Enhanced Proton Conductivity of Sulfonated Hybrid Poly(arylene ether ketone) Membranes by Incorporating an Amino–Sulfo Bifunctionalized Metal–Organic Framework for Direct Methanol Fuel Cells

Novel side-chain-type sulfonated poly­(arylene ether ketone) (SNF-PAEK) containing naphthalene and fluorine moieties on the main chain was prepared in this work, and a new amino–sulfo-bifunctionalized metal–organic framework (MNS, short for MIL-101-NH₂-SO₃H) was synthesized via a hydrothermal technology and postmodification. Then, MNS was incorporated into a SNF-PAEK matrix as an inorganic nanofiller to prepare a series of organic–inorganic hybrid membranes (MNS@SNF-PAEK-XX). The mechanical property, methanol resistance, electrochemistry, and other properties of MNS@SNF-PAEK-XX hybrid membranes were characterized in detail. We found that the mechanical strength and methanol resistances of these hybrid membranes were improved by the formation of an ionic cross-linking structure between −NH₂ of MNS and −SO₃H on the side chain of SNF-PAEK. Particularly, the proton conductivity of these hybrid membranes increased obviously after the addition of MNS. MNS@SNF-PAEK-3% exhibited the proton conductivity of 0.192 S·cm^–1, which was much higher than those of the pristine membrane (0.145 S·cm^–1) and recast Nafion (0.134 S·cm^–1) at 80 °C. This result indicated that bifunctionalized MNS rearranged the microstructure of hybrid membranes, which could accelerate the transfer of protons. The hybrid membrane (MNS@SNF-PAEK-3%) showed a better direct methanol fuel cell performance with a higher peak power density of 125.7 mW/cm² at 80 °C and a higher open-circuit voltage (0.839 V) than the pristine membrane

Synergistic Utilization of a CeO₂‑Anchored Bifunctionalized Metal–Organic Framework in a Polymer Nanocomposite toward Achieving High Power Density and Durability of PEMFC

The free radicals produced during the long-term operation of fuel cells can accelerate the chemical degradation of the proton exchange membrane (PEM). In the present work, the widely used free radical scavenger CeO2 was anchored on amino-functionalized metal–organic frameworks, and flexible alkyl sulfonic acid side chains were tethered onto the surface of inorganic nanoparticles. The prepared CeO2-anchored bifunctionalized metal–organic framework (CeO2-MNCS) was used as a promising synergistic filler to modify the Nafion matrix for addressing the detrimental effect of pristine CeO2 on the performance and durability of PEMs, including decreased proton conductivity and the migration problem of CeO2. The obtained hybrid membranes exhibited a high proton conductivity up to 0.239 S cm–1, enabling them to achieve a high power density of 591.47 mW cm–2 in a H2/air PEMFC single cell, almost 1.59 times higher than that of recast Nafion. After 115 h of acceleration testing, the OCV decay ratio of the hybrid membrane was decreased to 0.54 mV h–1, which was significantly lower than that of recast Nafion (2.18 mV h–1). The hybrid membrane still maintained high power density, low hydrogen crossover, and unabated catalytic activity of the catalyst layer after the durability test. This study provides an effective one-stone-two-birds strategy to develop highly durable PEMs by immobilizing CeO2 without sacrificing proton conductivity, allowing for the realization of improvement on the performance and sustained durability of PEMFC simultaneously

Polyoxometalate-Cross-Linked Proton Exchange Membranes with Post-Assembled Nanostructures for High-Temperature Proton Conduction

High-temperature proton exchange membranes (HT-PEMs) are key components in high-temperature energy storage and conversion technologies, which require excellent proton conductivity and mechanical strength. However, it is difficult for HT-PEMs to balance their mechanical and conductive properties. Here, we present a strategy to prepare HT-PEMs based on the combination of polyoxometalate (POM)-dominated noncovalent cross-linking and H3PO4 (PA)-induced post-assembly. Hybrid membranes containing polyvinylpyrrolidone (PVP), poly­(terphenyl piperidine) (PTP), and H3PW12O40 (PW) are prepared, where the polymers are electrostatically cross-linked by PW and maintain certain mobility. When the membranes adsorb PA, the polarity difference between the PVP–PW–PA moieties and the PTP–PW–PA moieties increases, causing the chains to rearrange into bicontinuous structures via a post-assembly process. The resultant membranes show a break strength over 7 MPa and a proton conductivity of ∼55 mS cm–1 at 160 °C. The high-temperature supercapacitors based on such membranes exhibit a specific capacitance of 145.4 F g–1 and a capacitance retention of 80% after 3000 charge–discharge cycles at 150 °C. Their H2/air fuel cells display a peak power of 273.6 mW cm–2 at 160 °C. This work provides a paradigm for using POMs as dynamic cross-linkers to fabricate nanostructured PEMs, which paves a feasible route to developing high-performance electrolyte materials

Construction of Proton Transport Highways Induced by Polarity-Driving in Proton Exchange Membranes to Enhance the Performance of Fuel Cells

The approach to constructing proton transport channels via direct adjustments, including hydrophilia and analytical acid concentration in hydrophilic domains, has been proved to be circumscribed when encouraging the flatter hydrophilic–hydrophobic microphase separation structures and reducing conductivity activation energy. Here, we propose a constructive solution by regulating the polarity of hydrophobic domains, which indirectly varies the aggregation and connection of hydrophilic ion clusters during membrane formation, enabling orderly self-assembly and homogeneously distributed microphase structures. Accordingly, a series of comb-shaped polymers were synthesized with diversified optimization, and more uniformly distributed ion cluster lattices were subsequently observed using high-resolution transmission electron microscopy. Simultaneously, combining with density functional theory calculations, we analyzed the mechanism of membrane degradations caused by hydroxyl radical attacks. Experimental results demonstrated that, facilitated by proper molecule polarity, beneficial changes of bond dissociation energy could extend the membrane lifetime more than the protection from side chains near ether bonds, which were deemed to reduce the probability of attacks by the steric effect. With the optimal strategy chosen among various trials, the maximum power density of direct methanol fuel cell and H2/air proton exchange membrane fuel cell was enhanced to 95 and 485 mW cm–2, respectively