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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.

[Image: see text] The application of machine learning to predict materials properties measured by experiments are valuable yet difficult due to the limited amount of experimental data. In this work, we use a multifidelity random forest model to learn the experimental formation enthalpy of materials with prediction accuracy higher than the Perdew–Burke–Ernzerhof (PBE) functional with linear correction, PBEsol, and meta-generalized gradient approximation (meta-GGA) functionals (SCAN and r(2)SCAN), and it outperforms the hotly studied deep neural network-based representation learning and transfer learning. We then use the model to calibrate the DFT formation enthalpy in the Materials Project database and discover materials with underestimated stability. The multifidelity model is also used as a data-mining approach to find how DFT deviates from experiments by explaining the model output.

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.

The crucial role of electrolyte cations in CO2 electroreduction has received intensive attention. One prevailing theory is that through electrostatic interactions or direct coordination, larger cations such as Cs+ can better stabilize the key intermediate species for CO and multicarbon (C2+) product generation, for example, on silver and copper. Herein, we show that smaller, acidic alkali metal cations greatly enhance CO2-to-methanol conversion kinetics (Li+ > Na+ > K+ > Cs+) on an immobilized molecular cobalt catalyst unlike the trend for CO and C2+. Through kinetic isotope effect studies and electrokinetic analyses, we found that hydration shell of a cation serves as a proton donor in the rate-determining protonation step of adsorbed CHO where acidic cations promote the proton-coupled electron transfer. This study reveals the promotional effect of cation solvation environment on CO2 electroreduction beyond the widely acknowledged stabilizing effect of cations.

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.

Solid polymer electrolytes have the potential to enable safer and more energy dense batteries; however, a deeper understanding of their ion conduction mechanisms, and how they can be optimized by rational molecular design, is needed to realize this goal. Here, we investigate the impact of anion dissociation energy on ion conduction in solid polymer electrolytes via a novel class of ionenes prepared using acyclic diene metathesis polymerization of highly dissociative, liquid crystalline fluorinated aryl sulfonimide-tagged ("FAST”) anion monomers. These polyanions with various cations (Li+, Na+, K+, and Cs+) form well-ordered lamellae that are thermally stable up to 180 °C and feature domain spacings that correlate with cation size, providing channels lined with dissociative FAST anions. Electrochemical impedance spectroscopy (EIS) and differential scanning calorimetry (DSC) experiments, along with nudged elastic band (NEB) calculations, suggest that cation motion in these materials operates via an ion hopping mechanism. Moreover, the activation energy for Li+ conduction is 59 kJ/mol, which is amongst the lowest for systems that are proposed to operate via an ion conduction mechanism that is decoupled from polymer segmental motion. Furthermore, the addition of a 1 equivalent of a cation-coordinating solvent to these materials led to a >1000-fold increase in ionic conductivity without detectable disruption of the lamellar structure, suggesting selective solvation of the lamellar ion channels. This work demonstrates a novel molecular design strategy to facilitate controlled formation of dissociative anionic channels, which translates to significant enhancements in ion conduction in solid polymer electrolytes.

The cost-effective production of green hydrogen is one of the most important challenges for a sustainable energy transition. To decrease the cost in the production of hydrogen through electrolysis, there are several obstacles that must be overcome. For instance, more active and stable anodes made of abundant and cheap materials will contribute to lowering the capital and operational expenditure of the process. It is well-known that the oxidation of water requires high overpotentials, which is the main limitation for the performance of the device. In this context, substituting the oxidation of water (OER) at the anode of electrolyzers by the oxidation of biomass-derived substances contribute to the overall process by decreasing the power input of the devices and, in some cases, by producing value-added chemicals. Herein, we re-visited some of the most important fundamental aspects of the (electro-)oxidation of alcohols and polyols on metal-based catalysts, focusing on reaction descriptors. Then, we moved to the (electro-)oxidation of these molecules on metal oxides, re-visiting some of the literature about their application in heterogeneous catalysis and for OER, to get insights about the relation of the structure of the materials and their activity. Due to the lack of fundamental knowledge about the electro-oxidation of alcohols and polyols on metallic oxides and to the vast literature about the use of perovskite oxides for OER, we propose to start systematic studies using perovskite oxides for the electrooxidation of alcohols and polyols. Consequently, we presented results for LaCoO3, LaFeO3, LaMnO3, and LaNiO3, and propose a mechanism for the electro-oxidation of glycerol based on the formation and reactivity of MOH(O) species. We believe that fundamental and systematic studies in this topic would permit the establishment of reaction descriptors, speeding up the searching for suitable materials for this reaction and paving the way for a most cost-effective production of green hydrogen.

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.

In this perspective, we highlight results of a research consortium devoted to advancing understanding of oxygen reduction reaction (ORR) catalysis as a means to inform fuel cell science.

A molten-salt Na–O2 battery featuring a liquid Na negative electrode and Ni positive electrode was found to form Na2O2 on discharge, enabled by nitrate redox where NO3− is reduced to Na2O and NO2−, then reactions with O2 produce Na2O2 and reform NO3−.

To address the intermittency problems of variable renewable energy (VRE) in low-carbon energy systems, flexibility has become increasingly important. Electrified transportation exhibits great potentialto provide essential flexibility. In this work, we analyzed and compared the flexibility values of battery electric vehicles (BEVs) and fuel cell electric vehicles (FCEVs) for planning and operating interdependent electricity and hydrogen supply infrastructures while considering battery degradation impacts and costs. A cross-scale framework involving both macro-level and micro-level models was proposed to compute the values of flexible EV charging. At the macro level, a sector-coupling planning model was adopted to estimate the system cost reduction from flexible EV charging incorporating battery degradation costs. Battery degradation cost computation for BEVs was based on micro-level simulations of battery degradation via a porous electrode theory-based model under various charging-time constraints and temperatures. The results show that the flexibility values of BEVs are significantly reduced by considering the battery degradation cost and becomes comparable to those of FCEVs. Fast charging and a low-temperature environment could reduce the flexibility values of BEVs due to increased degradation. Under theelectrolytic-hydrogen only pathway, with more stronglycoupled power and hydrogen supply chains, the flexibility values of BEVs are significantly reduced because of the substitution effect of the less expensive flexibility from hydrogen storage. Our findings imply that policies (e.g., the hydrogen pathway) and relevant management technologies (e.g., battery fast charging and thermal management) for BEV battery degradation mitigation are crucial to shaping the comparative flexibility advantage of the two transportation electrification pathways.

The surface wettability of catalysts is typically controlled via surface treatments that promote catalytic performance. Here we report on potential-regulated hydrophobicity/hydrophilicity at cobalt-based oxide interfaces with an alkaline solution. The switchable wetting of single particles, directly related to their activity and stability towards the oxygen evolution reaction, was revealed by electrochemical liquid-phase transmission electron microscopy. Analysis of the movement of the liquid in real time revealed distinctive wettability behaviour associated with specific potential ranges. At low potentials, an overall reduction of the hydrophobicity of the oxides was probed. Upon reversible reconstruction towards the surface oxyhydroxide phase, electrowetting was found to cause a change in the interfacial capacitance. At high potentials, the evolution of molecular oxygen, confirmed by operando electron energy-loss spectroscopy, was accompanied by a globally thinner liquid layer. This work directly links the physical wetting with the chemical oxygen evolution reaction of single particles, providing fundamental insights into solid–liquid interfacial interactions of oxygen-evolving oxides., Surface treatments can tune catalysts’ wettability, which can be used to promote their catalytic performance. Now, a potential-dependent dynamic wetting behaviour of cobalt-based oxide catalysts is identified before and during the oxygen evolution reaction.

Summary Manganese dioxide is abundant, low-cost, and has the potential to be utilized as a semi-solid electrode for long-duration energy storage technologies such as flow batteries. However, the more stringent pumping requirements of semi-solid electrodes compared to the electrolytes of all-liquid flow battery might limit their techno-economic feasibility. Here, we developed a rechargeable MnO2 semi-solid electrode, performed electrochemical and rheological characterizations, and bottom-up techno-economic analysis of the Zn-MnO2 semi-solid flow battery (SSFB) system. The high power needed for pumping (ranging from 8% to 50% of the power output) leads to a system with high cost of power. Using our experimental results, we suggest strategies to minimize the pumping power requirement for Zn-MnO2 SSFB. As a result of the low cost of its chemical constituents, we show that a Zn-MnO2 SSFB can be cheaper than Li-ion and vanadium redox flow battery solutions for long discharge durations (e.g., >24 h per cycle).

The cost-effective production of green hydrogen is one of the most important challenges for a sustainable energy transition. To decrease the cost in the production of hydrogen through electrolysis, there are several obstacles that must be overcome. For instance, more active and stable anodes made of abundant and cheap materials will contribute to lowering the capital and operational expenditure of the process. It is well-known that the oxidation of water requires high overpotentials, which is the main limitation for the performance of the device. In this context, we believe that substituting the oxidation of water (OER) at the anode of electrolyzers by the oxidation of biomass-derived substances could contribute to the overall process by decreasing the power input of the devices and, in some cases, by producing value-added chemicals. Herein, we re-visited some of the most important fundamental aspects of the (electro-)oxidation of alcohols and polyols on metal-based catalysts, focusing on reaction descriptors. Then, we moved to the (electro-)oxidation of these molecules on metal oxides, re-visiting some of the literature about their application in heterogeneous catalysis and for OER, to get insights about the relation of the structure of the materials and their activity. Due to the lack of fundamental knowledge about the electro-oxidation of alcohols and polyols on metallic oxides and to the vast literature about the use of perovskite oxides for OER, we propose to start systematic studies using perovskite oxides for the electrooxidation of alcohols and polyols. We believe that fundamental studies in this topic would permit the establishment of reaction descriptors, speeding up the searching for suitable materials for this reaction and paving the way for a most cost-effective production of green hydrogen.

As Li-ion battery costs decrease, energy density and thus driving range remains a roadblock for mass-market vehicle electrification. While Li-metal anodes help achieve Department of Energy targets of 500 Wh kg−1 (750 Wh l−1), Li Coulombic efficiencies fall below the 99.95+% required for 1,000+ cycles. Here we examine historical electrolyte developments underlying increased Coulombic efficiency and discuss emerging frameworks that support rational strategies to move beyond 99.9%. While multiple electrolytes reach 98–99% Coulombic efficiency over subsets of cycles, achieving >99.9% Coulombic efficiency consistently throughout cycling is an as yet unmet challenge. We analyse important interplays between electrolyte, solid electrolyte interphase composition, plating–stripping kinetics and Li morphology, many of which are only recently being quantified experimentally at the Li interface, and which collectively determine Coulombic efficiency. We also discuss forward-looking strategies that, if mastered, represent new opportunities to refine understanding and support new record values of Coulombic efficiency in the coming years. Irreversibility is one of the biggest obstacles in realizing practical Li-metal batteries. This Review surveys the trends in Coulombic efficiency (CE)—a reversibility indicator—reported for Li-metal batteries over the last five decades, abstracts key CE descriptors and analyses promising strategies to improve CE.

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.

Historically, materials informatics has relied on human-designed descriptors of materials structures. In recent years, graph neural networks (GNNs) have been proposed for learning representations of crystal structures from data end-to-end producing vectorial embeddings that are optimized for downstream prediction tasks. However, a systematic scheme is lacking to analyze and understand the limits of GNNs for capturing crystal structures. In this work, we propose to use human-designed descriptors as a bank of human knowledge to test whether black-box GNNs can capture the knowledge of crystal structures. We find that current state-of-the-art GNNs cannot capture the periodicity of crystal structures well, and we analyze the limitations of the GNN models that result in this failure from three aspects: local expressive power, long-range information, and readout function. We propose an initial solution, hybridizing descriptors with GNNs, to improve the prediction of GNNs for materials properties, especially phonon internal energy and heat capacity with 90% lower errors, and we analyze the mechanisms for the improved prediction. All the analysis can be extended easily to other deep representation learning models, human-designed descriptors, and systems such as molecules and amorphous materials.

Oxygen reduction reaction (ORR) is a crucial process that drives the operation of several energy storage devices. ORR can proceed on the neat carbon surface in the absence of a catalyst, and its electrochemical activity is determined by its microstructure and chemical composition. Oxygen functional groups unavoidably existing on the carbon surface can serve as adsorption sites for ORR intermediates; the presence of some oxygen functionalities gives rise to an increase in the density of electronic states (DOS) at the Fermi level (FL). Both factors should have a positive impact on the electron transfer rate that was demonstrated for ORR in aqueous media. To study the O-groups effect on the aprotic ORR, which is now of interest due to the extensive development of aprotic metal-air batteries, we use model oxidized carbon electrodes (HOPG and single-layer graphene). We demonstrate that oxygen functionalities (epoxy, carbonyl, and lactone) do not affect the rate of one-electron oxygen reduction in aprotic media in the absence of metal cations since their introduction practically does not increase DOS at FL. However, in Li+-containing electrolytes, oxygen groups enhance both the rate of second electron transfer and carbon degradation due to its oxidation by LiO2 yielding carbonate species.