Li-ion battery electrolytes play a crucial role in enabling electrochemical energy storage and conversion, where the solvation of Li+ ions strongly influences the battery performance and stability. Understanding how salt concentration and counteranion chemistry affect both the enthalpic and entropic contributions to Li+ solvation could enable new design principles for next-generation electrolytes. In this work, we seek to rationalize the composition dependence of ionic Seebeck coefficients in dimethyl sulfoxide (DMSO) and 1,2-dimethoxyethane (DME) electrolytes based on independent measurements of the entropy of mixing, bulk configurational entropy (derived from heating the solidified electrolyte to the measurement temperature), ion pairing, and temperature dependence of Li+ solvation enthalpy. In DMSO electrolytes with negligible ion pairing, the measured ionic Seebeck coefficients were governed solely by entropy through the combined influence of the entropy of mixing and the configurational entropy of Li+. On the other hand, in DME electrolytes where ion pairing was significant, enthalpic contributions due to ion pairing, as well as the temperature dependence of solvation enthalpy, dominated. These findings provide new molecular-level insights into how electrolyte composition and structure drive Li+ solvation thermodynamics, informing future strategies for designing advanced electrolytes with improved performance.

We present a techno-economic optimization model for the design and dynamic operation of proton exchange membrane (PEM) electrolyzers, for enabling cost-effective hydrogen production. This model integrates a 0-D model of the electrolyzer stack, process-wide mass and energy balances, operational constraints, and an empirical relation to characterize degradation as a function of operating current density. Utilizing a decomposition-based solution approach, the model predicts optimal electrolyzer size, operation, and necessary hydrogen storage to satisfy hydrogen demand across various technology and electricity price scenarios. Analysis for 2022 electricity prices and technology costs shows that including use-dependent degradation raises the levelized cost of hydrogen (LCOH) from $4.56/kg to $6.60/kg and increases frequency of stack replacement (2 vs. 7 years). However, by 2030, we anticipate a significant reduction in LCOH to $2.50/kg due to lower capital expenses, leading to longer stack lifetimes and less hydrogen storage. The proposed modeling framework is adaptable to study other electrochemical systems relevant for decarbonization.

Proton Exchange Membrane (PEM) electrolysis is a promising pathway for producing low-carbon hydrogen via electrolysis coupled to variable renewable energy (VRE). This study introduces a physics-based PEM electrolyzer model into an integrated design and scheduling optimization routine, allowing for a comprehensive evaluation of the impact of reactor level metrics (e.g., cathode pressure and current density) on the levelized cost of hydrogen (LCOH) across various cost, technology, and electricity supply scenarios. Benefits of the static versus dynamic operation of PEM systems are outlined explicitly. The economic viability of a grid-based PEM electrolyzer producing 50,000 kg of hydrogen per day is assessed for both 2021 and 2035 technology and grid scenarios. Results show that dynamic operation reduces the LCOH by 8% under the 2021 scenario (4.98-4.57 $/kg-H-2 at maximum current density 2 A/cm(2)). Under 2035 price, cost, and technology assumptions (maximum current density 4 A/cm(2)), the LCOH ranges between 2.18 and 3.93 $/kg-H-2 under static operation, and between 1.42 and 2.84 $/kg-H-2 under dynamic operation, resulting in LCOH reductions of 20-50% depending on the electricity price profile. In addition, partial differential pressure mode with a cathode pressure of 5 bar was found to be the most cost-effective way to compress hydrogen to 30 bar in the 2021 scenario, while full differential pressure mode is preferred in the 2035 scenario. Finally, the study revealed that grid-based hydrogen production in 2021 does not meet the carbon intensity (CI) criteria for clean hydrogen in recent U.S. legislation, highlighting the need for additional measures to be considered for grid-connected electrolysis to qualify as "clean" hydrogen. These results suggest that capital cost reduction alone will not achieve low-cost electricity-based hydrogen production, emphasizing the need for further reductions in the cost of low-CI electricity to attain affordable and lower-carbon hydrogen production.

Machine learning (ML) is gaining popularity as a tool for materials scientists to accelerate computation, automate data analysis, and predict materials properties. The representation of input material features is critical to the accuracy, interpretability, and generalizability of data-driven models for scientific research. In this Perspective, we discuss a few central challenges faced by ML practitioners in developing meaningful representations, including handling the complexity of real-world industry-relevant materials, combining theory and experimental data sources, and describing scientific phenomena across timescales and length scales. We present several promising directions for future research: devising representations of varied experimental conditions and observations, the need to find ways to integrate machine learning into laboratory practices, and making multi-scale informatics toolkits to bridge the gaps between atoms, materials, and devices.

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 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 (ADMET) polymerization of highly dissociative, liquid crystalline fluorinated aryl sulfonimide-tagged ("FAST") anion monomers. These ionenes 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. The activation energy for Li+ conduction is 59 kJ/mol, which is among the lowest for systems that are proposed to operate via an ion conduction mechanism that is decoupled from polymer segmental motion. Moreover, the addition 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 that molecular design can facilitate controlled formation of dissociative anionic channels that translate to significant enhancements in ion conduction in solid polymer electrolytes.

Rechargeable lithium metal batteries (LMBs) hold promise to deliver high energy densities, but their commercial application is hampered by challenges such as inhomogeneous lithium deposition or capacity fading due to irreversible processes at electrode interfaces. Focusing on polymer-based electrolytes, the importance of realistic benchmarks in energy density as well as key characteristics governing the cycling reversibility of cells are thoroughly discussed, evaluating projected energy densities of lab-scale and multilayered pouch cells. To facilitate a meaningful comparison of reported cell data, the average energy released per cycle is highlighted as a metric. In addition, the electrochemical performance of polymer-based systems is compared with liquid- and ceramic-based systems, covering recent advances while offering perspectives toward further advancement of high performance and durable energy storage applications based on LMBs.

Understanding the interplay between local structure and dynamics is critical for establishing design rules for advanced ion-conducting electrolytes. In this work, a set of Li-salt in liquid electrolytes is studied using dielectric relaxation spectroscopy (DRS) to examine correlations between several electrolyte properties, including conductivity, dielectric relaxation time and strength, ionicity, and viscosity. These properties were evaluated by changing ion concentration, solvent type, and anion type. DRS was used to identify relaxation processes associated with the solvent and different ion-solvent coordinating structures, and the dielectric properties are reported for the first time for a majority of these systems. The behavior of viscosity and conductivity were shown to change similarly with concentration when accounting for the local coordinating environment, regardless of the salt or solvent type. τα, the dielectric relaxation time of the solvent-ion complexes, is shown to be independent of ion content at low salt concentrations, when solvent separated ion pairs are the dominant ion-solvent complex. However, at high ion concentrations, a new relationship, a power-law dependence, was identified between molar conductivity and τα, as well as viscosity and τα, demonstrating that the dependence of molar conductivity or viscosity on τα is controlled in part by the solvent type, due to variation in shielding between contact ion pairs and aggregates. In contrast, there was not a clear change in the dependence of molar conductivity or viscosity on τα with changing anion. Furthermore, the effective dipole moments of the ion-solvent complexes were determined, and found to decrease with increasing ion concentration, as contact ion pairs and aggregates form. This systematic analysis of the wide range of Li-salts and solvents, and discussion of relations between different local structures and dynamic processes that contribute to conductivity, helps lay a foundation for the design of new liquid electrolytes.

As demand for hydrogen electrolysis increases with therenewableenergy transition, it is critical to ensure that the supply of requiredresources for these technologies is sufficient to match demand. Severalstudies have set forth projections for H-2 production targetsto achieve net-zero emissions by mid-century, where proton exchangemembrane (PEM) electrolyzers feature prominently. As compared to othercommercially available electrolyzers, PEM systems exhibit high currentdensities that favor flexible operation to utilize intermittent renewableenergy sources but rely on relatively scarce iridium (Ir) for catalysis.In this work, we model the supply of Ir resources available for PEMelectrolysis and compare it to the Ir required to meet plausible H-2 production targets for 2030 and 2050. In order for Ir supplyto be sufficient for 2030 H-2 production targets, significantimprovement in average operational current density or Ir loading wouldbe required compared to today's averages of 2 A/cm(2) and 2 mg/cm(2), respectively. By 2050, current technologymay be sufficient to meet the lower end of H-2 productiontargets (83 Mt), with modest technological advances needed in caseH(2) demand exceeds these levels.

Single-ion conducting polymers (SICs) are promising candidates for the next generation of safer polymer electrolytes due to their stability and high transference number. However, the conductivity in SICs is often limited by the mobility of the polymer backbone as the ion mobility is coupled to segmental relaxations. We present polymer blend electrolytes, consisting of a precise single Li-ion conducting polymer with a (trifluoromethanesulfonyl)imide anion pendant group and a low molar mass poly(ethylene oxide) (PEO). Dielectric relaxation spectroscopy is used to probe both the ion transport properties and segmental dynamics of these blends, and X-ray scattering is used to evaluate their morphology. PEO associates with the ionic groups of the SIC, forming a miscible blend with pathways that promote ion transport. At a high PEO content (an ethylene oxide to Li+ ratio of 10), ionic conductivities greater than 10(-5) and 10(-4) S cm(-1) are achieved at 90 and 130 degrees C, respectively. A comparison of conductivities and polymer relaxation times shows that the high PEO content blends exhibit superionic transport, in which there is some decoupling of the Li-ion motion from the backbone mobility. This superionic transport is uncommon in single Li-ion conductors above the glass transition temperature, thus this work presents a critical step toward establishing design rules for superionic transport in SICs.

We present a set of sulfonated monodisperse telechelic polyethylene ionomers that demonstrate ion transport of metal cations in layered ionic assemblies. These semicrystallineionomers have precisely 48 backbone carbons with a sulfonatedgroup at each end and are fully neutralized by a counterion,C48(SO3X)2(X = Li+or Na+). The morphology of these polymersis characterized by using X-ray scattering, and ionic conductivity is probed by using electrochemical impedance spectroscopy. Thesetelechelic polyethylenes exhibit well-defined ionic layers at alltemperatures below the melting point, and the crystal packing ofthe backbone varies with temperature. The polyethylene backbone packs in hexagonal crystals at high temperatures in bothC48(SO3Li)2and C48(SO3Na)2, with Arrhenius activation energies (Ea) for ion transport of 120 and 53 kJ mol-1, respectively,indicating that decoupled ion transport is possible through these layered ionic assemblies. TheEain this hexagonal regime issignificantly lower thanEaat room temperature where C48(SO3Li)2exhibits disordered crystals and C48(SO3Na)2exhibitsorthorhombic crystallites, highlighting the impact of polymer packing between the ionic layers. At intermediate temperatures (120-160 degrees C) the hexagonal crystal structure in C48(SO3Na)2coexists with an unidentified crystal phase that appears to have superior iontransport properties. When compared to other single ion conductors of the same functionality, C48(SO3Na)2also demonstrates the importance of ionic assembly shape and identifies ionic layers as a promising strategy relative to assemblies with less order

Designing polymers with controlled nanoscale morphologies and scalable synthesis is of great interest in the development of fluorine-free materials for proton-exchange membranes in fuel cells. This study focuses on a precision polyethylene with phenylsulfonic acid branches at every fifth carbon, p5PhSA, with a high ion-exchange capacity (4.2 mmol/g). The polymers self-assemble into hydrophilic and hydrophobic co-continuous nanoscale domains. In the hydrated state, the hydrophilic domain, composed of polar sulfonic acid moieties and water, serves as a pathway for efficient mesoscopic proton conductivity. The morphology and proton transport of p5PhSA are evaluated under hydrated conditions using in situ X-ray scattering and electrochemical impedance spectroscopy techniques. At 40 degrees C and 95% relative humidity, the proton conductivity of p5PhSA is 0.28 S/cm, which is four times greater than Nafion 117 under the same conditions. Atomistic molecular dynamics (MD) simulations are also used to elucidate the interplay between the structure and the water dynamics. The MD simulations show strong nanophase separation between the percolated hydrophilic and hydrophobic domains over a wide range of water contents. The percolated hydrophilic nanoscale domain facilitates the rapid proton transport in p5PhSA and demonstrates the potential of precise hydrocarbon-based polymers as processible and effective protonexchange membranes.

Polymers bearing phosphonic acid groups have been proposed as anhydrous proton-conducting membranes at elevated operating temperatures for applications in fuel cells. However, the synthesis of phosphonated polymers and the control over the nanostructure of such polymers is challenging. Here, we report the straightforward synthesis of phosphonic acid-terminated, long-chain aliphatic materials with precisely 26 and 48 carbon atoms (C26PA2 and C48PA2). These materials combine the structuring ability of monodisperse polyethylenes with the ability of phosphonic acid groups to form strong hydrogen-bonding networks. Anhydride formation is absent so that charge carrier loss by a condensation reaction is avoided even at elevated temperatures. Below the melting temperature (Tm), both materials exhibit a crystalline polyethylene backbone and a layered morphology with planar phosphonic acid aggregates separated by 29 and 55 Å for C26PA2 and C48PA2, respectively. Above Tm, the amorphous polyethylene (PE) segments coexist with the layered aggregates. This phenomenon is especially pronounced for the C26PA2 and is identified as a thermotropic smectic liquid crystalline phase. Under these conditions, an extraordinarily high correlation length (940 Å) along the layer normal is observed, demonstrating the strength of the hydrogen bond network formed by the phosphonic acid groups. The proton conductivity in both materials in the absence of water reaches 10-4 S/cm at 150 °C. These new precise phosphonic acid-based materials illustrate the importance of controlling the chemistry to form self-assembled nanoscale aggregates that facilitate rapid proton conductivity.