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Although the peak power density of anion exchange membrane fuel cells (AEMFCs) has been raised from ˜0.1 to ˜1.4 W cm-2 over the last decade, a majority of AEMFCs reported in the literature have not been demonstrated to achieve consistently high performance and steady-state operation. Poly(olefin)-based AEMs with fluorine substitution on the aromatic comonomer show considerably higher dimensional stability compared to samples that do not contain fluorine. More importantly, fluorinated poly(olefin)-based AEMs exhibit high hydroxide conductivity without excessive hydration due to a new proposed mechanism where the fluorinated dipolar monomer facilitates increased hydroxide dissociation and transport. Using this new generation of AEMs, a stable, high-performance AEMFC is operated for 120 h. When the fuel cell configuration is subjected to a constant current density of 600 mA cm-2 under H2/O2 flow, the cell voltage declines only 11% (from 0.75 to 0.67 V) for the first 20 h during break-in and the cell voltage loss is low (0.2 mV h-1) over the subsequent 100 h of cell testing. The ease of synthesis, potential for low-cost commercialization, and remarkable ex situ properties and in situ performance of fluoropoly(olefin)-based AEM renders this material a benchmark membrane for practical AEMFC applications. [ABSTRACT FROM AUTHOR]

In situ measurement of hydrocarbons in water is critical for assuring the safety and quality of drinking water and in environmental remediation activities such as the cleanup of oil spills. Thus, effective detection methods of hydrocarbons in aqueous environments are important and several methods have been used for this type of sensing, including spectroscopic techniques, fiber optic sensors, and chromatography. However, under aqueous conditions, small amounts of hydrocarbons are difficult to detect due to their low concentration in water and robust sensing of these types of compounds in an aqueous environment remains a challenging analytical task. Hydrophobic polymer coatings have been widely used to concentrate hydrocarbons for attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) detection at the surface of an ATR crystal by preventing water molecules from penetrating into the polymer coating while absorbing hydrocarbons. However, in typical coating designs only thin films (＜5 μm) can be applied onto the ATR sensor due to the decrease in detection limit and sensitivity to hydrocarbons with increasing film thickness. This paper demonstrates that a semi-crystalline linear low-density polyethylene (LLDPE) polymer coating with thicker thickness (40 μm) can be applied effectively for in situ ATR-FTIR detection of hydrocarbons in aqueous solution. The ATR signal is enhanced by the polymer coating which swells in response to the hydrocarbons and prevents water accumulation at the IR detection interface. Coating the ATR element with a LLDPE film (crystallinity = 12%) reduced the detection time for various hydrocarbons, including toluene, benzene and chloroform. The detection limits and kinetics of the ATR-FTIR detection were not significantly altered when the thickness of the LLDPE coating was increased to improve its mechanical properties which represents a significant improvement from coatings published in the literature. The LLDPE coating described in this research has the potential to be applied as a sensor coating for rapid detection of hydrocarbon-based substances or non-polar biomolecules in aqueous environments. [ABSTRACT FROM AUTHOR]

Mechanically tough, cross-linked anion exchange membranes (AEM) based on poly(2,6-dimethylphenylene oxide) (PPO) were achieved by introducing a hydrophilic and flexible Jeffamine (O,O'-bis(2-aminopropyl)polypropylene glycol-block-poly(ethylene glycol)-block-polypropylene glycol 500) cross-linker into the cationic macromolecular network. The Jeffamine cross-linked AEMs demonstrated outstanding strength and flexibility and were mechanically tougher than AEM samples based on benzyltrimethylammonium (BTMA) functionalized PPO alone. The hydrated BTMA40 membrane showed 52% elongation at break, while the Jeffamine-based J10PPO sample had a 167% elongation at break. In addition, the hydroxide (OH-) conductivity of the J10PPO sample was 52 mS/cm at 80 °C with a swelling ratio of 61%, while BTMA60 suffered severe swelling above 60 °C. The alkaline stabilities of the AEMs with different degrees of Jeffamine cross-linking were evaluated in 1 M NaOH at 80 °C for 500 h. During the 500 h degradation test, J10PPO exhibited the greatest cation stability. The OH- conductivity of this membrane decreased by 30% over 500 h. In contrast, the OH- conductivity of BTMA40 decreased to 9.6 mS/cm at 20 °C, which is 60% lower than the value measured for the sample before the stability test. Based on the high-performance Jeffamine cross-linked AEM, a Pt-catalyzed fuel cell with a peak power density of 314 mW/cm2 was demonstrated at 60 °C under 100% related humidity. [ABSTRACT FROM AUTHOR]

Bases can promote keto-enol tautomerism, a prevalent form of prototropic tautomerism, and facilitate the ring opening of anhydride ring structures. The intrinsic chemical distinctions between these processes provide an opportunity to modulate these seemingly parallel reactions. However, this potential remains largely unexplored. In this work, we report homophthalic anhydride, the first molecule exhibiting simultaneous halochromism, turn-on fluorescence (halofluorochromism), and subsequent self-destruction. Through comprehensive spectroscopic analysis and theoretical calculations, we unravel the mechanisms underlying these phenomena, revealing that the pivotal roles of the base's basicity and nucleophilicity specifically allow us to achieve controlled durations of color change and turn-on fluorescence. Capitalizing on these intriguing properties, we develop a highly dynamic CMY (cyan-magenta-yellow) palette ideal for entity encryption and anti-counterfeiting applications. Our work reshapes the understanding of the relationship between the basicity and nucleophilicity of bases, enriching the comprehension of keto-enol tautomerism and homophthalic anhydride chemistry, and unveils a spectrum of potential applications.

Spin-cast NAFION samples were prepared on silicon native oxide and gold substrates with film thicknesses ranging from 5 to 250 nm. The influence of NAFION film thickness on the infrared spectrum of the polymer was investigated in substrate overlayer attenuated total reflection (SO-ATR) geometry at incident angles between 60° and 65°. In the grazing angle SO-ATR geometry, the thickness of the film significantly affected the position and absorbance of characteristic peaks in the FTIR spectrum of NAFION. Two major peaks in the NAFION spectrum at 1220 cm -1 (predominantly v as (CF 2 ) and v as (SO 3 - )) and 1150 cm -1 (predominantly v as (CF 2 )) appeared to systematically blueshift to 1256 and 1170 cm -1 , respectively, as the thickness of the film decreased from 250 to 5 nm. The changes in the NAFION thin film FTIR spectrum can be attributed to two factors; (1) ordering of NAFION at the interface during spin coating and film formation and (2) the increase in the p-polarization character of the infrared evanescent wave as the polymer film became thinner between the internal reflection element and the film substrate overlayer. The increase in p-polarization resulted in an increase in characteristic peak absorbances of dipoles aligned normal to the substrate due to the overlayer enhancement of the electric field with NAFION films on Si or Au film substrates. These results show that the specific thin film sampling geometry, especially in internal reflection experiments, must be considered to rationally quantify changes in NAFION thin film infrared spectra.