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Surface chemistry modification of positive electrodes has been used widely to decrease capacity loss during Li-ion battery cycling. Recent work shows that coupled LiPF6 decomposition and carbonate dehydrogenation is enhanced by increased metal-oxygen covalency associated with increasing Ni and/or lithium de-intercalation in metal oxide electrode, which can be responsible for capacity fading of Ni-rich oxide electrodes. Here we examined the reactivity of lithium nickel, manganese, cobalt oxide (LiNi0.6Mn0.2Co0.2O2, NMC622) modified by coating of Al2O3, Nb2O5 and TiO2 with a 1 M LiPF6 carbonate-based electrolyte. Cycling measurements revealed that Al2O3-coated NMC622 showed the least capacity loss during cycling to 4.6 VLi compared to Nb2O5-, TiO2- coated and uncoated NMC622, which was in agreement with smallest electrode impedance growth during cycling from electrochemical impedance spectroscopy (EIS). Ex-situ infrared spectroscopy of charged Nb2O5- and TiO2-coated NMC622 pellets (without carbon nor binder) revealed blue peak shifts of 10 cm−1, indicative of dehydrogenation of ethylene carbonate (EC), but not for Al2O3-coated NMC622. X-ray Photoelectron Spectroscopy (XPS) of charged TiO2-coated NMC622 electrodes (carbon-free and binder-free) showed greater salt decomposition with the formation of lithium-nickel-titanium oxyfluoride species, which was in agreement with ex-situ infrared spectroscopy showing greater blue shifts of P-F peaks with increased charged voltages, indicative of species with less F-coordination than salt PF6− anion on the electrode surface. Greater salt decomposition was coupled with the increasing dehydrogenation of EC with higher coating content on the surface. This work shows that Al2O3 coating on NMC622 is the most effective in reducing carbonate dehydrogenation and accompanied salt decomposition and rendering minimum capacity loss relative to TiO2 and Nb2O5 coating.

We studied the magnetic ordering of thin films and bulk crystals of rutile RuO$_2$ using resonant X-ray scattering across the Ru L$_2$ absorption edge. Combining polarization analysis and azimuthal-angle dependence of the magnetic Bragg signal, we have established the presence of G-type antiferromagnetism in RuO$_2$ with T$_N$ $>$ 300 K. In addition to revealing a spin-ordered ground state in the simplest ruthenium oxide compound, the persistence of magnetic order even in nanometer-thick films lays the ground for potential applications of RuO$_2$ in antiferromagnetic spintronics., 5 pages, 4 figures

Transition metal perovskite oxides are promising electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells, but a lack of fundamental understanding of oxide surfaces impedes the rational design of novel catalysts with improved device efficiencies. In particular, understanding the surface chemistry of oxides is essential for controlling both catalytic activity and long-term stability. Thus, elucidating the physical nature of species on perovskite surfaces and their catalytic enhancement would generate new insights in developing oxide electrocatalysts. In this article, we perform near-ambient pressure XPS of model brownmillerite Sr2Co2O5 (SCO) epitaxial thin films with different crystallographic orientations. Detailed analysis of the Co 2p spectra suggests that the films lose oxygen as a function of temperature. Moreover, deconvolution of the O 1s spectra shows distinct behavior for (114)-oriented SCO films compared to (001)-oriented SCO films, where an additional bulk oxygen species is observed. These findings indicate a change to a perovskite-like oxygen chemistry that occurs more easily in (114) SCO than (001) SCO, likely due to the orientation of oxygen vacancy channels out-of-plane with respect to the film surface. This difference in surface chemistry is responsible for the anisotropy of the oxygen surface exchange coefficient of SCO and may contribute to the enhanced ORR kinetics of La0.8Sr0.2CoO3-δ thin films by SCO surface particles observed previously.

© 2016 Springer Science+Business Media New York. Transition metal perovskite oxides are promising electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells, but a lack of fundamental understanding of oxide surfaces impedes the rational design of novel catalysts with improved device efficiencies. In particular, understanding the surface chemistry of oxides is essential for controlling both catalytic activity and long-term stability. Thus, elucidating the physical nature of species on perovskite surfaces and their catalytic enhancement would generate new insights in developing oxide electrocatalysts. In this article, we perform near-ambient pressure XPS of model brownmillerite Sr2Co2O5(SCO) epitaxial thin films with different crystallographic orientations. Detailed analysis of the Co 2p spectra suggests that the films lose oxygen as a function of temperature. Moreover, deconvolution of the O 1s spectra shows distinct behavior for (114)-oriented SCO films compared to (001)-oriented SCO films, where an additional bulk oxygen species is observed. These findings indicate a change to a perovskite-like oxygen chemistry that occurs more easily in (114) SCO than (001) SCO, likely due to the orientation of oxygen vacancy channels out-of-plane with respect to the film surface. This difference in surface chemistry is responsible for the anisotropy of the oxygen surface exchange coefficient of SCO and may contribute to the enhanced ORR kinetics of La0.8Sr0.2CoO3-δthin films by SCO surface particles observed previously.

© 2015 American Chemical Society.Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities of LiCoO2 nanorods with sizes in the range from 9 to 40 nm were studied in alkaline solution. The sides of these nanorods were terminated with low-index surfaces such as (003), while the tips were terminated largely with high-index surfaces such as (104), as revealed by high-resolution transmission electron microscopy. Electron energy loss spectroscopy demonstrated that low-spin Co3+ prevailed on the sides, while the tips exhibited predominantly high- or intermediate-spin Co3+. We correlated the electronic and atomic structure to higher specific ORR and OER activities at the tips as compared to the sides, which was accompanied by more facile redox of Co2+/3+ and higher charge transferred per unit area. These findings highlight the critical role of surface terminations and electronic structures of transition-metal oxides on the ORR and OER activity.

Compact solid discharge products enable energy storage devices with high gravimetric and volumetric energy densities, but solid deposits on active surfaces can disturb charge transport and induce mechanical stress. In this Letter we develop a nanoscale continuum model for the growth of Li2O2 crystals in lithium-oxygen batteries with organic electrolytes, based on a theory of electrochemical non-equilibrium thermodynamics originally applied to Li-ion batteries. As in the case of lithium insertion in phase-separating LiFePO4 nanoparticles, the theory predicts a transition from complex to uniform morphologies of Li2O2 with increasing current. Discrete particle growth at low discharge rates becomes suppressed at high rates, resulting in a film of electronically insulating Li2O2 that limits cell performance. We predict that the transition between these surface growth modes occurs at current densities close to the exchange current density of the cathode reaction, consistent with experimental observations., 8 pages, 6 figs

Transition metal nitrides have shown promise as electrocatalysts in proton exchange membrane fuel cells and electrolyzers, but the instability of these nitrides in acid has limited their function for such technologies. On the other hand, having fast, complete nitride dissolution and ammonia formation in acid can offer new opportunities for distributed, on-demand ammonia generation. Optimizing nitride chemistries for these clean energy applications requires design principles for nitride dissolution and ammonia formation in acid. Here, we report that lowering the nitrogen 2p band center of transition metal nitrides relative to the Fermi level weakens metal–nitrogen bonds and increases labile metallic character, reducing dissolution reaction barriers and boosting ammonia formation kinetics in acid. Increasing the solubility of dissolved metal cations further facilitates the decomposition of nitrides in acid by prohibiting surface oxide passivation. These findings highlight essential future directions for preventing nitride dissolution or facilitating ammonia production for diverse acidic applications.

Li–O2 batteries can provide greater gravimetric energy than Li-ion batteries but suffer from poor efficiency and cycle life due to the instability of aprotic electrolytes. In this study, we show that the apparent four-electron oxygen reduction to form Li2O in Li–O2 batteries with molten nitrate is facilitated by the electrochemical reduction of nitrate to nitrite, and subsequent chemical oxidation of nitrite to nitrate by molecular oxygen, instead of a four-electron oxygen reduction aided by disproportionation of Li2O2 generated from two-electron reduction of molecular oxygen. By examining a series of transition metal catalysts using experiments and computation, optimizing the surface binding of nitrate to enhance the kinetics of the electrochemical reduction of nitrate to nitrite, as well as increasing the kinetics of nitrite oxidation by O2 was shown to increase the discharge voltage and render the observed high-rate capability for NiO-based surfaces in Li–O2 batteries.

RuO2 and IrO2 are among the most active catalysts for the Oxygen Evolution Reaction (OER). Recently, it was demonstrated that the catalytic surface of these oxides plays a role in the reaction, where a hydrogen bond with a neighbor OH group stabilizes an unconventional −OO intermediate (−OO-H), prior to O2 evolution. Quantum chemical calculations neglecting solvation effects indicated that this intermediate is more stable than the conventional −OOH, and that deprotonation of the stabilizing −OH is the rate limiting step for OER on RuO2(110) and RuO2(100). In this work, we investigate the role of water molecules on the relative stability of −OOH and −OO-H oxygenates on RuO2 (110) by means of density functional theory calculations combined with ab initio Molecular Dynamics simulations (AIMD). We show that the two intermediates participate in a hydrogen bonding network with water to a similar extent, but leading to different interfacial water structures, with possible implications on interfacial proton dynamics and reaction kinetics. Moreover, −OOH can spontaneously convert to −OO-H through a process mediated by water, demonstrating the critical role of explicitly including water in the model. This study provides further mechanistic insights on the role of the oxide surface chemistry in the OER mechanism and highlights the importance of explicitly treating the catalyst/water interfaces including dynamical aspects to assess the stability and the interconversion mechanism of key surface species, since the adoption of static solvation approaches tends to overestimate the energetic difference between −OOH and −OO-H reaction intermediates.

The oxygen evolution reaction is central to making chemicals and energy carriers using electrons. Combining the great tunability of enzymatic systems with known oxide-based catalysts can create breakthrough opportunities to achieve both high activity and stability. Here we report a series of metal hydroxide–organic frameworks (MHOFs) synthesized by transforming layered hydroxides into two-dimensional sheets crosslinked using aromatic carboxylate linkers. MHOFs act as a tunable catalytic platform for the oxygen evolution reaction, where the π–π interactions between adjacent stacked linkers dictate stability, while the nature of transition metals in the hydroxides modulates catalytic activity. Substituting Ni-based MHOFs with acidic cations or electron-withdrawing linkers enhances oxygen evolution reaction activity by over three orders of magnitude per metal site, with Fe substitution achieving a mass activity of 80 A gcatalyst-1 at 0.3 V overpotential for 20 h. Density functional theory calculationscorrelate the enhanced oxygen evolution reaction activity with the MHOF-based modulation of Ni redox and the optimized binding of oxygenated intermediates.

Direct methanol fuel cells (DMFCs) using alkaline electrolytes are of interest due to the applicability of nonprecious metal-based materials for electrocatalysts. However, the lack of understanding of the methanol oxidation reaction (MOR) mechanism in alkaline media hinders the development of active catalysts for the MOR. In this work, ambient-pressure XPS and in situ surface-enhanced infrared spectroscopy were performed on the Pt surface in order to gain experimental insights into the reaction pathway for the MOR. We present a comprehensive reaction mechanism for the MOR in alkaline media and show that the MOR proceeds via two different pathways depending on the electrode potential. We confirmed the formation of partially hydrogenated CO adsorbates [HxCOad···(OH) (1 < x < 3)] via water and/or hydroxide ion-mediated dissociation of methanol. The HxCOad···(OH) species were further dehydrogenated to COad in the potential range of 0.40-0.60 VRHE and subsequently oxidized to CO2 by reactive OHad on the Pt surface at 0.65 VRHE (pathway I). Furthermore, H3C-Oad intermediates were observed at potentials higher than 0.9 VRHE, at which the MOR proceeds mainly via H3C-Oad instead of COad intermediates (pathway II). The oxidation current related to this conversion from H3C-Oad to CO2 (pathway II) dominates the overall MOR current, suggesting that the H3C-Oad pathway could be one of the keys to enhancing the MOR activity in an alkaline environment. Our findings pave the way toward a design strategy for MOR electrocatalysts with improved activity based on the experimental reaction mechanisms that have been identified.

Proton activity at the electrified interface is central to the kinetics of proton-coupled electron transfer (PCET) reactions for making chemicals and fuels. Here we employ a library of protic ionic liquids in an interfacial layer on platinum and gold to alter local proton activity, where the intrinsic oxygen-reduction reaction (ORR) activity is enhanced up to fivefold, exhibiting a volcano-shaped dependence on the pKa of the ionic liquid. The enhanced ORR activity is attributed to strengthened hydrogen bonds between ORR products and ionic liquids with comparable pKas, resulting in favourable PCET kinetics. This proposed mechanism is supported by in situ surface-enhanced Fourier-transform infrared spectroscopy and our simulation of PCET kinetics based on computed proton vibrational wavefunctions at the hydrogen-bonding interface. These findings highlight opportunities for using non-covalent interactions between hydrogen-bonded structures and solvation environments at the electrified interface to tune the kinetics of ORR and beyond. Understanding the role of hydrogen bonds at the electrode interface is important for controlling the kinetics of the oxygen-reduction reaction. Here the authors modify gold and platinum surfaces with a series of protic ionic liquids to show that pKa can be used to optimize proton-coupled electron transfer through hydrogen bonding.

The production of molecular hydrogen by catalyzing water splitting is central to achieving the decarbonization of sustainable fuels and chemical transformations. In this work, a series of structure-making/breaking cations in the electrolyte were investigated as spectator cations in hydrogen evolution and oxidation reactions (HER/HOR) in the pH range of 1 to 14, whose kinetics was found to be altered by up to 2 orders of magnitude by these cations. The exchange current density of HER/HOR was shown to increase with greater structure-making tendency of cations in the order of Cs+ < Rb+ < K+ < Na+ < Li+, which was accompanied by decreasing reorganization energy from the Marcus-Hush-Chidsey formalism and increasing reaction entropy. Invoking the Born model of reorganization energy and reaction entropy, the static dielectric constant of the electrolyte at the electrified interface was found to be significantly lower than that of bulk, decreasing with the structure-making tendency of cations at the negatively charged Pt surface. The physical origin of cation-dependent HER/HOR kinetics can be rationalized by an increase in concentration of cations on the negatively charged Pt surface, altering the interfacial water structure and the H-bonding network, which is supported by classical molecular dynamics simulation and surface-enhanced infrared absorption spectroscopy. This work highlights immense opportunities to control the reaction rates by tuning interfacial structures of cation and solvents.

Polymer electrolytes (PEs) have attracted tremendous research interest for their potential to offer improved safety and energy capacity in next-generation battery technologies. Among the different classes of PEs, single-ion conductors (SICs) are particularly interesting due to their high transference numbers. Nevertheless, a detailed understanding of how molecular structure impacts the properties of SIC-PEs is absent, limiting the ability to design improved materials. Here, we present the synthesis and characterization of a new class (seven examples provided) of polyanions featuring fluorinated aryl sulfonimide tagged (FAST) anions as side chains. These "polyFAST"salts are shown to outperform the widely used poly[(4-styrenesulfonyl) (trifluoromethanesulfonyl)imide] due to their strongly electron-withdrawing side chains and enhanced distance between anionic sites, providing higher electronic conductivities at all salt concentrations and in some cases superior electrochemical oxidative stability. Moreover, they provide a platform for discovery of fundamental relationships between macromolecular composition, as programmed through monomer structure, and SIC-PE bulk properties. Finally, we leverage the electron-deficient nature of polyFAST salts to demonstrate a new poly(solvate ionic liquid) (polySIL) concept that offers a promising pathway toward high-performance PEO-free SIC-PEs.

Understanding the nature of active sites is central to controlling (electro)catalytic activity. Here we employed surface X-ray scattering coupled with density functional theory and surface-enhanced infrared absorption spectroscopy to examine the oxygen evolution reaction on RuO2 surfaces as a function of voltage. At 1.5 VRHE, our results suggest that there is an –OO group on the coordinatively unsaturated ruthenium (RuCUS) site of the (100) surface (and similarly for (110)), but adsorbed oxygen on the RuCUS site of (101). Density functional theory results indicate that the removal of –OO from the RuCUS site, which is stabilized by a hydrogen bond to a neighbouring –OH (–OO–H), could be the rate-determining step for (100) (similarly for (110)), where its reduced binding on (100) increased activity. A further reduction in binding energy on the RuCUS site of (101) resulted in a different rate-determining step (–O + H2O – (H+ + e−) → –OO–H) and decreased activity. Our study provides molecular details on the active sites, and the influence of their local coordination environment on activity. Understanding the nature of active sites is central to controlling the activity of a given catalyst. This work combines operando characterization and computational techniques to examine the oxygen evolution reaction mechanism on RuO2 surfaces.

ConspectusThe transition from fossil fuels to renewable energy requires the development of efficient and cost-effective energy storage technologies. A promising way forward is to harness the energy of intermittent renewable sources, such as solar and wind, to perform (electro)catalytic reactions to generate fuels, thus storing energy in the form of chemical bonds. However, current catalysts rely on the use of expensive, rare, or geographically localized elements, such as platinum. Widespread adoption of new (electro)catalytic technologies hinges on the discovery and development of materials containing earth-abundant elements, which can efficiently catalyze an array of (electro)chemical reactions.In the context of catalysis, descriptors provide correlations between fundamental physical properties, such as the electronic structure, and the resulting catalytic activity. The use of easily accessible descriptors has proven to be a powerful method to advance and accelerate discovery and design of new catalyst materials. The position of the oxygen electronic 2p band center has been proposed to capture the basic physical properties of oxides, including oxygen vacancy formation energy, diffusion barrier of oxygen ions, and work function. Moreover, the adsorption strength of relevant reaction intermediates at the surface of oxides can be strongly correlated with the energy of the oxygen 2p states, which affects the catalytic activity of reactions, such as oxygen electrocatalysis, and oxidative dehydrogenation of organic molecules. Such descriptors for catalytic activity can be used to predict the activity of new catalysts and understand trends and behavior among different catalysts.In this Account, we discuss how the energy of the oxygen 2p states can be used as a descriptor for oxide bulk and surface chemical properties. We show how the oxide redox properties vary linearly with the position of the oxygen 2p band center with respect to the Fermi level, and we discuss how this descriptor can be expanded across different materials and structural families, including possible generalizations to compounds outside oxides. We highlight the power of the oxygen 2p band center to predict the catalytic activity of oxides. We conclude with an outlook examining under which conditions this descriptor can be applied to predict oxide properties and possible opportunities for further refining and accelerating property predictions of oxides by leveraging material databases and machine learning.

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.

According to the conventional understanding, the oxygen evolution reaction on metal oxide surfaces involves four proton-coupled electron transfer steps with *OH, *O, and *OOH reaction intermediates. Recently, several alternative reaction mechanisms with lower overpotentials were proposed for highly active catalysts. While for such reaction mechanisms additional intermediates leading to nonelectrochemical reaction steps could be considered, they are usually neglected when the thermodynamic overpotential of such mechanisms is investigated. We show here that this is a valid approximation for endothermic nonelectrochemical steps, which only affect the kinetics, while exothermic nonelectrochemical steps can also affect the thermodynamic overpotential. We show this on the basis of density functional theory calculations for one of those proposed mechanisms on surfaces of different perovskite oxides and oxynitrides. We find that for weakly binding surfaces the *O adsorbate spontaneously adopts a bidentate bridged dimer structure in a nonelectrochemical step with an energy gain in excess of 1 eV. This decrease in free energy needs to be compensated by an equivalent increase in magnitude of the electrochemical steps, which can affect the thermodynamic overpotential. This change may result in reaction mechanisms without nonelectrochemical steps having smaller thermodynamic overpotentials and thus being more favorable.

Surface oxygen vacancies have been widely discussed to be crucial for tailoring the activity of various chemical reactions from CO, NO, to water oxidation by using oxide-supported catalysts. However, the real role and potential function of surface oxygen vacancies in the reaction remains unclear because of their very short lifetime. Here, it is reported that surface oxygen vacancies can be well confined electrostatically for a polarization screening near the perimeter interface between Pt {111} nanocrystals and the negative polar surface (001) of ferroelectric PbTiO3. Strikingly, such a catalyst demonstrates a tunable catalytic CO oxidation kinetics from 200 °C to near room temperature by increasing the O2 gas pressure, accompanied by the conversion curve from a hysteresis-free loop to one with hysteresis. The combination of reaction kinetics, electronic energy loss spectroscopy (EELS) analysis, and density functional theory (DFT) calculations, indicates that the oxygen vacancies stabilized by the negative polar surface are the active sites for O2 adsorption as a rate-determining step, and then dissociated O moves to the surface of the Pt nanocrystals for oxidizing adsorbed CO. The results open a new pathway for tunable catalytic activity of CO oxidation.

The use of non-precious catalysts (e.g., transition metal oxides) in electrochemical energy technologies in acid (e.g., proton exchange membrane fuel cells and electrolyzers) has been significantly hampered by the instability of such catalysts at low pHs. While first-row late transition metal oxides based on Fe, Co, and/or Ni have been reported with comparable or higher catalytic activity for the alkaline oxygen reduction and oxygen evolution reactions than their precious-metal-based counterparts (e.g., Pt and IrO2),[1] these oxide catalysts are not stable in acid.[2] Moreover, Mn-based oxides are more acid-stable than those based on late transition metals[1] and can be potentially stabilized by reaching dissolution-deposition equilibrium at moderately acidic pHs,[3] but they still corrode and deactivate in strong acid and after long operation.[4] To tackle this challenge, extensive efforts over the past decades have been focused on combining active, yet unstable metal oxides with corrosion-resistant oxides.[5-7] Nevertheless, having a higher fraction of corrosion-resistant elements results in more acid-stable, yet less active catalysts, indicating an activity-stability trade-off.[2,5,6] To design transition metal oxide catalysts (such as Mn-based oxides) with an optimal trade-off or bypass this limitation, it is critical to establish their stability descriptors in acid. These descriptors can offer a fundamental understanding of oxide dissolution and provide guiding principles to enhance their intrinsic stability. In this work, we employed a library of Mn-based oxides with diverse structures and Mn oxidation states to identify oxide stability descriptors in acid based on intrinsic electronic structure and energetic parameters. Using time-dependent dissolution experiments and density functional theory calculations, greater amounts and faster kinetics of oxide dissolution in acid were correlated with decreased Mn oxidation states, which are accompanied by lowered Mn-O covalency, weakened Mn-O bonds, and reduced barriers for key reaction steps (such as protonation, vacancy formation, and metal ion solvation). Such design principles were shown broadly with a computational screening across a vast chemical space of ~1,000 Mn-based oxides, where an Mn oxidation state of 4+ was found to give rise to the lowest energetic driving force for the dissolution of Mn-based oxides in acid. Moreover, limiting the percentage of ionic metal substituents in oxides and using more acidic substituents were shown to stabilize Mn-based oxides in acid. These findings can provide novel insights into designing acid-stable Mn-based oxides for renewable energy storage and conversion. References: [1] C. Wei, R. R. Rao, J. Peng, B. Huang, I. E. L. Stephens, M. Risch, Z. J. Xu, Y. Shao-Horn, Adv. Mater. 2019, 31, 1806296. [2] K. K. Rao, Y. Lai, L. Zhou, J. A. Haber, M. Bajdich, J. M. Gregoire, Chem. Mater. 2022, 34, 899. [3] M. Huynh, D. K. Bediako, D. G. Nocera, J. Am. Chem. Soc. 2014, 136, 6002. [4] A. Li, H. Ooka, N. Bonnet, T. Hayashi, Y. Sun, Q. Jiang, C. Li, H. Han, R. Nakamura, Angew. Chem. Int. Ed. 2019, 58, 5054. [5] R. Frydendal, E. A. Paoli, I. Chorkendorff, J. Rossmeisl, I. E. L. Stephens, Adv. Energy Mater. 2015, 5, 1500991. [6] L. Zhou, A. Shinde, J. H. Montoya, A. Singh, S. Gul, J. Yano, Y. Ye, E. J. Crumlin, M. H. Richter, J. K. Cooper, H. S. Stein, J. A. Haber, K. A. Persson, J. M. Gregoire, ACS Catal. 2018, 8, 10938. [7] L. Zhou, H. Li, Y. Lai, M. Richter, K. Kan, J. A. Haber, S. Kelly, Z. Wang, Y. Lu, R. S. Kim, X. Li, J. Yano, J. K. Nørskov, J. M. Gregoire, ACS Energy Lett. 2022, 7, 993. Figure 1

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.

Anionic redox in positive electrode materials in Li-ion batteries provides an additional redox couple besides conventional metal redox, which can be harvested to further boost the energy density of current Li-ion batteries. However, the requirement for the reversible anionic redox activity remains under debate, hindering the rational design of new materials with reversible anionic redox. In this work, we employed differential electrochemical mass spectrometry (DEMS) to monitor the release of oxygen and to quantify the reversibility of the anionic redox of Li2Ru0.75M0.25O3 (M = Ti, Cr, Mn, Fe, Ru, Sn, Pt, Ir) upon first charge. X-ray absorption spectroscopy, coupled with density functional theory (DFT) calculations, show that various substituents have a minimal effect on the nominal metal redox, yet more ionic substituents and reduced metal-oxygen covalency introduce irreversible oxygen redox, accompanied with easier distortion of the M-O octahedron and a smaller barrier for forming an oxygen dimer within the octahedron. Therefore, a strong metal-oxygen covalency is needed to enhance the reversible oxygen redox. We proposed an electron-phonon-coupled descriptor for the reversibility of oxygen redox, laying the foundation for high-throughput screening of novel materials that enable reversible anionic redox activity. This journal is

Understanding the adsorption and oxidation of NO on metal oxides is of immense interest to environmental and atmospheric (bio)chemistry. Here, we show that the surface oxygen activity, defined as the oxygen 2p-band centre relative to the Fermi level, dictates the adsorption and surface coverage of NOx and the kinetics of NO oxidation for La1−xSrxCoO3 perovskites. Density functional theory and ambient-pressure X-ray photoelectron spectroscopy revealed favourable NO adsorption on surface oxygen sites. Increasing the surface oxygen activity by increasing the strontium substitution led to stronger adsorption and greater storage of NO2, which resulted in more adsorbed nitrogen-like species and molecular nitrogen formed upon exposure to CO. The NO oxidation kinetics exhibited a volcano trend with surface oxygen activity, centred at La0.8Sr0.2CoO3 and with an intrinsic activity comparable to state-of-the-art catalysts. We rationalize the volcano trend by showing that increasing the NO adsorption enhances the oxidation kinetics, although NO adsorption that is too strong poisons the surface oxygen sites with adsorbed NO2 to impede the kinetics. Understanding the mechanism for the catalytic conversion of NOx is crucial to develop superior greenhouse gas abatement schemes, although it remains challenging. Here, the authors reveal important aspects of the redox properties of NOx on a La1–xSrxCoO3 perovskite by a combination of density functional theory calculations and ambient-pressure X-ray photoelectron spectroscopy.

Ni-rich positive electrodes for Li-ion batteries can provide enhanced initial discharge capacity yet suffer from significant capacity degradation upon cycling. Fluorination of Ni-rich NMC811 positive electrodes results in a capacity retention of more than 90% after 100 cycles upon cycling to 4.4 VLi. The increased cycling stability of F-modified NMC811 can be attributed to the modification of the oxide electronic structures, where density functional theory calculations shows that incorporating fluorine into the oxide lattice decrease the driving force of carbonate dissociation on the oxide surface. In situ infrared (IR) spectroscopy and ex situ X-ray photoelectron spectroscopy (XPS) further supports this argument by showing less carbonate oxidation for F-modified LiNi0.8Mn0.1Co0.1O2 (NMC811) than as-received NMC811 upon charging. The reduced carbonate oxidation is coupled with minimal salt decomposition on the electrode surface, as revealed by XPS. Further comparing in situ IR and XPS with that of the heat-treated NMC811 and Li2CO3 allows for decoupling the solvent decomposition products, where oxides are responsible for the vinylene carbonate formation with two hydrogens removed whereas surface metal carbonates promote dehydrogenated ethylene carbonate with just one hydrogen removed. This work points towards the importance of the anion engineering to increase the cycling stability of Ni-rich NMC positive electrodes.

Layered lithium nickel, manganese, and cobalt oxides (NMC) are among the most promising commercial positive electrodes in the past decades. Understanding the detailed surface and bulk redox processes of Ni-rich NMC can provide useful insights into material design options to boost reversible capacity and cycle life. Both hard X-ray absorption (XAS) of metal K-edges and soft XAS of metal L-edges collected from charged LiNi0.6Mn0.2Co0.2O2 (NMC622) and LiNi0.8Mn0.1Co0.1O2 (NMC811) showed that the charge capacity up to removing ∼0.7 Li/f.u. was accompanied with Ni oxidation in bulk and near the surface (up to 100 nm). Of significance to note is that nickel oxidation is primarily responsible for the charge capacity of NMC622 and 811 up to similar lithium removal (∼0.7 Li/f.u.) albeit charged to different potentials, beyond which was followed by Ni reduction near the surface (up to 100 nm) due to oxygen release and electrolyte parasitic reactions. This observation points toward several new strategies to enhance reversible redox capacities of Ni-rich and/or Co-free electrodes for high-energy Li-ion batteries.

Understanding (electro-)chemical reactions at the electrode–electrolyte interface (EEI) is crucial to promote the cycle life of lithium-ion batteries. In this study, we developed an in situ Fourier-transform infrared spectroscopy (FT-IR) method, which provided unprecedented information on the oxidation of carbonate solvents via dehydrogenation on LiNixMnyCo1−x−yO2 (NMC). While ethylene carbonate (EC) was stable against oxidation on Pt up to 4.8 VLi, unique evidence for dehydrogenation of EC on LiNi0.8Co0.1Mn0.1O2 (NMC811) at voltages as low as 3.8 VLi was revealed by in situ FT-IR measurements, which was supported by density functional theory (DFT) results. Unique dehydrogenated species from EC were observed on NMC811 surface, including dehydrogenated EC anchored on oxides, vinylene carbonate (VC) and dehydrogenated oligomers which could diffuse away from the surface. Similar dehydrogenation on NMC811 was noted for EMC-based and LP57 (1 M LiPF6 in 3 : 7 EC/EMC) electrolytes. In contrast, no dehydrogenation was found for NMC111 or surface-modified NMC by coatings such as Al2O3. In addition, while the dehydrogenation of solvents was observed in 1 M electrolytes with different anions, they were not observed on NMC811 in the concentrated electrolyte (EC/EMC with 3.1 M LiPF6), indicating lithium coordination could suppress dehydrogenation. Dehydrogenation of carbonates on NMC811 accompanied with rapid growth of interfacial impedance with increasing voltage revealed by electrochemical impedance spectroscopy (EIS), while the electrode–electrolyte combinations without dehydrogenation did not show significant impedance growth. Therefore, minimizing carbonate dehydrogenation on the NMC surface by tuning electrode reactivity and electrolyte reactivity is critical to develop high-energy Li-ion batteries with long cycle life.

Understanding and controlling the (electro) chemical reactions between positive electrodes and electrolytes is essential to enhance the cycle life and safety of Li-ion batteries. Previous computational and experimental studies have shown that greater capacity loss of LiNixMnyCo1-x-yO2 (NMC) with increased Ni content can be attributed to the enhanced chemical oxidation of carbonate solvents by dehydrogenation and increased salt decomposition. In this study, we examine the role of a diphenyl carbonate (DPC) additive on the interfacial reactivity of LiNi1/3Mn1/3Co1/3O2, LiNi0.6Mn0.2Co0.2O2, LiNi0.8Mn0.1Co0.1O2 (NMC111, NMC622 and NMC811). Diffuse reflectance infrared Fourier Transform (DRIFT) spectroscopy on NMCs showed that adding DPC in the electrolyte suppressed signals associated with dehydrogenation of ethylene carbonate (EC) from LiNi1/3Mn1/3Ni1/3O2 to LiNi0.8Mn0.1Ni0.1O2 (NMC111 to NMC811). In addition, having DPC in the electrolyte was accompanied with less PF6- salt anion decomposition to form less-fluorine coordinated species such as lithium nickel oxyfluorides or PF3O-like species as revealed by combined infrared spectroscopy and X-ray Photoelectron Spectroscopy (XPS) for Ni-rich NMCs. Such observations are in agreement with previous work showing that DPC can increase the cycling performance of NMC811. The reduced reactivity between NMC such as NMC811 and electrolyte with DPC can be attributed to the formation of surface reaction products from the electrochemical oxidation of DPC occurring at lower voltages compared to the chemical oxidative dehydrogenation of carbonates. This hypothesis is supported by in situ infrared spectroscopy measurements, which revealed electrochemical oxidation of diphenyl carbonate upon charging at 3.9 VLi, accompanied by the detection of a feature around 1824 cm-1 attributed to organic oxidation products adsorbed on the oxide surface, and a stable electrode/electrolyte interface on NMC811 at higher voltages.

The prospect of accessing anionic (oxygen) oxidation and reduction reversibly in lithium transition metal oxides for the positive electrode offers exciting opportunities to greatly boost the energy density of Li-ion batteries. Unfortunately, the physical mechanisms governing oxygen redox in these oxides remain under debate. In this article, density functional theory studies using maximally localized Wannier functions revealed that deintercalation of both lithium ions from Li2-xRuO3 as well as Li1-xNiO2 (Li3/2-xNi3/2O3) was dominated by the oxidation of nonbonding states of oxygen or bonding states of oxygen from metal-oxygen bonds, which was accompanied by moderate Ru/Ni oxidation and reduction in the O-O bond distance, facilitated by high metal-oxygen covalency in oxides. In contrast, deintercalation of lithium ions from Li2-xMnO3 as well as Li2-xTiO3 and Li2-xSnO3 was dominated by the oxidation of nonbonding states of oxygen to form O-O p sigma (σ) and πstates with accompanied distinct O-O peroxo-like bond formation but without Mn oxidation, which is facilitated by relatively low metal-oxygen covalency. Remarkably, the average oxygen phonon density of states (phonon DOS) of oxides with high metal-oxygen covalency like Li2-xRuO3, Li2-xIrO3, and Li1-xNiO2 was moved to higher frequencies while that of those with low covalency like Li2-xMnO3, Li2-xTiO3, and Li2-xSnO3 was moved to lower frequencies, which could promote oxygen and metal migration and structural instability, leading to irreversible oxygen redox. It is postulated that high metal-oxygen covalency is essential to enable reversible access of oxygen redox along with metal redox in transition metal oxides, which bridges different schools of thoughts for oxygen redox and provide new insights into design of new oxygen-redox capable positive electrodes.

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.

Rutile RuO2 is a highly active catalyst for a number of (electro)chemical reactions in aqueous solutions or in humid environments. However, the study of the interaction of RuO2 surfaces with water has been confined largely to the ultra-high vacuum environment, and to the thermodynamically stable (110) surface. In this work, we combine ambient pressure X-ray photoelectron spectroscopy, in situ surface diffraction and density functional theory calculations to investigate how four different facets of RuO2 interact with water under humid and electrochemical environments. The vacant coordinatively unsaturated Ru site (CUS) allows for the adsorption and dissociation of water molecules. Different surfaces exhibit unique binding energetics for -H2O and -OH and can allow for different degrees of hydrogen bonding between the adsorbates. Consequently, the degree of water dissociation is found to be sensitive to the surface crystallographic orientation - being maximum for the (101) surface, followed by the (110), (001) and (100) surfaces. This study identifies crystallographic orientation as an important parameter to tune not only the density of active sites but also the energetics for water dissociation; this finding is of great significance for many catalytic reactions, where water is a key reactant, or product.

Understanding the reactivity of the cathode surface is of key importance to the development of batteries. Here, density functional theory is applied to investigate the oxidative decomposition of the electrolyte component, ethylene carbonate (EC), on layered LixMO2 oxide surfaces. We compare adsorption energy trends of atoms and small molecules, on both surface oxygen and metal sites, as a function of the Li content of the surface. The oxygen sites are identified as the reactive site for the electrolyte oxidation reaction (EOR). We report reaction energies and NEB-calculated kinetic barriers for the initial oxidative decomposition of EC, and correlate both with the reaction energy of hydrogen adsorption on oxygen. The hydrogen adsorption energy scales with the distance between the Fermi level and the O-2p band center. We expect this model of the EOR to be valid for other organic electrolytes and other Li metal oxide surfaces, due to its simplicity, and the model leads to simple design principles for protective coatings.

Fundamental understanding of the reactivity between electrode and electrolyte is key to design the safety and life of Li-ion batteries. Herein X-ray photoelectron spectroscopy was used to examine the electrode/electrolyte interface (EEI) on carbon-free, binder-free LiCoO 2 powder and thin-film electrodes in LP57 electrolyte as function of potential. Upon charging of LiCoO 2 a marked growth of oxygenated and carbonated species was observed on the surface, consistent with electrolyte oxidation at high potentials. We also demonstrated that LiCoO 2 oxide surface was prone to decompose the salt starting at 4.1 V Li , as evidenced by the increase of LiF and Li x PF y O z species upon charging. By DFT calculations we proposed a correlation between the interface composition and the thermodynamic tendency of the EC solvent for dissociative adsorption on the Li x CoO 2 surface, through the generation of reactive acidic OH groups on the oxide surface, which can have a role in the observed salt decomposition. This is consistent with the evidence of HF and PF 2 O 2− species at 4.6 V Li observed by solution 19 F-NMR measurements. Finally we compared EEI composition between composite and model electrodes and discussed the changes and mechanisms induced by the electrode composition or the use of electrolyte additives. We showed that the addition of diphenyl carbonate (DPC) in the electrolyte has a strong impact on the formation of solvent and salt decomposition products at the EEI layer.

Solid-state electrolytes are attracting great interest for their applications in potentially safe and stable high-capacity energy storage technologies. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is widely used as a lithium ion source, especially in solid-state polymer electrolytes, due to its solubility and excellent chemical and electrochemical stability. Unfortunately, chemically inert LiTFSI cannot be easily modified to optimize its properties or allow for conjugation to other molecules, polymers, or substrates to prepare single-ion conducting polymer electrolytes. Chemical modifications of TFSI often Erode its advantageous properties. Herein, we introduce Fluorinated Aryl Sulfonimide Tagged (FAST) salts, which are derived from successive nucleophilic aromatic substitution (SNAr) reactions. Experimental studies and density functional theory calculations were used to assess the electrochemical oxidative stabilities, chemical stabilities, and degrees of ion dissociation of FAST salts as a function of their structures. FAST salts offer a platform for accessing functional sulfonimides without sacrificing many of the advantageous properties of TFSI.

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.

Catalysts for chemical and electrochemical reactions underpin many aspects of modern technology and industry, from energy storage and conversion to toxic emissions abatement to chemical and materials synthesis. This role necessitates the design of highly active, stable, yet earth-abundant heterogeneous catalysts. In this Review, we present the perovskite oxide family as a basis for developing such catalysts for (electro)chemical conversions spanning carbon, nitrogen, and oxygen chemistries. A framework for rationalizing activity trends and guiding perovskite oxide catalyst design is described, followed by illustrations of how a robust understanding of perovskite electronic structure provides fundamental insights into activity, stability, and mechanism in oxygen electrocatalysis. We conclude by outlining how these insights open experimental and computational opportunities to expand the compositional and chemical reaction space for next-generation perovskite catalysts.

Herein we investigate the reaction intermediates formed during CO oxidation on copper-substituted ceria nanoparticles (Cu0.1Ce0.9O2-x) by means of in situ spectroscopic techniques and identify an activity descriptor that rationalizes a trend with other metal substitutes (M0.1Ce0.9O2-x, M = Mn, Fe, Co, Ni). In situ X-ray absorption spectroscopy (XAS) performed under catalytic conditions demonstrates that O2-transfer occurs at dispersed copper centers, which are redox active during catalysis. In situ XAS reveals a dramatic reduction at the copper centers that is fully reversible under catalytic conditions, which rationalizes the high catalytic activity of Cu0.1Ce0.9O2-x. Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) show that CO can be oxidized to CO32- in the absence of O2. We find that CO32- desorbs as CO2 only under oxygen-rich conditions when the oxygen vacancy is filled by the dissociative adsorption of O2. These data, along with kinetic analyses, lend support to a mechanism in which the breaking of copper-oxygen bonds is rate-determining under oxygen-rich conditions, while refilling the resulting oxygen vacancy is ratedetermining under oxygen-lean conditions. On the basis of these observations and density functional calculations, we introduce the computed oxygen vacancy formation energy (Evac) as an activity descriptor for substituted ceria materials and demonstrate that Evac successfully rationalizes the trend in the activities of M0.1Ce0.9O2-x catalysts that spans three orders of magnitude. The applicability of Evac as a useful design descriptor is demonstrated by the catalytic performance of the ternary oxide Cu0.1La0.1Ce0.8O2-x, which has an apparent activation energy rivaling those of state-of-the-art Au/TiO2 materials. Thus, we suggest that cost-effective catalysts for CO oxidation can be rationally designed by judicious choice of substituting metal through the computational screening of Evac.

Electrolyte instability is one of the greatest impediments that must be overcome for the practical development of rechargeable aprotic Li-air batteries. In this work, we establish a comprehensive framework for evaluation of the stability of potential organic electrolytes for aprotic Li-air batteries that is based on four key descriptors: Bond dissociation energy, deprotonation free energy (i.e., Acidity), Nucleophilic substitution free energy, and Electrochemical oxidation/reduction. These parameters were calculated for several classes of organic compounds. The chemical stability of the molecules was studied experimentally under conditions designed to mimic the aprotic Li-air battery environment (heating in the presence of excess KO2 and Li2O2). In general, the calculated and experimental data agreed well for alkanes, alkenes, ethers, aromatics, carbonates, and S-containing and N-containing compounds. Using this dataset, we identified functional groups and other structural features of organic molecules that may be suitable for aprotic Li-air battery electrolyte design.

A recent meeting focused on accelerated materials design and discovery examined user requirements for a general, collaborative, integrative, and on-demand materials research platform.

The CO2 electroreduction reaction (CO2RR) is a promising avenue to convert greenhouse gases into high-value fuels and chemicals, in addition to being an attractive method for storing intermittent renewable energy. Although polycrystalline Cu surfaces have long been known to be unique in their capabilities of catalyzing the conversion of CO2 to higher-order C1 and C2 fuels, such as hydrocarbons (CH4, C2H4, etc.) and alcohols (CH3OH, C2H5OH), product selectivity remains a challenge. Rational design of more selective catalysts would greatly benefit from a mechanistic understanding of the complex, multiproton, and multielectron conversion of CO2. In this study, we select three metal catalysts (Pt, Au, Cu) and apply in situ surface enhanced infrared absorption spectroscopy (SEIRAS) and ambient-pressure X-ray photoelectron spectroscopy (APXPS), coupled to density-functional theory (DFT) calculations, to get insight into the reaction pathway for the CO2RR. We present a comprehensive reaction mechanism for the CO2RR and show that the preferential reaction pathway can be rationalized in terms of metal-carbon (M-C) and metal-oxygen (M-O) affinity. We show that the final products are determined by the configuration of the initial intermediates, C-bound and O-bound, which can be obtained from CO2 and (H)CO3, respectively. C1 hydrocarbons are produced via OCH3,ad intermediates obtained from O-bound CO3,ad and require a catalyst with relatively high affinity for O-bound intermediates. Additionally, C2 hydrocarbon formation is suggested to result from the C-C coupling between C-bound COad and (H)COad, which requires an optimal affinity for the C-bound species, so that (H)COad can be further reduced without poisoning the catalyst surface. It is suggested that the formation of C1 alcohols (CH3OH) is the most challenging process to optimize, as stabilization of the O-bound species would both accelerate the formation of key intermediates (OCH3,ad) but also simultaneously inhibit their desorption from the catalyst surface. Our findings pave the way toward a design strategy for CO2RR catalysts with improved selectivity, based on the experimental/theoretical reaction mechanisms that have been identified. These results also suggest that designing the electronic structure of the catalyst is not the sole determining factor to achieve highly selective CO2RR catalysis; rather, tuning additional experimental reaction conditions such as electrolyte-intermediate interactions also become critical.

Anion redox in lithium transition metal oxides such as Li(2)RuO(3) and Li(2)MnO(3,) has catalyzed intensive research efforts to find transition metal oxides with anion redox that may boost the energy density of lithium-ion batteries. The physical origin of observed anion redox remains debated, and more direct experimental evidence is needed. In this work, we have shown electronic signatures of oxygen-oxygen coupling, direct evidence central to lattice oxygen redox (O(2−)/(O(2))(n−)), in charged Li(2-x)RuO(3) after Ru oxidation (Ru(4+)/Ru(5+)) upon first-electron removal with lithium de-intercalation. Experimental Ru L(3)-edge high-energy-resolution fluorescence detected X-ray absorption spectra (HERFD-XAS), supported by ab-initio simulations, revealed that the increased intensity in the high-energy shoulder upon lithium de-intercalation resulted from increased O-O coupling, inducing (O-O) σ*-like states with π overlap with Ru d-manifolds, in agreement with O K-edge XAS spectra. Experimental and simulated O K-edge X-ray emission spectra (XES) further supported this observation with the broadening of the oxygen non-bonding feature upon charging, also originated from (O-O) σ* states. This lattice oxygen redox of Li(2-x)RuO(3) was accompanied by a small amount of O(2) evolution in the first charge from differential electrochemistry mass spectrometry (DEMS) but diminished in the subsequent cycles, in agreement with the more reduced states of Ru in later cycles from Ru L(3)-edge HERFD-XAS. These observations indicated that Ru redox contributed more to discharge capacities after the first cycle. This study has pinpointed the key spectral fingerprints related to lattice oxygen redox from a molecular level and constructed a transferrable framework to rationally interpret the spectroscopic features by combining advanced experiments and theoretical calculations to design materials for Li-ion batteries and electrocatalysis applications.

Aspuru-Guzik, Alán et al., To mark the occasion of Nature Chemistry turning 10 years old, we asked scientists working in different areas of chemistry to tell us what they thought the most exciting, interesting or challenging aspects related to the development of their main field of research will be — here is what they said.

The interfacial (electro)chemical reactions between electrode and electrolyte dictate the cycling stability of Li-ion batteries. Previous experimental and computational results have shown that replacing Mn and Co with Ni in layered LiNixMnyCo1-x-yO2 (NMC) positive electrodes promotes the dehydrogenation of carbonate-based electrolytes on the oxide surface, which generates protic species to decompose LiPF6 in the electrolyte. In this study, we utilized this understanding to stabilize LiNi0.8Mn0.1Co0.1O2 (NMC811) by decreasing free-solvent activity in the electrolyte through controlling salt concentration and salt dissociativity. Infrared spectroscopy revealed that highly concentrated electrolytes with low free-solvent activity had no dehydrogenation of ethylene carbonate, which could be attributed to slow kinetics of dissociative adsorption of Li+-coordinated solvents on oxide surfaces. The increased stability of the concentrated electrolyte against solvent dehydrogenation gave rise to high capacity retention of NMC811 with capacities greater than 150 mA h g-1 (77% retention) after 500 cycles without oxide-coating and Ni-concentration gradients or electrolyte additives.

Electrolytes with improved thermal and oxidative stability must be developed to achieve greater power and energy densities without compromising safety in modern energy storage devices. Because of their much-reduced solvent vapor pressure and expanded electrochemical windows, solvate ionic liquids (SILs) of lithium salts have recently attracted significant attention in this regard. The current palette of SILs is, however, limited to only a few suitable anions with limited chemical functionality. Guided by fundamental physical organic chemistry principles, we designed a new family of S-substituted fluorinated aryl sulfonamide-tagged anions that feature variable numbers of electronically neutral or withdrawing sulfide, sulfoxide, and sulfone substituents. Several salts of these electron deficient anions display very high electrochemical oxidative stability, good solubility, and a weakly coordinating nature that enables the synthesis of Li-based SILs with high thermal and electrochemical oxidative stability. This new family of functional, noncoordinating anions will potentially expand the scope of applications of SILs as safe electrolytes in battery devices.

The active phase responsible for low-temperature CO oxidation in nanoparticulate CuO/CeO2 catalysts was identified as surface-substituted CuyCe1-yO2-x. Contrary to previous studies, our measurements on a library of well-defined CuO/CeO2 catalysts have proven that the CuO phase is a spectator species, whereas the surface-substituted CuyCe1-yO2-x phase is active for CO oxidation. Using in situ X-ray absorption spectroscopy, we found that the copper ions in CuyCe1-yO2-x remain at high oxidation states (Cu3+ and Cu2+) under oxygen-rich catalytic conditions without any evidence for Cu+. Artificial neural network potential Monte Carlo simulations suggest that Cu3+ and Cu2+ preferentially segregate to the {100} surface of the CuyCe1-yO2-x nanoparticle, which is supported by aberration-corrected electron microscopy measurements. These results pave the way for understanding, at the atomic level, the mechanisms and descriptors pertinent for CO oxidation on these materials and hence the rational design of next-generation catalysts.

Understanding the structural, physical and chemical properties of the surface and interfaces of different metal-oxides and their possible applications in photo-catalysis and biology is a very important emerging research field. Motivated in this direction, this article would enable understanding of how different fluids, particularly water, interact with oxide surfaces. We have studied the water contact angle of 3d transition metal oxide thin films of SrTiO3, and of 4f rare-earth oxide thin films of Lu2O3. These metal oxides were grown using pulsed laser deposition and they are atomically flat and with known orientation and explicitly characterized for their structure and composition. Further study was done on the effects of oxygen vacancies on the water contact angle of the 3d and 4f oxides. For 3d SrTiO3 oxide with oxygen vacancies, we have observed an increase in hydroxylation with consequent increase of wettability which is in line with the previous reports whereas an interesting opposite trend was seen in the case of rare-earth Lu2O3 oxide. Density functional theory simulations of water interaction on the above mentioned systems have also been presented to further substantiate our experimental findings.

The direct partial oxidation of methane to methanol promises an energy-efficient and environmental-friendly utilization of natural gas. Unfortunately, current technologies confront a grand challenge in catalysis, particularly in the context of distributed sources. Research has been focused on the design of homogenous and heterogenous catalysts to improve the activation of methane under thermal and electrochemical conditions. However, the intrinsic relationship between thermal and electrochemical systems has not been exploited yet. This review intends to bridge the studies of thermal and electrochemical catalysts, in both homogenous and heterogenous systems, for methane activation from a mechanistic point of view. It is expected to provide a framework to rationalize the design of electrocatalysts beyond the state of art. First, methane activation systems reported previously are reviewed and classified into two basic mechanisms: dehydrogenation and deprotonation. Based on the mechanism types, activity and selectivity descriptors are defined to understand the performance of current catalysts and guide the design of future catalysts. Moreover, methods to enhance the activity and selectivity are discussed to emphasize the unique advantage of electrocatalysis in overcoming the limitations of traditional thermal catalysis. Finally, immense opportunities and challenges for catalyst design are discussed by unifying thermal and electrochemical catalysis.

Understanding the effect of electrode-electrolyte interface (EEI) on the kinetics of electrode reaction is critical to design high-energy Li-ion batteries. While electrochemical impedance spectroscopy (EIS) is used widely to examine the kinetics of electrode reaction in Li-ion batteries, ambiguities exist in the physical origin of EIS responses for composite electrodes. In this study, we performed EIS measurement by using a three-electrode cell with a mesh-reference electrode, to avoid the effect of counter electrode impedance and artefactual responses due to asymmetric cell configuration, and composite or oxide-only working electrodes. Here we discuss the detailed assignment of impedance spectra for LiCoO[subscript 2] as a function of voltage. The high-frequency semicircle was assigned to the impedance associated with ion adsorption and desorption at the electrified interface while the low-frequency semicircle was related to the charge transfer impedance associated with desolvation/solvation of lithium ions, and lithium ion intercalation/de-intercalation into/from LixCoO[subscript 2]. Exposure to higher charging voltages and greater hold time at high voltages led to no significant change for the high-frequency component but greater resistance and greater activation energy for the low-frequency circle. The greater charge transfer impedance was attributed to the growth of EEI layers on the charged LixCoO[subscript 2] surface associated with electrolyte oxidation promoted by ethylene carbonate dehydrogenation. Keywords: Batteries - Lithium, Electrode Kinetics, EIS, Electrode-Electrolyte Interface, Li-ion Batteries, BMW Group

The slow kinetics of the oxygen evolution reaction (OER) is the main cause of energy loss in many low temperature energy storage techniques, such as metal air batteries and water splitting. A better understanding of both the OER mechanism and the degradation mechanism on different transition metal (TM) oxides is critical for the development of the, next generation of oxides as OER catalysts. In this paper, we systematically investigated the catalytic mechanism and lifetime of ABO(3-delta) perovskite catalysts for the OER, where A = Sr or Ca and B = Fe or Co. During the OER process, the Fe-based AFeO(3-delta) oxides with (delta approximate to 0.5 demonstrate no activation of lattice oxygen or pH dependence of the OER activity, which is different from the SrCoO25 with similar oxygen 2p-band position relative to the Fermi level. The difference was attributed to the larger changes in the electronic structure during the transition from the oxygen-deficient brownmillerite structure to the fully oxidized perovskite structure and the poor conductivity in Fe-based oxides, which hinders the uptake of oxygen from the electrolyte to the lattice under oxidative potentials. The low stability of Fe-based perovskites under OER conditions in a basic electrolyte also contributes to the different OER mechanism compared with the Co-based perovskites. This work reveals the influence of TM composition and electronic structure on the catalytic mechanism and operational stability of the perovskite OER catalysts.

The (electro)chemical reactions between positive electrodes and electrolytes are not well understood. We examined the oxidation of a LiPF6-based electrolyte with ethylene carbonate (EC) with layered lithium nickel, manganese, and cobalt oxides (NMC). Density functional theory calculations showed that the driving force for EC dehydrogenation on oxides, yielding surface protic species, increased with greater Ni content in NMC. Ex situ infrared and Raman spectroscopy revealed experimental evidence for EC dehydrogenation on charged NMC surfaces. Protic species on charged NMC surfaces from EC dehydrogenation could further react with LiPF6 to generate less-coordinated F species such as PF3O-like and lithium nickel oxyfluoride species on charged NMC particles and HF and PF2O2- in the electrolyte. Larger degree of salt decomposition was coupled with increasing EC dehydrogenation on charged NMC with increasing Ni or lithium deintercalation. An oxide-mediated chemical oxidation of electrolytes was proposed, providing new insights in stabilizing high-energy positive electrodes and improving Li-ion battery cycle life.

Understanding reactions at the electrode/electrolyte interface (EEI) is essential to developing strategies to enhance cycle life and safety of lithium batteries. Despite research in the past four decades, there is still limited understanding by what means different components are formed at the EEI and how they influence EEI layer properties. We review findings used to establish the well-known mosaic structure model for the EEI (often referred to as solid electrolyte interphase or SEI) on negative electrodes including lithium, graphite, tin, and silicon. Much less understanding exists for EEI layers for positive electrodes. High-capacity Li-rich layered oxides yLi2-xMnO3·(1-y)Li1-xMO2, which can generate highly reactive species toward the electrolyte via oxygen anion redox, highlight the critical need to understand reactions with the electrolyte and EEI layers for advanced positive electrodes. Recent advances in in situ characterization of well-defined electrode surfaces can provide mechanistic insights and strategies to tailor EEI layer composition and properties.