The development of durable and cost-effective catalysts for the oxygen reduction reaction (ORR) is central to advancing proton exchange membrane fuel cells (PEMFCs). Herein, we report a highly active and stable electrocatalyst consisting of ultrafine Pt2Mo nanoparticles anchored onto a self-assembled, three-dimensionally ordered bamboo-like nitrogen-doped carbon nanotube (N-CNT) framework. The ordered N-CNT network provides interconnected diffusion channels, superior electrical conductivity, and uniform nanoparticle dispersion. Alloying Pt with Mo modulates the local atomic and electronic environment, as confirmed by advanced spectroscopic characterizations and DFT calculations, leading to optimized oxygen intermediate adsorption and accelerated ORR kinetics. Consequently, the Pt2Mo/N-CNT catalyst delivers a significantly higher mass activity and improved durability over commercial Pt/C, with negligible performance loss after extended cycling. These findings demonstrate a synergistic enhancement arising from atomic-scale alloy engineering and mesoscale structural ordering, offering a promising strategy for the rational design of next-generation fuel cell catalysts.

The Rouse dynamics of polymer chains in model nanocomposite polyethylene oxide/silica nanoparticles (NPs) was investigated using quasielastic neutron scattering. The apparent Rouse rate of the polymer chains decreases as the particle loading increases. However, there is no evidence of an immobile segment population on the probed time scale of tens of ps. The slowing down of the dynamics is interpreted in terms of modified Rouse models for the chains in the NP interphase region. Thus, two chain populations, one bulk-like and the other characterized by a suppression of Rouse modes, are identified. The spatial extent of the interphase region is estimated to be about twice the adsorbed layer thickness, or ≈2 nm. These findings provide a detailed description of the suppression of the chain dynamics on the surface of NPs. These results are relevant insights on surface effects and confinement and provide a foundation for the understanding of the rheological properties of polymer nanocomposites with well-dispersed NPs.

In this study, we investigated polymer chain dimensions in solid polymer electrolytes (SPEs) composed of hydrogenated and deuterated poly(ethylene carbonate/ethylene oxide) (h-/d-P(EC/EO)) copolymers and lithium bis(trifluoromethane)sulfonimide (LiTFSI) at various lithium-ion concentrations. The results were compared with h/d-poly(ethylene oxide) (PEO)/LiTFSI systems, extensively studied for their ionic conduction properties. The scattering intensity I(q) at low scattering vector q (≤ 0.4 Å−1) decreased with increasing lithium-ion concentration. From the low q data, the radius of gyration Rg of the polymer chains in SPE was estimated by the Guinier method. For both PEO and P(EC/EO) systems, with increasing the lithium-ion concentration (i.e., molar ratio of lithium ion to monomer, rs), Rg(rs) first decreased and then increased. Furthermore, the normalized Rg(rs) by Rg(0) exhibited a minimum at rs ≈ 0.15 for the PEO systems, whereas the P(EC/EO) system displayed a decrease in Rg to a higher rs (≈ 0.20) followed by a weak re-increase. Previous MD simulations (Y. Doi, et al., J. Phys. Chem. C2022, 126, 20,284) in the P(EC/EO)/LiTFSI systems have reported preferential coordination of carbonyl oxygens to lithium ions and an increase in the coordination number of oxygen atoms (resulting in the disrupted coordination structure) compared to the corresponding PEO systems, which can well explain the results in this study. The above experimental facts in this study are important findings in that they include data on new polymer systems other than PEO, while the number of reports for polymer conformation studies of SPE systems by SANS is still limited.

The association of ionizable polymers strongly affects their motion in solutions, where the constraints arising from clustering of the ionizable groups alter the macroscopic dynamics. The interrelation between the motion on multiple length and time scales is fundamental to a broad range of complex fluids including physical networks, gels, and polymer-nanoparticle complexes where long-lived associations control their structure and dynamics. Using neutron spin echo and fully atomistic, multimillion atom molecular dynamics (MD) simulations carried out to times comparable to that of chain segmental motion, the current study resolves the dynamics of networks formed by suflonated polystryene solutions for sulfonation fractions 0 <= f <= 0.09 across time and length scales. The experimental dynamic structure factors were measured and compared with computational ones, calculated from MD simulations, and analyzed in terms of a sum of two exponential functions, providing two distinctive time scales. These time constants capture confined motion of the network and fast dynamics of the highly solvated segments. A unique relationship between the polymer dynamics and the size and distribution of the ionic clusters was established and correlated with the number of polymer chains that participate in each cluster. The correlation of dynamics in associative complex fluids across time and length scales, enabled by combining the understanding attained from reciprocal space through neutron spin echo and real space, through large scale MD studies, addresses a fundamental long-standing challenge that underline the behavior of soft materials and affect their potential uses.

Most lithium batteries offer a wide range of applications. However, safety issues are still an unresolved issue for several applications. To solve the safety issue of Li-ion batteries, solid polymer electrolyte is a promising candidate to replace commercial liquid electrolyte. A 4-arm star poly(ethylene oxide) polymer with LiTFSI salt as an electrolyte was studied. The dynamics of this polymer were explored with the Quasi-Elastic Neutron Scattering technique. Furthermore, the influence of temperature and Li salt concentration on the polymer dynamics was investigated. The dynamics of the polymer ends of the arm show much higher flexibility than the core parts making those types of polymers attractive for further studies in battery research.

Spin-crossover (SCO) compounds are promising materials for a wide variety of industrial applications. However, the fundamental understanding of their nature of transition and its effect on the physical properties are still being fervently explored; the microscopic knowledge of their transition is essential for tailoring their properties. Here an attempt is made to correlate the changes in macroscopic physical properties with microscopic structural changes in the orthorhombic and monoclinic polymorphs of the SCO compound Fe(PM-Bia)2(NCS)2 (PM = N-2'-pyridylmethylene and Bia = 4-aminobiphenyl) by employing single-crystal X-ray diffraction, magnetization and DSC measurements. The dependence of macroscopic properties on cooperativity, highlighting the role of hydrogen bonding, π-π and van der Waals interactions is discussed. Values of entropy, enthalpy and cooperativity are calculated numerically based on the Slichter-Drickamer model. The particle size dependence of the magnetic properties is probed along with the thermal exchange and the kinetic behavior of the two polymorphs based on the dependence of magnetization on temperature scan rate and a theoretical model is proposed for the calculation of the non-equilibrium spin-phase fraction. Also a scan-rate-dependent two-step behavior observed for the orthorhombic polymorph, which is absent for the monoclinic polymorph, is reported. Moreover, it is found that the radiation dose from synchrotron radiation affects the spin-crossover process and shifts the transition region to lower temperatures, implying that the spin crossover can be tuned with radiation damage.

The dynamics of lithium ions and polymer chains were investigated at the molecular scale in the model polymer electrolyte Poly (ethylene oxide) (PEO)/Lithium bis(trifluoromethanesulfonyl)imide as a function of temperature. This system is known to present an intermediate range order from the arrangement of neighboring chain segments as well as an extended range order of cylindrically arranged chains. The collective dynamics of the systems at lengthscales matching these structural features was measured using Neutron Spin Echo spectroscopy, gaining insights into their lifetime. Moreover, using isotope substitution techniques the dynamics of the lithium ions with respect to the other atoms was probed. The obtained results are compared with the conductivity and the lithium self-diffusion coefficient measured by NMR to gain experimental insight on the molecular processes triggering lithium transport.

Poly(ethylene carbonate/ethylene oxide) P(EC/ EO) copolymer was synthesized from EC monomer as a new matrix component of solid polymer electrolytes (SPEs), and the correlation between polymer dynamics and ionic conductivity in the P(EC/EO)-based SPEs at various lithium salt weight fractions (wLi) was investigated by dielectric spectroscopy, rheology, and molecular dynamics (MD) simulations. With the addition of lithium salt, the molecular motions at various scales (i.e., from local to segmental and global motion scales) were found to change as follows: (i) the local motion of P(EC/EO) was slightly accelerated, and at wLi >= 0.22, it was separated into two relaxation modes, one faster and the other slower than that of P(EC/EO), (ii) the segmental motion of P(EC/EO) became significantly slower with the addition of lithium salt, and (iii) the global terminal relaxation became slightly slower with the increase of wLi. Thus, the motion of P(EC/EO) at various scales in SPEs changed with different trends with increasing lithium salt. It was also found that the temperature dependence of the ionic conductivity was described by a Vogel-Fulcher-Tammann-type function, which was correlated with the segmental motion, as is known in other SPE systems. Furthermore, from MD simulations, lithium ions are coordinated with the EC units more likely and with a closer distance than EO units in P(EC/EO), and the coordination number of oxygens around one lithium ion was estimated as 6-7 at the distance of 0.30 nm. These results suggest that the coordination structure of the oxygens around the lithium ion is slightly disrupted due to the presence of EC units compared to the chelating structure of pure PEO electrolytes.

Neutron spin echo (NSE) spectroscopy provides the ultimate energy resolution in quasi-elastic thermal and cold neutron scattering spectroscopy. A peculiarity of the SNS-NSE, the only NSE spectrometer at a pulsed beam port at the moment, is that the wavelength spread δλ/λ can be chosen during evaluation with an appropriate time channel binning. The Q-resolution can be adjusted in certain limits a posteriori by choosing the appropriate detector binning (as on a continuous source) and time channel binning. This can be exploited for samples with a strongly varying scattering function S ( Q , t ), e.g. due to Bragg peaks in a crystal or lamellar ordering in microemulsions. The data reduction software DrSpine allows for appropriate slicing and masking for this task. In this contribution the correlation function of microemulsions, thermodynamically stable mixtures of oil, water and surfactant, is measured with NSE on length scales where structural correlations are important, and data reduction strategies varying the Q-resolution by pixel and time channel grouping are discussed. The typical ”de Gennes narrowing” or structural narrowing is observed with a relaxation time proportional to I ( Q ). In these regions of strongly varying intensity it is shown that a too coarse grouping has an influence on the data reduction, with a broadened in Q of the apparent slowing down.

The polymer dynamics in concentrated solutions of poly(N-isopropyl acrylamide) (PNIPAM) in D2O/CD3OD mixtures is investigated in the one-phase region. Two polymer concentrations (9 and 25 wt%) and CD3OD contents in the solvent mixture of 0, 10 and 15 vol% are chosen. Temperature-resolved dynamic light scattering (DLS) reveals the collective dynamics. Two modes are observed, namely the fast relaxation of polymer segments within the blobs and the slow collective relaxation of the blobs. As the cloud point is approached, the correlation length related to the fast mode increases with CD3OD content. It features critical scaling behavior, which is consistent with mean-field behavior for the 9 wt% PNIPAM solution in pure D2O and with 3D Ising behavior for all other solutions. While the slow mode is not very strong in the 9 wt% PNIPAM solution in pure D2O, it is significantly more prominent as CD3OD is added and at all CD3OD contents in the 25 wt% solution, which may be attributed to enhanced interaction between the polymers. Neutron spin-echo spectroscopy (NSE) reveals a decay in the intermediate structure factor which indicates a diffusive process. For the polymer concentration of 9 wt%, the diffusion coefficients from NSE are similar to the ones from the fast relaxation observed in DLS. In contrast, they are significantly lower for the solutions having a polymer concentration of 25 wt%, which is attributed to the influence of the dominant large-scale dynamic heterogeneities. To summarize, addition of cosolvent leads to enhanced large-scale heterogeneities, which are reflected in the dynamic behavior at small length scales.

Neutron spin echo spectroscopy has been used under grazing incidence conditions to study the dynamics of SoyPC phospholipid membranes at the solid-liquid interface. The use of advanced neutron optical components such as a neutron prism and a resonator structure at the interface for an increase in intensity near the interface helped to study partially elastic waves in the phospholipid membrane as well as the influence of Ibuprofen on the membrane elasticity. Previously observed phase transitions of the surface layers of SoyPC from a lamellar structure to surface crystalline phases also showed their imprint in a suppresion of the phospholipid membrane dynamics.

The effect of an antimicrobial peptide, melittin, on the long-range collective and local undulation motions of bicontinuous microemulsions (B mu Es) was evaluated using dynamic light scattering (DLS) and neutron spin echo (NSE) spectroscopy. Small-angle neutron scattering (SANS) was also used to study the effect of melittin on the structure and the correlation length of B mu Es. B mu Es were isolated from Winsor-III systems formed by mixing aqueous melittin solutions containing sodium dodecyl sulfate with dodecane/1-pentanol mixtures at optimal salinity. An increase of melittin concentration linearly increased the diffusivity of the microemulsions (D-DLS) and decreased the bending rigidity (kappa(NSE)) up to an aqueous melittin concentration of 2 g/L, thus indicating an increase of interfacial fluidity. Further increase of melittin concentration above 2 g/L did not change D-DLS and slightly increased kappa(NSE). The changes reflect differences of interaction between melittin and B mu E surfactant monolayers at different melittin concentrations. At low concentrations, melittin is highly associated with the surfactant monolayers, likely ion-paired to the sulfate surfactant head groups and perhaps partially penetrating into the surfactant tail region. Above 2 g/L, an apparent saturation concentration, added melittin is less strongly associated with the monolayers. In contrast, the bare bending constant derived from SANS data (kappa(bare)) underwent only a minor decrease. Noting that kappa(bare) reflects contributions from both the elasticity and saddle-splay moduli, this suggests that kappa(bare) is not an effective indicator of dynamics for the B mu Es investigated. This study demonstrates that amphiphilic solubilizates can have a complex impact on dynamics of surfactant monolayers in microemulsions, with implications for transmembrane diffusion and the kinetics of release from the microemulsion phase, which are important characteristics for the use of B mu Es as delivery vehicles and host systems for (bio)chemical reactions.

Plastic crystals are a promising candidate for solid state ionic conductors. In this work, quasielastic neutron scattering is employed to investigate the center of mass diffusive motions in two types of plastic crystalline cyclic alcohols: cyclohexanol and cyclooctanol. Two separate motions are observed which are attributed to long-range translational diffusion (α-process) and cage rattling (fast β-process). Residence times and diffusion coefficients are calculated for both processes, along with the confinement distances for the cage rattling. In addition, a binary mixture of these two materials is measured to understand how the dynamics change when a second type of molecule is added to the matrix. It is observed that, upon the addition of the larger cyclooctanol molecules into the cyclohexanol solution, the cage size decreases, which causes a decrease in the observed diffusion rates for both the α- and fast β-processes.

A detailed understanding of the diffusion mechanisms of ions in pure and doped ionic liquids remains an important aspect in the design of new ionic-liquid electrolytes for energy storage. To gain more insight into the widely used imidazolium-based ionic liquids, the relationship between viscosity, ionic conductivity, diffusion coefficients, and reorientational dynamics in the ionic liquid 3-methyl-1-methylimidazolium bis(trifluoromethanesulfonyl)imide (DMIM-TFSI) with and without lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) was examined. The diffusion coefficients for the DMIM+ cation and the role of ion aggregates were investigated by using the quasielastic neutron scattering (QENS) and neutron spin echo techniques. Two diffusion mechanisms are observed for the DMIM+ cation with and without Li-TFSI, that is, translational and local. The data additionally suggest that Li+ ion transport along with ion aggregates, known as the vehicle mechanism, may play a significant role in the ion diffusion process. These dielectric-spectroscopy investigations in a broad temperature and frequency range reveal a typical α-β-relaxation scenario. The α relaxation mirrors the glassy freezing of the dipolar ions, and the β relaxation exhibits the signatures of a Johari-Goldstein relaxation. In contrast to the translational mode detected by neutron scattering, arising from the decoupled faster motion of the DMIM+ ions, the α relaxation is well coupled to the dc charge transport, that is, the average translational motion of all three ion species in the material. The local diffusion process detected by QENS is only weakly dependent on temperature and viscosity and can be ascribed to the typical fast dynamics of glass-forming liquids.

The capillary condensation in bicontinuous microemulsions takes place when two parallel surfaces are narrowed that result in a completely lamellar microemulsion. We expected that this phase transition is also observable when the amount of hydrophilic surfaces from clay particles is raised, because hydrophilic surfaces induce lamellar ordering locally. Using small angle neutron scattering, the structure of microemulsions was observed as a function of clay content. The critical concentration is indicated by discontinuous structural changes and depends on the platelet diameter and is explained by the free energy of the platelets competing with the fluctuating medium. The gel phase transition is observed in the spectroscopic measurements where the diffusion motion is widely suppressed in the gel phase, but otherwise superimposes with the membrane undulations.

We probe, for the first time, quantum tunneling in the methyl groups of the ionic liquid [DMIm][TFSI] facilitated by the presence of Bis(trifluoromethane)sulfonimide lithium salt. The observation of tunneling is made possible by crystallization, rather than vitrification, of [DMIm][TFSI] at low temperature. Neutron scattering measurements detect quantum tunneling excitations at ~27 μeV at temperatures below 30 K in the presence of LiTFSI at a concentration of 1 mol/kg, but not in salt-free [DMIm][TFSI]. This indicates that the methyl rotational potential barrier is reduced by the presence of LiTFSI, thus bringing the tunneling excitations into the measurable range. The salt-induced reduction of the rotational barrier is corroborated by quasi-elastic scattering data associated with stochastic re-orientation of methyl groups measured between 40 and 60 K.

The deep eutectic solvent glyceline formed by choline chloride and glycerol in 1:2 molar ratio is much less viscous compared to glycerol, which facilitates its use in many applications where high viscosity is undesirable. Despite the large difference in viscosity, we have found that the structural network of glyceline is completely defined by its glycerol constituent, which exhibits complex microscopic dynamic behavior, as expected from a highly correlated hydrogen-bonding network. Choline ions occupy interstitial voids in the glycerol network and show little structural or dynamic correlations with glycerol molecules. Despite the known higher long-range diffusivity of the smaller glycerol species in glyceline, in applications where localized dynamics is essential (e.g., in microporous media), the local transport and dynamic properties must be dominated by the relatively loosely bound choline ions.

Microemulsion systems consisting of oil, water and surfactant have been studied with neutron scattering techniques. The amount of surfactant needed to form a microemulsion can be dramatically reduced by the addition of small amounts of amphiphilic block copolymers (boosting effect). Here, we studied the influence of block copolymers with gradually changing amphiphilicity from hydrophilic to hydrophobic. Small angle neutron scattering (SANS), neutron spin echo spectroscopy (NSE) and phase diagram measurements in combination give access to the elastic properties of the membrane. The underlying NSE experiments for this interpretation rely on smallest changes of the relaxation curves (of ca. 1% steps) for still small changes of the bending rigidity (of ca. 10% steps). This high reliability of the experiments conducted at the SNS-NSE displays the accuracy of the instrument itself and the latest developments of the evaluation software, which were necessary to interpret such tiny changes of the bending rigidity reliably.

Lipid extracts are an excellent choice of model biomembrane; however at present, there are no commercially available lipid extracts or computational models that mimic microbial membranes containing the branched-chain fatty acids found in many pathogenic and industrially relevant bacteria. We advance the extract of Bacillus subtilis as a standard model for these diverse systems, providing a detailed experimental description and equilibrated atomistic bilayer model included as Supporting Information to this Letter and at ( http://cmb.ornl.gov/members/cheng ). The development and validation of this model represents an advance that enables more realistic simulations and experiments on bacterial membranes and reconstituted bacterial membrane proteins.