Facile synthesis of hierarchical triazine-based porous carbons for hydrogen storage

https://doi.org/10.1016/j.micromeso.2015.11.046Get rights and content

Highlights

  • Template-free synthesis of hierarchical triazine-based porous carbons.

  • Combination of cyclotrimerization of aromatic nitriles and carbonization.

  • High hydrogen uptake capacity (2.34%) at 273 K and 1.0 bar.

Abstract

Triazine-based porous carbon materials (TPCs) have been synthesized via cyclotrimerization of aromatic tetranitriles and in situ carbonization. The resulting TPCs have high surface area (above 1200 m2 g−1), large pore volume (above 1.4 cm3 g−1), and hierarchical pore structures with micropores (0.63–1.24 nm) and mesopores (2.4–20 nm). Gas adsorption experiments demonstrate their promising hydrogen uptake capacity, up to 2.34 wt% at 77 K and 1.0 bar, due to the hierarchical porosity that facilitates the diffusion and adsorption of gas molecules.

Introduction

The development of efficient and safe methods for hydrogen storage is still an essential prerequisite for utilization of hydrogen energy. One conventional approach is to chemisorb hydrogen as metal or chemical hydrides, which has been comprehensively investigated and proved fairly efficient [1], [2]. However, the high discharge temperature and poor cycle performance remain the bottleneck for their practical applications [2]. An alternative approach to store hydrogen is through physisorption in porous media, which has advantages of fast kinetics and complete reversibility [3]. Of various porous materials, porous carbons are of particular interest thanks to their easy availability and excellent stability.

A simple approach to achieve high hydrogen uptake in porous carbons is to increase the specific surface area [4]. Particular efforts have also been devoted to enhancing hydrogen uptake by creation of micropores, and ultramicropores (<0.7 nm) in particular, where improved interactions between carbon and hydrogen molecules are present [3], [5]. This approach seems more essential as micropores contribute dominantly to the high surface area and are most suitable for trapping of small gas molecules. On the other hand, purely microporous materials may have some limitations due to low permeability and restricted access to active sites for hydrogen adsorption. Mesopores, though they do not adsorb hydrogen efficiently, facilitate hydrogen transport in the porous media. To achieve fast and efficient hydrogen storage, an interconnected porous architecture with both micro- and mesoporosity (hierarchical structure) is thus essential.

To create hierarchical porous carbons, sacrificial-template-based method is typically employed [6], [7]. This method requires introduction and removal of templates and seems somewhat complicated and cost-ineffective. Thus, simple synthesis strategies are still highly desirable. Cyclotrimerization of aromatic nitriles has been proved highly efficient for construction of porous covalent triazine-based frameworks (CTFs) [8]. In such reaction, zinc chloride acts as both catalyst and solvent. Note that zinc chloride has also been widely used as activating reagents for synthesis of various carbon materials [9], [10]. Pushing the nitrile cyclotrimerization reaction further to the carbonization stage is expected to produce carbon materials with both microporosity and mesoporosity. A systematical study by Kuhn and co-workers has demonstrated that cyclotrimerization of nitriles in zinc chloride at 400 °C produces microporous polymers and that higher reaction temperatures (>600 °C) induce the formation of additional mesopores via carbonization [11]. Their subsequent work indicates that more equivalents of zinc chloride can also induce the carbonization (at 400 °C) and lead to the formation of mesopores, though micropores are still dominant in the final materials [12], [13].

Recently, we introduced a combined cyclotrimerization and carbonization process that allows the formation of a nitrogen-rich porous carbon (TPC-1) from a perfluorinated aromatic nitriles [14]. TPC-1 exhibits dominant micropores, though mesopores are present as well [14]. By use of different precursors and increasing amount of zinc chloride, triazine-based porous carbons (TPCs) with varying porosities and chemical compositions could be expected. Herein, we report two more TPCs that are prepared by combined cyclotrimerization and carbonization of two aromatic tetranitriles in twenty equivalents of zinc chloride. Both TPCs prove to be nitrogen-free and feature well-defined bimodal pore structure, thereby exhibiting exceptionally high hydrogen uptake capacities.

Section snippets

Materials

All chemicals were purchased from commercial suppliers and used without further purification unless otherwise stated. Anhydrous zinc chloride was further dried at 120 °C in vacuo overnight prior to use. Tetra(4-bromophenyl)methane [15] and tetra(4-bromophenyl)ethene [16] were synthesized according to reported procedures. Ultra-high-purity grade gases were used for all gas adsorption experiments.

Synthesis of monomers

Tetra(4-cyanobiphenyl)methane (M-2). To a round-bottom flask were added tetra(4-bromophenyl)methane

Synthesis and characterization of TPCs

The synthesis routes to TPCs are presented in Scheme 1. The two aromatic tetranitrile monomers (M-2 and M-3) are synthesized via fourfold palladium-catalyzed Suzuki coupling reaction between tetra(4-bromophenyl)methane/-ethene and 4-cyanophenylboronic acid. Heating the mixture of the monomer and zinc chloride in a sealed glass ampoule at 400 °C produces the desired porous carbon materials (TPC-2 and TPC-3, from M-2 and M-3, respectively). Note that Ren et al. [17] and Bhunia et al. [18] have

Conclusions

A simple one-pot procedure for synthesis of graphitic porous carbons has been developed. Cyclotrimerization of nitriles and in situ carbonization lead to the formation of TPCs, rather than the widely reported CTFs. In particular, TPC-2 has a high BET specific surface area, large pore volume, and hierarchical pore structures. These features make TPCs promising for hydrogen storage. We believe that the present method can be extended to a wide variety of nitrile precursors.

Acknowledgments

This work was supported by Chinese-Danish Center for Molecular Nanoelectronics funded by the National Science Foundation of China (No. 61261130092) and the Danish National Research Foundation. The financial support of the National Science Foundation of China (Grant no. 21374024) and the Ministry of Science and Technology of China (Grant 2014CB932204) is also acknowledged.

References (30)

  • B. Panella et al.

    Carbon

    (2005)
  • M.J. Valero-Romero et al.

    Micropor. Mesopor. Mater.

    (2014)
  • S. Yorgun et al.

    Micropor. Mesopor. Mater.

    (2009)
  • T.H. Wang et al.

    Carbon

    (2009)
  • B. Marchon et al.

    Carbon

    (1988)
  • S.-I. Orimo et al.

    Chem. Rev.

    (2007)
  • M. Felderhoff et al.

    Phys. Chem. Chem. Phys.

    (2007)
  • A.W.C. van den Berg et al.

    Chem. Commun.

    (2008)
  • G. Yushin et al.

    Adv. Funct. Mater.

    (2006)
  • B. Liu et al.

    J. Am. Chem. Soc.

    (2008)
  • P. Kuhn et al.

    Angew. Chem. Int. Ed.

    (2008)
  • P. Kuhn et al.

    J. Am. Chem. Soc.

    (2008)
  • P. Kuhn et al.

    Adv. Mater.

    (2009)
  • P. Kuhn et al.

    Macromolecules

    (2009)
  • X.-M. Hu et al.

    J. Mater. Chem. A

    (2014)
  • Cited by (15)

    • Tailoring morphological and chemical properties of covalent triazine frameworks for dual CO<inf>2</inf> and H<inf>2</inf> adsorption

      2022, International Journal of Hydrogen Energy
      Citation Excerpt :

      Noteworthy, this adsorption capacity equals the highest value for CTF samples reported in the literature so far [33]. Moreover, it outperforms all related CTF materials [24–27,30–32,46,49,51,64–67] and most representative 2D POPs from the literature [68–72] including several Covalent Organic Frameworks (COFs) [73,74], Porous Polymer Frameworks (PPFs) [75] and Polymers of Intrinsic Microporosity (PIMs) [76–78] scrutinized under similar conditions (Table S2). The combination of two different building blocks together with the high synthetic temperature applied to the preparation of 4 have allowed to reach outstanding SSA and pore volumes, thus optimising the material morphological properties for a maximum H2 uptake.

    • Polyethylene glycol phase change material embedded in a hierarchical porous carbon with superior thermal storage capacity and excellent stability

      2021, Composites Science and Technology
      Citation Excerpt :

      The hierarchical porous material possesses a controllable multistage pore structure, large specific surface area and extremely high pore volume. These characteristics make it superior to single-aperture porous materials in wide range functional adaptions such as adsorption[11], catalysis[12], thermal energy storage[13], hydrogen storage[14], coating[15], and sensing[16]: the developed multistage pore structure offers the material a large contact area, high capacity for storage and diffusion. Among all kinds of porous materials with graded structure, hierarchical porous carbon (HPC) has collected a wide range of attention with respect to strong skeleton rigidity, chemical stability, high thermal conductivity, and designable topology.

    • Post-synthetic modification of fluorenone based hypercrosslinked porous copolymers for carbon dioxide capture

      2021, Journal of Solid State Chemistry
      Citation Excerpt :

      This hierarchical pore structure will enable the easy diffusion of CO2 molecules into the channels. At the same time, for purely microporous parent polymers, there can be limitations associated with the low permeability and restricted access of gas molecules into the pores, hence reducing the efficiency of CO2 adsorption [52]. Better CO2 adsorption parameters of post-synthetic modified HPCPs may also be substantiated by considering that the high charge density at the nitrogen-rich amine-modified HPCP framework may facilitate electrostatic attractive interaction with polarizable CO2 molecule inside the pores of the material [53].

    • Polyaniline-derived hierarchically porous nitrogen-doped carbons as gas adsorbents for carbon dioxide uptake

      2018, Microporous and Mesoporous Materials
      Citation Excerpt :

      However, considering intensive energy consumption and the corrosivity in the regeneration process, the development of new materials for selective carbon dioxide adsorption and capture is very urgent [6]. Zeolite [7], metal organic framework [8,9], porous carbon [10,11], and porous organic polymer [12,13] are strong competitors in fields of carbon dioxide uptake. Among these materials, porous carbon materials have become the most competitive carbon dioxide solid adsorbents because of their high specific surface area, mild adsorption condition, low energy consumption, high regeneration ability, and environmental friendliness as compared to other adsorbents.

    • Hierarchical porous carbons derived from microporous zeolitic metal azolate frameworks for supercapacitor electrodes

      2017, Materials Research Bulletin
      Citation Excerpt :

      On the other hand, the presence of mesopores can lead to high mobility of electrolyte ions to access the maximum surface area, which is evidenced by the excellent rate capability and cyclic stability of mesoporous carbon electrodes. Nevertheless, too many bigger pores or pores with too big diameter always lead to moderate even low surface area, which are not conducive to high-performanced supercapacitors [8–10]. Hence, hierarchical porous carbon materials combining micropores with considerable mesopores have enhanced performance for both power delivery and energy storage capacity.

    View all citing articles on Scopus
    View full text