# Highly Porous Organic Polymers for Hydrogen Fuel Storage
## 3 Highly Porous Organic Polymers for H\({}_{2}\) Storage
### Polymers of Intrinsic Microporosity (PIMs)  
[PERSON] et al. initially developed PIMs by crosslinking close planar phthalocyanine macrocycles, which retain high surface area and contain rigid and nonlinear linkers preventing stacking of the monomers. The original crosslinker was derived from an agent, 5,59,6,69-tetrahydroxy-3,39,39-tetramethyl-1,19-spirobisindane, to make PIM-1 as shown in Figure 6[75]. This coupling takes place under exceptionally mild reaction conditions, and in the absence of a transition metal. Other types of monomers and crosslinkers were also tried. However, it was found the PIM-1 retained the highest internal surface area, up to 1000 m\({}^{2}\)/g, and H\({}_{2}\) adsorption ability was close to 1.7 wt % at 77 K and 10 bar. The high performance of PIM-1 has led to additional studies including aging and high pressures. For example, in a recent study [PERSON] et al. demonstrated that PIM-1 is stable over 400 days, showing only modest loss of hydrogen storage capacity, from 2.60 wt % (77 K/100 bar) on day 1 to 1.90 wt % on day 400 [76]. Figure 6: Basic synthetic route of polymers of intrinsic microporosity. \begin{table}
\begin{tabular}{c c c c c} \hline
**Monomer** & **Crosslinker** & **SSA (m\({}^{2}\)/g)** & **H\({}_{2}\) Uptake** & **Ref.** \\ \hline VBC-DVB & VBC & 1300–1900 & 3 wt \% 77 K/1 bar & [52,53] \\ VCB & DVB & 1500 & 1.59 wt \% 77 K/1.13 bar & [65] \\ Carbazole bromophenyl-methanol & 1,10–Phenantroline & 1000 & 2.39 wt \% 77 K/1 bar & [66] \\ Carbazoles & FDA & 1000–1800 & 1.94 wt \% 77 K/1 bar & [67] \\ Carbazoles & DCX & 600–1900 & 0.9–17.7 wt \% 77 K/1 bar & [59] \\ Polyanilines & CH\({}_{2}\)I\({}_{2}\) & -500 & 2.2 wt \% 77 K/30 bar & [57] \\ Polypyrroles & CH\({}_{2}\)I\({}_{2}\) & -20–700 & 0.6–1.6 wt \% 77 K/4 bar & [58] \\ Bismalemilides & DVB & 841 & 0.82 wt \% 77 K/1 bar & [68] \\ TPB & CI & 1783 & 1.91 wt \% 77 K/1 bar & [69] \\ TPB & FDA & 1059 & 1.58 wt \% 77 K/1.13 bar & [70] \\ Benzene & FDA & 1391 & 1.45 wt \% 77 K/1.13 bar & [70] \\ Fluorene & BCMDP & 1700 & 1.63 wt \% 77 K/1 bar & [71] \\ TPE & FDA & 1980 & 1.76 wt \% 77 K/1 bar & [72] \\ \hline VBC-DVB: vinylbenzyl chloride-divinylbenzene; VBC: vinylbenzyl chloride; DCX: dichloroxyhene; DVB: divinylbenzene; FDA: formaldehyde dimethyl acetal; TPB: 1,3-diphenylbenzene; BCMDP: 4,4’-bis(chloromethyl)biphenyl; TPE: tetraphenylethylene. & \\ \end{tabular}
\end{table} 
Table 3: Hyper crosslinked polymers (HCPs) and their H\({}_{2}\) uptake. Using the same synthetic strategy, other types of PIMs were also synthesized, such as those composed of rigid and distorted macromolecules with fused-ring components, as shown in Figure 7. The Brunauer-Emmett-Teller (BET) surface (\(S_{\text{BET}}\)) area, based on the BET model for N\({}_{2}\) absorption, is 830 m\({}^{2}\)/g and the H\({}_{2}\) adsorption ability at 77 K and 1 bar is \(\sim\)1.43 wt % for cyclotricatechylene CTC-PIM polymers of Figure 7a [77]. Other PIMs based on same reaction mechanism with the similar monomers, and similar mild conditions for synthesis such as PIM-7, HATN-PIM, and Porph-PIM, were also studied by [PERSON] et al. [78; 79]. These investigators found that, for similar structures, both \(S_{\text{BET}}\), and the H\({}_{2}\) uptake ability are also similar. One PIM had a distinctly different structure made of non-planar units is Trip(R)-PIM (Figure 7b). This polymer results from a synthesis of triptycene subunits prepared through a dibenzodioxane formation reaction of hexahydroxltriptycene and tetrafluoroterephthalonitrile [80]. In this system, the surface area is much higher, \(\sim\)1760 m\({}^{2}\)/g, and the corresponding H\({}_{2}\) uptake capacity is 1.79 wt % at 77 K and 1 bar. Recently, a set of three triptycene based microporous polymers (TMPs), created through Friedel-Crafts alkylations between tryptocene and multi-bromomethyl substituted benzenes were prepared. These systems share the rigid backbones of PIMS with flexible benzylic bonds.