Exciting lattice oxygen of nickel–iron bi-metal alkoxide for efficient electrochemical oxygen evolution reaction

High efficiency, cost-effective and durable electrocatalysts are of pivotal importance in energy conversion and storage systems. The electro-oxidation of water to oxygen plays a crucial role in such energy conversion technologies. Herein, we report a robust method for the synthesis of a bimetallic alkoxide for efficient oxygen evolution reaction(OER) for alkaline electrolysis, which yields current density of 10 mA cm^-2 at an overpotential of 215 mV in 0.1 M KOH electrolyte. The cataly...     

Surface carboxyl groups enhance the capacities of carbonaceous oxygen electrodes for aprotic lithium−oxygen batteries: A direct observation on binder-free electrodes

In order to achieve the high capacities of carbonaceous oxygen diffusion electrodes for aprotic lithium–oxygen batteries (Li–O₂ batteries), most efforts currently focus on the design of rational porous architectures. Only few works study the surface chemistry effect that might be a critical factor influencing the capacities of carbonaceous electrodes. In addition, the surface chemistry effect is very difficult to be studied in composite electrodes due to the influences of binders and additives. Herein, we propose chemically activated carbon cloth (CACC) as an ideal model to investigate the effect of surface functional groups on the discharge capacities of carbonaceous oxygen electrodes for Li–O₂ batteries. The intrinsic surface chemistry effect on the performance of carbonaceous cathode is directly observed for the first time without the influences of binders and additives. Results indicate that the surface carboxyl groups introduced by the chemical treatment not only function as the appropriate nucleation sites for Li₂O₂ but also induce the formation of toroid-like Li₂O₂. Thus, the surface carboxyl modification enhances the discharge capacities from 0.48 mAh/cm² of pristine carbon cloth to 1.23 mAh/cm² of CACC. This work presents an effective way to further optimize the carbonaceous oxygen electrodes via surface functional group engineering     

A combined treatment of hydration and dynamical effects for the modeling of host–guest binding thermodynamics: the SAMPL5 blinded challenge

As part of the SAMPL5 blinded experiment, we computed the absolute binding free energies of 22 host–guest complexes employing a novel approach based on the BEDAM single-decoupling alchemical free energy protocol with parallel replica exchange conformational sampling and the AGBNP2 implicit solvation model specifically customized to treat the effect of water displacement as modeled by the Hydration Site Analysis method with explicit solvation. Initial predictions were affected by the lack of treatment of ionic charge screening, which is very significant for these highly charged hosts, and resulted in poor relative ranking of negatively versus positively charged guests. Binding free energies obtained with Debye–Hückel treatment of salt effects were in good agreement with experimental measurements. Water displacement effects contributed favorably and very significantly to the observed binding affinities; without it, the modeling predictions would have grossly underestimated binding. The work validates the implicit/explicit solvation approach employed here and it shows that comprehensive physical models can be effective at predicting binding affinities of molecular complexes requiring accurate treatment of conformational dynamics and hydration.     

Proposition for the acylation mechanism of serine proteases: A one-step process?

This work proposes a very detailed ab initio study of the hypothesis for a one-step serine protease acylation process with one water molecule acting as the main catalyst reactant. For the 11 increasing complexity models considered, the minimum and transition state conformations for the reaction are determined by full geometry optimizations at the ab initio self-consistent field (SCF ) levels within several basis sets, from MINI-1 to 6-31G, and, for the smallest complexes, at the post-SCF MP2 level within the 6-31G** basis set. The related thermodynamical quantities are calculated for all the conformations. The influence of the oxyanion hole stabilizer and of the dyad His57-Asp102 is quantified and a very good agreement is obtained with point mutagenesis. The activation barrier is found in the range 15–18 kcal/mol. © 1996 John Wiley & Sons, Inc.     

Is fullerene C60 large enough to host an aromatic molecule?

The endohedral complex of fullerene with benzene was studied with computational chemistry methods. The changes of structural parameters, such as bond lengths of host and guest and volume increments accompanying complex formation, were investigated, as well as the transfer of electron density between host and guest. The results obtained with three DFT functionals, which were recently designed for weak interactions, were compared. A three‐centered hydrogen bond between H atom of benzene and two atoms of fullerene was found. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

A New Approach to C60-Containing Polyphosphazenes by Polymerization of Phosphonitrile Chloride Trimer in the Presence of C60

A novel synthetic strategy was developed to prepare polyphosphazenes containing C60 moieties. Thus, the phosphonitrile chloride trimer underwent thermal ring-opening polymerization （ROP） in the presence of C60 molecules to yield the reactive macromolecular intermediate, C60-containing poly（dichlorophosphazene）. And then, the other groups could be linked to the phosphazene backbone by nucleophilic substitution reaction of the chlorine atoms in this intermediate to produce a series of C60-containing polyphosphazene. The polymer exhibits good solubility in common organic solvents and is thermally stable.     

A synthetic approach to the phorboxazoles – A strategy for the synthesis of the C1–C19 polyketide fragment

A synthetic approach to the C1–C19 polyketide fragment of the phorboxazoles is disclosed here. While an initial two-directional approach was efficient, it did not proceed in a high enough yield to justify moving forward. A subsequent successful strategy for the generation of the C11–C15 pyrans of both of the phorboxazoles was achieved, and the installation of the C9 stereocenter was able to be demonstrated. Furthermore, an efficient route for the preparation of the C1–C8 fragment with suitable functionality to allow for elaboration into the complete C1–C19 fragment, with the capricious C2–C3 Z-geometry installed, was also achieved.     

A new methodology for the development of numerical methods for the numerical solution of the Schr?dinger equation

In the present paper we introduce a new methodology for the construction of numerical methods for the approximate solution of the one-dimensional Schr?dinger equation. The new methodology is based on the requirement of vanishing the phase-lag and its derivatives. The efficiency of the new methodology is proved via error analysis and numerical applications.     

Are the continuum and the lattice representation of freely jointed chains equivalent?

The partition function and force elongation relation of freely jointed chains of rigid rod segments are calculated for arbitrary dimensions in the continuum and on a lattice. The qualitative differences between these models are discussed for polymers embedded in spaces of various dimensions. These investigations show that chains of rigid rod segments in higher dimensions are equivalent to chains of segments with internal degree of freedom in lower dimensions. Networks composed of these chains show a similar behaviour as uniaxial stretching experiments of rubber-like materials.     

Is fullerene C60 large enough to host a multiply bonded dimetal?

Some dimetal fullerenes M 2@C 60 (M = Cr, Mo, W) have been studied with computational quantum chemistry methods. The transition metal diatomic molecules Cr 2, Mo 2, W 2 form exohedral complexes with C 60, while U 2 forms a highly symmetric endohedral compound and it is placed in the center of the C 60 cavity. This highly symmetric structure is an artifact due to the small size of the C 60 cavity, which constrains U 2 at the center. If a larger cavity is used, like C 70 or C 84, U 2 preferentially binds the internal walls of the cavity and the U-U bond no longer exists.     

A new method to analyze polarization curves — its application for the determination of kinetic parameters for oxygen reduction

A new method has been developed to analyze current–potential curves. The treatment was applied to determine the kinetic parameters of oxygen reduction. The reduction of oxygen was studied on thin-film platinum electrodes in alkaline solution. For the purpose of comparison the kinetic parameters were determined by the traditional method of constructing Tafel plots.     

Recent strategic advances for the activation of benzylic C–H bonds for the formation of C–C bonds

Alkylarenes, obtained from abundant hydrocarbon feedstock sources, are an attractive starting material for the formation of complex molecular architectures. Conventional activation strategies of the relatively inert sp³-hybridized benzylic C–H bonds usually require relatively harsh conditions and are difficult to apply to the synthesis of fine chemicals. The present review describes recent strategic advances for the activation of benzylic C–H bonds for the catalytic formation of C–C bonds. In particular, two activation methods, i.e., strategies that generate benzylic radicals or benzyl anions, are discussed.     

Empirical equations for the temperature dependence of calcite-water oxygen isotope fractionation from 10 to 70°C

Although the temperature dependence of calcite‐water oxygen isotope fractionation seems to have been well established by numerous empirical, experimental and theoretical studies, it is still being discussed, especially due to the demand for increased accuracy of paleotemperature calculations. Experimentally determined equations are available and have been verified by theoretical calculations (considered as representative of isotopic equilibrium); however, many natural formations do not seem to follow these relationships implying either that existing fractionation equations should be revised, or that carbonate deposits are seriously affected by kinetic and solution chemistry effects, or late‐stage alterations. In order to test if existing fractionation‐temperature relationships can be used for natural deposits, we have studied calcite formations precipitated in various environments by means of stable isotope mass spectrometry: travertines (freshwater limestones) precipitating from hot and warm waters in open‐air or quasi‐closed environments, as well as cave deposits formed in closed systems. Physical and chemical parameters as well as oxygen isotope composition of water were monitored for all the investigated sites. Measuring precipitation temperatures along with oxygen isotope compositions of waters and calcites yielded empirical environment‐specific fractionation–temperature equations: [1] 1000 · lnα = 17599/T – 29.64 [for travertines with a temperature range of 30 to 70°C] and [2] 1000 · lnα = 17500/T – 29.89 [for cave deposits for the range 10 to 25°C]. Finally, based on the comparison of literature data and our results, the use of distinct calcite‐water oxygen isotopic fractionation relationships and application strategies to obtain the most reliable paleoclimate information are evaluated. Copyright © 2010 John Wiley & Sons, Ltd.     

Extended Veytsman statistics for the solid–fluid transition in the framework of lattice fluid

Lattice fluid can describe a vapor–liquid transition but not a solid–fluid transition. In this work, we propose a simple and analytic term which yields a solid–fluid transition when coupled with a lattice based equation of state (EOS). The proposed term is derived based on the two assumptions that (1) solid can be considered as highly associated phase affected by strong attractive force and (2) this force is distinct from the conventional attractive forces yielding a vapor–liquid transition. To formulate these assumptions, we extend Veytsman statistics by modifying its density dependency. The derived term was combined with a quasi-chemical nonrandom lattice fluid theory (QLF) developed by the authors. The combined model was found to require only two parameters besides 3 QLF parameters for physical properties calculation of three phases. When tested against equilibrium properties of 8 components, the combined model was found to closely reproduce melting pressure, sublimation pressure, and vapor pressure, but underestimate solid density as well as heat of melting at the triple point temperature. It was found that the present approach can yield a solid–liquid transition at all temperatures.     

A combined electrochemical and DFT study of the lattice strain effect on the surface reactivity of Pd

We report a combined study of electrochemical experiments and ab initio calculations on tuning the surface reactivity of Pd via a compressive lattice strain achieved by employing nanoparticles of Pd-Cu alloys with a Pd-rich surface.Surface oxygen-containing species were used as the probing molecule for revealing the surface reactivity.Both density functional theory (DFT) calculations and experiments showed linear relationships,with very close slopes,between the adsorption strength of OH_(ads) and the Pd lattice constant.Not only is this work a successful realization of controllable modulation in the surface reactivity,but it also provides valuable information for the rational design of Pd-based catalysts for fuel cell applications.     

Complete active space analysis of a reaction pathway: Investigation of the oxygen–oxygen bond formation

Water nucleophilic attack is an important step in water oxidation reactions, which have been widely studied using density functional theory (DFT). Nevertheless, a single-determinant DFT picture may be insufficient for a deeper insight into the process, in particular during the oxygen–oxygen bond formation. In this work, we use complete active space self-consistent field calculations and describe an approach for a complete active space analysis along a reaction pathway. This is applied to the water nucleophilic attack at a Ru-based catalyst, which has successfully been used for efficient water oxidation and in silico design of new water oxidation catalysts recently.     

On the thermochemistry of intercalation of n-alkylamines into α-titanium hydrogenphosphate

Lamellar-titanium hydrogenphosphate (-TiP) suspended in water or 1,2-dichloroethane (dce) intercalates 7.70 meq g¹ ofn-alkylamines (C₁-C₄), as determined by potentiometry and thermogravimetry. The thermal decomposition of the intercalates takes place in three stages: dehydration, removal of amines, and condensation of the hydrogenphosphate to pyrophosphate. The increase in the-TiP interlayer distance (7.56×10² pm) during the intercalation was followed by x-ray powder diffraction. The standard enthalpy (rH _m ^o ) involved in the overall reaction O₃PO-H + RNH₂ O₃P-O^{– +}H₃NR, which was determined by reaction-dissolution calorimetry, correlates linearly with the number of carbons in the alkyl chain and with the interlamellar distance. An intercalation mechanism is proposed, starting from the amine protonation by POH groups and its insertion between the sheets. An increase in enthalpy of –2.67 and +2.56 kJ mol^–1 or –1.24 and +1.20 kJ mol^–1/10² pm for each CH₂ group of then-alkyl chain in dce and water, respectively, for this series of amines is proposed.