The study, published in Frontiers in Physics, is a comprehensive first-principles investigation of hydrogen adsorption on pristine and metal-decorated silicon carbide nanotubes, or SiCNTs. Led by Vusala Nabi Jafarova of Azerbaijan State Oil and Industry University in Baku, the research team systematically compared how nickel and platinum atoms—two technologically important transition metals with fundamentally different electronic structures—alter the hydrogen-binding behavior of the same nanotube platform. The choice of comparison is deliberate and scientifically elegant: nickel possesses partially filled 3d orbitals that tend to promote strong orbital hybridization and hydrogen activation, whereas platinum contains more spatially extended 5d orbitals that typically provide balanced adsorption and high structural stability. By placing these two metals under identical computational conditions, the researchers could isolate exactly how electronic structure governs adsorption mechanism.

Silicon carbide nanotubes themselves are an intriguing alternative to the carbon nanotubes that dominated early hydrogen-storage research. They offer superior thermal stability, enhanced chemical resistance, and an intrinsic polarity arising from their silicon-carbon bonds, which can potentially improve adsorption characteristics. Experimental work has already shown that purified SiCNTs exhibit roughly fifty percent higher hydrogen-storage capacities than their carbon counterparts, together with nearly five times faster hydrogen uptake and completely reversible desorption. But pristine SiCNTs interact only weakly with hydrogen molecules, primarily through van der Waals forces, resulting in low adsorption energies and poor storage performance. The calculated adsorption energy for a single hydrogen molecule on an undecorated SiCNT in the new study was a mere −0.184 electron-volts—far too feeble for practical use. Surface functionalization with transition metals has emerged as the most effective strategy to overcome this limitation.

The team performed all calculations using spin-polarized density functional theory within the generalized gradient approximation, employing the Perdew-Burke-Ernzerhof functional as implemented in the Atomistix ToolKit package. They modeled an (8,0) SiCNT as a one-dimensional periodic nanotube with at least fifteen angstroms of vacuum spacing to eliminate spurious interactions between periodic images, and used a double-zeta polarized basis set with norm-conserving pseudopotentials. Rigorous convergence tests confirmed that their k-point sampling and mesh cutoff of 150 Ry delivered total energies converged to within one milli-electron-volt per atom. The researchers examined multiple possible adsorption configurations—hollow, bridge, top-C, and top-Si sites—and tested parallel, perpendicular, and tilted initial orientations of the hydrogen molecule, allowing all structures to relax freely without symmetry constraints until the maximum force on each atom fell below 0.0001 eV/Å.

The first critical question was whether the metal atoms would stay put. The calculated binding energy of nickel on the SiCNT surface was −1.44 eV, confirming energetically favorable anchoring without spontaneous desorption. Platinum, remarkably, anchored even more strongly, with a binding energy of −4.10 eV—significantly stronger chemisorption that makes clustering or desorption energetically unfavorable. To verify that these decorated systems could survive real-world conditions, the team ran ab initio molecular dynamics simulations at 300 Kelvin under the NVT ensemble with a Nosé-Hoover thermostat for five picoseconds. Both the nickel- and platinum-decorated systems with adsorbed hydrogen preserved their structural integrity throughout, with no noticeable metal desorption, structural collapse, or severe nanotube distortion. This thermal robustness is essential for any practical storage material operating at room temperature.

With stable anchoring confirmed, the researchers investigated successive hydrogen adsorption by adding one, two, and three hydrogen molecules near the active metal sites. The results revealed a clear performance hierarchy: nickel-decorated SiCNT outperformed platinum-decorated SiCNT, which in turn dramatically outperformed the pristine nanotube. For a single hydrogen molecule, the adsorption energies were −1.991 eV for nickel decoration, −1.747 eV for platinum decoration, and just −0.184 eV for the pristine tube. As hydrogen loading increased, the average adsorption energy gradually decreased in magnitude—falling to −1.353 and −0.882 eV/H2 for nickel and to −0.930 and −0.614 eV/H2 for platinum—indicating progressive saturation of the metal adsorption sites while still preserving favorable hydrogen uptake. Structural analysis showed why: the hydrogen-hydrogen bond elongated from 0.74 angstroms in the free molecule to 0.90 angstroms on nickel and 1.00 angstroms on platinum, signaling partial activation of the molecule, while additional hydrogen molecules at higher loadings drifted away from the metal centers with separations reaching three to nearly four angstroms.

The electronic origin of this behavior emerged from detailed density-of-states calculations. Metal decoration introduced new electronic states at the Fermi level, promoting orbital hybridization between metal d-states and hydrogen 1s-states. Nickel 3d orbitals showed pronounced hybridization with hydrogen 1s states, whereas platinum 5d states exhibited comparatively weaker electronic coupling and a more balanced electronic structure. Quantitative analysis of the occupied d-band centers revealed that hydrogen adsorption shifted the nickel d-band center downward from −1.376 to −1.482 eV, accompanied by a dramatic reduction in the d-state density at the Fermi level from 2.047 to 0.987 states per eV—clear evidence of adsorption-induced redistribution of the nickel 3d states. The platinum d-band center, by contrast, shifted from −3.139 to −3.479 eV after one hydrogen molecule, then rebounded toward −2.933 eV at higher loadings, reflecting a more complex, coverage-dependent electronic response.

Charge-transfer analyses painted an equally vivid mechanistic picture. Mulliken population analysis showed that the nickel atom’s population decreased from 4.873 to 4.861 after adsorbing one hydrogen molecule, with the two hydrogen atoms acquiring populations of 0.532 and 0.511—slight asymmetry indicating polarization of the adsorbed molecule. Platinum showed a similar but more moderate response, its population dropping from 5.008 to 4.984. Electron-density-difference maps confirmed that nickel induced stronger and more localized charge redistribution concentrated around the metal-hydrogen interface, whereas platinum exhibited a more delocalized and spatially distributed electronic response. Complementary Bader charge analysis, performed independently using a plane-wave PAW approach with an all-electron density reconstructed at a density mesh cutoff of 10,000 Ha, validated these findings: the average charge redistribution per hydrogen molecule decreased with increasing loading for both metals, from +0.0343 to +0.0307 e/H2 for nickel and from −0.0582 to −0.0161 e/H2 for platinum, confirming progressive saturation of the adsorption centers. Notably, all optimized configurations retained nearly zero total spin magnetic moment, confirming that hydrogen adsorption is governed by charge redistribution and orbital hybridization rather than magnetic effects.

The new results align well with previous theoretical and experimental studies. Singh and Solanki had earlier reported adsorption energies of −0.608 eV and −0.861 eV for platinum- and nickel-decorated SiCNTs respectively, and while the present values are considerably larger, both studies consistently demonstrate that hydrogen adsorption is governed by strong metal-hydrogen interactions accompanied by substantial charge redistribution. Experimental gravimetric measurements by Barghi and colleagues confirmed that metal-modified SiCNTs exhibit significantly enhanced hydrogen uptake compared with pristine tubes, and that purified SiCNTs deliver completely reversible hydrogen desorption. The authors caution, however, that a definitive assessment of reversible hydrogen-storage performance requires further thermodynamic and kinetic investigations, including hydrogen desorption pathways, activation barriers, and finite-temperature behavior. The relatively strong interaction observed for the first adsorbed hydrogen molecule suggests these materials may also be valuable for hydrogen activation in catalytic applications.

The broader significance lies in the design principles the study establishes. Nickel decoration provides superior hydrogen activation and adsorption capability through stronger charge transfer and more pronounced orbital hybridization, making it the better choice for applications requiring strong hydrogen binding. Platinum decoration, despite its weaker hydrogen adsorption, offers strong structural stability, more balanced adsorption behavior, and the strongest anchoring to the nanotube substrate—attributes that may prove advantageous where durability and moderate interaction strength are priorities. The progressive decrease in adsorption strength with increasing hydrogen loading suggests improved adsorption reversibility, a crucial property for practical storage cycles. By systematically correlating adsorption energetics, structural evolution, electronic structure, orbital hybridization, charge transfer, and thermal stability within a unified first-principles framework, the researchers have delivered a rational design roadmap for metal-functionalized SiCNTs—bringing the vision of safe, efficient, and reversible solid-state hydrogen storage one quantum-mechanical step closer to reality.

Subject of Research: Physics

Article Title: First-principles investigation of hydrogen adsorption and storage mechanisms on Ni- and Pt-decorated SiCNTs toward green energy applications

Article References: Jafarova, V. N., Bashirov, S., Scurtu, I. C., Jafarova, A. N., Ahmadova, A. J., Hasanova, R. A., & Bayramova, F. A. (2026). First-principles investigation of hydrogen adsorption and storage mechanisms on Ni- and Pt-decorated SiCNTs toward green energy applications. Frontiers in Physics, 14, Article 1892335. https://doi.org/10.3389/fphy.2026.1892335

Image Credits: AI Generated

DOI: 10.3389/fphy.2026.1892335

Keywords: hydrogen storage, density functional theory, silicon carbide nanotubes, transition metal decoration, clean energy, nanotechnology, First-principles, investigation, hydrogen, adsorption, storage, mechanisms