Sterically Hindered Pyridine-Linked Sulfonated Polytriazoles: Fabrication of Membranes and Investigation of Single Fuel Cell Performance

Abstract

The semifluorinated sulfonated polytriazoles could integrate the benefits of both enhanced proton conductivity and chemical stability, which makes them one of the best choices for the fabrication of proton exchange membranes (PEM) for fuel cell applications. Herein we report a series of semifluorinated sulfonated polytriazoles, prepared from 2,2′-hindered pyridine functionalized nonsulfonated diazide (PYFAZ) and dialkyne (PYAK). The degrees of sulfonation of the polytriazoles (PYPYSH-XX) were varied by using DSSAZ as one of the sulfonated diazide comonomer in the polymer synthesis. The polymers showed a weight-average molecular weight of up to 450 800 g·mol–1, and their chemical structures were confirmed by FTIR and NMR techniques. The solution cast membranes showed phase-separated morphology with well-defined hydrophilic and hydrophobic domains. The membranes were mechanically robust (tensile strength up to 65.5 MPa, Young modulus of 2.37 GPa), were thermally stable, and exhibited a very high oxidative stability of 48 h (PYPYSH-70). The elongation at the break of the membranes was above 13%, somewhat lower in comparison to that of Nafion-117. Nevertheless, it was possible to fabricate a good quality electrode membrane assembly. The membranes show proton conduction in the range of 95–184 mS·cm–1 (80 °C) and a power density of 599–966 mW·cm–2 (H2/O2) depending on their degree of sulfonation. All these results indicate the potential use of these membranes in PEMFCs.

2,5-Substituted Thiophene Functionalized Semifluorinated Polytriazoles and Evaluation of Low-Temperature Proton Exchange Membrane Application with Elevated Oxidative Stability

“…The presence of a sulfur-containing heterocycle in THFAZ made this diazide thermally more stable. No glass-transition temperature ( T g ) was identified for THFTSH- XX polymers, which was consistent with earlier-reported PYFTSH- XX -based results , (Figure S7). Strong triazole–sulfonic acid hydrogen-bonding restricted the motion of the polymer chains.…”

“…Multiple macroscopic characteristics of PEM such as water uptake, swelling ratio, proton conductivity, and fuel cell performance were vastly shaped by phase morphology. The morphology of sulfonated copolymer-type PEMs exhibited the coexistence of hydrophobic/hydrophilic domains with contact mode atomic force microscopy (AFM), allowing the examination of a two-phase segregated morphology. ,− A highly nanodispersed morphology is profoundly desirable for a high-performing PEM material. The hydrophobic phase and hydrophilic phase of the copolymers were assigned as bright and dark regions, respectively .…”

“…A characteristic alteration of morphology was observed with an increase in DS, which was similar to previously reported SPTZs. 29 The hydrophilic clusters represented as dark spots were solitarily dispersed in both THFTSH-70 and THFTSH-80 although cluster sizes were significantly longer in THFTSH-80 (Figure 7a,7b). In THFTSH-90, a significant development of connections among hydrophilic clusters was noticeable, and a percolation effect arose out of that (Figure 7c).…”

“…Oxidative stability was estimated with 10 × 10 mm 2 specimens following an earlier-reported process. 29 5.00 kV. A 3 nm layer of gold was coated on a polymer surface with 10 mA current for 60 s using a Cressington108 Auto Sputter Coater, before SEM imaging.…”

Poly(fluorenyl terphenyl piperidinium) with Sulfonated Side Chains for the Application of High-Temperature Proton Exchange Membranes

“…Proton exchange membrane fuel cells (PEMFCs) are promising electrochemical devices that can efficiently convert chemical energy in fuels (such as hydrogen, biogas, and methanol) into electrical energy and have attracted much attention because of their clean, efficient, and fast start-up. − PEMFCs have been developed for decades and are currently on the verge of mass commercialization for automotive applications . Among the different types of PEMFCs, high-temperature proton exchange membrane fuel cells (HT-PEMFCs), which operate at higher temperatures of 100–200 °C, have been considered the most promising energy conversion devices owing to their several outstanding properties, such as increased CO tolerance, accelerated kinetics, and a simple water/heat management system, compared to traditional PEMFCs, which operate at temperatures below 80 °C. − High-temperature proton exchange membranes (HT-PEMs) are one of the core components of HT-PEMFCs and can conduct protons from the anode to the cathode at high temperatures without relying on water and can directly influence the performance of HT-PEMFCs.…”