First-principles calculations to investigate role of 4d electrons spin (Mo/Tc) in half metallic ferromagnetism,and thermoelectric characteristics of Rb2(Tc,Mo)X6 (X =Cl,Br)

The absolute spin polarization, stable structures, and non-toxic nature of vacancy-ordered double perovskites (DPs) make them merging materials for spintronic. Therefore, in the present study, the role of 4 d electrons of Mo/Tc has been focused comprehensively to monitor the ferromagnetism in Rb₂(Tc, Mo)X₆ (X = Cl, Br). The electronic and magnetic behaviors have been analyzed by modified Back and Johnson potential and thermoelectric effect by BoltzTrap code. The tolerance and octahedral factor show the existence of structures, while formation energy calculations ensure thermodynamic stability. The density of electron states at the Fermi level and the Heisenberg model report the spin polarization and Curie temperature. The density of states exposed half-metallic ferromagnetism and the transition of electrons spin to endorse the exchange mechanism. The control of ferromagnetism by electron functionality has been analyzed regarding exchange energies, crystal field energies, double exchange model, exchange constants, and hybridization process. Furthermore, shifting a magnetic moment from Mo/Tc to Rb and Cl/Br sites dominates the ferromagnetism due to the exchange of electrons spin instead of magnetic clusters. Finally, the Seebeck coefficient, conductivity of electrons, and power factor have discussed the thermoelectric effect on spin functionality and thermoelectric performance.     

Modelling of a PEM Fuel Cell System with Propane ATR Reforming

Proton exchange membrane fuel cells (PEMFCs) are promising power sources not only for electric vehicles, but also for portable and stationary applications. In this paper, a 5 kW PEMFC system, suggested for domestic power applications with propane autothermal reforming, is modelled with PRO/II® from SIMSCI. When the fuel cell is operated at 2 atm, 80 °C, a hydrogen conversion of 0.75 and at an air stoichiometry 3.0, with the energies of the compressor and expander coupled with a 75% adiabatic efficiency, the system efficiency is calculated to be 34.8%. Different operating pressures and temperatures are studied; lower system efficiency is shown at higher pressure, lower temperature, and greater air stoichiometry. The simulation shows a significant drop in system efficiency for a lowered compressor and expander adiabatic efficiency. With an increase in this value from 50% to 85%, the system efficiency increases from 23.1% to 40.6%. The simulation reveals that it is critical to design special compressors and expanders for fuel cells with higher adiabatic efficiencies so that higher system efficiency can be achieved.