The clustering-triggered emission mechanism guides the rational design of nonaromatic polyurethanes with intrinsic emissions including room-temperature phosphorescence.

The perfluorosulfonic acid (PFSA) proton exchange membrane (PEM) is the key component for hydrogen fuel cells (FCs). We used in situ synchrotron scattering to investigate the PEM morphology evolution and found a “stream-reservoir” morphology, which enables efficient proton transport. The short-side-chain (SSC) PFSA PEM is fabricated under the guidance of morphology optimization, which delivered a proton conductivity of 193 milliSiemens per centimeter [95% relativity humidity (RH)] and 40 milliSiemens per centimeter (40% RH) at 80°C. The improved glass transition temperature, water permeability, and mechanical strength enable high-temperature low-humidity FC applications. Performance improvement by 82.3% at 110°C and 25% RH is obtained for SSC-PFSA PEM FCs compared to Nafion polymer PEM devices. The insights in chain conformation, packing mechanism, crystallization, and phase separation of PFSAs build up the structure-property relationship. In addition, SSC-PFSA PEM is ideal for high-temperature low-humidity FCs that are needed urgently for high-power-density and heavy-duty applications.

Photoluminescent polymers with merely nonaromatic chromophores have attracted rapidly growing attention owing to their importance in the significant fundamental, encryption, and anticounterfeiting fields. Based on the clustering-triggered emission mechanism, through-space conjugation and conformational rigidification of nonaromatic chromophores are crucial to photoluminescence, which are also dependent on molecular arrangement. Herein, polyamide-6 (PA-6) with well-defined molecular arrangements was thus studied. The luminescence from the PA-6 solution is enhanced upon aggregation from solution to amorphous solid and further boosted with the formation of highly regular molecular arrangement. More importantly, both blue and green fluorescence from PA-6/formic acid (FA) solutions were observed because of the variable clusters formed among PA-6 and FA. To make clear of this, PA-6 cast film (PCF) and PA-6 electrospun film (PEF) were prepared and belonged to α-(antiparallel molecular arrangement) and γ (parallel molecular arrangement)-form crystals, as confirmed by Fourier transform infrared, X-ray diffraction, and Raman measurements. The relationship between molecular arrangement and luminescence of PA-6 molecules was clarified by their photophysical properties in solids and solutions. Notably, color-tunable cryogenic phosphorescence of PA-6 solids was also detected. Such aggregation-enhanced emission and tunable phosphorescence of PA-6 solids are ascribed to the formation of diversified amide clusters together with remarkably rigidified molecular conformations owing to the highly regular molecular arrangement in the aggregated states.

Benefiting from its large specific surface with functional -OH/-F groups, Ti3C2Tx, a typical two-dimensional (2D) material in the recently developed MXene family, was synthesized and used as a filler to improve the properties of the short side-chain (SSC) perfluorosulfonic acid (PFSA) proton exchange membrane. It is found that the proton conductivity is enhanced by 15% while the hydrogen permeation is reduced by 45% after the addition of 1.5 wt% Ti3C2Tx filler into the SSC PFSA membrane. The improved proton conductivity of the composite membrane could be associated with the improved proton transport environment in the presence of the hydrophilic functional groups (such as -OH) of the Ti3C2Tx filler. The significantly reduced hydrogen permeation could be attributed to the incorporation of the impermeable Ti3C2Tx 2D fillers and the decreased hydrophilic ionic domain spacing examined by the small angle X-ray scattering (SAXS) for the composite membrane. Furthermore, improved thermo-mechanical properties of the SSC/Ti3C2Tx composite membrane were measured by dynamic mechanical analyzer (DMA) and tensile strength testing. The demonstrated higher proton conductivity, lower hydrogen permeation, and improved thermo-mechanical stability indicate that the SSC/Ti3C2Tx composite membranes could be a potential membrane material for PEM fuel cells operating above the water boiling temperature.

Nitrogen-doped reduced graphene oxide-metal(metal oxides) nanoparticle (N-rGO-M(MO) NPs, M ¼ Fe, MO: M ¼ Co, Mn) composites were prepared through a facile and general method at high temperature (800 C). M(MO) were well-dispersed and tightly anchored on graphene sheets, which were doped with nitrogen simultaneously and further loaded with Pt nanoparticles. Those results showed a more positive onset potential, higher cathodic density, and higher electron transfer number for the ORR in alkaline media. Furthermore, N-rGO-metal(metal oxides)-Pt (N-rGO-M(MO)-Pt) nanoparticles show better durability than the commercial Pt/C catalyst, and can be used as promising potential materials in practical applications.

The property of perfluorinated sulfonic acid (PFSA) membranes depends not only on the ion exchange capacity (IEC), but also on the chemical structure of the functional side-chain and the phase-separation morphology. Two PFSA membranes, the long side-chain (LSC) and the short side-chain (SSC), have been investigated to study the structure−property relationship, covering the ionic domain structure and the proton transport. The proton conductivity of the SSC PFSA membrane is 143 and 209 mS/cm at 30 °C and 80 °C in water, which is 30− 40% higher than that of the LSC PFSA membrane (103 and 161 mS/cm). The bound-to-free water ratio in the hydrated membranes was analyzed by differential scanning calorimetry and Raman spectroscopy, which show that a higher ratio accounts for the improved proton conductivity of the SSC PFSA membrane. The chain mobility was analyzed by solid-state nuclear magnetic resonance, which reveals that the side chain of the SSC membrane more readily self-assembles. This result was verified by the morphology from transmission electron microscopy. The small-angle X-ray scattering results show that the SSC PFSA membrane exhibits smaller domain spacing between the ionic clusters in dehydrated membranes. These observations, a larger ionic cluster and smaller domain spacing in the dehydrated SSC membrane, indicate a reduced size of the hydrophobic assembly feature domains, and the ionic channel connectivity is better in the SSC, which can be another key issue for its improved proton conductivity, in addition to the higher IEC and higher proton mobility.

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