Статья поступила в редакцию 15.05.14. Ред. рег. № 2000
The article has entered in publishing office 15.05.14. Ed. reg. No. 2000
УДК 541.67:541.142
О ТЕРМОДИНАМИЧЕСКИХ ХАРАКТЕРИСТИКАХ ГИДРИРОВАННЫХ МОНО- И ПОЛИГРАФЕНОВЫХ НАНОСТРУКТУР В СВЯЗИ С ПРОБЛЕМОЙ ХРАНЕНИЯ ВОДОРОДА В ЭКО-АВТОМОБИЛЯХ С ТОПЛИВНЫМИ ЭЛЕМЕНТАМИ
Ю. С. Нечаев
ФГУП «ЦНИИчермет им. И.П. Бардина», Институт металловедения и физики металлов им. Г.В. Курдюмова, 2-ая Бауманская ул., 9/23, 105005 Москва, Российская Федерация
Заключение совета рецензентов 22.05.14 Заключение совета экспертов 05.06.14 Принято к публикации 11.06.14
Рассматриваются аналитические результаты определения характеристик и механизмов термодинамической стабильности и соответствующих термодинамических характеристик ряда гидрированных моно- и полислойных графеновых наноструктур, а именно:
1) гидрированный (с обеих сторон) графен состава CH (теоретический графан и экспериментальный графан); 2) теоретический гидрированный (с одной из сторон) графен состава CH; 3) теоретический гидрированный (с одной из сторон) графен состава C2H (графон); 4) экспериметнтальные гидрированные эпитаксиальный графен, двухслойный эпитаксиальный графен и многослойный эпитаксиальный графен (на SiO2 или другой подложке); 5) экспериментальные и теоретические гидрированные углеродные однослойные нанотрубки и экспериментальный гидрированный фуллерен C60H36; 6) экспериментальные графеновые поверхностные «наноблистеры», гидрированные с их внутренней стороны (до графанового состава) и содержащие «интерколированный» газообразный молекулярный водород высокого давления, образующиеся на поверхности высоко ориентированного пиролитического графита (HOPG) или эпитаксиального графена при их обработке атомарным газообразным водородом; 7) экспериментальные гидрированные (до графанового состава) графитовые нановолокна с «интерколированными» в них нанообластями твердого (или жидкого) молекулярного водорода с высокой плотностью, что связано с разработкой прорывной нанотехнологии хранения водорода в эко-автомобилях с топливными элементами и другими проблемами водородной энергетики.
Ключевые слова: гидрированные моно- и полиграфеновые наноструктуры, термодинамическая стабильность, проблема эффективного хранения водорода в эко-автомобилях с топливными элементами.
ON THERMODYNAMIC CHARACTERISTICS OF HYDROGENATED GRAPHENE-BASED NANOSTRUCTURES, RELEVANCE TO THE PROBLEM OF THE HYDROGEN STORAGE IN FUEL-CELL-POWERED ECOLOGICAL VEHICLES
Yu.S. Nechaev
Bardin Institute for Ferrous Metallurgy Kurdjumov Institute of Metals Science and Physics Vtoraya Baumanskaya St., 9/23, Moscow 105005, RUSSIA Yuri1939@inbox.ru
Referred 22.05.14 Expertise 05.06.14 Accepted 11.06.14
The present analytical study is devoted to the current problem of the thermodynamic stability, and related thermodynamic characteristics of the following graphene layers systems: 1) double-side hydrogenated graphene of composition CH (theoretical graphane) and experimental graphane; 2) theoretical single-side hydrogenated graphene of composition CH; 3) theoretical singleside hydrogenated graphene of composition C2H (graphone); 4) experimental hydrogenated epitaxial graphene, bilayer graphene and a few layer graphene on SiO2 or other substrates; 5) experimental and theoretical single-external side hydrogenated singlewalled carbon nanotubes, and experimental hydrofullerene C60H36; 6) experimental single-internal side hydrogenated (up to C2H or CH composition) graphene nanoblisters with intercalated high pressure H2 gas inside them, formed on a surface of highly oriented pyrolytic graphite or epitaxial graphene under the atomic hydrogen treatment; and 7) experimental hydrogenated graphite nanofibers - multigraphene with intercalated solid H2 nanoregions of high density inside them, relevant to solving the current problem of the hydrogen storage in fuel-cell-powered ecological vehicles and other clean energy applications.
Keywords: hydrogenated graphene mono- and multylayer systems (nanostructures), the thermodynamic stability, the problem of the hydrogen storage in fuel-cell-powered ecological vehicles
Международный научный журнал «Альтернативная энергетика и экология» № 10 (150) 2014 © Научно-технический центр «TATA», 2014
1. Introduction
As has been noted in a number of articles of 20072014, the hydrogenation of graphene (a single layer of carbon atoms arranged in a honeycomb lattice ([1, 2] and others)), as a prototype of covalent chemical functionalization and an effective tool to open the band gap of graphene, is of fundamental importance.
It is relevance to the actual problem of the hydrogen on-board storage, and also to the actual related problem of the thermodynamic stability and thermodynamic characteristics of the following systems:
1) double-side hydrogenated graphene (theoretical graphane of composition CH [3, 4] and experimental graphane [5]);
2)theoretical single-side hydrogenated graphene of composition CH (SSHG, [6-8]);
3)theoretical single-side hydrogenated graphene of composition C2H (graphone, [9]);
4)experimental hydrogenated epitaxial graphene, bigraphene and a few layer graphene on SiO2 or other substrates ([5] and others);
5)experimental and theoretical single-external-side hydrogenated single-walled carbon nanotubes of composition about C2H and experimental hydrofullerene C60H36 ([10-13], analytical review [14]);
6)experimental single-internal-side hydrogenated graphene nanoblisters - single-side graphane* nanoblisters possessing of a very high Young's modulus and corresponding binding energy (with intercalated into them H2 gas of a high pressure) formed on surface of highly oriented pyrolytic graphite (HOPG) or epitaxial graphene under the definite atomic hydrogen treatment ([15-21]);
7)experimental hydrogenated graphite nanofibers -multigraphane* nanofibers [18-21] possessing of a very high Young's modulus and corresponding binding energy (with intercalated into them solid H2 of a high density, that is relevance to the problem of the hydrogen on-board storage (Supplement 1).
In this analytical review, results are presented of the thermodynamic analysis and comparison of some theoretical and experimental data (especially, from the most cited works [3, 5] and from the near non-cited ones [18-21]).
As was noted in [8], the double-side hydrogenation of graphene is now well understood, at least from theoretical point of view. For example, Sofo et al. [3] predicted theoretically a new insulating material of CH composition called graphane (double-side hydrogenated graphene), in which each hydrogen atom adsorbs on top of a carbon atom from both sides (so that hydrogen atoms adsorbed in different carbon sublattices are on different sides of the monolayer plane). The formation of graphane was attributed to the efficient strain relaxation for the sp3 hybridization, accompaning with a strong (diamond-like or other) distortion of the graphene network [3, 22]. In contrast to graphene (zero-gap semiconductor), graphane is an insulator with an energy gap£g «5.4 eV [23,4].
If only hydrogen atoms adsorbed on one side of graphene (in graphane) are retained, we obtain graphone
of C2H composition, which is a magnetic semiconductor with £g » 0.5 eV and a Curie temperature Tc ~ 300-400 K [24].
As was noted in [6], neither graphone nor graphane are suitable for real practical applications, since the former has a low value of Eg and undergoes rapid disordering because of hydrogen migration to neighboring vacant sites even at a low temperature [9] and the latter cannot be prepared on a solid substrate.
Single-side hydrogenated graphene (SSHG) of CH composition [7, 25] is an alternative: in contrast to graphane, hydrogen atoms are adsorbed only one side; in contrast to graphone, they are adsorbed on all carbon atoms rather than on every second carbon atom. The value of Eg in SSHG is sufficiently high (by 1.6 e V lower than in graphane [7, 6]), and it can be prepared on a solid substrate in principle [6]. But, this quasi-two-dimensional carbon-hydrogen theoretical system is shown [6] to have a relatively low thermal stability, which makes it difficult to use SSGG in practice.
As was noted in [7], it may be inappropriate to call ; e ~ the covalently bonded SSHG system sp3 hybridized, since the characteristic bond angle of 109.5° is not present anywhere, i.e., there is no diamond-like strong distortion of the graphene network, rather than in graphane [3]. Generally in the case of a few hydrogen atoms interacting with graphene or even for graphane, the underlining carbon atoms are displaced from their locations (i.e., there may be the diamond-like local | distortion of the graphene network), showing the o signature of sp3 bonded system. However, in SSHGrapene all the carbon atoms remain in one plane, s making it difficult to call it sp3 hybridized; obviously, this is some specific .s/x-likc hybridization. Such model is taken into account when the further consideration (in ; this analytical study) of works [10-21].
In a number of works considered in [25], it was | shown that hydrogen chemisorption corrugates the graphene sheet (in fullerene, carbon nanotube [26], graphite [27] and graphene [28]), and transforms it from | a semimetal into a semiconductor [3, 5]; this can even induce magnetic moments [29-31].
It is worth to repeat that the prediction [3] for the double-side hydrogenated graphene (a free-standing membrane) was partially (in terms of [8]) confirmed by Elias et al. [5]. They [5] demonstrated that graphene can react with atomic hydrogen, which transforms this highly conductive zero-overlap semimetal into an insulator of a high thermal stsbility, and the double-side hydrogenation of graphene is reversible. The authors [5] themselves expressed some doubts, relevance to the complete adequacy of the experimental graphane [5] to the theoretical one [3]. They [5] supposed, alternatively, that the produced by them experimental graphane (a free-stan
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