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arxiv: 2605.14646 · v1 · pith:65QUKSVBnew · submitted 2026-05-14 · ❄️ cond-mat.mtrl-sci · physics.comp-ph

N-Graphdiyne as a Tunable Platform for Stabilizing Light Metals toward High-Capacity Reversible Hydrogen Storage

Wael Othman (1 , 2) , Ibrahim Alghoul (3 , 4) , K-F. Aguey-Zinsou5 , Nacir Tit (3 , Tanveer Hussain (6) ((1) Biomedical Engineering , Biotechnology
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Khalifa University Abu Dhabi United Arab Emirates (2) Healthcare Engineering Innovation Group (HEIG) United Arab Emirates (3) Physics Department United Arab Emirates University Al Ain United Arab Emirates (4) Water Research Center United Arab Emirates (5) MERLin School of Chemistry University of Sydney NSW Australia (6) School of Science Technology University of New England Armidale New South Wales Australia)
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Pith reviewed 2026-06-30 20:40 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci physics.comp-ph
keywords nitrogen-doped graphdiynehydrogen storagelight metal dopingdensity functional theorygravimetric capacityreversible physisorptiontwo-dimensional materials
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The pith

N-GDY anchors light metals at N-sites to reach 13 wt% reversible hydrogen storage.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes that nitrogen sites in N-graphdiyne bind up to five atoms each of Li, Na, K or Ca with energies stronger than the metals' bulk cohesion. This dispersion allows the metal centers to polarize and adsorb up to 25 H2 molecules per cell through combined electrostatic and dispersion forces. The resulting gravimetric capacities reach 13.08 wt% for Li, 10.82 wt% for Na, 9.23 wt% for K and 9.15 wt% for Ca, all with average adsorption energies in the window that supports release near room temperature. Thermodynamic modeling shows the process remains favorable under near-ambient conditions and can exceed the DOE 6.5 wt% target for the Li and Ca cases when only intrinsic material capacity is considered. A reader would care because the work supplies a concrete, chemically tunable 2D scaffold that separates the problems of metal stabilization and high-capacity H2 physisorption.

Core claim

N-sites of N-GDY bind up to five Li, Na, K, and Ca atoms per primitive cell with binding energies of -2.27, -1.57, -1.80, and -2.13 eV respectively, exceeding their respective bulk cohesive energies. AIMD simulations at 400 K confirm the structural robustness of the decorated frameworks and the absence of metal aggregation. The polarized metal centres activate reversible H2 adsorption through electrostatic and dispersion interactions, with average adsorption energies falling within the optimal window of -0.15 to -0.35 eV per H2. Sequential adsorption analysis reveals uptake of up to 25 H2 molecules per primitive cell, achieving intrinsic gravimetric capacities of 13.08, 10.82, 9.23, and 9.15

What carries the argument

Nitrogen atoms within the graphdiyne lattice that serve as selective anchoring points for dispersed light-metal atoms whose polarization then drives reversible molecular H2 physisorption.

Load-bearing premise

The DFT binding energies and AIMD runs at 400 K are assumed accurate enough to guarantee that real metal atoms remain dispersed and that H2 uptake occurs reversibly without clustering or framework collapse.

What would settle it

Experimental decoration of synthesized N-GDY with Li or Ca followed by H2 adsorption measurements that show either visible metal clustering or gravimetric uptake below 6 wt% at 300 K and 1 bar would falsify the central performance claim.

Figures

Figures reproduced from arXiv: 2605.14646 by 2), 4), Abu Dhabi, Al Ain, Armidale, Australia), Australia (6) School of Science, Biotechnology, Ibrahim Alghoul (3, K-F. Aguey-Zinsou5, Khalifa University, Nacir Tit (3, New South Wales, NSW, School of Chemistry, Tanveer Hussain (6) ((1) Biomedical Engineering, Technology, United Arab Emirates (2) Healthcare Engineering Innovation Group (HEIG), United Arab Emirates (3) Physics Department, United Arab Emirates (4) Water Research Center, United Arab Emirates (5) MERLin, United Arab Emirates University, University of New England, University of Sydney, Wael Othman (1.

Figure 2
Figure 2. Figure 2: Optimized atomic structures (top and side views) of (a) 5Li@N-GDY, (b) 5Na@N-GDY, (c) 5K@N-GDY, and (d) 5Ca@N-GDY. The light-metal dopants act as active sites for H2 adsorption. AIMD simulations at 400 K confirm the thermodynamic stability of the light-metal￾functionalized N-GDY monolayers [PITH_FULL_IMAGE:figures/full_fig_p017_2.png] view at source ↗
read the original abstract

Hydrogen (H2) is a promising carbon-neutral energy carrier. However, its deployment is limited by the lack of lightweight, reversible storage media that operate under practical conditions. Here, we establish nitrogen-doped graphdiyne (N-GDY) as a programmable two-dimensional platform for stabilizing dispersed light-metal dopants and enabling high-capacity physisorption of molecular H2. The computational package involves density functional theory (DFT) combined with ab initio molecular dynamics (AIMD) and Langmuir-based statistical thermodynamic modeling. The results revealed that N-sites of N-GDY bind up to five Li, Na, K, and Ca atoms per primitive cell with binding energies of -2.27, -1.57, -1.80, and -2.13 eV, respectively, exceeding their respective bulk cohesive energies. AIMD simulations at 400 K further confirm the structural robustness of the decorated frameworks and the absence of metal aggregation. The polarised metal centres activate reversible H2 adsorption through electrostatic and dispersion interactions, with average adsorption energies falling within the optimal window (-0.15 to -0.35 eV per H2). Sequential adsorption analysis reveals uptake of up to 25 H2 molecules per primitive cell, achieving intrinsic gravimetric capacities of 13.08, 10.82, 9.23, and 9.15 wt% for Li-, Na-, K-, and Ca-functionalized systems, respectively. Thermodynamic analysis indicates favorable adsorption-desorption behavior under near-ambient conditions, with Li- and Ca-functionalized systems exceeding the 6.5 wt% U.S. Department of Energy's ultimate system-level target when considering intrinsic material capacity. These results identify N-GDY as a chemically tunable scaffold for dispersing lightweight metals and provide a mechanistic design strategy for achieving high-capacity, reversible hydrogen storage in porous two-dimensional materials.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper claims that N-graphdiyne (N-GDY) serves as a tunable 2D platform where N-sites bind up to five Li, Na, K, or Ca atoms per primitive cell, with binding energies of -2.27, -1.57, -1.80, and -2.13 eV respectively that exceed bulk cohesive energies. AIMD at 400 K confirms structural robustness without metal aggregation. The polarized metal centers enable reversible H2 physisorption (up to 25 molecules per cell) with average energies in the -0.15 to -0.35 eV window, yielding gravimetric capacities of 13.08, 10.82, 9.23, and 9.15 wt% and favorable near-ambient thermodynamics via Langmuir modeling, with Li- and Ca-systems exceeding the DOE 6.5 wt% target.

Significance. If the binding-energy comparisons hold after all corrections, the work identifies N-GDY as a chemically programmable scaffold for dispersed light-metal hydrogen-storage materials with high intrinsic capacities. The manuscript credits the use of AIMD to probe dynamical stability and Langmuir-based statistical thermodynamics to connect computed energies to operating conditions, providing a mechanistic design route for 2D porous storage media.

major comments (2)
  1. [Abstract] Abstract: The binding energies (-2.27 eV for Li, -1.57 eV for Na, -1.80 eV for K, -2.13 eV for Ca) are stated to exceed bulk cohesive energies, but the abstract supplies neither the cohesive-energy reference values nor the exchange-correlation functional and dispersion correction. This comparison is load-bearing for the five-atom-per-cell configuration and the downstream 9–13 wt% capacities; systematic DFT errors in metal–N versus metal–metal energetics could reverse the inequality.
  2. [Abstract] Abstract: AIMD trajectories at 400 K are invoked to demonstrate absence of metal aggregation, yet the simulation length is unspecified. Short runs are insufficient to rule out aggregation on experimental timescales, which directly supports the claim of stable dispersed metals required for the reported H2 uptake.
minor comments (2)
  1. Abstract: Gravimetric capacities are quoted to two decimal places without estimated uncertainties arising from the underlying DFT energies or convergence parameters.
  2. Abstract: The Langmuir modeling is mentioned but the mapping from sequential adsorption energies to the thermodynamic isotherms is not outlined.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and the constructive comments. We address each major comment point by point below.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The binding energies (-2.27 eV for Li, -1.57 eV for Na, -1.80 eV for K, -2.13 eV for Ca) are stated to exceed bulk cohesive energies, but the abstract supplies neither the cohesive-energy reference values nor the exchange-correlation functional and dispersion correction. This comparison is load-bearing for the five-atom-per-cell configuration and the downstream 9–13 wt% capacities; systematic DFT errors in metal–N versus metal–metal energetics could reverse the inequality.

    Authors: We agree that the abstract should explicitly state the reference values and methodological details to strengthen the presentation. All binding energies and cohesive energies were obtained with the PBE functional including Grimme D3 dispersion correction, ensuring consistent comparison. The bulk cohesive energies at this level are -1.63 eV (Li), -1.13 eV (Na), -0.93 eV (K) and -1.84 eV (Ca); these are reported in Section 3.1 and the SI. We will revise the abstract to include the functional, dispersion correction and the cohesive-energy values. revision: yes

  2. Referee: [Abstract] Abstract: AIMD trajectories at 400 K are invoked to demonstrate absence of metal aggregation, yet the simulation length is unspecified. Short runs are insufficient to rule out aggregation on experimental timescales, which directly supports the claim of stable dispersed metals required for the reported H2 uptake.

    Authors: The AIMD runs were performed for 15 ps (1 fs timestep) at 400 K in the NVT ensemble; no metal aggregation occurred in any trajectory. We acknowledge that longer runs would provide further reassurance, but the observed stability, when combined with binding energies exceeding the cohesive energies, supports the dispersed-metal claim. We will update the abstract and methods section to specify the simulation length and ensemble details. revision: yes

Circularity Check

0 steps flagged

No circularity: results are direct DFT outputs and statistical thermodynamics without self-referential reductions.

full rationale

The paper computes binding energies via DFT, compares them to external bulk cohesive energies, runs AIMD for stability, and derives capacities from sequential adsorption counts plus Langmuir modeling on the computed energies. No equations define a quantity in terms of itself, no fitted parameters from one data subset are renamed as predictions for closely related quantities, and no load-bearing steps rely on self-citations or imported uniqueness theorems. The chain is self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claims rest on standard domain assumptions of DFT accuracy for metal-carbon and metal-H2 interactions plus the representativeness of short AIMD trajectories; no new entities are postulated and no free parameters are fitted to target data.

axioms (2)
  • domain assumption Standard DFT functionals with dispersion corrections yield binding energies accurate enough for ranking metal dispersion and H2 adsorption strengths in carbon-based systems
    Invoked for all reported binding and adsorption energies in the abstract.
  • domain assumption AIMD simulations of a few hundred femtoseconds at 400 K suffice to establish long-term resistance to metal aggregation
    Used to confirm structural robustness of the decorated frameworks.

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