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Hydrogen storage enhancement

Experimental and theoretical assessment of the enhanced hydrogen adsorption on polycyclic aromaic hydrocarbons upon decoration with alkali metals. A. M. Reider, S. Kollotzek, P. Scheier, F. Calvo, E. Yurtsever, F. Pirani, M. Bartolomei, M. I. Hernández, T. González-Lezana, J. Campos-Martínez. International Journal of Hydrogen Energy, 58, 525-535 (2024). DOI: 10.1016/j.ijhydene.2024.01.244 Hydrogen storage by physisorption on carbon-based materials is limited by comparatively low adsorption energies. However, decoration of the carbon substrate with alkali, alkaline earth, or other metal atoms has been proposed as a means to enhance adsorption energies. The decoration affects also the stability of these materials since it makes them more stable and resilient in the repeated cycles of charge and discharge that would be required for a good material devoted to storage. We investigate hydrogen storage capacities of small polycyclic aromatic hydrocarbons (PAHs) cations grown in ultracold helium nanodroplets by analyzing the ion abundances and stabilities. The observations are assessed with quantum chemical calculations and atomistic simulations. It is experimentally shown that the addition of an alkali ion significantly enhances the hydrogen adsorption of the studied PAHs, up to 25% over the bare PAH in the experimental conditions studied here, and the simulations confirm this general trend except for some minor residual discrepancies in the special stabilities (magic numbers). Several approaches to study larger and different PAH compounds are also proposed, and for all cases it is found that alkali decoration increases energy stability by more than 100%.
Atrevete a ser científica

Marta I. Hernández, participó el día 26 de enero de 2023, en las charlas sobre la actividad “Atrévete a ser científica” con motivo del inicio del Día internacional de la Mujer y la Niña en la Ciencia. El centro educativo elegido fue el C.E.I.P.S.O. Eugenio Muro que forma parte de la red de centros STEM (Science, Technology, Engineering, and Mathematics) de la Comunidad de Madrid. La presentación estuvo compartida con científicas de prestigio de varios institutos del CSIC (IFF, IEM, IO, IQFR e Instituto Cajal). En las charlas se presentó la vida y obra de la científica estadounidense Mildred Dresselhaus (1930 – 2017), primera mujer en ser nombrada catedrática por el Massachusetts Institute of Technology (MIT) en 1968. La actividad “Atrévete a ser científica” es una iniciativa que recorrerá distintos centros educativos de primaria, secundaria y bachillerato en los próximos días con el fin de contar al alumnado la historia de científicas de renombre, en muchas ocasiones plagada de dificultades y sin reconocimiento, y su aportación al desarrollo científico. Así mismo, la actividad pretende fomentar debates y organizar encuestas entre los alumnos sobre la elección de carreras científicas y promover el espíritu crítico para contrastar datos y fuentes documentales.
quantum sieving RPMD

“Isotopic separation of helium through graphyne membranes: a ring polymer molecular dynamics study.” Somnath Bhowmick, Marta I. Hernández, José Campos-Martínez, Yuri V. Suleimanov. Physical Chemistry Chemical Physics, 23, 18547-18557 (2021). DOI: 10.1039/D1CP02121D OPEN ACCESS Microscopic-level understanding of the separation mechanism for two-dimensional (2D) membranes is an active area of research due to potential implications of this class of membranes for various technological processes. Helium (He) purification from the natural resources is of particular interest due to the shortfall in its production. In this work, we applied the ring polymer molecular dynamics (RPMD) method to graphdiyne (Gr2) and graphtriyne (Gr3) 2D membranes having variable pore sizes for the separation of He isotopes, and compare for the first time with rigorous quantum calculations. We found that the transmission rate through Gr3 is many orders of magnitude greater than Gr2. The selectivity of either isotope at low temperatures is a consequence of a delicate balance between the zero-point energy effect and tunneling of 4He and 3He. In particular, a remarkable tunneling effect is reported on the Gr2 membrane at 10 K, leading to a much larger permeation of the lighter species as compared to the heavier isotope. RPMD provides an efficient approach for studying the separation of He isotopes, taking into account quantum effects of light nuclei motions at low temperatures, which classical methods fail to capture.
Permeation of chemisorbed hydrogen through graphene

“Permeation of chemisorbed hydrogen through graphene: a flipping mechanism elucidated.” Massimiliano Bartolomei, Marta I. Hernández, José Campos-Martínez, Ramón Hernández-Lamoneda, G. Giorgi. Carbon, xx, xxx (2021). DOI:10.1016/j.carbon.2021.02.056 Author’s copy The impermeability of defect-free graphene to all gases has been recently contested since experimental evidence (see Nature 579, 229-232 (2020)) of hydrogen transmission through a two-dimensional carbon layer has been obtained. By means of density functional theory computations here we elucidate a flipping mechanism which involves the insertion of a chemisorbed hydrogen atom in the middle of a C-C bond via a transition state that is relatively stable due to a sp2 rehybridization of the implicated carbon atoms. Present results suggest that transmission for hydrogenated graphene at low local coverage is highly unlikely since other outcomes such as hydrogen diffusion and desorption exhibit quite lower activation enthalpies. However, at high local coverage, with a given graphenic ring tending to saturation, the proposed flipping mechanism becomes competitive leading to a significantly exothermic process. Moreover, for a specific arrangement of four neighboring chemisorbed hydrogen atoms the flipping of one of them becomes the most likely outcome with a low activation enthalpy (about 0.8 eV), which is in the range of the experimental estimation. The effect of charge doping is investigated and it is found that electron doping can help to reduce the related activation enthalpy and to slightly enhance its exothermicity. Finally, an analysis of corresponding results for deuterium substitution is also presented.
i-link 2020

“Design of New Materials for Hydrogen Storage”, a C.S.I.C. International Program for the promotion of international scientific collaboration with foreign institutions. Instituto de Física Fundamental (CSIC), in collaboation with University of Innsbruck, University of Grenoble (CNRS) and University of Toulouse (CNRS).
Mini-colloquium streaming Talk at “CMD2020GEFES”

“Separation of 3He/4He isotopes by Nanoporous Graphene” M. Bartolomei, M. I. Hernández, C. Moreno, A. Mugarza, J . Campos-Martínez. Graphene layers with carefully tailored nanopores[1] could be useful tools as filters at the molecularlevel. Not only molecules of different size could be sieved but it might be also possible to use this 2Dmaterials as appropriate filters for isotopic separation. We present first results on separation of 3He/4Heon the nanoporous graphene (NPG) structure proposed in Ref.[1]. Thermal rates coefficients orpermeances as well as selectivity ratios are obtained through rigorous 3D wave packet calculations[2]and intermolecular potentials[3] based on high-level ab-initio calculations that are fit to an adequateanalytical formula. Results show that this type of material can be competitive and in many sensesmuch more appropriate than other typical 2D material proposed for these purposes[4]. References:[1] Moreno, C.; Vilas-Varela, M.; Kretz, B.; García-Lekue, A.; Costache, M. V.; Paradinas, M.; Panighel, M.;Ceballos, G.; Valenzuela, S. O.; Peña, D.; Mugarza A. Science (2018), 360, 199–203.[2] Gijón, A.; Campos-Martínez, J.; Hernández, M. I. The Journal of Physical Chemistry C (2017), 121, 19751–19757.[3] a) Bartolomei, M.; Carmona-Novillo, E.; Hernández, M. I.; Campos-Martínez, J.; Pirani, F.; Giorgi, G.;Yamashita, K. J. Phys. Chem. Lett. (2014), 5, 751–755. b) Bartolomei, M.; Carmona-Novillo, E.; Hernández, M. I.; Campos-Martínez, J.; Pirani, F.; Giorgi, G. J. Phys. Chem. C (2014), 118, 29966–29972.[4] Hernández, M. I.; Bartolomei, M.; Campos-Martínez, J . Phys. Chem. A (2015), 119, 10743–10749, http://www.cmd2020gefes.eu
Review Ions Helium Nanodroplets

We review the solvation of atomic, molecular or cluster ions in HNDs. After briefly discussing the properties of snowballs in bulk helium we consider experimental conditions for the efficient synthesis of charged, doped HNDs. We show that the cluster ions observed in conventional mass spectrometers originate from fission of highly charged HNDs. The ionization threshold of HNDs doped with alkalis reveals the minimum cluster size required for full immersion. The abundance distributions of HeNX± ions frequently reveal local anomalies or magic numbers. We demonstrate that the abundance is approximately proportional to the evaporation energy. Observed and calculated magic numbers will be compiled, including data for ions solvated in molecular hydrogen. Alternative methods to forming HeNX± that do not employ HNDs will be summarized. Electronic excitation spectra of C60+ and polycyclic aromatic hydrocarbon ions reveal the properties of the helium adsorption layer in quantitative detail. Next we discuss theoretical efforts to describe the interaction between ions and helium. We close with summarizing the size dependence of physical quantities computed for atomic alkali and alkaline earth cations in helium, such as binding energy, superfluid fraction, structural order, radial density profiles, and the existence of first and higher solvation shells. “Solvation of ions in Helium”. Tomás González-Lezana, Olof Echt, Michael Gatchell, Massimiliano Bartolomei, José Campos-Martínez and Paul Scheier. International Rev. Phys. Chem., 39 , 465-516 (2020). DOI: 10.1080/0144235X.2020.1794585
FPU-2019

Oferta para la realizacióon de Tesis Doctoral dentro del programa FPU2019 (Phd. offer within FPU2019 Program).INTERMOL offers two possible projects ending in a Ph.D (Tesis Doctoral). Publicada Convocatoria contratos predoctorales FPU 2019 (pinchar aquí/ click here) “Almacenamiento de hidrógeno en materiales 2D nanoporosos dopados con iones” The quest for clean, safe and affordable sources of energies has spurred research in many directions and one of the most promising combustible species that has been found is hydrogen since its combustion generates only water, releasing at the same time a great amount of energy. Hydrogen is the lightest molecule and the storage and release of this new generation of fuels is a key step in developing an attractive industrial manufactured product for a sustainable and green society[1].Traditional storage devices including high pressure deposit, or liquid transport and storage are not suitable for individual or community uses and it might not be adequate even in large storage production and conversion facilities. To avoid these problems the use of porous materials has been presented as an efficient alternative because of the high specific surface that helps increasing the gravimetric capacity. We think that porous carbon materials are worth to explore as one of these candidates for hydrogen storage at a room temperature. Since the the binding of hydrogen molecules to these porous or nanoporous substrates is ruled by weak intermolecular forces, the management of transport and refilling operations will be simple and safe. However, these interactions should be somehow stronger in order to increase the gravimetric capacity. Doping of carbon materials with alkali and alkali-earth metal has been proposed as a mean to enhance the adsorption energy while stabilizing the substrate against destruction during adsorption/desorptionprocess[2]. We propose to study the adsorption of hydrogen on ion-doped carbon materials as a reliable alternative for hydrogen storage. Our group has already experience in dealing with nanoporous materials [3-5], and is collaborating with other groups in the study of large clusters involving H2 with Li+, and Cs + [6]. The project includes the computation of adequate interaction potential energy surface, and classical and quantum Monte Carlo techniques for the adsorption problem. The dynamical processes and the proposition of nanoporous carbon materials will be dealt with molecular dynamics simulations with a special emphasis in the possible influence of quantum effects for what we will rely on quantum wave packet techniques and transition state theory[4]. References:[1] J. Alonso et al., J. Material Res., 28, 499 (2013).[2] A. Kaiser et al., Int. J. Hydrogen Energy, 43, 3078 (2017).[3] M. Bartolomei et al., J. Phys. Chem. C, 118, 29966 (2014).[4] A. Gijón et al., J. Phys. Chem. C., 121, 19751-19757 (2017).[5] M. I. Hernández et al., J. Phys. Chem. A, 119, 10743 (2015).[6] M. Rastogi et al., Phys. Chem. Chem. Phys., 20, 25569 (2018). “2D membranes based on graphene and h-BN: permeation and diffusion of protons and hydrogen atoms” In the last years two-dimensional (2D) materials have emerged as a new family of building blocks for membranes which are expected to achieve low transport resistance as well as high selectivity. Among them we highlight graphene and hexagonal boron nitride (h-BN) which have been recently reported (experiments from the group of Geim in Manchester (UK)) to allow proton or hydrogen conduction with low energy barriers, opening the possibility to use them as efficient proton transfer membranes or hydrogen isotope separation medium. However, how protons or hydrogens conduct across or along the 2D crystal is still unclear since recent theoretically predictions do not fully agree with the experimental findings. The aim of this project is to theoretically provide a reliable interpretation of the above mentioned experimental results by means of density functional theory (DFT) and density functional tight binding (DFTB) approaches. In particular, the use of molecular prototypes to describe the membranes based on graphene and h-BN is first proposed and the possibility of their protonation/hydrogenation will be carefully investigated. Then, the different mechanisms capable to efficiently produce the proton /hydrogen permeation and diffusion across and along the 2D plane will be studied and assessed. The project will also take into account the role of the solvent, as well as that of the use of periodic models to describe the 2D membranes.
Frontiers of Molecular Physics

XXXVII Bienal de la Real Sociedad Española de Física El GEFAM organiza un Simposio dentro de la próxima Reunión Bienal de la RSEF en Zaragoza https://eventos.unizar.es/20274/detail/bienalrsef2019.html titulado “Fronteras en Física Molecular” que tendrá lugar las tardes del lunes 15 y martes 16 de julio de 2019. El Simposio pretende ofrecer un marco para la reunión de científicos afines a las ciencias moleculares y la discusión de diferentes tópicos en la frontera de nuestro campo, donde nuestra experiencia y forma de trabajar tiene mucho que aportar. En esta ocasión contamos con la participación especial del Prof. Paul Scheier (Inst. Ion Physics and Applied Physics, Univ. Innsbruck), que impartirá una conferencia plenaria el martes por la mañana. El Simposio consistirá en cuatros sesiones con comunicaciones orales así como dos sesiones de posters, durante la pausa-café, que será precedida por una breve presentación oral del contenido de los mismos. ¡Animamos a todos a participar! DESCARGA POSTER INFORMATIVO /DOWNLOAD !! Información relevante (más detalles en la página web de la Bienal): * Envío de resúmenes (preferiblemente en inglés): abierto, hasta el 18 de marzo. * Inscripción: del 1 Marzo al 1 de Junio (para presentadores de trabajos). Recordar que la inscripción es muy reducida si se es socio (o se se hace uno socio justo antes) de la RSEF. * Animamos especialmente a los más jóvenes, ya que – La organización de la Bienal otorgará 4 premios muy interesantes, (ver: https://eventos.unizar.es/20274/section/14043/bienalrsef2019.html) – El GEFAM ofrece 3 bolsas de viaje (hasta 250 euros) para los socios jóvenes del GEFAM (<35 años). Ponerse en contacto con el comité organizador para la realización del trámite. – El GEFAM ofrece inscripción gratuita durante un año en el GEFAM y la RSEF a aquéllos participantes (<35 años) que no sean miembros. Ponerse en contacto con el comité organizador para la realización del trámite. A vuestra disposición, José Campos Martínez (jcm@iff.csic.es), Tomás González-Lezana (t.gonzalez.lezana@csic.es) Massimiliano Bartolomei (maxbart@iff.csic.es) Marta I. Hernández (marta@iff.csic.es)
Cooperative mechanism proton permeation of graphene

M. Bartolomei, M. I. Hernández, J. Campos-Martínez, R. Hernández-Lamoneda Carbon 144 (2019) 724-730 Graphene multi-protonation: A cooperative mechanism for proton permeation The interaction between protons and graphene is attracting a large interest due to recent experimentsshowing that these charged species permeate through the 2D material following a low barrier (~ 0.8 eV) activated process. A possible explanation involves the flipping of a chemisorbed proton (rotation of the C-H+ bond from one to the other side of the carbon layer) and previous studies have found so far that the energy barriers (around 3.5 eV) are too high to explain the experimental findings. Contrarily to the previously adopted model assuming an isolated proton, in this work we consider protonated graphene at high local coverage and explore the role played by nearby chemisorbed protons in the permeation process. By means of density functional theory calculations exploiting large molecular prototypes for graphene it is found that, when various protons are adsorbed on the same carbon hexagonal ring, the permeation barrier can be reduced down to 1.0 eV. The related mechanism is described in detail and could shed a new light on the interpretation of the experimental observations for proton permeation through graphene.

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