PAF‐6 Doped with Phosphoric Acid through Alkaline Nitrogen Atoms Boosting High‐Temperature Proton‐Exchange Membranes for High Performance of Fuel Cells

Abstract

High‐temperature proton‐exchange‐membrane fuel cells (HT‐PEMFCs) can offer improved energy efficiency and tolerance to fuel/air impurities. The high expense of the high‐temperature proton‐exchange membranes (HT‐PEMs) and their low durability at high temperature still impede their further practical applications. In this work, a phosphoric acid (PA)‐doped porous aromatic framework (PAF‐6‐PA) is incorporated into poly[2,2′‐(p‐oxydiphenylene)‐5,5′‐benzimidazole] (OPBI) to fabricate novel PAF‐6‐PA/OPBI composite HT‐PEMs through solution‐casting. The alkaline nitrogen structure in PAF‐6 can be protonated with PA to provide proton hopping sites, and its porous structure can enhance the PA retention in the membranes, thus creating fast pathways for proton transfer. The hydrogen bond interaction between the rigid PAF‐6 and OPBI can also enhance the mechanical properties and chemical stability of the composite membranes. Consequently, PAF‐6‐PA/OPBI exhibits an optimal proton conductivity of 0.089 S cm−1 at 200 °C, and peak power density of 437.7 mW cm−2 (Pt: 0.3 mg cm−2), which is significantly higher than that of the OPBI. The PAF‐6‐PA/OPBI provides a novel strategy for the practical application of PBI‐based HT‐PEMs.

Construction of Successive Proton Conduction Channels to Accelerate the Proton Conduction Process in Flexible Proton Exchange Membranes

“…By contrast, the σ values were 1.04 × 10 –1 and 1.81 × 10 –1 S cm –1 for (K/PA/S) 3 -50/PA, 1.24 × 10 –1 and 2.02 × 10 –1 S cm –1 for (K/PA/S) 3 /PA-50, and 7.10 × 10 –2 and 1.21 × 10 –1 S cm –1 for (K/PA/S) 3 -f/PA. The results were comparable with 1.098 × 10 –1 S cm –1 at 180 °C for PA-TABPP and 8.9 × 10 –2 S cm –1 at 200 °C for 10%PAF-6-PA/OPBI, lower than 2.35 × 10 –1 S cm –1 at 160 °C for (Kevlar-CdTe-PA) 4 /85%PA but higher than 6.1 × 10 –2 S cm –1 at 170 °C for NbPBI-TSPDO 30 /PA and 7.0 × 10 –2 S cm –1 at 160 °C for AmPBI–PIL-5-MXene-3/PA . From our perspective, a higher content of PA molecules resulted in the improvement of σ values, which was reflected in more proton conduction carriers and reduced proton conduction resistance.…”

“…The invariable E a values meant similar proton conduction resistance, which was derived from the fine microstructure integrity of successive proton conduction channels . By contrast, the reported E a values were 14.47 kJ mol –1 for 10%PAF-6-PA/OPBI, 14.40 kJ mol –1 for NbPBI-TSPDO 30 /PA, 12.39 kJ mol –1 for PA-TABPP, and 13.2 kJ mol –1 for (Kevlar-CdTe-PA) 4 /85%PA . Increased proton conductivity was achieved because PA molecules constituted successive proton conduction channels in the prepared PA-doped membranes.…”

“…The sulfonic acid groups constituted proton conduction channels, which could remedy the defects of polytetrafluoroethylene being incapable of conducting protons . Recently, Zhu and co-workers designed the well-established hydrogen bonding network to facilitate fast proton hopping through the Grotthuss mechanism …”

“…56 Recently, Zhu and co-workers designed the wellestablished hydrogen bonding network to facilitate fast proton hopping through the Grotthuss mechanism. 6 3.9. Proton Conductivity Stability.…”

“…Proton exchange membrane fuel cells (PEMFCs) are suitable to serve as clean energy systems owing to some advantages of high energy conversion efficiency, negligible pollution emission, etc. , As the key component, proton exchange membranes (PEMs) have been believed to dominate the efficiency and the practicability of PEMFCs. − At present, high-temperature PEMFCs with the working temperature of 100–200 °C and low humidity have been attracting more and more attention owing to the accelerated ion conduction, simplified internal systems, enhanced catalyst efficiency, etc. , The outstanding high-temperature PEMs are thus required to cater to the development of high-temperature PEMFCs. − Although some high-temperature PEMs, such as PA-doped polybenzimidazole (PBI) and cross-linked PBI, have achieved a milestone in the reinforced electrochemical performance at elevated temperatures without humidification, − the continuous research of designing and constructing high-temperature PEMs with adequate flexibility is needed to meet various application requirements. − …”