Encapsulation and substitution of Fe in C12A7 (12CaO⋅ 7Al2O3)

Framework modification by doping of Fe3+ ions in C12A7 has been recently considered for tailoring its thermal, electronic, and optical properties. Here, we use density functional theory calculations to predict the thermodynamical stability and electronic structures of a single Fe atom encapsulated and substituted by both stoichiometric and electride forms of C12A7. In both forms, exoergic encapsulation is observed, and the resultant complexes exhibit magnetic behavior inferring that they are promising magnetic material candidates for spintronic devices. While the electride form of C12A7 transfers 0.86e to Fe, only a small amount of charge (0.14e) is transferred from Fe to the cages in the stoichiometric form. Substitution of Fe for Al in both forms of C12A7 is endoergic, and the electride form is more favorable by 1.60 eV than the stoichiometric form. Both encapsulation and substitution introduce Fe sub-bands between the top of the valence band and the Fermi energy level, featuring them as promising materials in catalysis, optics, and electronics

Hydrogen Technologies for Mobility and Stationary Applications: Hydrogen Production, Storage and Infrastructure Development

The present chapter focuses on hydrogen technologies for both stationary and mobility/transportation applications. Hydrogen production from sustainable resources for the generation of pure and low cost hydrogen is described in the chapter. Several potential hydrogen production techniques are introduced and analyzed. The challenges and the advantages of each production method will be discussed. Furthermore, the chapter will introduce hydrogen infrastructure development for mobility applications and will discuss hydrogen storage challenges. Hydrogen production for fuel cell technologies requires an improvement regarding sustainability of the hydrogen supply and an improvement regarding decentralized hydrogen production. Moreover, hydrogen economy as far requires a large scale and long term storage solution to meet the increasing demand

Mg₆MnO₈ as a Magnesium-Ion Battery Material: Defects, Dopants and Mg-Ion Transport

Rechargeable magnesium ion batteries have recently received considerable attention as an alternative to Li- or Na- ion batteries. Understanding defects and ion transport is a key step in designing high performance electrode materials for Mg-ion batteries. Here we present a classical potential based atomistic simulation study of defects, dopants and Mg-ion transport in Mg6MnO8. The formation of Mg-Mn anti-site defect cluster is calculated to be the lowest energy process (1.73 eV/defect). The Mg Frenkel is calculated to be the second most favourable intrinsic defect and its formation energy is 2.84 eV/defect. Three-dimensional long range Mg-ion migration path with overall activation energy of 0.82 eV is observed suggesting that the diffusion of Mg-ions in this material is moderate. Substitutional doping of Ga on the Mn site can increase the capacity of this material in the form of Mg interstitials. The most energetically favourable isovalent dopant for Mg is found to be Fe. Interestingly, Si and Ge exhibit exoergic solution enthalpy for doping on the Mn site requiring experimental verification

Metal-Hydride-Based Hydrogen Storage as Potential Heat Source for the Cold Start of PEMFC in Hydrogen-Powered Coaches: A Comparative Study of Various Materials and Thermal Management Techniques

The successful and fast start-up of proton exchange membrane fuel cells (PEMFCs) at subfreezing temperatures (cold start) is very important for the use of PEMFCs as energy sources for automotive applications. The effective thermal management of PEMFCs is of major importance. When hydrogen is stored in hydride-forming intermetallics, significant amounts of heat are released due to the exothermic nature of the reaction. This excess of heat can potentially be used for PEMFC thermal management and to accelerate the cold start. In the current work, this possibility is extensively studied. Three hydride-forming intermetallics are introduced and their hydrogenation behavior is evaluated. In addition, five thermal management scenarios of the metal hydride beds are studied in order to enhance the kinetics of the hydrogenation. The optimum combination of the intermetallic, hydrogenation behavior, weight and complexity of the thermal management system was chosen for the study of thermal coupling with the PEMFCs. A 1D GT-SUITE model was built to stimulate the thermal coupling of a 100 kW fuel cell stack with the metal hydride. The results show that the use of the heat from the metal hydride system was able to reduce the cold start by up to 8.2%