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Nafion, a perfluoro-sulfonic acid (PFSA)-based polymer, is a promising material that will help realize the commercialization of proton exchange membrane-based fuel cells (PEMFCs) and proton exchange membrane water electrolyzers (PEMWEs). However, Nafion also exhibits reduced mechanical and dimensional stability and increased hydrogen crossover under cell operating conditions in real operational settings, that is, in a hydrated state or in water at 60–80 °C. These factors may negatively affect cell efficiency and durability and thus must be addressed. To overcome these limitations, polyamide-coated Nafion composite membranes were developed for the first time via interfacial polymerization. 3,5-Diaminobenzoic acid (DABA), which contains carboxyl functional groups, was used as a monomer to add hydrophilicity to the membrane, and the coating layer thickness was controlled by adjusting the DABA content. A nanoscale polyamide (PA) layer was coated on the surface of Nafion-212 to fabricate a membrane, PA-c3-Nafion. PA-c3-Nafion was found to show ion conductivity 13.6% higher than that of a pristine Nafion-212 membrane at 80 °C, while providing improved mechanical performance and dimensional stability. In particular, at 95% RH, the hydrogen permeability of PA-c3-Nafion was 16.4% lower than that of Nafion-212 while, in a fully hydrated state, the hydrogen permeability of PA-c3-Nafion was 21.2% lower than that of Nafion-212. The LSV test results also showed that the degree of hydrogen crossover was significantly lower in PA-c3-Nafion than in Nafion-212.

As hydrogen emerges as a next-generation clean energy source, the production of hydrogen is generating much research interest. Water electrolysis, one of the promising methods of hydrogen production, has the advantage of no resource depletion or carbon dioxide emissions. In this study, a Pt@C core–shell catalyst in which an N-containing carbon layer covers individual Pt nanoparticles was applied to the hydrogen evolution reaction (the cathodic reaction of water electrolysis), and the effect of the carbon shell on the activity and stability of the catalyst was investigated. The catalyst was synthesized by simple annealing of Pt-aniline complexes at 600 °C in a N2 atmosphere. The thermal decomposition of aniline during annealing resulted in N-containing carbon shells. The carbon shell had a positive effect on both the activity and stability of the catalyst in the hydrogen evolution reaction. Graphitic N and pyridinic N on the carbon shell, along with Pt, served as active sites for the hydrogen evolution reaction, increasing the catalytic activity. The carbon shell also effectively protected the Pt core from dissolution and agglomeration while allowing the transport of the reactant protons through the shell, improving stability with minimal loss of catalytic activity.

Development of an efficient and stable electrocatalyst for the oxygen evolution reaction (OER) is crucial to generate hydrogen via water splitting as a sustainable fuel. Nickel iron layered double hydroxides (NF-LDHs) are considered the most promising electrocatalysts for alkaline water oxidation among various low-cost transition metal-based electrocatalysts although exact mechanisms are still on debate. Herein, we disclose that quaternary multimetallic Ni–Fe–Al–Co LDHs (NFAC-MELDHs) function as one of the best catalysts for alkaline as well as seawater oxidation due to the synergetic effects among the four different redox-flexible metals. The multimetallic Ni–Fe–Al–Co LDHs are prepared via the metal–organic framework (MOF)-derived electrochemical incorporation of fourth transition metal (Co) into ternary Ni–Fe–Al LDHs grown by a hydrothermal reaction. Moreover, we reveal an exact electrocatalytic mechanism for the OER in NFAC-MELDHs via ex situ spectroscopies in combination with density functional theory (DFT) calculations. Redox-flexible Fe is identified with a real active site in synergy with the neighboring metals stabilizing adsorption of oxygen intermediates and simultaneously facilitating charge transfer. In consequence, NFAC-MELDHs exhibit one of the lowest overpotentials of 220 and 280 mV for affording a current density of 100 mA cm−2 in alkaline and simulating seawater solutions, respectively. More importantly, activity and stability merits in electrocatalysis for the OER are improved in the sequence of unary, binary, ternary, and quaternary LDHs, implying that catalyst design using multimetals for LDHs is a highly promising strategy.

Nafion, as a perfluorosulfonic acid (PFSA)-based polymer, is a key material that contributes to the commercialization of proton exchange membrane fuel cells (PEMFCs). The high dependence on relativ...

Cobalt–iron sulfides supported on N-doped carbon were synthesized as energy storage material using ball milling followed by carbonization. As-synthesized materials were structurally analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. Furthermore, cobalt–iron sulfides supported on N-doped carbon were coated on Ni foam, and their electrochemical performance was tested in a 3-M KOH electrolyte. The as-fabricated Co–Fe–S-2 electrode registered a specific capacitance of 1252 F g−1 at 1 A g−1 and also showed capacitance retention of 66.4% at 20 A g−1. In addition, asymmetric supercapacitors (ASC) were fabricated using the as-synthesized electrode materials and it had a voltage window of 0–1.6 V. Among them, the activated carbon (AC)//Co–Fe–S-2 ASC device showed maximum specific capacitance of 169.3 F g−1 at 1 A g−1, and it registered maximum energy density of 59.6 Wh kg−1 at power density of 0.796 kW kg−1. The AC//Co–Fe–S-2 device delivered a rate capability of 55.6% at 30 A g−1, and it reveals a capacitance retention of 76.3% over 5000 cycles. Herein we also found that ball-milling-assisted synthesis of Co–Fe–S-2 electrode material is a promising candidate for high-performance ASCs.

The key to popularizing proton exchange fuel cells is developing highly active, stable, and cost-effective catalysts for oxygen reduction reaction. Pd is considered as an alternative to Pt due to its high tolerance to poisoning and electronic similarity with Pt, which is a robust but expensive catalyst. However, its vulnerability to dissolving in acidic media prevents the use of Pd as an oxygen reduction reaction catalyst. In this study, a facile synthesis method was developed to prepare a carbon-encapsulated Pd catalyst using aniline. The oxidative polymerization of aniline with a Pd precursor formed Pd nanoparticles embedded in a rod-shaped polyaniline matrix. The polyaniline matrix was carbonized using heat treatment, which then acted as a source of N-containing carbon layer that protects Pd nanoparticles from dissolution and improves oxygen reduction reaction activity. The stability and oxygen reduction reaction activity of the synthesized Pd catalyst were strongly dependent on the heat treatment temperature. The Pd catalysts heat-treated at 300 °C and 500 °C exhibited improved activity and stability as compared to commercial Pd/C. We envision that this method is suitable for mass production of active and stable oxygen reduction reaction catalysts in proton exchange fuel cells.

We report semi-interpenetrating polymer network (semi-IPN) membranes prepared easily from a cross-linked network using poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) with interpenetrated Nafion for both proton-exchange membrane fuel cell (PEMFC) and proton-exchange membrane water electrolyzer (PEMWE) applications. Thermal esterification between PAA and PVA induced three-dimensional cross-linking to improve mechanical toughness and reduce hydrogen crossover, while the hydrophilic nature of the PAA-PVA-based cross-linked matrix still enhanced the water uptake (WU) and hence conductivity of the Nafion penetrant. The semi-IPN membrane (NPP-95) composed of Nafion, PAA, and PVA with a ratio of 95:2.5:2.5 showed a hexagonal cylindrical morphology and improved thermal, mechanical, and dimensional stability compared to a recast Nafion membrane (re-Nafion). The membrane was also highly effective at managing water due to its low WU and high conductivity. Furthermore, its hydrogen permeability was 49.6% lower than that of re-Nafion under the actual fuel cell operating conditions (at 100% RH and 80 °C). NPP-95 exhibited significantly improved conductivity and PEMFC performance compared to re-Nafion with a current density of 1561 mA/cm2 at a potential of 0.6 V and a peak power density of 1179 mW/cm2. Furthermore, in the PEMWE performances, NPP-95 displayed about a 1.5-fold higher current density of 4310 mA/cm2 at 2.0 V and much lower ohmic resistance than re-Nafion between 60 and 80 °C.

Methanol crossover is one of the largest problems in direct methanol fuel cells (DMFCs). Methanol passing from the anode to the cathode through the membrane is oxidized at the cathode, degrading the DMFC performance, and the intermediates of the methanol oxidation reaction (MOR) cause cathode catalyst poisoning. Therefore, it is essential to develop a cathode catalyst capable of inhibiting MOR while promoting the oxygen reduction reaction (ORR), which is a typical cathode reaction in DMFCs. In this study, a carbon-encapsulated Pt cathode catalyst was synthesized for this purpose. The catalyst was simply synthesized by heat treatment of Pt-aniline complex-coated carbon nanofibers. The carbon shell of the catalyst was effective in inhibiting methanol from accessing the Pt core, and this effect became more prominent as the graphitization degree of the carbon shell increased. Meanwhile, the carbon shell allowed O

In this study, we design and synthesize a new host and two new highly efficient green-emitting heteroleptic Ir(III) complexes. These new materials are based on an amide-bridged, trifluromethyl-substituted, phenylpyridine skeleton with a longer alkyl chain as the main ligand, and on a phosphine oxide containing symmetrical dipyridinylphosphinate and asymmetrical phenyl(pyridin-2-yl)phosphinate as ancillary ligands. Their thermal, photophysical, electrochemical, and electroluminescent (EL) properties are fully investigated. The solution-processed green devices were fabricated using bis[5-ethylhexyl-8-trifluoromethyl-5H-benzo(c)(1,5)naphthyridin-6-one](dipyridinylphosphinate)iridium(III) as dopant, and (4′-(9H-carbazol-9-yl)-[1,1′-biphenyl]-4-yl)di-o-tolylphosphine oxide (m-CBPPO1) and TPBi as hosts. The optimized devices containing a symmetrical-type ancillary ligand show excellent EL performance with a maximum current efficiency (CEmax) of 68.72 cd A−1 and a maximum external quantum efficiency (EQEmax) of 20.82% without compromising the color purity. This is one of the best reported CEmax values with high EQE for solution-processed phosphorescent organic light-emitting diodes (PHOLEDs). To the best of our knowledge, this is the first report on green solution-processed PHOLEDs with EQE over 20% by using phosphine oxide functionalized symmetrical type ancillary ligand. Furthermore, these devices with symmetrical Ir(III) complexes show better device stability than that of asymmetrical Ir(III) complexes, which is attributed to the formation of undesirable isomers in asymmetrical complexes.

An efficient synthesis of nitrogen and sulfur co-doped graphene-like carbon sheets from coir pith bio-waste through the mechanical activation method is reported in this study. The structural characterization reveals the presence of a graphene-like carbon sheet, which is uniformly doped with nitrogen and sulfur atoms in a carbon network. The nitrogen and sulfur co-doped graphene-like carbon sheets (NSG) has amorphous nature with a defective porous carbon structure and it depicts the maximum specific capacitance of 247.1 F g−1 at 0.2 A g−1 and a capacitance retention of 75.2% at 10 A g−1. The synthesized NSG-10 registered a maximum energy density of 33.6 Wh kg−1 at 0.2 A g−1 and shows the maximum power density of 4220.0 W kg−1 at 10.0 A g−1. Furthermore, a symmetric supercapacitor (SSC) device shows the device capacitance of 33.7 F g−1 at 0.2 A g−1 when operated at 1.0 V. The SSC device gives a capacitance retention of 82.0% at 10 A g−1 and reveals an excellent stability with no losses in capacitance with 100% columbic efficiency over 10,000 cycles. The results suggest that the proposed methodology is a simple and unique way to synthesize heteroatoms-doped graphene-like carbon sheets from biomass materials for a supercapacitor.

In this study, the facile and direct formation of platinum catalyst on a carbon paper (gas diffusion layer) via the sonochemical deposition method is demonstrated. An ultrasound irradiation with a carbon paper substrate in a platinum precursor solution formed interconnected platinum grains on the carbon paper surface. The surface morphology and deposition amount of platinum were strong functions of both ultrasound parameters (power and time) and solution composition. The platinum-deposited carbon paper was then directly used as a gas diffusion electrode in PEMFC without adding the ionomer. This exhibited high stability in the accelerated stress test in a single cell operation. The interconnected grains of platinum on carbon paper had high resistance to dissolution in an oxidizing environment and the absence of carbon support also enhanced resistance to carbon oxidation. Although the overall performance did not exceed that of the commercial Pt/C, this approach may be an option to form a stable platinum catalyst for PEMFCs.

A novel approach to fluorine-rich carbon (FC) shell formation on an electron-rich metal surface based on the electronegativity concept is reported. Basically, highly electronegative elements are strongly attracted by low electronegative/electron-rich elements through dipole interaction, which leads to the formation of fluorine-rich carbon shells on metals at various fluorine quantities. Herein, nitrogen-rich hollow carbon spheres decorated with fluorine-rich carbon shell covered metals (FC@M/NHCS, M = Fe, Co, and FeCo) were synthesized by co-polymerization on SiO2, adsorption of metal precursors, and etching of the SiO2, followed by sintering. The fluorine content, quantified by XPS and SEM-EDS studies, decreased according to FeCo > Fe > Co in FC@M/NHCS. HAADF-STEM elemental mapping studies clearly confirmed fluorine-rich carbon shell formation on the metal surface. The influence of fluorine content order in the as-synthesized materials was reflected in their capacitance performances. FC@FeCo/NHCS electrode depicted the maximum specific capacitance of 302.0 F g−1 at 0.2 A g−1 in 6 M KOH medium, delivering excellent stability with no losses over 5000 cycles at 5 A g−1. The symmetric supercapacitor (SSC) devices operated at 1.5 V by delivering maximum device specific capacitance of 51.2 F g−1 at 0.2 A g−1. It exhibited 81.3% of capacitance retention at 10 A g−1 with the FC@FeCo/NHCS. The maximum energy density of 15.3 W h kg−1 at 0.2 A g−1 and the maximum power density of 5100 W kg−1 at 10 A g−1 were delivered by the FC@FeCo/NHCS device. This study provides an ideal way for synthesizing fluorine-rich carbon materials for high energy storage/conversion applications.

Background Metabolic syndrome is associated with cardiovascular diseases and is characterized by insulin resistance. Recent studies suggest that the triglyceride/high-density lipoprotein cholesterol (TG/HDLC) ratio predicts insulin resistance better than individual lipid levels, including TG, total cholesterol, low-density lipoprotein cholesterol (LDLC), or HDLC. We aimed to elucidate the relationship between the TG/HDLC ratio and metabolic syndrome in the general Korean population. Methods We evaluated the data of adults ≥20 years old who were enrolled in the Korean National Health and Nutrition Examination Survey in 2013 and 2014. Subjects with angina pectoris, myocardial infarction, stroke, or cancer were excluded. Metabolic syndrome was defined by the harmonized definition. We examined the odds ratios (ORs) of metabolic syndrome according to TG/HDLC ratio quartiles using logistic regression analysis (SAS ver. 9.4; SAS Institute Inc., Cary, NC, USA). Weighted complex sample analysis was also conducted. Results We found a significant association between the TG/HDLC ratio and metabolic syndrome. The cutoff value of the TG/HDLC ratio for the fourth quartile was ≥3.52. After adjustment, the OR for metabolic syndrome in the fourth quartile compared with that of the first quartile was 29.65 in men and 20.60 in women (P

Performance of a polymer electrolyte membrane fuel cell with a Pd cathode catalyst was systemically investigated in this study. The Pd catalyst was directly formed on a gas diffusion layer by using electrodeposition (Pd/GDL). The electrodeposition formed aggregates of Pd nanoparticles on a gas diffusion layer with the preferred orientation of Pd(111) and Pd(200). In addition, the Pd aggregates mainly formed on the top surface of the gas diffusion layer. The membrane electrode assembly was fabricated with Pd/GDL as the cathode. The performance of the membrane electrode assembly was investigated by varying hot pressing parameters and back pressures, and the operating condition for the polymer electrolyte membrane fuel cell was optimized. Notably, introducing back pressure increased operating current density at 0.6 V by up to 45%. Durability of the membrane electrode assembly was also examined. Negligible deterioration of surface morphology of the Pd catalyst was observed even after accelerated stress testing, except for a slight increase in particle size. The results indicate that deterioration of the Pd cathode catalyst was not a major factor affecting overall single-cell performance degradation.

The enantioselective synthesis of quaternary carbon stereocenters and application to natural products has been a formidable challenge to synthetic organic chemists. Ways to quaternary stereocenters are demanded very much given the prevalence of the centers in various attractive natural products. One of the most promising methods for the purpose is the Pd-catalyzed alkylation of prochiral stabilized enolates. Although these methods have been useful, regioselectivity can be meet only in the case of single acidic site or a large pKa difference between two acidic sites to prevent the mixture formation. Instead, Tsuji allylation pathway from allyl enol carbonates which would be formed regioselectively by controlled methods prevented the production of mixtures of allylated products and allowed the neutral reaction conditions to yield good to excellent selectivity. Recently, we published the stereoselective synthesis of (-)mesembrane 1 which contains a quarternary center. Mesembrane 1 is a well known member of the Sceletium alkaloids, which has the basic structural element of cis-3a-aryloctahydroindole skeleton 2 (Figure 1). In the previous synthesis, we have applied desymmetrization of 1,3-dicarbonyl groups of cyclohexadione by intramolecular condensation with chiral amides. The maximum selectivity was moderately 3:1. So, we wanted to find out the strategy which would afford enhanced selectivity, and decided to combine Tsuji asymmetric allylation and the resoluting condensation step using a proper chiral auxilary. In the condensation step, it is anticipated that the energy difference of the diastereomeric aminol intermediates formed from attack of chiral amide to carbonyl group presumably would cause the difference of formation rates and the final production yields. We should find out the matching chiral auxiliary which would result in optimum resolution in the cyclization process to afford the desired isomer with better selectivity (Scheme 1). First, in the condensation reaction of chiral amide and carbonyl group of 7, we wanted to see how much resoluting selectivity would be generated through diastereomeric aminol intermediate (Table 1). The inseparable amide ketone diastereomers 7 could be prepared by employing the known procedure from 3. Cyclization has been found to proceed best in toluene at 65 C in the presence of TsOH. Among four chiral auxiliaries selected for the preparation of 7, two (Entry 1 and 2) provided 2:1 selectivity in 50 and 70% yields. Although the selectivity was moderate, we expected that this step would be helpful to increase the selectivity as an ancillary step and provide a known chiral intermediate. We have tried asymmetric allylation of allyl enol carbonate 9 to find out the optimum condition including the best chiral ligand. The required intermediate 9 was prepared from 3 by the reaction with allyl chloroformate in 67% yield as a single isomer. Various reaction conditions have been adopted in the allylation reaction using several known chiral ligands. And we found that (R,R)-ANDEN-phenyl Trost ligand 11 (5.5 mol %) afforded the best selectivity 83:17 in 58% yield in toluene at −78 C in the presence of Pd2(dba)3 (2.5 mol %). The isomeric ratio was determined by chiral HPLC column chromatography (Scheme 2). At this stage the absolute configuration of the quarternary center could not be determined

We have examined the hydrolysis reaction of Na atoms at the surface of thin water−ice films by using the techniques of Cs+ reactive ion scattering and low energy sputtering. Na atoms are adsorbed onto amorphous D2O−ice films, and the reaction products formed at the ice film surfaces are examined for ionic (both positive and negative) species as well as neutral molecules for the temperature range of 95−135 K and Na coverage below the multilayer regime. The hydrolysis reaction produces isolated sodium and hydroxide ions as well as a sodium hydroxide molecule. Efficient solvation of these products by water molecules at high temperature alters their distribution near the ice film surface. Hydroxide ions tend to reside at the film surface, whereas sodium ions migrate to the film interior. NaOD molecules are efficiently solvated by water molecules at high temperature, but a substantial portion of the molecules remains undissociated.

We studied the interactions of CO2 with ice films prepared in either a neutral or basic condition, with emphasis on the examination of feasibility for the reaction between CO2 and hydroxide ion present at the ice surfaces. To this end, Cs+ reactive ion scattering (RIS) and low-energy sputtering (LES) techniques were used to scrutinize the chemical species present at the surfaces, in conjunction with temperature-programmed desorption (TPD) to monitor the desorbing species. Ice films were grown in a nonporous amorphous phase or a crystalline phase. Excess hydroxide ions were added onto the ice film surfaces by the hydrolysis of Na atoms. TPD experiments showed that CO2 molecules desorbed from the ice film surfaces before the onset of water sublimation near 140 K, regardless of the presence or absence of excess hydroxide ions. CO2 adsorption did not produce CO2−water complexes nor hydrolysis products on both film surfaces in the temperature range 80−180 K. The nonreactivity of CO2 toward hydroxide ion at the...

We have studied the adsorption and dissolution phenomena of sodium halide salts (NaF, NaCl, and NaBr) at the surface of amorphous D2O−ice films for the temperature range 105−140 K by the techniques of low-energy sputtering, reactive ion scattering, and temperature-programmed desorption mass spectrometry. These salts readily dissociate to ions at the ice surface. The dissociated Na+ and F- ions migrate from the surface to the interior at temperatures above 125 K, while Cl- and Br- ions stay at the surface, leading to the spatial separation of ions near the ice surface. Br- shows a slightly higher propensity for residing at the surface than Cl-, most likely due to its less efficient solvation by surface water molecules. The ion separation process is driven by thermodynamic forces specific to the ions. The speed of ion migration depends strongly on ice temperature, indicating that the ion motion is limited by the diffusion of water molecules.

We studied the interaction of SO2 with ice films at temperatures above 80 K, with emphasis on the examination of the precursor states of SO2 hydrolysis, or SO2 surface complexes. Cs+ reactive ion scattering (RIS) and low energy sputtering (LES) techniques were used to examine the surface reaction products, in conjunction with temperature-programmed desorption (TPD) to monitor the desorbing species. The study indicated that the reaction of SO2 with the ice surface occurred through several distinct intermediate states, including a solvated SO2 species, a DSO2 species, and a strongly ionic molecular species, and these intermediates could be isolated on the ice surface due to kinetic trapping.

The effect of hydroxide ions on proton transfer and H/D isotopic exchange of water molecules was examined at the surface of amorphous ice films at temperatures of 92-140 K. Excess hydroxide ions were provided onto a D(2)O-ice film by the hydrolysis of Na atoms, and H(2)O was adsorbed onto the surface for a submonolayer coverage. The H/D isotopic exchange between H(2)O and D(2)O molecules on the ice film surface was monitored as a function of reaction time and temperature by using the techniques of reactive ion scattering and low-energy sputtering. The result was compared with that obtained on a hydroxide-free ice film. At a temperature of 92 K, proton transfer occurred from water mostly to adjacent hydroxide ions. The proton transfer distance and the H/D exchange reaction rate increased with increase in temperature above 105 K. The H/D exchange reaction propagated to several water molecules on the surface at 100-120 K. Kinetic measurement in this temperature range deduced the Arrhenius activation energy for the reaction, E(a) = 9.6+/-2.0 kJ mol(-1). The study shows that hydroxide ions promote the H/D exchange reaction on the ice surface compared with that on a hydroxide-free ice surface, but the promotion effect is moderate and the H/D exchange occurs on a substantial energy barrier. It is suggested that the stabilization of hydroxide ions at the ice surface produces an energy barrier for the proton transfer.

We have examined the elementary molecular processes responsible for proton transfer and HD exchange in thin ice films for the temperature range of 100-140 K. The ice films are made to have a structure of a bottom D(2)O layer and an upper H(2)O layer, with excess protons generated from HCl ionization trapped at the D(2)OH(2)O interface. The transport behavior of excess protons from the interfacial layer to the ice film surface and the progress of the HD exchange reaction in water molecules are examined with the techniques of low energy sputtering and Cs(+) reactive ion scattering. Three major processes are identified: the proton hopping relay, the hop-and-turn process, and molecular diffusion. The proton hopping relay can occur even at low temperatures (120 K), and it transports a specific portion of embedded protons to the surface. The hop-and-turn mechanism, which involves the coupling of proton hopping and molecule reorientation, increases the proton transfer rate and causes the HD exchange of water molecules. The hop-and-turn mechanism is activated at temperatures above 125 K in the surface region. Diffusional mixing of H(2)O and D(2)O molecules additionally contributes to the HD exchange reaction at temperatures above 130 K. The hop-and-turn and molecular diffusion processes are activated at higher temperatures in the deeper region of ice films. The relative speeds of these processes are in the following order: hopping relayhop and turnmolecule diffusion.