Julio Ricardo Sambrano

The compositional families AB$_5$, A$_7$B$_2$, AB, and AB$_2$, present in the Ni-Zr and Ni-Hf systems, are of interest due to their applications in hydrogen storage materials. In this work, we investigate the thermodynamic, elastic, anisotropic, and vibrational properties of Ni$_5$X, Ni$_7$X$_2$, NiX, and NiX$_2$(X = Zr, Hf) using first-principles calculations. The calculated lattice parameters agree well with available experimental and theoretical data. All the investigated compounds exhibit negative enthalpies of formation, indicating that they are energetically favorable, with the NiX phase showing the most negative enthalpy of formation. Ni$_5$X exhibits the highest macroscopic mechanical moduli, indicating greater resistance to deformation. On the other hand, ductility indicators (Pugh's, Poisson's ratio) suggest that NiX$_2$ is the most ductile among the investigated compounds. The elastic anisotropy analysis indicated that the NiX phase exhibits the highest anisotropy universal index. Phonon dispersion calculations show no imaginary frequencies for any compound, confirming the dynamical stability of all investigated phases. Within the Debye-Wang quasi-harmonic model, the thermal expansion coefficients show an inverse correlation with the isothermal bulk modulus at low temperatures in both binary systems, while the calculated heat capacities of NiZr and NiZr$_2$ reproduce the available experimental data at high temperatures, supporting the thermodynamic approach adopted.

Phase-dependent optoelectronic, excitonic properties and solar energy conversion efficiency of up to 33% of monolayer Y ₂ TeO ₂ MOenes (1T and 2H Phases).

Two-dimensional carbon nitride materials have emerged as promising candidates for multifunctional applications. Motivated by the growing interest in carbon nitride-based two-dimensional materials, we investigated the hydrogen storage capacity of a Li-decorated P–C3N (Li@P–C3N) monolayer using density functional theory (DFT) calculations. Upon functionalization with Li atoms, the P–C3N monolayer can accommodate up to 12 H2 molecules, achieving a hydrogen storage capacity of 9.59 wt % with adsorption energies ranging from −0.18 to −0.13 eV per H2. The calculated material-level gravimetric capacity exceeds the numerical value of the DOE system-level gravimetric target. The hydrogen adsorption mechanism on Li@P–C3N was analyzed through charge transfer analysis, projected density of states (PDOS), and noncovalent interaction (NCI) analysis. The thermal stability of both pristine P–C3N and Li@P–C3N systems was examined using ab initio molecular dynamics (AIMD). Furthermore, the dynamical stability of Li@P–C3N was confirmed through phonon dispersion calculations. The reversibility of hydrogen adsorption in the Li@P–C3N + 12H2 system was also investigated using AIMD simulations. These results demonstrate that Li-decorated P–C3N is a highly efficient candidate for hydrogen storage. Therefore, experimental investigations of P–C3N are strongly encouraged to validate its potential for reversible hydrogen storage applications.