Enable the Domino-Like Structural Recovering in Bismuth Anode to Achieve Fast and Durable Na/K Storages.

Alloying-type anodes show capacity and density advantages for sodium/potassium-ion batteries (SIBs/PIBs), but they encounter serious structural degradation upon cycling, which cannot be resolved through conventional nanostructuring techniques. Herein, we present an in-depth study to reveal the intrinsic reason for the pulverization of bismuth (Bi) materials upon (de)alloying, and report a novel particle-in-bulk architecture with Bi nanospheres inlaid in the bulk carbon (BiNC) to achieve durable Na/K storage. We simulate the volume-expansion-resistant mechanism of Bi during the (de)alloying reaction, and unveil that the irreversible phase transition upon (de)alloying underlies the fundamental origin for the structural degradation of Bi anode, while a proper compressive stress (~10 %) raised by the bulk carbon can trigger a "domino-like" Bi crystal recovering. Consequently, the as obtained BiNC exhibits a record high volumetric capacity (823.1 mAh cm-3 for SIBs, 848.1 mAh cm-3 for PIBs) and initial coulombic efficiency (95.3 % for SIBs, 96.4 % for PIBs), and unprecedented cycling stability (15000 cycles for SIBs with only 0.0015 % degradation per cycle), outperforming the state-of-the-art literature. This work provides new insights on the undesirable structural evolution, and proposes basic guidelines for design of the anti-degradation structure for alloy-type electrode materials.

Development of Dissolved Oxygen Sensor Based on Time-domain Lifetime Measurement with a Sensing Film Fabricated by Embedding PtOEP in Highly Stable and Highly Hydrophobic Fluorinated Matrix.

A dissolved oxygen sensor was developed based on time-domain lifetime measurement with an oxygen sensing film. The oxygen sensing film was fabricated by embedding PtOEP in a highly stable and highly hydrophobic fluorinated matrix synthesized from methacrylate, fluorinated methacrylate, and 3-(tris(trimethylsilyloxy)silyl)propyl methacrylate via free radical polymerization. The fluorinated methacrylate provided the high stability and the 3-(tris(trimethylsilyloxy)silyl)propyl methacrylate provided the extra hydrophobicity. The PtOEP was excited using pulsed signals from a green-light LED and the fluorescence lifetime was evaluated by time-domain lifetime measurement. The dynamical quenching of fluorescence response by dissolved oxygen was calibrated using the Stern-Volmer plot with a high τ 0 / τ 100 ratio of 5.68 and a Stern-Volmer constant of 0.112 mg-1 dm3 . It was demonstrated that the dissolved oxygen sensing film showed high stability under the varied excitation intensity and long-term stability in the accelerated aging experiment and the repeated freeze-thaw-cycling tests.

Synthesis and Characterization of Poly(5'-hexyloxy-1',4-biphenyl)-b-poly(2',4'-bispropoxysulfonate-1',4-biphenyl) with High Ion Exchange Capacity for Proton Exchange Membrane Fuel Cell Applications.

Proton exchange membrane (PEM) is pivotal for proton exchange membrane fuel cells (PEMFCs). In the present work, a block copolymer with hydrophilic alkyl sulfonated side groups and hydrophobic flexible alkyl ether side groups, poly(5'-hexyloxy-1',4-biphenyl)-b-poly(2',4'-bispropoxysulfonate-1',4-biphenyl) (HBP-b-xBPSBP), is designed and synthesized by copolymerization of the hydrophilic and hydrophobic oligomers. The oligomers are synthesized via a Pd-catalyzed Suzuki cross-coupling of 1,3-dibromo-5-hexyloxybenzene, and 3,3'-[(4,6-dibromo-1,3-phenylene)bis(oxy)]bis(propane-1-sulfonate) or 1,4-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene. The good solubility and film-forming characteristics are achieved via the introduction of flexible hexyloxy side groups, and high ion exchange capacity (IEC) is achieved via the introduction of high density of alkyl sulfonated side groups. The HBP-b-0.5BPSBP has the highest IEC of 3.17 mmol/g, the highest proton conductivity of 43.5 mS/cm at 95 °C and 90% relative humidity (RH) and low methanol permeability of 6.45×10-7  cm2 /s. Meanwhile, crosslinked HBP-b-xBPSBP exhibits promising water uptake, swelling ratio and low methanol permeability. These characteristics are attributed to the crosslinked structure and the hydrophilic/hydrophobic nanophase separation morphology promoted by the poly(m-phenylene) main chains, flexible alkyl ether groups, and alkyl sulfonated side groups.

Sulfonation Mechanism of Polysulfone in Concentrated Sulfuric Acid for Proton Exchange Membrane Fuel cell Applications.

The sulfonated polysulfone is a competitive proton-conducting material for proton exchange membrane fuel cells because of its relatively low cost and adequate performance compared with the perfluorinated sulfonic acid ionomers. This material can be economically synthesized by postsulfonation of commercial polysulfone; however, the inadequate sulfonation degree and the chain-scission degradation during sulfonation prevent the further optimization of its overall performance. In this work, the sulfonation mechanism of polysulfone is studied in terms of the transition state and activation energy based on density functional theory calculations, and the optimization of sulfonation processing parameters are discussed.

PdPt Bimetal-Functionalized SnO2 Nanosheets: Controllable Synthesis and its Dual Selectivity for Detection of Carbon Monoxide and Methane.

Bimetallic nanoparticles (NPs) usually exhibit some novel properties due to the synergistic effects of the two distinct metals, which is expected to play an important role in the field of gas sensing. PdPt bimetal NPs with Pd-rich shell and Pt-rich core were successfully synthesized and used to modify SnO2 nanosheets. The 1P-PdPt/SnO2-A sensor obtained by self-assemblies of PdPt NPs exhibited temperature-dependent dual selectivity to CO at 100 °C and CH4 at 320 °C. Furthermore, the sensor possessed good long term stability and antihumidity interference. The activation energy of adsorption for CO and CH4 were estimated by the temperature-dependent response process modeled using Langmuir adsorption kinetics, which proved that the lower activation energy of adsorption corresponded to better sensing performance. The gas-sensing mechanism based on the diffusion depth of the tested gas in the sensing layer was discussed. The dramatically improved sensing performance could be ascribed to the high catalytic activity of PdPt bimetal, the electron sensitization of PdO, and Schottky barrier-type junctions at the interface between SnO2 and PdPt NPs. Our present results demonstrate that bimetal NPs with special structure and components can significantly improve the gas-sensing performance of metal oxide semiconductor and the obtained sensor has great potential in monitoring coal mine gas.

Dynamic Fluctuation of U3+ Coordination Structure in the Molten LiCl-KCl Eutectic via First Principles Molecular Dynamics Simulations.

The dynamic fluctuation of the U3+ coordination structure in a molten LiCl-KCl mixture was studied using first principles molecular dynamics (FPMD) simulations. The radial distribution function, probability distribution of coordination numbers, fluctuation of coordination number and cage volume, self-diffusion coefficient and solvodynamic mean radius of U3+, dynamics of the nearest U-Cl distances, and van Hove function were evaluated. It was revealed that fast exchange of Cl- occurred between the first and second coordination shells of U3+ accompanied with fast fluctuation of coordination number and rearrangement of coordination structure. It was concluded that 6-fold coordination structure dominated the coordination structure of U3+ in the molten LiCl-KCl-UCl3 mixture and a high temperature was conducive to the formation of low coordinated structure.

Highly Active Carbon Supported Pd-Ag Nanofacets Catalysts for Hydrogen Production from HCOOH.

Hydrogen is regarded as a future sustainable and clean energy carrier. Formic acid is a safe and sustainable hydrogen storage medium with many advantages, including high hydrogen content, nontoxicity, and low cost. In this work, a series of highly active catalysts for hydrogen production from formic acid are successfully synthesized by controllably depositing Pd onto Ag nanoplates with different Ag nanofacets, such as Ag{111}, Ag{100}, and the nanofacet on hexagonal close packing Ag crystal (Ag{hcp}). Then, the Pd-Ag nanoplate catalysts are supported on Vulcan XC-72 carbon black to prevent the aggregation of the catalysts. The research reveals that the high activity is attributed to the formation of Pd-Ag alloy nanofacets, such as Pd-Ag{111}, Pd-Ag{100}, and Pd-Ag{hcp}. The activity order of these Pd-decorated Ag nanofacets is Pd-Ag{hcp} > Pd-Ag{111} > Pd-Ag{100}. Particularly, the activity of Pd-Ag{hcp} is up to an extremely high value, i.e., TOF{hcp} = 19 000 ± 1630 h(-1) at 90 °C (lower limit value), which is more than 800 times higher than our previous quasi-spherical Pd-Ag alloy nanocatalyst. The initial activity of Pd-Ag{hcp} even reaches (3.13 ± 0.19) × 10(6) h(-1) at 90 °C. This research not only presents highly active catalysts for hydrogen generation but also shows that the facet on the hcp Ag crystal can act as a potentially highly active catalyst.

A density functional theory protocol for the calculation of redox potentials of copper complexes.

A density functional theory (DFT) protocol for the calculation of redox potentials of copper complexes is developed based on 13 model copper complexes. The redox potentials are calculated in terms of Gibbs free energy change of the redox reaction at the theory level of CAM-B3LYP/6-31+G(d,p)/SMD, with the overall Gibbs free energy change being partitioned into the Gibbs free energy change of the gas phase reaction and the Gibbs free energy change of solvation. In addition, the calculated Gibbs free energy change of solvation is corrected by a unified correction factor of -0.258 eV as the second-layer Gibbs free energy change of solvation and other interactions for each redox reaction. And an empirical Gibbs free energy change of solvation at -0.348 eV is applied to each water molecule if the number of inner-sphere water molecule changes during the redox reaction. Satisfactory agreements between the DFT calculated and experimental results are obtained, with a maximum absolute error at 0.197 V, a mean absolute error at 0.114 V and a standard deviation at 0.133 V. Finally, it is concluded that the accurate prediction of redox potentials is dependent on the accurate prediction of geometrical structures as well as on geometrical conservation during the redox reaction.

Hydrogen transfer reaction in polycyclic aromatic hydrocarbon radicals.

Density functional theory calculations have been successfully applied to investigate the formation of hydrocarbon radicals and hydrogen transfer pathways related to the chemical vapor infiltration process based on model molecules of phenanthrene, anthra[2,1,9,8-opqra]tetracene, dibenzo[a,ghi]perylene, benzo[uv]naphtho[2,1,8,7-defg]pentaphene, and dibenzo[bc,ef]ovalene. The hydrogen transfer reaction rate constants are calculated within the framework of the Rice-Ramsperger-Kassel-Marcus theory and the transition state theory by use of the density functional theory calculation results as input. From these calculations, it is concluded that the hydrogen transfer reaction between two bay sites can happen almost spontaneously with energy barrier as low as about 4.0 kcal mol(-1), and the hydrogen transfer reactions between two armchair sites possess lower energy barrier than those between two zigzag sites.

Hydrogen bond and proton transport in acid-base complexes and amphoteric molecules by density functional theory calculations and 1H and 31P nuclear magnetic resonance spectroscopy.

Intermolecular and intramolecular hydrogen bond (H-bond) and proton transport in acid-base complexes and amphoteric molecules consisting of phosphonic acid groups and nitrogenous heterocyclic rings are investigated by density functional theory calculations and (1)H NMR and (31)P NMR spectroscopy. It is concluded that a phosphonic acid group can act both as H-bond donor and H-bond acceptor, while an imine nitrogen atom can only act as H-bond acceptor and an amine group as H-bond donor. And the intramolecular H-bond is weaker than the intermolecular H-bond attributing to configurational restriction. In addition, the strongest H-bond interaction is observed between a phosphonic acid and a 1H-indazole because of the formation of double H-bonds. The (1)H NMR and (31)P NMR chemical shifts for the acid-base complexes are consistent with the density functional theory calculations. From the (1)H NMR chemical shifts, fast proton exchange is observed between a phosphonic acid and 1H-benzimidazole or 1H-indazole. Finally, it is proposed that polymeric material tethered with 1H-benzimidazole or 1H-indazole rings is a favorable component for high-temperature proton exchange membranes based on acid-base complexes or acid-base amphoteric molecules.

Proton transport pathways in an acid-base complex consisting of a phosphonic acid group and a 1,2,3-triazolyl group.

The proton transport pathways in an acid-base complex consisting of a phosphonic acid group and a 1,2,3-triazolyl group were studied using density functional theory (DFT) calculations in terms of stable configurations and transition states of the molecular or ionic dimers and trimers and verified by proof-of-concept experiments including experimental measurements of overall conductivity and (1)H NMR and FTIR spectroscopy of the methylphosphonic acid (MPA) and 1,2,3-triazole (Tri) complex as well as overall proton conductivity of polymeric blend of poly(vinylphosphonic acid) (PVPA) and poly(4-vinyl-1H-1,2,3-triazole) (PVTri). From the DFT calculations of dimers and trimers composed of ethylphosphonic acid (EPA), Tri, and their deprotonated counterparts, it was concluded that the intermolecular hydrogen bonds of the transition states corresponding to proton transport are much shorter than those of stable configurations, but the O-H and N-H bonds are much longer than those of stable configurations. The tautomerization activation energy decreases from 0.927-1.176 eV in Tri-Tri dimers to 0.336-0.444 eV in the EPA-Tri dimers. From the proof-of-concept experiments, about a 50 fold increase in overall conductivity was observed in the MPA-Tri complex consisting of 10% (molar ratio) MPA compared to pure Tri, and the calculated activation energy is consistent with the experimental activation energy evaluated from temperature dependence of proton conductivity of pure Tri and the MPA-Tri complex. In addition, the fast proton exchange between MPA and Tri, consistent with the DFT calculations, was verified by (1)H NMR and FTIR spectroscopy. Finally, a polymeric blend of PVPA and PVTri was prepared, and its proton conductivity at about 2.1 mS·cm(-1) in anhydrous state at 100 °C was observed to be significantly higher than that of PVPA or of poly(VPA-co-1-vinyl-1,2,4-triazole). The proton conductivity of the polymeric PVPA and PVTri blend in humidity state is in the same range as that of NAFION 117.

Nucleophile-dependent regioselective reaction of (S)-4-benzyl-2-fluoroalkyl-1,3-oxazolines.

Nucleophile-dependent regioselectivities in the nucleophilic reaction of (S)-4-benzyl-2-fluoroalkyl-1,3-oxazoline to different types of fluorinated compounds were investigated experimentally and theoretically. The ring opening of (S)-4-benzyl-2-bromodifluoromethyl-1,3-oxazoline by arenethiolates exclusively occurred at the C5 position of the 1,3-oxazoline ring, whereas completely different regioselectivity was observed for a unimolecular radical nucleophilic substitution (S(RN)1) at the terminal bromine atom of the CF2Br group when arenolates were employed as the nucleophiles. The reaction of (S)-4-benzyl-2-trifluoromethyl-1,3-oxazoline with nucleophiles such as arenethiols, arenols, and TMSCl underwent nucleophilic ring opening in a regiospecific way, while the use of TMSCF3 was determined to proceed through nucleophilic addition to the C═N bond.

Mg-doped VO2 nanoparticles: hydrothermal synthesis, enhanced visible transmittance and decreased metal-insulator transition temperature.

This paper reports the successful preparation of Mg-doped VO2 nanoparticles via hydrothermal synthesis. The metal-insulator transition temperature (T(c)) decreased by approximately 2 K per at% Mg. The Tc decreased to 54 °C with 7.0 at% dopant. The composite foils made from Mg-doped VO2 particles displayed excellent visible transmittance (up to 54.2%) and solar modulation ability (up to 10.6%). In addition, the absorption edge blue-shifted from 490 nm to 440 nm at a Mg content of 3.8 at%, representing a widened optical band gap from 2.0 eV for pure VO2 to 2.4 eV at 3.8 at% doping. As a result, the colour of the Mg-doped films was modified to increase their brightness and lighten the yellow colour over that of the undoped-VO2 film. A first principle calculation was conducted to understand how dopants affect the optical, Mott phase transition and structural properties of VO2.

Synthesis, spectra, and electron-transfer reaction of aspartic acid-functionalized water-soluble perylene bisimide in aqueous solution.

An aspartic acid-functionalized water-soluble perylene bisimide, N,N'-di(2-succinic acid)-perylene-3,4,9,10-tetracarboxylic bisimide (PASP) was synthesized and characterized. It has absorbance maximum A(0-0) and A(0-1) at 527 and 498 nm (ε ≈ 1.7 × 10(4) L cm(-1) mol(-1)) respectively in pH 7.20 HEPES buffer. Two quasi-reversible redox processes with E1/2 at -0.17 and -0.71 V (vs Ag/AgCl) respectively in pH 7-12.5 aqueous solutions. PASP can react with Na2S in pure aqueous solution to form monoanion radical and dianion species consecutively. PASP(-•) has EPR signal with g = 1.998 in aqueous solution, whereas PASP(2-) is EPR silent. The monoanion radical formation is a first-order reaction with k = 8.9 × 10(-2) s(-1). Dianion species formation is a zero-order reaction and the rate constant is 4.3 × 10(-8) mol L(-1) s(-1). The presence of H2O2 greatly increases the radical formation rate constant. PASP as a two-electron transfer reagent is expected to be used in the water photolysis.

Probing the acid-base equilibrium in acid-benzimidazole complexes by 1H NMR spectra and density functional theory calculations.

The acid-base equilibrium in acid (phenylphosphonic acid, methylsulfonic acid, phosphoric acid, hydrochloric acid, acetic acid, and sulfuric acid)-benzimidazole (BIm) complexes was studied by (1)H NMR spectra, FTIR spectra, and density functional theory (DFT) calculations. The DFT optimized structures of the acid-BIm complexes, the vibrational frequencies of the acidic protons, and potential profiles were applied to study the equilibrium between the acids and BIm. In gas phase, it was shown that the strong sulfuric acid could completely protonate BIm and the other acids could only incompletely protonate BIm. When the polarizable continuum model of DMSO was applied, it was shown that all the acids could completely protonate BIm, except the weak acetic acid and phenylphosphonic acid. Furthermore, the potential profile for the PPoA-BIm shows double-well structure facilitating the free movement of the acidic proton between PPoA and BIm. If an explicit solvent molecule of DMSO was included into an acid-BIm complex, significant changes in equilibrium between acid and BIm are observed. The potential profiles for the MSA-BIm and HCl-BIm show very flat bottom wells, facilitating the free movement of proton between the acid and BIm. These calculations were consistent with the (1)H NMR chemical shifts of the immobile protons of the benzimidazole ring in DMSO-d(6) and the FTIR spectra of the acid-BIm complexes.

Intermolecular momentum transfer in poly(perfluorosulfonic acid) membrane hydrated by aqueous solution of methanol: A molecular dynamics simulation study.

Intermolecular momentum transfer in methanol-water mixture solvated poly(perfluoro-sulfonic acid) membrane is studied in terms of center of mass velocity cross-correlation functions between molecular mass centers in their first coordination shells based on molecular dynamics simulations. Moreover, the center of mass velocity cross-correlation functions are also decomposed into longitudinal and transversal contributions. The fastest momentum transfer is observed between hydronium cation and water molecule due to the strong hydrogen bond interaction. The center of mass velocity cross-correlation functions reach peak value in about 36 fs, corresponding to a single collision with a neighboring molecule. For the momentum transfer between the water molecule and methanol molecule, the peaking time is 70 fs or about twice of that between hydronium cation and water molecule. Oscillation of the center of mass velocity cross-correlation functions between hydronium cation and water molecule is also observed due to the cage effect in their equilibrium positions.

Evaluation of electroosmotic drag coefficient of water in hydrated sodium perfluorosulfonate electrolyte polymer.

The electroosmotic drag coefficient of water molecules in hydrated sodium perfluorosulfonate electrolyte polymer is evaluated on the basis of the velocity distribution functions of the sodium cations and water molecules with an electric field applied using molecular dynamics simulations. The simulation results indicate that both velocity distribution functions of water molecules and of sodium cations agree well with the classic Maxwellian velocity distribution functions when there is no electric field applied. If an electric field is applied, the distribution functions of velocity component in directions perpendicular to the applied electric field still agree with the Maxwellian velocity distribution functions but with different temperature parameters. In the direction of the applied electric field, the electric drag causes the velocity distribution function to deviate from the Maxwellian velocity distribution function; however, to obey the peak shifted Maxwellian distribution function. The peak shifting velocities coincide with the average transport velocities induced by the electric field, and could be applied to the evaluation of the electroosmotic drag coefficient of water. By evaluation of the transport velocities of water molecules in the first coordination shells of sodium cations, sulfonate anion groups, and in the bulk, it is clearly shown that the water molecules in the first coordination shell of sodium cations are the major contribution to the electroosmotic drag and momentum transfer from water molecules within the first coordination shell to the other water molecules also contributes to the electroosmotic drag.

New torsion potential expression for molecules without rotational symmetry.

A new torsion potential function for bond rotations without rotational symmetry is proposed. This function is composed of a few Gaussian-type terms each corresponding to an eclipsed conformation of the 1,2 substituents of the C-C bonds. Different from the truncated Fourier series or the truncated cosine polynomial, it is easy to determine how many terms are needed to represent any type of torsion potential barrier at a glance using the Gaussian-type function. It could also intuitively deduce the physical meaning of the expansion parameters of the new torsion potential function, which corresponds to the barrier height, the dihedral defining the eclipsed conformations, and the size of the substituents, respectively. The new torsion potential function is also applied to the 1, 2-substituted haloethanes with satisfactory results, where three Gaussian-type terms corresponding to the fully eclipsed and the partially eclipsed conformations are needed.

Molecular dynamics simulations of electroosmosis in perfluorosulfonic acid polymer.

An atomistic MD simulation method has been developed to study the electroosmotic drag in the hydrated perfluorosulfonic acid polymer. The transport characteristics of the hydroniums and water molecules are evaluated from their velocity distribution functions with an electric field applied. It is shown that the microstructure of the hydrated perfluorosulfonic acid polymer is not perturbed significantly by the electric field up to 2 V/microm, and the velocity distribution functions obey the peak shifted Maxwell velocity distribution functions. The evaluated peak shifting velocities are only about 1% of the average thermal motion. The hydronium flow and water flow are evaluated from the average transport velocities or the peak shifting velocities. The electroosmotic drag coefficients from the MD simulations are in good correspondence with the experimental values. It is also shown that the electroosmotic drag coefficient has no or weak temperature dependence.

Methanol distribution and electroosmotic drag in hydrated poly(perfluorosulfonic) acid membrane.

The methanol distribution and electroosmotic drag in hydrated poly(perfluorosulfonic) acid electrolyte membrane are studied using molecular dynamics simulations under various electric fields applied. The results indicate that the methanol molecules are preferentially distributed near the hydrophobic PFSA backbones with their methyl groups in contact with the fluorine atoms and their hydroxyl groups pointing to the hydrophilic subphase. As the hydroxyl groups of methanol forming hydrogen bonds, hydroxyl groups are more likely to accept hydrogen atoms than to donate hydrogen atoms. The calculated methanol diffusion coefficient is in good correspondence with experimental values, and the electroosmotic drag coefficient for methanol is much smaller than that of water molecules.