DataSheet_1_The metabolism of nonstructural carbohydrates, lipids, and energy in two Cycas species with differential tolerance to unexpected freezing stress.doc

IntroductionWith the climate warming, the occurrence of freezing events is projected to increase in late spring and early autumn in the Northern Hemisphere. Observation of morphological traits showed that Cycas panzhihuaensis was more tolerant to unexpected freezing stress than C. bifida. Energy balance is crucial for plant tolerance to stress. Here, we aimed to determine whether the different responses of the two species to the unpredicted freezing stress were associated with the metabolism of energy and related substances.MethodsThe effects of unexpected freezing temperatures on C. panzhihuaensis and C. bifida were studied by measuring chlorophyll fluorescence parameters, energy charge and the profile of nonstructural carbohydrates (NSC) and lipids.ResultsC. panzhihuaensis exhibited higher stability of photosynthetic machinery than C. bifida under unpredicted freezing events. Significant interaction between species and treatments were observed in the energy charge, the level of NSC and its most components and the amount of most lipid categories and lipid classes. The decrease of soluble sugar and the increase of neutral glycerolipids at the early freezing stage, the accumulation of membrane glycerolipids at the late freezing stage and the continuous decrease of energy charge during the freezing period were the characteristics of C. panzhihuaensis responding to unexpected freezing stress. The degradation of membrane glycerolipids and the continuous decrease of soluble sugar during the freezing period and the accumulation of neutral glycerolipids and energy charge at the late freezing stage represented the characteristics of C. bifida responses.DiscussionThe different freezing sensitivity between C. panzhihuaensis and C. bifida might be associated with the differential patterns of the metabolism of energy, NSC and lipids. C. panzhihuaensis possesses the potential to be introduced to the areas of higher latitudes and altitudes.</p

Amination modification of graphene oxide for the in-situ synthesis of sulfonated polyimide-based composite proton exchange membranes

To mitigate the severe degradation of mechanical properties and stability of highly sulfonated proton exchange membranes (PEMs) caused by the sulfonic acid groups, amino-functionalized graphene oxide (AGO) was embedded into sulfonated polyimide (SPI) for the in-situ synthesis of a composite proton exchange membrane. The introduction of AGO nanoparticles facilitated the enhancement of the crystallinity of the composite membrane, with the well-constructed interface and dispersion. The resulting AGO-SPI composite membrane exhibited high mechanical strength and stability. The fracture strength of AGO-SPI composite membrane was approximately 61 MPa, which was 1.85 times higher than that of pure SPI. Meanwhile, the weight loss of AGO-SPI composite membrane in Fenton's reagent was only 2.11 %. Additionally, at 90 °C/98 % RH, the proton conductivity of AGO-SPI composite membrane reached 50.1 mS cm−1, which was 3.53 times higher than that of pristine SPI. The results suggest the promising application prospects of the proton exchange composite membrane.</p

Fabricating rapid proton conduction pathways with sepiolite nanorod-based ionogel/Nafion composites via electrospinning

The major limitation of conventional sulfonated polymer proton-exchange membranes (PEMs) is their strong reliance on water molecules for proton conduction, causing a significant reduction in proton conductivity under low-humidity conditions. In this study, a one-dimensional ionogel (IL@Sep) confined within sepiolite (Sep) nanorods was prepared using ionic liquid (1-butyl-3-methylimidazolium trifluoromethanesulfonate) and supercritical CO2. Subsequently, IL@Sep was blended with a Nafion solution, and electrospinning was used to fabricate the composite fiber PEM suitable for low-humidity environments. The results revealed that the electrospun (ES)-Nafion/IL@Sep composite fiber membrane exhibited significantly enhanced mechanical properties, water absorption, and proton conductivity. At an IL@Sep content of 2 wt%, the Nafion/2IL@Sep membrane exhibited a proton conductivity of 231 mS cm−1 at 80 °C/98 % relative humidity (RH) and 113 mS cm−1 at 80 °C/40 % RH. Moreover, the single-cell assembled with this composite membrane exhibited good gas tightness and achieved a peak power density of 779 mW cm−2 at 60 °C/80 % RH, which was ∼1.45 times that of the Nafion 212 membrane single-cell. This study indicates that electrospinning-assisted ionogel-modified ES-Nafion/IL@Sep composite fiber membranes have potential suitability for use in proton-exchange membrane fuel cells under varying humidity conditions.</p

Graphene Oxide-Intercalated Montmorillonite Layered Stack Incorporated into Poly(2,5-Benzimidazole) for Preparing Wide-Temperature Proton Exchange Membranes

In this study, graphene oxide-intercalated montmorillonite (GO-MMT) layered stacks were introduced into a poly(2,5-benzimidazole) (ABPBI) matrix via in situ synthesis to prepare composite membranes (GO-MMT/ABPBI) for wide-temperature range (0–180 °C) fuel cell applications. After the introduction of GO-MMT nanocomposites, the ABPBI membranes showed improved tensile strength, water and phosphoric acid retention ratio, and proton conductivity. The GO-MMT/ABPBI membrane was highly conductive when operated from 0 to 180 °C and attained proton conductivities of 50.3 mS/cm (0% RH/180 °C) and 38.3 mS/cm (98% RH/90 °C), respectively, which were about 1.6 and 1.7 times those of the pristine ABPBI membrane under the same conditions. This improved performance was because the nanolayered stacks of GO-MMT confined phosphoric acid and water within its interchannels via hydrogen bonds. This paper demonstrates the potential application of composite membranes in fuel cells with a wide operating temperature range

Polyethyleneimine-filled sepiolite nanorods-embedded poly(2,5-benzimidazole) composite membranes for wide-temperature PEMFCs

Proton-exchange membrane fuel cells (PEMFCs) that operate from room temperature to high temperatures (e.g., 200 °C) are desired for fuel cells used in vehicles and combined heat and power systems. In this work, polyethyleneimine-filled sepiolite nanorods (PEI@SNR)-embedded poly(2,5-benzimidazole) composites (ABPBI/PEI@SNR) were synthesized in-situ to enhance their proton conductivity and minimize phosphoric acid (PA) leaching. They were then applied in PEMFCs between room temperature and 200 °C. The physicochemical and electrochemical properties of the composite membranes were characterized. The composite membranes showed enhanced thermal, oxidative, and dimensional stability and achieved proton conductivities above 0.01 S/cm from 40 to 200 °C at a relative humidity of 0–100%. This performance was attributed to abundant hydrogen bonds between PA, ABPBI, and PEI, and the strong retention of bound water within sepiolite nanorods (SNRs). The maximum power density of the cell based on the PA-doped ABPBI/5PEI@SNR composite membrane reached 0.16 W/cm2 at 80 °C and 0.27 W/cm2 at 180 °C and an anhydrous environment, which were respectively 2.2 and 1.5 times higher than those of the PA-doped ABPBI membrane. The cell performance was much better than previously reported zeolite-embedded polybenzimidazole membrane-based PEMFCs, indicating that the composite membranes have good application prospects in PEMFCs operating over a wide temperature range.</p

Polyethyleneimine-filled sepiolite nanorods-embedded poly(2,5-benzimidazole) composite membranes for wide-temperature PEMFCs

Proton-exchange membrane fuel cells (PEMFCs) that operate from room temperature to high temperatures (e.g., 200 °C) are desired for fuel cells used in vehicles and combined heat and power systems. In this work, polyethyleneimine-filled sepiolite nanorods (PEI@SNR)-embedded poly(2,5-benzimidazole) composites (ABPBI/PEI@SNR) were synthesized in-situ to enhance their proton conductivity and minimize phosphoric acid (PA) leaching. They were then applied in PEMFCs between room temperature and 200 °C. The physicochemical and electrochemical properties of the composite membranes were characterized. The composite membranes showed enhanced thermal, oxidative, and dimensional stability and achieved proton conductivities above 0.01 S/cm from 40 to 200 °C at a relative humidity of 0–100%. This performance was attributed to abundant hydrogen bonds between PA, ABPBI, and PEI, and the strong retention of bound water within sepiolite nanorods (SNRs). The maximum power density of the cell based on the PA-doped ABPBI/5PEI@SNR composite membrane reached 0.16 W/cm2 at 80 °C and 0.27 W/cm2 at 180 °C and an anhydrous environment, which were respectively 2.2 and 1.5 times higher than those of the PA-doped ABPBI membrane. The cell performance was much better than previously reported zeolite-embedded polybenzimidazole membrane-based PEMFCs, indicating that the composite membranes have good application prospects in PEMFCs operating over a wide temperature range.</p

Advances in ionogels for proton-exchange membranes

To ensure the long-term performance of proton-exchange membrane fuel cells (PEMFCs), proton-exchange membranes (PEMs) have stringent requirements at high temperatures and humidities, as they may lose proton carriers. This issue poses a serious challenge to maintaining their proton conductivity and mechanical performance throughout their service life. Ionogels are ionic liquids (ILs) hybridized with another component (such as organic, inorganic, or organic-inorganic hybrid skeleton). This design is used to maintain the desirable properties of ILs (negligible vapor pressure, thermal stability, and non-flammability), as well as a high ionic conductivity and wide electrochemical stability window with low outflow. Ionogels have opened new routes for designing solid-electrolyte membranes, especially PEMs. This paper reviews recent research progress of ionogels in proton-exchange membranes, focusing on their electrochemical properties and proton transport mechanisms.</p

Sulfonation modification of halloysite nanotubes for the in-situ synthesis of polybenzimidazole-based composite proton exchange membranes in wide-temperature range applications

Phosphoric acid-doped polybenzimidazole (PA–PBI) membranes face challenges, such as the easy loss of free PA and the reduced mechanical strength caused by the “plasticization effect” of PA, limiting their application in a wide temperature range. In this study, sulfonated halloysite (sHNT) was used to modify poly(2,5-benzimidazole) (ABPBI) for the in-situ synthesis of a composite proton exchange membrane. The introduction of halloysites in the composite membrane enabled the capturing of PA and water, while its nanoporous structure provided additional paths for proton conduction. Sulfonation modification of halloysite improved the interfacial compatibility between the inorganic particles and the polymer matrix, with the –SO3H groups providing extra proton hopping sites. Due to the well-constructed interface, the resulting sHNT/ABPBI composite membrane exhibited high mechanical strength and excellent proton conductivity across a wide temperature range. The 3 % sHNT/ABPBI composite membrane exhibited a breaking strength of approximately 130 MPa, which was 1.6 times that of pure ABPBI. Moreover, the proton conductivity of the composite exceeded 0.01 S cm−1 at temperatures ranging from 40 to 180 °C. At 160 °C, the peak power density of the PA-doped 3 % sHNT/ABPBI composite membrane was 0.212 W cm−2, which was 1.33 times higher than that of the pure ABPBI membrane. These results show that the composite membrane has potential applications in a wide temperature range.</p