Penetration of Hydrogen into Polymer Electrolyte Membrane for Fuel Cells by Quantum and Molecular Dynamics Simulations

The advent of the Hydrogen Society created great interest around hydrogen-based energy a decade ago, with several types of vehicles based on hydrogen fuel cells already being produced in the automotive sector. For highly efficient fuel cell systems, the control of hydrogen inside a polymer-based electrolyte membrane is crucial. In this study, we investigated the molecular behavior of hydrogen inside a polymer-based proton-exchange membrane, using quantum and molecular dynamics simulations. In particular, this study focused on the structural difference of the pendent-like side chain polymer, resulting in the penetration ratio of hydrogen into the membrane deriving from the penetration depth of the membrane’s thickness while keeping the simulation time constant. The results reveal that the penetration ratio of the polymer with a shorter side chain was higher than that with the longer side chain. This was justified via two perspectives; electrostatic and van der Waals molecular interactions, and the structural difference of the polymers resulting in the free volume and different behavior of the side chain. In conclusion, we found that a longer side chain is more trembling and acts as an obstruction, dominating the penetration of hydrogen inside the polymer membrane

Estimation of heat transfer coefficient of water and ethylene glycol mixture in nanopipe via non-equilibrium coarse-grained molecular dynamics

Using coarse-grained molecular dynamics, we estimated the heat transfer coefficient (HTC) of coolant, a mixture (50:50 wt%) of water and ethylene glycol (EG), in a Fe nanopipe. In the Newtonian flow regime, the pipe was heated at 325 K. The HTC increased rapidly along the nanopipe at the thermal boundary layer (TBL). The HTC was estimated to be 3.08 ?? 10 8 W/m 2 K, and those of water and EG were 1.24 ?? 10 8 and 1.87 ?? 10 8 W/m 2 K, respectively. A relationship between the TBL and the HTC existed along the pipe and that the heat transfer mainly occurred in the TBL

Tailoring Graphene Nanosheets for Highly Improved Dispersion Stability and Quantitative Assessment in Nonaqueous Solvent

Aggregation is a critical limitation for the practical application of graphene-based materials. Herein, we report that graphene oxide (GO) nanosheets chemically modified with ethanolamine (EA), ethylene glycol (EG), and sulfanilic acid (SA) demonstrate superior dispersion stability in organic solvents, specifically EG, based on the differences in their covalent chemistries. Functionalized GO was successfully dispersed in EG at a concentration of 9.0 mg mL-1 (0.50 vol %), the highest dispersion concentration reported to date. Moreover, our study introduces a unique analytical method for the assessment of dispersion stability and successfully quantifies the instability index based on transmission profiles under centrifugation cycles. Interestingly, GO-EG and GO-EA exhibited highly improved dispersion stabilities approximately 96 and 48 times greater than that of GO in EG solvent, respectively. This finding highlights the critical role of surface functional groups in the enhancement of chemical affinity and miscibility in the surrounding media. We anticipate that the novel structural designs and unique tools presented in this study will further the understanding and application of chemically functionalized carbon materials.ope

Parametric Study of Lennard???Jones Potentials to Predict Physical Behavior via Coarse-Grained Molecular Dynamics Simulations of Water and Ethylene Glycol Over Wide Temporal and Spatial Scales

To develop advanced and elaborate nanotechnologies, the behavior of materials must be understood at the nanoscale. Since direct observation is not generally possible experimentally, molecular dynamics simulations have been used to estimate nanoscale behavior, although simulations still have spatio-temporal limitations. Thus, coarse-grained molecular dynamics (CGMD) simulations have been suggested to study the physical properties and molecular behavior of mesoscale systems. A ???bead??? composed of several atoms or molecules can represent the physical properties of a materials. In this study, we performed CGMD simulations of water and ethylene glycol, represented by Lennard???Jones parameters with various numbers of molecules within a single bead, to determine interaction parameters by comparing our results against empirically determined physical properties. Our results show the possible range of the number of molecules per bead satisfying a particular physical property such as density and self-diffusion coefficient. These data yielded the most suitable number of molecules to be included in a bead for CGMD simulations containing water and ethylene glycol. Moreover, we identified and discussed the effects of time scale factor, of which the empirically applicable range of 4???10, on self-diffusivity coefficients

Theoretical study on enhancement of heat transfer of nanofluids with functionalized graphene flakes in confined nanopipe system

In order to find a suitable type of nanoparticles to improve the heat transfer of nanofluids, the role of nanoparticles should be elucidated. The nanoparticles are known to affect the heat transfer, and here we investigated the role of nanoparticles using a nanopipe model system. Specifically, the heat transfer phenomena of nanofluids containing hydrophobic (i.e., hydrogenated) and hydrophilic (i.e., carboxylated) functionalized graphene flakes (GFs) were compared. Confined nanopipe (i.e., 325 K) with a diameter of 400 ?? system were adopted for the heat transfer and coarse-grained molecular dynamics (CGMD) simulations were performed. In the nanofluids, GF-concentrated layer was formed near the pipe wall, which induced the high HTC value of nanofluids. We found that after the thermal change of fluid became constant (i.e., thermally fully developed region), the thermal boundary layer was maintained for 100 ?? due the GF-concentrated layer. The thermal boundary layer and HTC was thicker and higher when using carboxylated GF, which was more soluble in the coolant