Reversible Hydrogen Storage in Metal-Decorated Honeycomb Borophene Oxide

Two-dimensional (2D) boron-based materials are receiving much attention as H2 storage media due to the low atomic mass of boron and the stability of decorating alkali metals on the surface, which enhance interactions with H2. This work investigates the suitability of Li, Na, and K decorations on 2D honeycomb borophene oxide (B2O) for H2 storage, using dispersion corrected density functional theory (DFT-D2). A high theoretical gravimetric density of 8.3 wt % H2 is achieved for the Li-decorated B2O structure. At saturation, each Li binds to two H2 with an average binding energy of -0.24 eV/H2. Born-Oppenheimer molecular dynamics simulations at temperatures of 100, 300, and 500 K demonstrate the stability of the Li-decorated structure and the H2 desorption behavior at different temperatures. Our findings indicate that Li-decorated 2D B2O is a promising material for reversible H2 storage and recommend experimental investigation of 2D B2O as a potential H2 storage medium.Process and EnergyEngineering ThermodynamicsTeam Poulumi De

Coupling mesoscale transport to catalytic surface reactions in a hybrid model

In heterogeneous catalysis, reactivity and selectivity are not only influenced by chemical processes occurring on catalytic surfaces but also by physical transport phenomena in the bulk fluid and fluid near the reactive surfaces. Because these processes take place at a large range of time and length scales, it is a challenge to model catalytic reactors, especially when dealing with complex surface reactions that cannot be reduced to simple mean-field boundary conditions. As a particle-based mesoscale method, Stochastic Rotation Dynamics (SRD) is well suited for studying problems that include both microscale effects on surfaces and transport phenomena in fluids. In this work, we demonstrate how to simulate heterogeneous catalytic reactors by coupling an SRD fluid with a catalytic surface on which complex surface reactions are explicitly modeled. We provide a theoretical background for modeling different stages of heterogeneous surface reactions. After validating the simulation method for surface reactions with mean-field assumptions, we apply the method to non-mean-field reactions in which surface species interact with each other through a Monte Carlo scheme, leading to island formation on the catalytic surface. We show the potential of the method by simulating a more complex three-step reaction mechanism with reactant dissociation. Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Complex Fluid ProcessingEngineering Thermodynamic

Hydrogen dissociation in Li-decorated borophene and borophene hydride: An ab-initio study

Lithium (Li) dopants have garnered attention as a means to enhance hydrogen (H2) binding energies and capacities in 2D boron-based materials. However, it is unclear if and how these dopants affect H2 dissociation and chemisorption. Using density functional theory (DFT) and nudged elastic band (NEB) calculations, reaction pathways for H2 dissociation on borophene-hydride and striped-borophene are investigated in the presence of Li dopants. Our results indicate that tuning the Li-loading can increase the reversibility and the rate of dehydrogenation for both borophene-hydride and striped borophene. In particular, for Li-doped borophene-hydride, the heat of reaction for H2 release is reduced by more than 85% compared to the pristine structure (1.97 eV/H2). Our results signify that Li-doping can considerably change the H2 chemisorption properties of striped-borophene and borophene-hydride, and can lead to promising materials for H2 storage.Engineering ThermodynamicsTeam Poulumi De

Thermodynamic and Transport Properties of H₂/H₂O/NaB(OH)₄ Mixtures Using the Delft Force Field (DFF/B(OH)₄^-)

Sodium borohydride (NaBH4) has a high hydrogen (H2 ) gravimetric capacity of 10.7 wt %. NaBH4 releases H2 through a hydrolysis reaction in which aqueous NaB(OH)4 is formed as a byproduct. NaB(OH)4 strongly influences the thermophysical properties of aqueous solutions (i.e., densities, viscosities, and electrical conductivities) and the hydrolysis reaction kinetics and conversion of NaBH4. Here, molecular dynamics (MD) simulations are performed to compute viscosities, electrical conductivities, and self-diffusivities of H2 , Na+, and B(OH)4- for a temperature and concentration range of 298-353 K and 0-5 mol NaB(OH)4/kg water, respectively. Continuous fractional component Monte Carlo (CFCMC) simulations are used to compute the solubilities of H2 and activities of water in aqueous NaB(OH)4 solutions for the same temperature and concentration range. A new force field is developed (Delft force field of B(OH)4-: DFF/B(OH)4-) in which B(OH)4- is modeled as a tetrahedral structure with a scaled charge of −0.85. The OH group in B(OH)4- is modeled as a single interaction site. This force field is based on TIP4P/2005 water and the Madrid-2019 Na+ force field. The MD simulations can accurately capture the densities and viscosities within 2.5% deviation from available experimental data at 298 K up to a concentration of 5 mol NaB(OH)4/kg water. The computed electrical conductivities deviate by ca. 10% from experimental data at 298 K for the same concentration range. Based on the molecular simulations results, engineering equations are developed for shear viscosities, self-diffusivities of H2, Na+, and B(OH)4-, and solubilities of H2, which can be used to design and model NaBH4 hydrolysis reactors.Engineering ThermodynamicsComplex Fluid ProcessingTeam Poulumi De

Accurate Free Energies of Aqueous Electrolyte Solutions from Molecular Simulations with Non-polarizable Force Fields

Non-polarizable force fields fail to accurately predict free energies of aqueous electrolytes without compromising the predictive ability for densities and transport properties. A new approach is presented in which (1) TIP4P/2005 water and scaled charge force fields are used to describe the interactions in the liquid phase and (2) an additional Effective Charge Surface (ECS) is used to compute free energies at zero additional computational expense. The ECS is obtained using a single temperature-independent charge scaling parameter per species. Thereby, the chemical potential of water and the free energies of hydration of various aqueous salts (e.g., NaCl and LiCl) are accurately described (deviations less than 5% from experiments), in sharp contrast to calculations where the ECS is omitted (deviations larger than 20%). This approach enables accurate predictions of free energies of aqueous electrolyte solutions using non-polarizable force fields, without compromising liquid-phase properties.Engineering ThermodynamicsTeam Poulumi De

A New Force Field for OH^-for Computing Thermodynamic and Transport Properties of H₂and O₂in Aqueous NaOH and KOH Solutions

The thermophysical properties of aqueous electrolyte solutions are of interest for applications such as water electrolyzers and fuel cells. Molecular dynamics (MD) and continuous fractional component Monte Carlo (CFCMC) simulations are used to calculate densities, transport properties (i.e., self-diffusivities and dynamic viscosities), and solubilities of H2 and O2 in aqueous sodium and potassium hydroxide (NaOH and KOH) solutions for a wide electrolyte concentration range (0-8 mol/kg). Simulations are carried out for a temperature and pressure range of 298-353 K and 1-100 bar, respectively. The TIP4P/2005 water model is used in combination with a newly parametrized OH- force field for NaOH and KOH. The computed dynamic viscosities at 298 K for NaOH and KOH solutions are within 5% from the reported experimental data up to an electrolyte concentration of 6 mol/kg. For most of the thermodynamic conditions (especially at high concentrations, pressures, and temperatures) experimental data are largely lacking. We present an extensive collection of new data and engineering equations for H2 and O2 self-diffusivities and solubilities in NaOH and KOH solutions, which can be used for process design and optimization of efficient alkaline electrolyzers and fuel cells. Engineering ThermodynamicsProcess and EnergyTeam Poulumi De

Interfacial Tensions, Solubilities, and Transport Properties of the H₂/H₂O/NaCl System: A Molecular Simulation Study

Data for several key thermodynamic and transport properties needed for technologies using hydrogen (H2), such as underground H2 storage and H2O electrolysis are scarce or completely missing. Force field-based Molecular Dynamics (MD) and Continuous Fractional Component Monte Carlo (CFCMC) simulations are carried out in this work to cover this gap. Extensive new data sets are provided for (a) interfacial tensions of H2 gas in contact with aqueous NaCl solutions for temperatures of (298 to 523) K, pressures of (1 to 600) bar, and molalities of (0 to 6) mol NaCl/kg H2O, (b) self-diffusivities of infinitely diluted H2 in aqueous NaCl solutions for temperatures of (298 to 723) K, pressures of (1 to 1000) bar, and molalities of (0 to 6) mol NaCl/kg H2O, and (c) solubilities of H2 in aqueous NaCl solutions for temperatures of (298 to 363) K, pressures of (1 to 1000) bar, and molalities of (0 to 6) mol NaCl/kg H2O. The force fields used are the TIP4P/2005 for H2O, the Madrid-2019 and the Madrid-Transport for NaCl, and the Vrabec and Marx for H2. Excellent agreement between the simulation results and available experimental data is found with average deviations lower than 10%.Geoscience and EngineeringMechanical, Maritime and Materials EngineeringTeam Poulumi DeyProcess and Energ

Computation of Electrical Conductivities of Aqueous Electrolyte Solutions: Two Surfaces, One Property

In this work, we computed electrical conductivities under ambient conditions of aqueous NaCl and KCl solutions by using the Einstein-Helfand equation. Common force fields (charge q = ±1 e) do not reproduce the experimental values of electrical conductivities, viscosities, and diffusion coefficients. Recently, we proposed the idea of using different charges to describe the potential energy surface (PES) and the dipole moment surface (DMS). In this work, we implement this concept. The equilibrium trajectories required to evaluate electrical conductivities (within linear response theory) were obtained by using scaled charges (with the value q = ±0.75 e) to describe the PES. The potential parameters were those of the Madrid-Transport force field, which accurately describe viscosities and diffusion coefficients of these ionic solutions. However, integer charges were used to compute the conductivities (thus describing the DMS). The basic idea is that although the scaled charge describes the ion-water interaction better, the integer charge reflects the value of the charge that is transported due to the electric field. The agreement obtained with experiments is excellent, as for the first time electrical conductivities (and the other transport properties) of NaCl and KCl electrolyte solutions are described with high accuracy for the whole concentration range up to their solubility limit. Finally, we propose an easy way to obtain a rough estimate of the actual electrical conductivity of the potential model under consideration using the approximate Nernst-Einstein equation, which neglects correlations between different ions.Engineering ThermodynamicsTeam Poulumi De