Materials Science and Engineering

Recent studies have reported long-range charge transport in peptide- and protein-based fibers and wires, rendering this class of materials as promising charge-conducting interfaces between biological systems and electronic devices. In the complex molecular environment of biomolecular building blocks, however, it is unclear which chemical and structural dynamic features support electronic conductivity. Here, we investigate the role of finite temperature fluctuations on the electronic structure and its implications for conductivity in a peptide-based fiber material composed of an antiparallel coiled coil hexamer, ACC-Hex, building block. All-atom classical molecular dynamics (MD) and first-principles density functional theory (DFT) are combined with interpretable machine learning (ML) to understand the relationship between physical and electronic structure of the peptide dimer subunit of ACC-Hex. For 1101 unique MD "snapshots" of the ACC peptide dimer, hybrid DFT calculations predict a significant variation of near-gap orbital energies among snapshots, with an increase in the predicted number of nearly degenerate states near the highest occupied molecular orbital (HOMO), which suggests improved conductivity. Interpretable ML is then used to investigate which nuclear conformations increase the number of nearly degenerate states. We find that molecular conformation descriptors of interphenylalanine distance and orientation are, as expected, highly correlated with increased state density near the HOMO. Unexpectedly, we also find that descriptors of tightly coiled peptide backbones, as well as those describing the change in the electrostatic environment around the peptide dimer, are important for predicting the number of hole-accessible states near the HOMO. Our study illustrates the utility of interpretable ML as a tool for understanding complex trends in large-scale ab initio simulations.

DNA-stabilized silver nanoclusters (DNA-AgN) are atomically precise and sequence-tuned nanomaterials with potential applications for deep tissue biomedical imaging. Here, a dual-emissive DNA-AgN is presented with fluorescence in the first near-infrared (NIR-I) spectral window and microsecond-lived photoluminescence in the second near-infrared (NIR-II) spectral window. High-resolution electrospray ionization mass spectrometry showed that the emitter has the molecular formula (DNA)2[Ag17]11+. The crystallization of (DNA)2[Ag17]11+ was unsuccessful, which prevented the use of X-ray diffraction to determine its structure. However, sequence variations of the templating DNA oligomer provided insights into nucleobases that are critical for stabilizing the Ag1711+. Moreover, addition of an adenosine or thymidine at the 5′-end of the stabilizing DNA strand maintained the composition and photophysical properties of the (DNA)2[Ag17]11+, suggesting a potential site for conjugation with biomolecules to enable targeted labeling in future bioimaging applications.

Many contemporary imaging systems seek tunable focusing components with minimal form factors and versatile functionalities; however, existing solutions are typically limited in size, efficiency, and tuning speed. Here, low-loss all-dielectric metasurfaces integrated with liquid crystals (LCs) are used to demonstrate highly compact multifunctional zoom components. The phase profiles imparted by the metalens are modulated in real time by means of field-dependent LCs, enabling electrically driven continuous focal length variation and active bifocal imaging with low applied voltages (<10 V). These applications are achieved through the systematic design and validation of resonant metasurface elements that ensure the desired metalens response in each LC state. We engineer and fabricate a high-contrast voltage-actuated continuous-zoom LC-metalens with up to 18% total shift in focal length. Additionally, we fabricate simplified large-diameter LC-metalenses, composed of only a few resonator types, that facilitate electrically tunable multidepth imaging. These results demonstrate the promise of electrically controlled LC-embedded zoom-metasurfaces to serve as lightweight and ultrathin multifunctional focusing components, with prospective uses in next-generation imaging devices.

Polymer design requires fine control over syntheses and a thorough understanding of their macromolecular structure. Herein, near-atomic level imaging of polymers is achieved, enabling the precise determination of one of the most important macromolecular characteristics: molecular weight. By judiciously designing and synthesizing different linear metal(loid)-rich homopolymers, subnanoscale polymer imaging is achieved through annular dark field-scanning transmission electron microscopy (ADF-STEM), owing to the incorporation of high Z atoms in the side chain of the monomeric units. The molecular weight of these polymers can be precisely determined by detecting and counting their metal(loid) atoms upon ADF-STEM imaging, at sample concentrations as low as 10 μg·mL-1. Notably, a commonly used C, H, and O-containing polymer (i.e., poly(methyl acrylate)) that was thus far inaccessible at the atomic scale is derivatized to allow for subnano-level imaging, thus expanding the scope of our approach toward the atomic-level visualization of commodity polymers.

It remains a grand challenge to develop electrocatalysts with simultaneously high activity, long durability, and low cost for the oxygen evolution reaction (OER), originating from two competing reaction pathways and often trade-off performances. The adsorbed evolution mechanism (AEM) suffers from sluggish kinetics due to a linear scaling relationship, while the lattice oxygen mechanism (LOM) causes unstable structures due to lattice oxygen escape. We propose a MoZnFeCoNi high-entropy alloy (HEA) incorporating AEM-promoter Mo and LOM-active Zn to achieve dual activation and stabilization for efficient and durable OER. Density functional theory and chemical probe experiments confirmed dual-mechanism activation, with representative Co-Co†-Mo sites facilitating AEM and Zn-O†-Ni sites enhancing LOM, resulting in an ultralow OER overpotential (η10 = 221 mV). The multielement interaction, high-entropy structure, and carbon network notably enhance structural stability for durable catalysis (>1500 hours at 100 mA cm-2). Our work offers a viable approach to concurrently enhance OER activity and stability by designing HEA catalysts to enable dual-mechanism synergy.

Electric double layers (EDLs) play a fundamental role in various electrochemical processes such as colloidal dispersions, surface charging, and charge-transfer reactions. Increasingly, the role of EDLs on reaction kinetics is being studied[1], revealing their importance in predicting the intrinsic and electrolyte-dependent kinetics of electrochemical reactions. Despite the extensive history of EDL modeling, there remain challenges in predicting the impact of EDL structure on reaction kinetics. The characteristic length of EDL for non-dilute solutions (typically 10 – 100 nanometers) exceeds the grasp of regular ab initio molecular dynamics (AIMD) simulations. While continuum models offer a means to estimate the quasi-equilibrium structure of EDLs with substantially lower computational cost than molecular dynamics, conventional continuum models require parameter fitting[2] due to their lack of appropriate expressions for microscopic interactions. Furthermore, the lack of a commonly accepted micro-kinetic model to evaluate the role of the EDL structure on the reaction kinetics prevents the optimization of the interface for improved reaction rates. In this talk, we propose a novel modeling framework for analyzing micro-kinetics that accounts for the contributions of EDL structure by leveraging our recently developed continuum EDL model [3] and density functional theory (DFT) calculations. Our previous work showed that the continuum model can accurately predict differential capacitance for EDL charging without necessitating parameter-fitting by incorporating microscopic interactions such as electron spillover, entropy due to solute size variation, and polarization of solvent and solute molecules [3]. We refine the continuum EDL model to account for the interactions between adsorbate coverage and EDL structure. This model utilizes DFT results, i.e., free energies and charge distributions of the adsorbates at potential of zero charge, as input properties. The model calculates the adsorbates’ coverage to minimize the total grand potential, while accounting for both the effect of electrostatic potential on the adsorbate free energy and the effect of adsorbate charge density on the electrostatic potential simultaneously. The transition state of the rate determining step is treated as an adsorbate species, with its coverage evaluated in the same manner as the other adsorbates, which is used to evaluate the reaction rate based on transition state theory. This model framework enables us to evaluate the intrinsic and electrolyte-dependent kinetic activity with reasonable computational resources. Finally, we apply this model to investigate the kinetics of hydrogen evolution and oxidation reactions (HER/HOR) having favorable comparisons with measured cation- and pH- dependent kinetics[4]. The results suggest that the charge distribution of the transition state can significantly affect electrolyte-dependent kinetics of electrochemical reactions, highlighting the importance of further analyzing the effects of EDL structures on reaction kinetics. Acknowledgements: This work was partially supported by the by the Center for Ionomer-based Water Electrolysis (CIWE), a DOE sponsored Energy Earthshot Research Center under contract number DE-AC02-05CH11231, and by a CRADA with Toyota Central R&D Labs., Inc. Part of this work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The authors acknowledge the HydroGen Energy Materials Network from the Department of Energy, Hydrogen and Fuel Cell Technologies Office for funding under Contract numbers DE-AC02-05CH11231. Reference: [1] Shin, S.J., et al., On the importance of the electric double layer structure in aqueous electrocatalysis. Nat Commun, 2022. 13(1): p. 174. [2] Huang, J., Density-Potential Functional Theory of Electrochemical Double Layers: Calibration on the Ag(111)-KPF(6) System and Parametric Analysis. J Chem Theory Comput, 2023. 19(3): p. 1003-1013. [3] Shibata, M., S., et al., Parameter-fitting-free Continuum Modeling of Electrical Double Layer in Aqueous Electrolyte, Submitted. [4] Huang, B., et al., Cation- and pH-Dependent Hydrogen Evolution and Oxidation Reaction Kinetics. JACS Au, 2021. 1(10): p. 1674-1687. Figure 1

To combat the rise of antibiotic-resistance in bacteria and the resulting effects on healthcare worldwide, new technologies are needed that can perform rapid antibiotic susceptibility testing (AST). Conventional clinical methods for AST rely on growth-based assays, which typically require long incubation times to obtain quantitative results, representing a major bottleneck in the determination of the optimal antibiotic regimen to treat patients. Here, we demonstrate a rapid AST method based on the metabolic activity measured by fluorescence lifetime imaging microscopy (FLIM). Using lab strains and clinical isolates of Escherichia coli with tetracycline-susceptible and resistant phenotypes as models, we demonstrate that changes in metabolic state associated with antibiotic susceptibility can be quantitatively tracked by FLIM. Our results show that the magnitude of metabolic perturbation resulting from antibiotic activity correlates with susceptibility evaluated by conventional metrics. Moreover, susceptible and resistant phenotypes can be differentiated in as short as 10 min after antibiotic exposure. This FLIM-AST (FAST) method can be applied to other antibiotics and provides insights into the nature of metabolic perturbations inside bacterial cells resulting from antibiotic exposure with single cell resolution.

Oxide ceramic electrolytes (OCEs) have great potential for solid-state lithium metal (Li0) battery applications because, in theory, their high elastic modulus provides better resistance to Li0 dendrite growth. However, in practice, OCEs can hardly survive critical current densities higher than 1 mA/cm2. Key issues that contribute to the breakdown of OCEs include Li0 penetration promoted by grain boundaries (GBs), uncontrolled side reactions at electrode-OCE interfaces, and, equally importantly, defects evolution (e.g., void growth and crack propagation) that leads to local current concentration and mechanical failure inside and on OCEs. Here, taking advantage of a dynamically crosslinked aprotic polymer with non-covalent -CH3⋯CF3 bonds, we developed a plastic ceramic electrolyte (PCE) by hybridizing the polymer framework with ionically conductive ceramics. Using in-situ synchrotron X-ray technique and Cryogenic transmission electron microscopy (Cryo-TEM), we uncover that the PCE exhibits self-healing/repairing capability through a two-step dynamic defects removal mechanism. This significantly suppresses the generation of hotspots for Li0 penetration and chemomechanical degradations, resulting in durability beyond 2000 hours in Li0-Li0 cells at 1 mA/cm2. Furthermore, by introducing a polyacrylate buffer layer between PCE and Li0-anode, long cycle life >3600 cycles was achieved when paired with a 4.2 V zero-strain cathode, all under near-zero stack pressure.

Bipolar membranes (BPMs) enable isolated acidic/alkaline regions in electrochemical devices, facilitating optimized environments for electrochemical separations and catalysis. For economic viability, BPMs must attain stable, high current density operation with low overpotentials in a freestanding configuration. We report an asymmetric, graphene oxide (GrOx)-catalyzed BPM capable of freestanding electrodialysis operation at 1 A cm-2 with overpotentials <250 mV. Use of a thin anion-exchange layer improves water transport while maintaining near unity Faradaic efficiency for acid and base generation. Voltage stability exceeding 1100 h with an average drift of 70 μV/h at 80 mA cm-2 and 100 h with an average drift of −300 μV/h at 500 mA cm-2 and implementation in an electrodialysis stack demonstrate real-world applicability. Continuum modeling reveals that water dissociation in GrOx BPMs is both catalyzed and electric-field enhanced, where low pKa moieties on GrOx enhance local electric fields and high pKa moieties serve as active sites for surface-catalyzed water dissociation. These results establish commercially viable BPM electrodialysis and provide fundamental insight to advance design of next-generation devices.

Short-range ordering (SRO) in multi-principal element alloys influences material properties such as strength and corrosion. While some degree of SRO is expected at equilibrium, predicting the kinetics of its formation is challenging. We present a simplified isothermal concentration-wave (CW) model to estimate an effective relaxation time of SRO formation. Estimates from the CW model agree to within a factor of five with relaxation times obtained from kinetic Monte Carlo (kMC) simulations when above the highest ordering instability temperature. The advantage of the CW model is that it only requires mobility and thermodynamic parameters, which are readily obtained from alloy mobility databases and Metropolis Monte Carlo simulations, respectively. The simple parameterization of the CW model and its analytical nature makes it an attractive tool for the design of processing conditions to promote or suppress SRO in multicomponent alloys.