Ultrafast Proton Conduction in an Aqueous Electrolyte Confined in Adamantane-like Micropores of a Sulfonated, Aromatic Framework

Thermodynamically Stable Functionalization of Microporous Aromatic Frameworks with Sulfonic Acid Groups by Inserting Methylene Spacers

“…Combined with the EA and the EDX measurements (Table S2, ESI), the Suzuki cross-coupling led to a crosslinking degree of 86% and a stoichiometry for PAF-303 listed in Table 1. The irreversible bond formation of the Suzuki cross-coupling reaction led to a partial interpenetration for the amorphous framework (Figure S2, ESI), which is already mentioned for PAF-1 by simulation [32,33] and experimentally observed for PAF-303 [31,37]. This interpenetration forms a high number of micropores, which are shown in the strong adsorption of Ar at small partial pressures (<0.05) (Figure 1b).…”

“…The deconvolution of the SP 13 C MAS NMR spectrum (Figure 1a) gives a ratio for the C-1-to CH2-Cl signal of about one-to-one and for C-1 to the aromatic carbon of about 1.8 (Table S1, ESI). Combined with the results of the EDX This high interconnecting pore space and surface area, where the linker units are well accessible, allows for further reactions [38][39][40][41] such as introducing acidic units for proton conduction [30,31]. To achieve the introduction of these chemical-and temperature-stable proton-conducting units in the framework, PAF-303 reacts with formaldehyde and HCl to the intermediate ClMPAF-303 (Scheme 1).…”

“…The introduced sulfonic acid groups led to strong interactions with the adsorbed water molecules [20], high ion-exchange capacities (IECs) and excellent proton conductivities. We already reported sulfonated porous aromatic frameworks (SPAFs), which have an amorphous structure and contain a high ratio of accessible micropores [30,31], whereas the interpenetration of the structure rises with increasing numbers of phenyl rings in the spacers [32,33]. Introducing SO 3 H groups to SPAF-2 0.8 , enabled a six-times higher IEC than Nafion ® [31].…”

“…We already reported sulfonated porous aromatic frameworks (SPAFs), which have an amorphous structure and contain a high ratio of accessible micropores [30,31], whereas the interpenetration of the structure rises with increasing numbers of phenyl rings in the spacers [32,33]. Introducing SO 3 H groups to SPAF-2 0.8 , enabled a six-times higher IEC than Nafion ® [31]. Please note that the PAF framework of the SPAF-2 equals the one used for this work but was renamed PAF-303 for consistency with the recent literature [34].…”

“…The high charge concentration combined with the adsorbed water phase enables a proton conductivity of about 1 S cm −1 . This is supported by water, with a high diffusion coefficient of the water molecules being stored in micropores [31]. Moreover, the sulfonic acid groups are bonded directly to the framework backbone, which leads to a reversible bond, known in organic chemistry as a protection group [35].…”