Lithium ion conductivity in many structural families can be tuned by many orders of magnitude, with some rivaling that of liquid electrolytes at room temperature. Unfortunately, fast lithium conductors exhibit poor stability against lithium battery electrodes. In this article, we report a fundamentally new approach to alter ion mobility and stability against oxidation of lithium ion conductors using lattice dynamics. By combining inelastic neutron scattering measurements with density functional theory, fast lithium conductors were shown to have low lithium vibration frequency or low center of lithium phonon density of states. On the other hand, lowering anion phonon densities of states reduces the stability against electrochemical oxidation. Olivines with low lithium band centers but high anion band centers are promising lithium ion conductors with high ion conductivity and stability. Such findings highlight new strategies in controlling lattice dynamics to discover new lithium ion conductors with enhanced conductivity and stability.

Recent work on superionic conductors has demonstrated the influence of lattice dynamics and the softness of the lattice on ionic transport. When examining either the changes in the acoustic phonon spectrum or the whole phonon density of states, both a decreasing activation barrier of migration and a decreasing entropy of migration have been observed, highlighting that the paradigm of "the softer the lattice, the better" does not always hold true. However, both approaches to monitor the changing lattice dynamics probe different frequency ranges of the phonon spectrum, and thus, it is unclear if they are complementary. In this work, we investigate the lattice dynamics of the superionic conductor Na

Understanding and controlling non-covalent interactions associated with solvent molecules and redox-inactive ions provide new opportunities to enhance the reaction entropy changes and reaction kinetics of metal redox centers, which can increase the thermodynamic efficiency of energy conversion and storage devices. Here, we report systematic changes in the redox entropy of one-electron transfer reactions including [Fe(CN)6]3-/4-, [Fe(H2O)6]3+/2+and [Ag(H2O)4]+/0induced by the addition of redox inactive ions, where approximately twenty different known structure making/breaking ions were employed. The measured reaction entropy changes of these redox couples were found to increase linearly with higher concentration and greater structural entropy (having greater structure breaking tendency) for inactive ions with opposite charge to the redox centers. The trend could be attributed to the altered solvation shells of oxidized and reduced redox active species due to non-covalent interactions among redox centers, inactive ions and water molecules, which was supported by Raman spectroscopy. Not only were these non-covalent interactions shown to increase reaction entropy, but they were also found to systematically alter the redox kinetics, where increasing redox reaction energy changes associated with the presence of water structure breaking cations were correlated linearly with the greater exchange current density of [Fe(CN)6]3-/4-., United States. Department of Energy. Office of Basic Energy Science (Award Number DE-SC0001299/DE-FG02-09ER46577), Hong Kong (China). Innovation and Technology Commission (Project No. ITS/ 020/16FP), United States. Department of Energy (Contract No. DE-AC02-5CH11231)

The average vibrational frequencies of Lithium sublattice or Li-phonon band centers have been correlated with the migration barriers of Li-ion in solid-state Li-ion conductors. In this talk, we present a computational screening of ~14,000 Li-containing compounds in the Materials Project database using this lattice-dynamic descriptor to identify new promising Li-ion conductors. After pre-screening the database for structural stability, electronic conductivity and compositions, we arrived at ~1200 compounds whose phonon band centers were computed using an optimized computational approach called Quickhesswhich requires only 2 DFT calculations per compounds. In addition to newly predicted Li-ion conductors, we also discussed broad correlations between the oxidation potential as well as anion p-band centers and the anion-phonon band centers, whose origin can be understood in term of covalency/ionicity of the cation-anion bonds in the structure. Finally, combining a low computed Li phonon-band center with the computed electrochemical stability window and the structural stability based on their energy above hull, 18 compounds were predicted to be promising Li-ion conductors. One of these newly predicted compounds, Li3ErCl6 was synthesized and was shown to exhibit a measured room-temperature conductivity of 0.3 mS/cm for the ball-milled amorphous sample and 0.05 mS/cm in the crystalline state, which further shows the promise of high-throughput search of Li-ion conductors based on lattice dynamics descriptors.

This Review is focused on ion-transport mechanisms and fundamental properties of solid-state electrolytes to be used in electrochemical energy-storage systems. Properties of the migrating species significantly affecting diffusion, including the valency and ionic radius, are discussed. The natures of the ligand and metal composing the skeleton of the host framework are analyzed and shown to have large impacts on the performance of solid-state electrolytes. A comprehensive identification of the candidate migrating species and structures is carried out. Not only the bulk properties of the conductors are explored, but the concept of tuning the conductivity through interfacial effects-specifically controlling grain boundaries and strain at the interfaces-is introduced. High-frequency dielectric constants and frequencies of low-energy optical phonons are shown as examples of properties that correlate with activation energy across many classes of ionic conductors. Experimental studies and theoretical results are discussed in parallel to give a pathway for further improvement of solid-state electrolytes. Through this discussion, the present Review aims to provide insight into the physical parameters affecting the diffusion process, to allow for more efficient and target-oriented research on improving solid-state ion conductors.

We show how to extract from a sufficiently long time series of stationary fluctuations of chemical reactions an estimate of the entropy production. This method, which is based on recent work on fluctuation theorems, is direct, non-invasive, does not require any knowledge about the underlying dynamics, and is applicable even when only partial information is available. We apply it to simple stochastic models of chemical reactions involving a finite number of states, and for this case, we study how the estimate of dissipation is affected by the degree of coarse-graining present in the input data., Accepted in Journal of Chemical Physics