Preparation and Study of Sulfonated Co-Polynaphthoyleneimide Proton-Exchange Membrane for a H2/Air Fuel Cell

Abstract

The sulfonated polynaphthoyleneimide polymer (co-PNIS70/30) was prepared by copolymerization of 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODAS) and 4,4’-methylenebisanthranilic acid (MDAC) with ODAS/MDAC molar ratio 0.7/0.3. High molecular weight co-PNIS70/30 polymers were synthesized either in phenol or in DMSO by catalytic polyheterocyclization in the presence of benzoic acid and triethylamine. The titration reveals the ion-exchange capacity of the polymer equal to 2.13 meq/g. The membrane films were prepared by casting polymer solution. Conductivities of the polymer films were determined using both in- and through-plane geometries and reached ~96 and ~60 mS/cm, respectively. The anisotropy of the conductivity is ascribed to high hydration of the surface layer compared to the bulk. SFG NMR diffusometry shows that, in the temperature range from 213 to 353 K, the 1H self-diffusion coefficient of the co-PNIS70/30 membrane is about one third of the diffusion coefficient of Nafion® at the same humidity. However, temperature dependences of proton conductivities of Nafion® and of co-PNIS70/30 membranes are nearly identical. Membrane–electrode assemblies (MEAs) based on co-PNIS70/30 were fabricated by different procedures. The optimal MEAs with co-PNIS70/30 membranes are characterized by maximum output power of ~370 mW/cm2 at 80 °C. It allows considering sulfonated co-PNIS70/30 polynaphthoyleneimides membrane attractive for practical applications.

Ionic Mobility in Ion-Exchange Membranes

“…At higher hydration degrees, the environment of cations in membranes becomes similar to that for aqueous solutions of their salts, and the NMR chemical shifts approach these for aqueous solutions. The energy of interactions of large cesium cations with water molecules is insufficient to destroy the network of hydrogen bonds of water molecules, and the dependence of the 133 Cs chemical shift values on hydration degree is not pronounced [96,98]. This conclusion correlates well with dependences of 1 H chemical shifts on hydration degree [99,100].…”

“…The correctness of these conclusions is proved by the fact that the diffusion coefficients for aqueous solutions of alkali metal chlorides, determined using both methods, are equal and close to the values found by NMR for membranes samples [ 107 ]. It should also be mentioned that the type of ion-exchange membrane significantly affects the ratio of the diffusion coefficients measured using NMR spectroscopy and conductivity [ 133 ].…”

Diffusion in Sulfonated Co-Polynaphthoyleneimide Proton Exchange Membranes with Different Ratios of Hydrophylic to Hydrophobic Groups Studied Using SFG NMR

“…22,39−42 We studied the temperature dependence of the self-diffusion coefficients for co-PNIS with the composition ODAS/MDAC = 70/30, which was wetted at 100% humidity. 43 It was found that D NMR has a similar temperature dependence in co-PNIS 70/30 and in Nafion with activation energies of 0.24 eV above and 0.32 eV below a crossover at T cr = 253 K. We expect that a variation of the ratio of the hydrophilic to hydrophobic polymer groups allows us to modify the diffusion pathways for water and, thus, the transport characteristics, as was observed for some other hydrocarbon-based membranes. 44−46 The goal of this work is to determine the dependence of the proton self-diffusion coefficients in co-PNIS polymers on the ratio of hydrophilic to hydrophobic groups at 100% humidity in a wide temperature range.…”

“…The chemical structure of co-polynaphthoylenimides based on MDAC, NTDA, and ODAS has been described in detail in our previous publications. 27,43,47,48 For the preparation of co-PNIS polymer films, the chemical components ODAS (0.5044 g, 0.0014 M), MDAC (0.1718 g, 0.0006 M), NTDA (0.5364 g, 0.002 M), benzoic acid catalyst (0.34 g, 0.0028 M), triethylamine solubilizer of ODAS (0.303 g, ∼0.003 M), and phenol or DMSO as solvents (10.0 g) were placed in a three-piece flask equipped with a stirrer and a capillary for introducing argon. 26,47 The reaction mass mixture was heated in an argon flow to 80 °C while stirring until all monomers were dissolved.…”

“…A co-PNIS membrane with a lower level of sulfonation has been previously studied. 43 2.4. Diffusion Measurements.…”