Combustion-generated nanoparticles produced in a benzene flame: A multiscale approach

This paper details the multiscale methodology developed to analyze the formation of nanoparticles in a manner that makes it possible to follow the evolution of the structures in a chemically specific way. The atomistic model for particle inception code that combines the strengths of kinetic Monte Carlo and molecular dynamics is used to study the chemical and physical properties of nanoparticles generated in a premixed fuel-rich benzene flame, providing atomistic scale structures (bonds, bond angles, dihedral angles) as soot precursors evolve into a three-dimensional structure. Morphology, density, porosity, and other physical properties are computed. Two heights corresponding to two different times in the benzene flame, experimentally studied by Bittner and Howard [Proc. Combust. Inst. 18, 1105 (1981)], were chosen to examine the influence of different environments on structural properties of the particles formed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87870/2/054302_1.pd

Morphology of supported polymer electrolyte ultra-thin films: a numerical study

Morphology of polymer electrolytes membranes (PEM), e.g., Nafion, inside PEM fuel cell catalyst layers has significant impact on the electrochemical activity and transport phenomena that determine cell performance. In those regions, Nafion can be found as an ultra-thin film, coating the catalyst and the catalyst support surfaces. The impact of the hydrophilic/hydrophobic character of these surfaces on the structural formation of the films has not been sufficiently explored yet. Here, we report about Molecular Dynamics simulation investigation of the substrate effects on the ionomer ultra-thin film morphology at different hydration levels. We use a mean-field-like model we introduced in previous publications for the interaction of the hydrated Nafion ionomer with a substrate, characterized by a tunable degree of hydrophilicity. We show that the affinity of the substrate with water plays a crucial role in the molecular rearrangement of the ionomer film, resulting in completely different morphologies. Detailed structural description in different regions of the film shows evidences of strongly heterogeneous behavior. A qualitative discussion of the implications of our observations on the PEMFC catalyst layer performance is finally proposed

Atomistic Simulation of Water Percolation and Proton Hopping in Nafion Fuel Cell Membrane

We have performed a detailed analysis of water clustering and percolation in hydrated Nafion configurations generated by classical molecular dynamics simulations. Our results show that at low hydration levels H2O molecules are isolated and a continuous hydrogen-bonded network forms as the hydration level is increased. Our quantitative analysis has established a hydration level (λ) between 5 and 6 H2O/SO3− as the percolation threshold of Nafion. We have also examined the effect of such a network on proton transport by studying the structural diffusion of protons using the quantum hopping molecular dynamics method. The mean residence time of the proton on a water molecule decreases by 2 orders of magnitude when the λ value is increased from 5 to 15. The proton diffusion coefficient in Nafion at a λ value of 15 is about 1.1 × 10−5 cm2/s in agreement with experiment. The results provide quantitative atomic-level evidence of water network percolation in Nafion and its effect on proton conductivity

Progress in the use of ionic liquids as electrolyte membranes in fuel cells

This work provides a critical review of the progress in the use of Room Temperature Ionic Liquids (RTILs) as Proton Exchange Membrane (PEM) electrolytes in Fuel Cells (FCs). It is well-known that for an efficient early commercialisation of this technology it is necessary to develop a proton exchange membrane with high proton conductivity without water dependency capable of working at temperatures above 100 °C. The use of ionic liquids as electrolytes in electrochemical devices is an emerging field due to their high conductivity, as well as their thermal, chemical and electrochemical stability under anhydrous conditions. This paper attempts to give a general overview of the state-of-the-art, identifies the key factors for future research and summarises the recent progress in the use of ionic liquids as an innovative type of PEMs.This research was supported by the Ministry of Education, Culture and Sport under the Project CTQ2012-31639 (MINECO, SPAIN-FEDER2001–2013)

Molecular mechanism of CO₂ absorption in phosphonium amino acid ionic liquid

The time-scale and site preferential interaction of CO2 absorption in tetra-butylphosphonium lysinate amino acid ionic liquid is examined using molecular dynamics simulations.</p

Treatment of shape and Auger resonances using the dilated electron propagator

An overview of the dilated electron propagator method based on operators defined on biorthogonal orbitals from bivariationally obtained complex scaled SCF procedure is presented and discussed. Results from applications to atomic and molecular electron attachment and detachment resonances using different decouplings of the dilated electron propagator are analyzed to adduce the role of correlation and relaxation effects in the formation and decay of shape and Auger resonances. Feynman-Dyson amplitudes of the dilated electron propagator are examined to try and unravel the mechanistic underpinnings of these resonances. (C) 2002 Wiley Periodicals, Inc

The (2)Pi(g) shape resonance in electron-acetylene scattering: an investigation using the dilated electron propagator method

The zeroth order (Sigma(0)), the second order (Sigma(2)), the diagonal two particle-one hole Tamm Dancoff approximation (Sigma(2ph-TDA)) and the corresponding quasi-particle decouplings of the dilated electron propagator have been used to investigate the (2)Pi(g) C2H2- shape resonance. The results compare favourably with the experimental and other theoretical results. A plot of the resonant Feynman-Dyson Amplitudes establishes that the capture of the impinging electron is indeed in the pi(g)* orbital of the acetylene molecule. The resonant orbital on the real line shows the attributes of the acetylene lowest unoccupied molecular orbital and for the optimal complex scaling parameter shows a depletion of electron density near the carbon nuclei. (C) 1998