Electrospinning Machine| A facile method to construct proton exchange membranes based on metal organic frameworks decorating binary polymer nanofibers

The rapid development of renewable and clean energy can slow the consumption of fossil fuels, alleviating the global energy crisis. Proton Exchange Membrane Fuel Cells (PEMFCs), as an eco-friendly energy conversion technology, offer advantages like fast startup, high power density, and simple operation. To some extent, the Proton Exchange Membrane (PEM), a core component of PEMFCs, influences or even dominates their performance. Despite significant progress, challenges remain for PEMs in high-temperature (above water boiling point) or sub-zero environments.

Recently, Northeast University’s Che Quantong team published research in Journal of Materials Chemistry A titled “A facile method to construct proton exchange membranes based on metal organic frameworks decorating binary polymer nanofibers.” The study prepared a composite membrane (MOFs@CPNFs)-SPEEK via electrospinning, in-situ growth, and impregnation, demonstrating high and stable conductivity in extreme temperatures.

Binary polymer nanofibers as PEM substrates excel in accelerating proton conduction and enhancing fuel cell performance. Metal-Organic Frameworks (MOFs) show potential in PEMs due to high surface area, strong polymer adhesion, and capacity to host proton carriers. An ordered microstructure synergistically improves key properties. The (MOFs@CPNFs)-SPEEK membrane outperformed CPNFs-SPEEK and MOFs-SPEEK in conductivity and cell performance.

Figure 1:(A) (MOFs@CPNFs)-SPEEK preparation; (B) MOFs growth on CPNFs.

Figure 1(A) illustrates the membrane fabrication process. Figure 1(B)’s SEM images show MOFs’ in-situ growth on CPNFs, becoming denser over time, driven by intermolecular hydrogen bonds between MOFs/chitosan (CS) and MOFs/polyvinyl alcohol (PVA). Solvent evaporation facilitated MOFs@CPNFs’ integration with SPEEK polymer.

Figure 2:(A) σ at 80–160°C; (C)/(E) σ during heating/cooling (-30–30°C); (B)/(D)/(F) Arrhenius plots.

Proton conductivity (σ) and activation energy (Ea) evaluated proton conduction resistance. Figure 2(A) shows (MOFs@CPNFs)-SPEEK/PA had the highest σ, confirming MOFs-CPNFs synergy. Arrhenius plots revealed similar Ea values, indicating σ improvement stemmed from more phosphoric acid molecules participating in conduction. CPNFs’ fibrous microstructure further aided proton transport.

Figures3:(A)–(F) σ during 10 cycles (-25–30°C) for (MOFs@SPEEK)/PA, (CPNFs-SPEEK)/PA, and (MOFs@CPNFs)-SPEEK/PA.

Proton conductivity stability tests were conducted on the composite membrane. The results indicate that after ten cyclic tests, the conductivity values showed minimal variation. This satisfactory reproducibility is attributed to the negligible component leakage of the phosphoric acid-doped composite membrane and its stable microstructure. Building on this, follow-up work will focus on screening binary polymer nanofibers and optimizing MOFs to further develop proton exchange membranes with more pronounced and stable proton conductivity under both high and sub-zero temperatures.

Paper link: https://doi.org/10.1039/D5TA02971F