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Raman probing of carbon electrode and electrolyte under dynamic conditions is performed here using different aqueous electrolytes to elucidate the fundamental events occurring in electrochemical supercapacitor during charge–discharge processes. The areal capacitance ranges from 1.54 to 2.31 mF cm−2 and it is determined using different techniques. These findings indicate that the Helmholtz capacitance governs the overall charge-storage process instead of the space charge (quantum) capacitance commonly verified for HOPG electrodes in the range of ~ 3 to 7 µF cm−2. Molecular dynamics simulations are employed to elucidate the origin of the reversible Raman spectral changes during the charge–discharge processes. A correlation is verified between the reversible Raman shift and the surface excesses of the different ionic species. A theoretical framework is presented to relate the effect of the applied potential on the Raman shift and its correlation with the surface ionic charge. It is proposed that the Raman shift is governed by the interaction of solvated cations with graphite promoted by polarization conditions. It is the first time that a comparative study on different aqueous electrolyte pH and cation ion size has been performed tracking the Raman spectra change under dynamic polarization conditions and contrasting with comprehensive electrochemistry and dynamic molecular simulations studies. This study shines lights onto the charge-storage mechanism with evidence of Kohn anomaly reduction in the carbon electrode during the reversible adsorption/desorption and insertion/extraction of ionic species.

Lithium-air batteries have emerged as an interesting alternative for advanced energy storage devices. The complexity of such systems imposes great challenges. One of them resides in the selection of the lithium salt/solvent pair. Many electrolyte properties affect the operation of the batteries. Among these, the transport properties and structural features have a special place. Via molecular dynamics simulations, we have calculated solution viscosity, ionic diffusivities and conductivities, as well as structural information, for two different salts in dimethyl sulfoxide (DMSO): lithium hexafluorophosphate - LiPF6, and lithium pyrrolide - LiPyr, at different temperatures and salt molalities. We show that, despite similar ionic transport properties, Li+ solvation in the different salts is significantly different. Therefore, solutions with different solvation properties, which impact the overall battery performance, might present analogous ionic dynamics.

Lithium-air batteries have emerged as an interesting alternative for advanced energy storage devices. The complexity of such systems imposes great challenges. One of them resides in the selection of the lithium salt/solvent pair. Many electrolyte properties affect the operation of the batteries. Among these, the transport properties and structural features have a special place. Via molecular dynamics simulations, we have calculated solution viscosity, ionic diffusivities and conductivities, as well as structural information, for two different salts in dimethyl sulfoxide (DMSO): lithium hexafluorophosphate - LiPF6, and lithium pyrrolide - LiPyr, at different temperatures and salt molalities. We show that, despite similar ionic transport properties, Li+ solvation in the different salts is significantly different. Therefore, solutions with different solvation properties, which impact the overall battery performance, might present analogous ionic dynamics.

The lithium-air battery is getting attention as a good technology for energy storage. Nevertheless, the design of such a device still faces some crucial limitations. The most challenging one concerns the selection of electrodes and solvents to provide good performance during the cell operation. Based on literature evidence, we have selected three system configurations of electrode/electrolyte to be evaluated via molecular dynamics simulation: gold/DMSO (dimethyl sulfoxide), graphene/DMSO, and graphene/TEGDME (tetraethylene glycol dimethyl ether) using lithium hexafluorophosphate—LiPF6. We show that the local concentration distributions for DMSO and Li+ are highly influenced by the electrode material. Furthermore, the Li+ solvation shell presents a more complex arrangement when in composition with TEGDME. Additionally, the electrical double layer capacitance in this solvent shows high impedance to the electrode surface. This investigation noticed that the electric field plays a role over the system, contributing to the solvent organization and the electrical double layer formation. Overall, this study strengthens the idea that theoretical findings may contribute to a complementary investigation, leading some light over experimental Li-air battery data reported in the literature.

The numerical simulation of gas dispersion is of great importance in various areas of engineering such as optimisation, synthesis of chemical process, petroleum industry and process safety. The OpenFOAM (Open Field Operation and Manipulation) code is a free and open source computational fluid dynamics (CFD) program. The current research is focused on the development and customisation of a computational tool for handling gas dispersion of heavy gases, such a LNG and CO 2 . The novel CFD tool relies on OpenFOAM framework. The core of the work is based on the OpenFOAM solver rhoReactingBuoyantFoam to handle gas dispersion. A series of CFD simulations has been performed for methane and CO 2 . The source term of the former is modelled by HSM (Hybrid Switch Model). The model comprises contribution from HEM (Homogeneous Equilibrium Model) approach, frozen model and non-equilibrium model for CO 2 leak. The novel approach switches between equilibrium and non-equilibrium conditions based on the meta-stable parameter on the grounds of thermodynamics and experimental observations. Good agreement with experimental data is observed. Numerical findings for methane leakage from the proposed CFD tool are compared with experimental data and FLACS. Good agreement is observed.

In the current work the rhoReactingBuoyantFoam solver was customised for performing gas leak and gas dispersion modelling. Using experimental data from gas leaks the proposed modelling was investigated for subsonic and sonic releases. The gas molar fraction and velocity decay along the jet centreline were calculated using the modified reacting solver, and the numerical findings were compared with available experimental data. Different approaches for the turbulence closure problem were considered using standard two-equation models. The numerical stability of the solver was also investigated varying the CFL number for a set of simulations. The work also considered the modelling of gas cloud volume in a real engineering case. Standard computational setup for ANSYS-CFX was applied, and the same set of scenarios were modelled in OpenFOAM using the modified rhoReactingBuoyantFoam solver. The analysis considered 5 different leak directions and 4 wind directions in a typical industrial site. For all scenarios simulated, very good agreement with experimental data and with the commercial CFD (computational fluid dynamics) tool considered in this study was observed. The results are within 10% tolerance intervals. Detailed information of the modelling is also provided, which enable any CFD user to reproduce the results and also apply it for future analysis.