Mitigation of Silicon Contamination in Fuel Cell Gasket Materials through Silica Surface Treatment.

Gaskets and seals are essential components in the operation of proton exchange membrane (PEM) fuel cells and are required for keeping hydrogen and air/oxygen within their individual compartments. The durability of these gaskets and seals is necessary, as it influences not only the lifespan but also the electrochemical efficiency of the PEM fuel cell. In this study, the cause of silicon leaching from silicone gaskets under simulated fuel cell conditions was investigated. Additionally, to reduce silicon leaching, the silica surface was treated with methyltrimethoxysilane, vinyltriethoxysilane, and (3,3,3-trifluoropropyl)trimethoxysilane. Changes in the silica surface chemistry were investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, elemental analysis, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Inductively coupled plasma-optical emission spectroscopy analysis revealed that surface-treated silica was highly effective in reducing silicon leaching.

Mechanochemically functionalized and fibrillated microcrystalline cellulose as a filler in silicone foam: An integrated experimental and simulation investigation.

Fibrillated celluloses have gained significant attention due to their exceptional mechanical properties and eco-friendly characteristics, which make them suitable for various applications. In this study, we designed a precise approach for producing highly fibrillated microcrystalline cellulose (MCC) via ball-milling treatment using four typical silane coupling agents. The empirical data demonstrate that the fibrillization of MCC and the properties of fibrillated MCC are largely affected by the size and geometry of the functional groups of the silanes. After ball-milling, most MCC displayed enhanced e-beam tolerance and thermal stability, whereas the silane loading amount, surface area, and morphology of fibrillated MCC appeared to be random, which was exemplified by the proportional and non-proportional relationship between the loading amount and surface area of methyl silane- and phenyl silane-treated MCC, respectively. Density functional theory calculations and molecular dynamics simulations were employed to obtain the intricate details. The simulation results were in agreement with the experimental results. Finally, fibrillated MCC was incorporated into silicone foams as an additive. The thermal stability of fibrillated MCC with added silicone was greatly improved, and the tensile strength of fibrillated MCC-containing silicone foam was 44.1 and 5.4 times higher than that of the neat and MCC-containing silicone foams, respectively.

Improvement of Heat Resistance of Fluorosilicone Rubber Employing Vinyl-Functionalized POSS as a Chemical Crosslinking Agent.

Fluorosilicone rubber (F-LSR) is a promising material that can be applied in various cutting-edge industries. However, the slightly lower thermal resistance of F-LSR compared with that of conventional PDMS is difficult to overcome by applying nonreactive conventional fillers that readily agglomerate owing to their incompatible structure. Polyhedral oligomeric silsesquioxane with vinyl groups (POSS-V) is a suitable material that may satisfy this requirement. Herein, F-LSR-POSS was prepared using POSS-V as a chemical crosslinking agent chemically bonded with F-LSR through hydrosilylation. All F-LSR-POSSs were successfully prepared and most of the POSS-Vs were uniformly dispersed in the F-LSR-POSSs, as confirmed by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H-NMR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) measurements. The mechanical strength and crosslinking density of the F-LSR-POSSs were determined using a universal testing machine (UTM) and dynamic mechanical analysis (DMA), respectively. Finally, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) measurements confirmed that the low-temperature thermal properties were maintained, and the heat resistance was significantly improved compared with conventional F-LSR. Eventually, the poor heat resistance of the F-LSR was overcome with three-dimensional high-density crosslinking by introducing POSS-V as a chemical crosslinking agent, thereby expanding the potential fluorosilicone applications.

Optimization and Characterization of the F-LSR Manufacturing Process Using Quaternary Ammonium Silanolate as an Initiator for Synthesizing Fluorosilicone.

Due to the growing demand for versatile hybrid materials that can withstand harsh conditions (below -40 °C), fluorosilicone copolymers are becoming promising materials that can overcome the limited operating temperature of conventional rubber. In order to synthesize a fluorosilicone copolymer, a potent initiator capable of simultaneously initiating various siloxane monomers in anionic ring-opening polymerization (AROP) is required. In this study, tetramethyl ammonium silanolate (TMAS), a quaternary ammonium (QA) anion, was employed as an initiator for AROP, thereby fluoro-methyl-vinyl-silicone (FVMQ) and fluoro-hydrido-methyl-silicone (FHMQ) were successfully synthesized under optimized conditions. FT-IR, NMR, and GPC analyses confirmed that the chain length and functional group content of FVMQ and FHMQ are controlled by changing the ratio of the components. Moreover, fluorine-involved liquid silicone rubber (F-LSR) was prepared with FVMQ as the main chain and FHMQ as a crosslinker. The tensile strength, elongation, and hardness of each F-LSR sample were measured. Finally, it was confirmed through TGA, DSC, TR-test, and embrittlement testing that elastic retention at low temperatures improved even though the heat resistance slightly decreased as the trifluoropropyl group increased in F-LSR. We anticipate that the optimization of fluorosilicone synthesis initiated by QA and the comprehensive characterization of F-LSRs with different fluorine content and chain lengths will be pivotal to academia and industry.

Effect of the Particle Size and Layer Thickness of GNP Fillers on the Dielectric Properties and Actuated Strain of GNP-PDMS Composites.

Dielectric elastomer actuators (DEAs), a type of electroactive polymers (EAPs), are smart materials that are used in various fields such as artificial muscles and biomimetic robots. In this study, graphene nanoplatelets (GNPs), which are conductive carbon fillers, were added to a widely used DEA, namely, polydimethylsiloxane (PDMS), to improve its low actuated strain. Four grades of GNPs were used: H5, H25, M5, and M25 (here, the number following the letter indicates the average particle size of the GNPs in µm). The average layer thickness of the H grade is 13−14 nm and that of the M grade is 5−7 nm. PDMS composites were prepared by adding 0.5, 1, 2, and 3 wt% of each GNP, following which the mechanical properties, dielectric properties, and actuated strain of the composites were measured. The mechanical properties were found to increase as the particle size increased. Regarding the dielectric characteristics, it was found that the higher the aspect ratio of the filler, the easier the formation of a micro-capacitor network in the composite­this led to an increase in the dielectric constant. In addition, the higher amounts of GNPs in the composites also led to an increase in the dielectric constant. For the actuated strain analysis, the electromechanical sensitivity was calculated using the ratio of the dielectric constant to the Young's modulus, which is proportional to the strain. However, it was found that when the loss tangent was high, the performance of the actuated strain decreased owing to the conversion of electric energy into thermal energy and leakage current loss. As a result, the highest actuated strain was exhibited by the M25 composite, with an actuated strain value of 3.01% measured at a low electric field (<4 kV/mm). In conclusion, we proved that the GNP−PDMS composites with a thin layer and large particle size exhibited high deformation.

Simultaneous Effects of Carboxyl Group-Containing Hyperbranched Polymers on Glass Fiber-Reinforced Polyamide 6/Hollow Glass Microsphere Syntactic Foams.

The hollow glass microsphere (HGM) containing polymer materials, which are named as syntactic foams, have been applied as lightweight materials in various fields. In this study, carboxyl group-containing hyperbranched polymer (HBP) was added to a glass fiber (GF)-reinforced syntactic foam (RSF) composite for the simultaneous enhancement of mechanical and rheological properties. HBP was mixed in various concentrations (0.5-2.0 phr) with RSF, which contains 23 wt% of HGM and 5 wt% of GF, and the rheological, thermal, and mechanical properties were characterized systematically. As a result of the lubricating effect of the HBP molecule, which comes from its dendritic architecture, the viscosity, storage modulus, loss modulus, and the shear stress of the composite decreased as the HBP content increased. At the same time, because of the hydrogen bonding among the polymer, filler, and HBP, the compatibility between filler and the polymer matrix was enhanced. As a result, by adding a small amount (0.5-2.0 phr) of HBP to the RSF composite, the tensile strength and flexural modulus were increased by 24.3 and 9.7%, respectively, and the specific gravity of the composite was decreased from 0.948 to 0.917. With these simultaneous effects on the polymer composite, HBP could be potentially utilized further in the field of lightweight materials.

Deciphering van der Waals interaction between polypropylene and carbonated fly ash from experimental and molecular simulation.

Pollution emitted from power plants, including a considerable amount of fly ash (FA) and carbon dioxide (CO2), annually increases and is challenging from an environmentally friendly and sustainable point of view. To date, laboratory-scaled approaches cannot efficiently replace the FA-landfilling and mitigate the stress from CO2 emission. Here, a practically operatable fundamental work by combining carbonated FA (C-FA)-immobilizing CO2 in FA-and polypropylene (PP) matrix is reported and reveals abnormal mechanical and thermal features clarified by calculating van der Waals (vdW) interaction from an atomic scale. This is the first study wherein the interaction between instantaneous dipole moment-induced PP and fillers is simulated and examined. The vdW interactions at the (hetero)interfaces are -59.66, -82.30, and -224.39 kJ mol-1 Å-2 for PP, calcium oxide (CaO; before carbonation), and calcium carbonate (CaCO3; after carbonation), respectively, which provides concrete theoretical support for interesting findings such as the independence of tensile strength on filler loadings and "well-grown" interface-induced higher conductivity characteristics of the composites. Therefore, this work can offer practical solutions to mitigate pollution, provide a new perspective on fundamental physical interactions, and guide the development of practical next-generation composite materials.

Temperature dependence for high electrical performance of Mn-doped high surface area activated carbon (HSAC) as additives for hybrid capacitor.

Herein, we manufactured the positive and negative electrodes for the hybrid capacitor. The Mn-doped High surface area of Activated carbon composite used for the positive electrode and as-prepared composite was calcined at 600 °C and 800 °C. The morphological structures and pore-size distributions of MnYP-600HTT and MnYP-800HTT were characterized by means of XRD, SEM, EDAX, TEM, and BET. According to the BET specific surface-area evaluation, MnYP-600HTT and MnYP-800HTT were 1272.6 and 1388.1 m2/g, respectively. Total pore volumes were 0.627 and 0.687 cm3/g, which is beneficial for forming ion-transport channels in electrochemical reactions. The MnYP-600HTT electrode had a high specific capacity of 177.2 mAh/g at 20C, and the capacity retention was 64.8%. During the entire cycling, MnYP-600HTT had excellent cyclic stability in 500 cycles along with high efficiency. The robust design of the MnYP-600HTT and MnYP-800HTT cathode materials introduced in this work pave the way for designing next-generation supercapacitors operating at ultra-high C rates. The Mn-doped high surface of activated carbon had stable energy density and superior cycling stability that were demonstrated in supercapacitor systems.

Valorization of fly ash as a harmless flame retardant via carbonation treatment for enhanced fire-proofing performance and mechanical properties of silicone composites.

Owing to the environmental and economic problems arising from fly ash (FA), there have been various ongoing efforts over the past decades to find a use for it. Among the various applications of FA, its use as a filler in polymer composites has gained much attention. However, most studies have applied FA as a semi-reinforcing filler, which only marginally improves mechanical properties arising from the poor surface wettability of FA with polymer matrices. To solve this problem and to explore new applications, FA was carbonated by bubbling CO2 in water in this study. The carbonated FA was adopted as a fire-proofing filler in silicone rubber (SR). The surface properties and compositional changes of FA by carbonation were thoroughly examined. Mechanical and thermal properties of carbonated FA-filled SR were evaluated. In particular, the gas torch test confirmed that the carbonation of FA increased the penetration time of SR composites by 11%. In addition, the penetration time of the carbonated FA-filled SR composite was 2-3 times greater than that of the composites filled with commercially available fillers.

Synergistic Effects of Hybrid Carbonaceous Fillers of Carbon Fibers and Reduced Graphene Oxides on Enhanced Heat-Dissipation Capability of Polymer Composites.

In this study, we investigated the synergistic effects of thermally conductive hybrid carbonaceous fillers of mesophase pitch-based carbon fibers (MPCFs) and reduced graphene oxides (rGOs) on the thermal conductivity of polymer matrix composites. Micro-sized MPCFs with different lengths (50 µm, 200 µm, and 6 mm) and nano-sized rGOs were used as the thermally conductive fillers used for the preparation of the heat-dissipation polymer composites. For all MPCF fillers with a different length, the thermal conductivity values of the MPCF/epoxy composites were proportional to the MPCF length and loading amount (0-50 wt%) of MPCFs. For an MPCF:rGO weight ratio of 49:1 (total loading amount of 50 wt%), the thermal conductivity values of MPCF-rGO/epoxy composites loaded with MPCFs of 50 µm, 200 µm, and 6 mm increased from 5.56 to 7.98 W/mK (approximately 44% increase), from 7.36 to 9.80 W/mK (approximately 33% increase), and from 11.53 to 12.58 W/mK (approximately 9% increase) compared to the MPCF/epoxy composites, respectively, indicating the synergistic effect on the thermal conductivity enhancement. The rGOs in the MPCF-rGO/epoxy composites acted as thermal bridges between neighboring MPCFs, resulting in the formation of effective heat transfer pathways. In contrast, the MPCF-rGO/epoxy composites with MPCF:rGO weight ratios of 48:2 and 47:3 decreased the synergistic effect more significantly compared to rGO content of 1 wt%, which is associated with the agglomeration of rGO nanoparticles. The synergistic effect was inversely proportional to the MPCF length. A theoretical approach, the modified Mori-Tanaka model, was used to estimate the thermal conductivity values of the MPCF-rGO/epoxy composites, which were in agreement with the experimentally measured values for MPCF-rGO/epoxy composites loaded with short MPCF lengths of 50 and 200 µm.

Effective Heat Transfer Pathways of Thermally Conductive Networks Formed by One-Dimensional Carbon Materials with Different Sizes.

We investigated the heat transfer behavior of thermally conductive networks with one-dimensional carbon materials to design effective heat transfer pathways for hybrid filler systems of polymer matrix composites. Nano-sized few-walled carbon nanotubes (FWCNTs) and micro-sized mesophase pitch-based carbon fibers (MPCFs) were used as the thermally conductive materials. The bulk density and thermal conductivity of the FWCNT films increased proportionally with the ultrasonication time due to the enhanced dispersibility of the FWCNTs in an ethanol solvent. The ultrasonication-induced densification of the FWCNT films led to the effective formation of filler-to-filler connections, resulting in improved thermal conductivity. The thermal conductivity of the FWCNT-MPCF hybrid films was proportional to the MPCF content (maximum thermal conductivity at an MPCF content of 60 wt %), indicating the synergistic effect on the thermal conductivity enhancement. Moreover, the MPCF-to-MPCF heat transfer pathways in the FWCNT-MPCF hybrid films were the most effective in achieving high thermal conductivity due to the smaller interfacial area and shorter heat transfer pathway of the MPCFs. The FWCNTs could act as thermal bridges between neighboring MPCFs for effective heat transfer. Furthermore, the incorporation of Ag nanoparticles of approximately 300 nm into the FWCNT-MPCF hybrid film dramatically enhanced the thermal conductivity, which was closely related to a decreased thermal interfacial resistance at the intersection points between the materials. Epoxy-based composites loaded with the FWCNTs, MPCFs, FWCNT-MPCF hybrids, and FWCNT-MPCF-Ag hybrid fillers were also fabricated. A similar trend in thermal conductivity was observed in the polymer matrix composite with carbon-based hybrid films.

A palladium complex confined in a thiadiazole-functionalized porous conjugated polymer for the Suzuki-Miyaura coupling reaction.

Porous organic polymers (POPs) with well-distributed and tunable functional groups acting as ligands for specific reactions are promising supports for confining useful novel metals such as Pd, Au, and Pd. Herein, a thiadiazole-containing POP has been successfully synthesized and used for immobilizing Pd species. Pd immobilized inside the micropores (2.3 nm) of the POP material is easily prepared owing to a large amount of the strong anchoring group, thiadiazole, which is intrinsically distributed in the as-prepared POP. The rigid thiadiazole-containing polymer can stabilize the central metal rather than poisoning it. The as-prepared catalyst shows excellent catalytic activity in Suzuki-Miyaura coupling reactions under mild reaction conditions and low catalyst loading. Importantly, the intrinsically distributed thiadiazole ligands can stabilize the Pd moiety, preventing aggregation and leaching, and afford excellent catalytic lifetimes. Consequently, the catalyst can be reused 10 times without a significant loss of its catalytic activity.

Facile Analytical Methods to Determine the Purity of Titanium Tetrachloride.

We propose a simple method to investigate both the qualitative and quantitative properties of titanium tetrachloride. The selection and concentration of the employed solvent were found to be very important in the analysis of highly reactive titanium tetrachloride (TiCl4). Herein, we employed various concentrations of an acid solution to serve as a stabilizing medium. Qualitative analysis was performed via Fourier transform-infrared spectroscopy (FT-IR) and scanning electron microscope-energy dispersive spectroscopy (SEM-EDS). Additionally, the quantitative analysis was performed via inductively coupled plasma optical emission spectroscopy (ICP-OES). We concluded that both the qualitative and quantitative properties of titanium tetrachloride could be easily measured using a specific acidic solvent as a medium.

Correction: Efficient planar n-i-p type heterojunction flexible perovskite solar cells with sputtered TiO2 electron transporting layers.

Correction for 'Efficient planar n-i-p type heterojunction flexible perovskite solar cells with sputtered TiO2 electron transporting layers' by Sawanta S. Mali et al., Nanoscale, 2017, DOI: 10.1039/c6nr09032j.

Efficient planar n-i-p type heterojunction flexible perovskite solar cells with sputtered TiO2 electron transporting layers.

The development of hybrid organo-lead trihalide perovskite solar cells (PSCs) comprising an electron transporting layer (ETL), a perovskite light absorber and a hole transporting layer (HTL) has received significant attention for their potential in efficient PSCs. However, the preparation of a compact and uniform ETL and the formation of a uniform light absorber layer suffer from a high temperature processing treatment and the formation of unwanted perovskite islands, respectively. A low temperature/room temperature processed ETL is one of the best options for the fabrication of flexible PSCs. In the present work, we report the implementation of a room temperature processed compact TiO2 ETL and the synthesis of extremely uniform flexible planar PSCs based on methylammonium lead mixed halides MAPb(I1-xBrx)3 (x = 0.1) via RF-magnetron sputtering and a toluene dripping treatment, respectively. The compact TiO2 ETLs with different thicknesses (30 to 100 nm) were directly deposited on a flexible PET coated ITO substrate by varying the RF-sputtering time and used for the fabrication of flexible PSCs. The photovoltaic properties revealed that flexible PSC performance is strongly dependent on the TiO2 ETL thickness. The open circuit voltage (VOC) and fill factor (FF) are directly proportional to the TiO2 ETL thickness while the 50 nm thick TiO2 ETL shows the highest current density (JSC) of 20.77 mA cm-2. Our controlled results reveal that the room temperature RF-magnetron sputtered 50 nm-thick TiO2 ETL photoelectrode exhibits a power conversion efficiency (PCE) in excess of 15%. The use of room temperature synthesis of the compact TiO2 ETL by RF magnetron sputtering results in an enhancement of the device performance for cells prepared on flexible substrates. The champion flexible planar PSC based on this architecture exhibited a promising power conversion efficiency as high as 15.88%, featuring a high FF of 0.69 and VOC of 1.108 V with a negligible hysteresis under AM 1.5 G illumination. Furthermore, the mechanical bending stability revealed that the fabricated devices show stable PCE up to 200 bending cycles. The interface properties revealed that the 50 nm thick TiO2 ETL provides superior charge injection characteristics and low internal resistance. The present work provides a simplistic and reliable approach for the fabrication of highly efficient stable flexible perovskite solar cells.

A solution processed nanostructured p-type NiO electrode for efficient inverted perovskite solar cells.

Here we report a solution processed nanostructured NiO as a hole transport layer (HTL) for efficient inverted MAPb(I1-xBrx)3 (x = 0.3) perovskite solar cells (PSCs). The best performing p-i-n PSC exhibits 15.35% power conversion efficiency with a current density (JSC) of 19.85 mA cm-2, an open circuit voltage (VOC) of 1.056 V and a fill factor (FF) of 0.73. The developed method is simple and cost effective.

Electro-Catalytic Activity of RuO2-IrO2-Ta2O5 Mixed Metal Oxide Prepared by Spray Thermal Decomposition for Alkaline Water Electrolysis.

Oxygen evolution reaction for alkaline water electrolysis was studied using various mixed metal oxide catalysts. Mixed metal oxide electrodes consisting of RuO2, IrO2, and Ta2O5 with various ratios on a titanium substrate were prepared by spray thermal decomposition. The crystallinity of the synthesized catalyst was investigated via X-ray diffraction, and the oxidation state of each component was determined using X-ray photoelectron spectroscopy (XPS). Surface morphology was investigated by scanning electron microscopy, and the roughness factor was determined by cyclic voltammetry (CV) in 1 M H2SO4. Electo-catalytic activity for oxygen evolution reaction was measured by cyclic voltammetry (CV) in 1 M KOH at room temperature, and it was found to be strongly dependent.on composition of catalyst. Among all electrodes tested, catalyst with a composition of Ru:Ir:Ta = 1:2:2.5 exhibited the highest current density of 100 mA cm(-2) at 1.67 V, corresponding to an overpotential of 0.44 V.

Preparation and Characterization of Nanostructured Manganese Oxide for Supercapacitors.

Nanostructured manganese oxides were synthesized by a sol-gel method using manganese acetate (MnAc2) and citric acid (C6H8O7,) as precursors, and characterized by Brunauer-Emmett-Teller (BET) analysis, Barrett-Joyner-Halenda (BJH), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The nano-rod structure of MnO2 developed gradually when the calcination temperature varied from 380 to 580 degrees C. As the pH increased, the pore size increased, while the specific surface area decreased. The effects of the pH and calcination temperature on the electrochemical properties of the nano-MnO2 electrode, including the supercapacitive behavior, were investigated by cyclic voltammetry (CV) tests. The tests were performed between 0 and 0.8 V versus Ag/AgCl in 1 M Na2SO4 electrolyte at various scan rates (10-200 mVs(-1)). The specific capacitance of the SP-380 sample, prepared at pH 6, was equal to 269.3 Fg(-1). After 300 cycles, approximately a 3.4% increase of the specific capacitance was measured, confirming the excellent cyclability.

Fabrication and Characterization of Amorphous Cobalt-Doped Molybdenum Sulfide for Hydrogen Evolution Reaction.

In the present study, hydrogen evolution reaction (HER) by alkaline water electrolysis was conducted without using a precious metal catalyst. We synthesized an amorphous cobalt-doped molybdenum sulfide by electrodeposition using different cobalt loadings. The amorphous Co-MoSx produced was characterized by scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The cobalt doping and sulfidation procedure resulted in the successful fabrication of a candidate catalyst for the catalytic hydrogen evolution in alkaline solution with high intrinsic activity. Cobalt incorporated amorphous MoSx exhibited 3 times higher HER activity than non-promoted MoSx.

Synthesis and Electrochemical Analyses of Manganese Oxides for Super-Capacitors.

δ-Phase and α-phase manganese oxides were prepared using a hydrothermal method and their electrochemical properties were characterized. The influence of calcination temperature on the properties of manganese oxides was studied. Crystallinities were studied by X-ray diffraction, and scanning and transmission electron microscopy were utilized to examine morphologies. Average pore sizes and specific surface areas of samples were analyzed using the Barret-Joyner-Halenda and Brunauer-Emmett-Teller methods, respectively. After calcination in the range 300 degrees C to 600 degrees C, changes in morphology and crystallinity were observed. The flower-like shape of as synthesized samples became nanorod-like and the δ-phase changed to the α-phase. These changes may have been due to the removal of water during calcination. Furthermore, a transition stage in which the two phases coexisted was observed. Synthesized manganese oxides were mixed with carbon by sonification, to increase electric conductivity and to induce a synergistic effect between pseudo-capacitor and electric double layer capacitor (EDLC). Specific capacitances and rate durability of each composite were investigated by cyclic voltammetry in 1 M Na2SO4 electrolyte at different scan rates. MnO2 calcined at 400 degrees C exhibited the highest capacitance, probably due to its high surface area and more porous structure.