Differences in the Electrochemical Performance of Pt-Based Catalysts Used for Polymer Electrolyte Membrane Fuel Cells in Liquid Half- and Full-Cells.

A substantial amount of research effort has been directed toward the development of Pt-based catalysts with higher performance and durability than conventional polycrystalline Pt nanoparticles to achieve high-power and innovative energy conversion systems. Currently, attention has been paid toward expanding the electrochemically active surface area (ECSA) of catalysts and increase their intrinsic activity in the oxygen reduction reaction (ORR). However, despite innumerable efforts having been carried out to explore this possibility, most of these achievements have focused on the rotating disk electrode (RDE) in half-cells, and relatively few results have been adaptable to membrane electrode assemblies (MEAs) in full-cells, which is the actual operating condition of fuel cells. Thus, it is uncertain whether these advanced catalysts can be used as a substitute in practical fuel cell applications, and an improvement in the catalytic performance in real-life fuel cells is still necessary. Therefore, from a more practical and industrial point of view, the goal of this review is to compare the ORR catalyst performance and durability in half- and full-cells, providing a differentiated approach to the durability concerns in half- and full-cells, and share new perspectives for strategic designs used to induce additional performance in full-cell devices.

Additional Lithium Storage on Dynamic Electrode Surface by Charge Redistribution in Inactive Ru Metal.

Beyond a traditional view that metal nanoparticles formed upon electrochemical reaction are inactive against lithium, recently their electrochemical participations are manifested and elucidated as catalytic and interfacial effects. Here, ruthenium metal composed of ≈5 nm nanoparticles is prepared and the pure ruthenium as a lithium-ion battery anode for complete understanding on anomalous lithium storage reaction mechanism is designed. In particular, the pure metal electrode is intended for eliminating the electrochemical reaction-derived Li2 O phase accompanied by catalytic Li2 O decomposition and the interfacial lithium storage at Ru/Li2 O phase boundary, and thereby focusing on the ruthenium itself in exploring its electrochemical reactivity. Intriguingly, unusual lithium storage not involving redox reactions with electron transfer but leading to lattice expansion is identified in the ruthenium electrode. Size-dependent charge redistribution at surface enables additional lithium adsorption to occur on the inactive but more environmentally sensitive nanoparticles, providing innovative insight into dynamic electrode environments in rechargeable lithium chemistry.

Multidimensional Anodized Titanium Foam Photoelectrode for Efficient Utilization of Photons in Mesoscopic Solar Cells.

Mesoscopic solar cells based on nanostructured oxide semiconductors are considered as a promising candidates to replace conventional photovoltaics employing costly materials. However, their overall performances are below the sufficient level required for practical usages. Herein, this study proposes an anodized Ti foam (ATF) with multidimensional and hierarchical architecture as a highly efficient photoelectrode for the generation of a large photocurrent. ATF photoelectrodes prepared by electrochemical anodization of freeze-cast Ti foams have three favorable characteristics: (i) large surface area for enhanced light harvesting, (ii) 1D semiconductor structure for facilitated charge collection, and (iii) 3D highly conductive metallic current collector that enables exclusion of transparent conducting oxide substrate. Based on these advantages, when ATF is utilized in dye-sensitized solar cells, short-circuit photocurrent density up to 22.0 mA cm-2 is achieved in the conventional N719 dye-I3- /I- redox electrolyte system even with an intrinsically inferior quasi-solid electrolyte.

CopA3 peptide prevents ultraviolet-induced inhibition of type-I procollagen and induction of matrix metalloproteinase-1 in human skin fibroblasts.

Ultraviolet (UV) exposure is well-known to induce premature aging, which is mediated by matrix metalloproteinase-1 (MMP-1) activity. A 9-mer peptide, CopA3 (CopA3) was synthesized from a natural peptide, coprisin, which is isolated from the dung beetle Copris tripartitus. As part of our continuing search for novel bioactive natural products, CopA3 was investigated for its in vitro anti-skin photoaging activity. UV-induced inhibition of type-I procollagen and induction of MMP-1 were partially prevented in human skin fibroblasts by CopA3 peptide in a dose-dependent manner. At a concentration of 25 µM, CopA3 nearly completely inhibited MMP-1 expression. These results suggest that CopA3, an insect peptide, is a potential candidate for the prevention and treatment of skin aging.

Redirection Strategy Switching: Selective Redirection Controller for Dynamic Environment Adaptation.

In this paper, we present the Selective Redirection Controller (SRC), which selects the optimal redirection controller based on the physical and virtual environment in Redirected Walking (RDW). The primary advantage of SRC over existing controllers is its dynamic switching among four different redirection controllers (S2C, TAPF, ARC, and SRL) based on the user's environment, as opposed to using a single fixed controller throughout the experience. By switching between redirection controllers based on the context around the user, SRC aims to optimize the advantages of each redirection strategy. The SRC model is trained using reinforcement learning to dynamically and instantaneously switch redirection controllers based on the user's environment. We evaluated the performance of SRC against traditional redirection controllers through simulations and user studies conducted in various physical and virtual environments. The findings indicate that SRC reduces the number of resets significantly compared to traditional redirection controllers. Heat map visualization was utilized during the development process to analyze which redirection controller SRC chooses based on the different environments around the user. SRC alternates between redirection techniques based on the user's environment, maximizing the advantages of each strategy for a superior RDW experience.

MARR : A Multi-Agent Reinforcement Resetter for Redirected Walking.

The reset technique of Redirected Walking (RDW) forcibly reorients the user's direction overtly to avoid collisions with boundaries, obstacles, or other users in the physical space. However, excessive resetting can decrease the user's sense of immersion and presence. Several RDW studies have been conducted to address this issue. Among them, much research has been done on reset techniques that reduce the number of resets by devising reset direction rules or optimizing them for a given environment. However, existing optimization studies on reset techniques have mainly focused on a single-user environment. In a multi-user environment, the dynamic movement of other users and static obstacles in the physical space increase the possibility of resetting. In this study, we propose Multi-Agent Reinforcement Resetter (MARR), which resets the user taking into account both physical obstacles and multi-user movement to minimize the number of resets. MARR is trained using multi-agent reinforcement learning to determine the optimal reset direction in different environments. This approach allows MARR to effectively account for different environmental contexts, including arbitrary physical obstacles and the dynamic movements of other users in the same physical space. We compared MARR to other reset technologies through simulation tests and user studies, and found that MARR outperformed the existing methods. MARR improved performance by learning the optimal reset direction for each subtle technique used in training. MARR has the potential to be applied to new subtle techniques proposed in the future. Overall, our study confirmed that MARR is an effective reset technique in multi-user environments.

Effect of Precursor Status on the Transition from Complex to Carbon Shell in a Platinum Core-Carbon Shell Catalyst.

Encapsulating platinum nanoparticles with a carbon shell can increase the stability of core platinum nanoparticles by preventing their dissolution and agglomeration. In this study, the synthesis mechanism of a platinum core-carbon shell catalyst via thermal reduction of a platinum-aniline complex was investigated to determine how the carbon shell forms and identify the key factor determining the properties of the Pt core-carbon shell catalyst. Three catalysts originating from the complexes with different platinum to carbon precursor ratios were synthesized through pyrolysis. Their structural characteristics were examined using various analysis techniques, and their electrochemical activity and stability were evaluated through half-cell and unit-cell tests. The relationship between the nitrogen to platinum ratio and structural characteristics was revealed, and the effects on the electrochemical activity and stability were discussed. The ratio of the carbon precursor to platinum was the decisive factor determining the properties of the platinum core-carbon shell catalyst.

Effect of surface segregation on the methanol oxidation reaction in carbon-supported Pt-Ru alloy nanoparticles.

Ru and Pt-Ru (Pt:Ru = 1:1) nanoparticles supported on carbon black were prepared by the borohydride reduction method using oleylamine as a stabilizer in an anhydrous ethanol solvent. We investigated the effect of Pt segregation to the surface of alloy nanoparticles on the methanol oxidation reaction (MOR). As-prepared Pt(1)Ru(1)/C showed a narrow size distribution and a relatively uniform particle distribution on a carbon support. However, its electrocatalytic activity toward the MOR was poor due to the high surface concentration of Ru. As duration time of heat treatment at 200 degrees C was increased up to 2 h, the surface composition of Pt atoms was increased without significant particle growth due to thermally induced segregation of Pt atoms, which were revealed by TEM images, X-ray photoelectron spectroscopy (XPS) analysis, changes in the potentials of zero total charge (pztc), and increase in the oxidation charge of "reduced CO(2)". In particular, from the combination of CO adlayer oxidation and "reduced CO(2)" oxidation charges, the increased surface concentration of Pt of alloy catalysts was relatively quantified when compared to its as-prepared state. Cyclic voltammograms in 0.1 M HClO(4) solution with 0.5 M methanol showed that Pt(1)Ru(1)/C annealed for 2 h at 200 degrees C in a flow of mixture gas of Ar and H(2) (5 vol %) had a less positive onset potential for the MOR. These results demonstrate a definitive contribution from segregation of Pt atoms to the MOR activity.

Effects of trunk rehabilitation with kinesio and placebo taping on static and dynamic sitting postural control in individuals with chronic stroke: A randomized controlled trial.

Background: Impaired trunk postural control is common after stroke. Combining kinesio taping with trunk rehabilitation has been shown to enhance the recovery of postural control ability in patients with stroke.Objective: We investigated whether the combination of kinesio taping with trunk rehabilitation would improve dynamic and static sitting stability after stroke.Methods: Twenty-eight patients with stroke were recruited and randomly assigned to one of the two 8-week trunk rehabilitation programs with kinesio (experimental group) or placebo taping (control group). Outcome measures were dynamic forward, dynamic backward, affected-side, and unaffected-side sway areas, static sway area and length, and the total limit of stability (LOS) area. The variables were measured using the BioRescue analysis system. All outcome measures were assessed at baseline and after 8 weeks of trunk rehabilitation.Results: Significant increases were observed in the dynamic forward, dynamic backward, affected-side, and unaffected-side sway areas, and the total LOS area, in the experimental and control groups, whereas decreases were observed in the static sway area and length. The dynamic forward sway area was significantly higher in the experimental group than in the control group, but there were no significant differences between the groups in the other variables.Conclusions: Trunk rehabilitation is effective for improving dynamic and static sitting stability after stroke. The addition of kinesio taping to the back muscles further increases forward mobility.

A nitrogen and fluorine enriched Fe/Fe3C@C oxygen reduction reaction electrocatalyst for anion/proton exchange membrane fuel cells.

Nitrogen-doped carbon-encapsulated non-noble metals are promising electrocatalytic alternatives to Pt for the oxygen reduction reaction (ORR). Herein, we describe the efficient synthesis of nitrogen- and fluorine-doped carbon-encapsulated Fe/Fe3C (NFC@Fe/Fe3C) crystals from a Fe-poly(aniline-fluoro-aniline) co-polymer and demonstrate their use as efficient ORR electrocatalysts in acidic and alkaline environments. X-ray diffraction patterns, scanning electron microscopy, transmission electron microscopy, Raman spectra, and X-ray photoelectron spectroscopy are used to determine the structural properties of NFC@Fe/Fe3C. Of the NFC@Fe/Fe3C catalysts, NFC@Fe/Fe3C-9 demonstrates superior ORR electrocatalytic activity in both alkaline and acidic environments. NFC@Fe/Fe3C-9 follows a four-electron-transfer ORR pathway in alkaline and acidic media. Under alkaline conditions, NFC@Fe/Fe3C-9 displays a half-wave potential (E1/2) as 0.870 V, which is 16 mV higher than that of Pt/C, and its durability decay is 26 mV over 50 000 cycles. In acidic medium, the NFC@Fe/Fe3C-9 electrode shows inferior ORR performance than does Pt/C, but it is more durable, with only 27 mV decay over 30 000 cycles. A single cell performance of NFC@Fe/Fe3C-9 was tested with a proton-exchange membrane fuel cells (PEMFC) and an anion-exchange membrane fuel cell (AEMFC) with an active area of 5 cm2. The PEMFC single cell exhibits the maximum power density of 237 mW cm-2 with a back pressure of 250 kPa, while the AEMFC delivers a maximum power density of 96 mW cm-2 without back pressure.

Enhancement of service life of polymer electrolyte fuel cells through application of nanodispersed ionomer.

In polymer electrolyte fuel cells (PEFCs), protons from the anode are transferred to the cathode through the ionomer membrane. By impregnating the ionomer into the electrodes, proton pathways are extended and high proton transfer efficiency can be achieved. Because the impregnated ionomer mechanically binds the catalysts within the electrode, the ionomer is also called a binder. To yield good electrochemical performance, the binder should be homogeneously dispersed in the electrode and maintain stable interfaces with other catalyst components and the membrane. However, conventional binder materials do not have good dispersion properties. In this study, a facile approach based on using a supercritical fluid is introduced to prepare a homogeneous nanoscale dispersion of the binder material in aqueous alcohol. The prepared binder exhibited high dispersion characteristics, crystallinity, and proton conductivity. High performance and durability were confirmed when the binder material was applied to a PEFC cathode electrode.

Membrane/Electrode Interface Design for Effective Water Management in Alkaline Membrane Fuel Cells.

The recent development of ultrathin anion exchange membranes and optimization of their operating conditions have significantly enhanced the performance of alkaline-membrane fuel cells (AMFCs); however, the effects of the membrane/electrode interface structure on the AMFC performance have not been seriously investigated thus far. Herein, we report on a high-performance AMFC system with a membrane/electrode interface of novel design. Commercially available membranes are modified in the form of well-aligned line arrays of both the anode and cathode sides by means of a solvent-assisted molding technique and sandwich-like assembly of the membrane and polydimethylsiloxane molds. Upon incorporating the patterned membranes into a single-cell system, we observe a significantly enhanced performance of up to ∼35% compared with that of the reference membrane. The enlarged interface area and reduced membrane thickness from the line-patterned membrane/electrode interface result in improved water management, reduced ohmic resistance, and effective utilization of the catalyst. We believe that our findings can significantly contribute further advancements in AMFCs.

PtRu/C catalyst slurry preparation for large-scale decal transfer with high performance of proton exchange membrane fuel cells.

The large-area membrane-electrode assembly (MEA) has been fabricated using the decal transfer method with a methanol (MeOH)-based PtRu/C catalyst slurry. The stability of slurry dispersion is important when using a large-area decal transfer method to ensure the integrity of the electrode. In order to prepare stable and well dispersed catalyst slurry, a suitable solvent for the PtRu/C catalyst should be selected. We considered the physical properties of various organic solvents, including ionomer solubility, dielectric constant, and catalyst particle surface physical properties. We found that the MeOH-based PtRu/C slurry dispersion showed the best stability and dispersibility of catalyst-ionomer agglomerates. It was also confirmed that the MeOH-based slurry has the most suitable characteristics for coating the slurry on the substrate film. The decal technique-based MEA using this slurry showed excellent performance when compared with the spray method-based MEA. Furthermore, the large-area PtRu/C MEA with an active area of 51.84 cm2 was fabricated and excellent performance was realized even when a reforming gas was used.

From grass to battery anode: agricultural biomass hemp-derived carbon for lithium storage.

Biomass-derived carbon, as a low-cost material source, is an attractive choice to prepare carbon materials, thus providing an alternative to by-product and waste management. Herein, we report the preparation of carbon from hemp stem as a biomass precursor through a simple, low-cost, and environment-friendly method with using steam as the activating agent. The hemp-derived carbon with a hierarchically porous structure and a partial graphitization in amorphous domains was developed, and for the first time, it was applied as an anode material for lithium-ion battery. Natural hemp itself delivers a reversible capacity of 190 mA h g-1 at a rate of 300 mA g-1 after 100 cycles. Ball-milling of hemp-derived carbon is further designed to control the physical properties, and consequently, the capacity of milled hemp increases to 300 mA h g-1 along with excellent rate capability of 210 mA h g-1 even at 1.5 A g-1. The milled hemp with increased graphitization and well-developed meso-porosity is advantageous for lithium diffusion, thus enhancing electrochemical performance via both diffusion-controlled intercalation/deintercalation and surface-limited adsorption/desorption. This study not only demonstrates the application of hemp-derived carbon in energy storage devices, but also guides a desirable structural design for lithium storage and transport.

Guided cracking of electrodes by stretching prism-patterned membrane electrode assemblies for high-performance fuel cells.

Guided cracks were successfully generated in an electrode using the concentrated surface stress of a prism-patterned Nafion membrane. An electrode with guided cracks was formed by stretching the catalyst-coated Nafion membrane. The morphological features of the stretched membrane electrode assembly (MEA) were investigated with respect to variation in the prism pattern dimension (prism pitches of 20 µm and 50 µm) and applied strain (S ≈ 0.5 and 1.0). The behaviour of water on the surface of the cracked electrode was examined using environmental scanning electron microscopy. Guided cracks in the electrode layer were shown to be efficient water reservoirs and liquid water passages. The MEAs with and without guided cracks were incorporated into fuel cells, and electrochemical measurements were conducted. As expected, all MEAs with guided cracks exhibited better performance than conventional MEAs, mainly because of the improved water transport.

A facile synthetic strategy for iron, aniline-based non-precious metal catalysts for polymer electrolyte membrane fuel cells.

The development of a low cost and highly active alternative to the commercial Pt/C catalysts used in the oxygen reduction reaction (ORR) requires a facile and environmentally-friendly synthesis process to facilitate large-scale production and provide an effective replacement. Transition metals, in conjunction with nitrogen-doped carbon, are among the most promising substitute catalysts because of their high activity, inexpensive composition, and high carbon monoxide tolerance. We prepared a polyaniline-derived Fe-N-C catalyst for oxygen reduction using a facile one-pot process with no additional reagents. This process was carried out by ultrasonicating a mixture containing an iron precursor, an aniline monomer, and carbon black. The half-wave potential of the synthesized Fe-N-C catalyst for the ORR was only 10 mV less than that of a commercial Pt/C catalyst. The optimized Fe-N-C catalyst showed outstanding performance in a practical anion exchange membrane fuel cell (AEMFC), suggesting its potential as an alternative to commercial Pt/C catalysts for the ORR.

Potential effect of compounds isolated from Coffea arabica against UV-B induced skin damage by protecting fibroblast cells.

Ultraviolet (UV) radiation has adverse effects on extracellular matrix (ECM) proteins, leading to formation of wrinkles a hallmark of premature skin aging. The adverse effects of UV radiation are associated with induction of matrix metalloproteinases (MMPs) expression and degradation of collagen and elastin. The present study investigated anti-wrinkle effects of chlorogenic acid (CGA), pyrocatechol (PC) and 3,4,5-tricaffeoyl quinic acid (TCQ), isolated from beans of Coffea arabica, against UV-B stimulated mouse fibroblast cells (CCRF) by measuring expression levels of MMP-1, 3, 9, and type-I procollagen. The three compounds were isolated and purified from coffee grounds using column chromatography and structural examination was evaluated by nuclear magnetic resonance (NMR) analysis. Among the three isolated compounds, CGA effectively suppressed the expression of the MMP-1, 3, and 9 and increased synthesis of type-I procollagen as compared UV-B-stimulated CCRF cells. In addition, CGA dose-dependently inhibited intracellular reactive oxygen species (ROS) production in CCRF cells stimulated by UV radiation. Moreover, CGA displayed a good sun protection factor (SPF) and in vitro DNA damage protection together with inhibition of enzyme xanthine oxidase. The enzyme inhibitory kinetic behavior of CGA was determined by Lineweaver-Burk plot, displayed a mixed type enzyme inhibition with 260.3±4.5µM, Ki value. The results indicate that CGA has potential to be used as a preventive agent against premature skin aging induced by UV radiation.

3D macroporous electrode and high-performance in lithium-ion batteries using SnO2 coated on Cu foam.

A three-dimensional porous architecture makes an attractive electrode structure, as it has an intrinsic structural integrity and an ability to buffer stress in lithium-ion batteries caused by the large volume changes in high-capacity anode materials during cycling. Here we report the first demonstration of a SnO2-coated macroporous Cu foam anode by employing a facile and scalable combination of directional freeze-casting and sol-gel coating processes. The three-dimensional interconnected anode is composed of aligned microscale channels separated by SnO2-coated Cu walls and much finer micrometer pores, adding to surface area and providing space for volume expansion of SnO2 coating layer. With this anode, we achieve a high reversible capacity of 750 mAh g(-1) at current rate of 0.5 C after 50 cycles and an excellent rate capability of 590 mAh g(-1) at 2 C, which is close to the best performance of Sn-based nanoscale material so far.

High-performance Fuel Cell with Stretched Catalyst-Coated Membrane: One-step Formation of Cracked Electrode.

We have achieved performance enhancement of polymer electrolyte membrane fuel cell (PEMFC) though crack generation on its electrodes. It is the first attempt to enhance the performance of PEMFC by using cracks which are generally considered as defects. The pre-defined, cracked electrode was generated by stretching a catalyst-coated Nafion membrane. With the strain-stress property of the membrane that is unique in the aspect of plastic deformation, membrane electrolyte assembly (MEA) was successfully incorporated into the fuel cell. Cracked electrodes with the variation of strain were investigated and electrochemically evaluated. Remarkably, mechanical stretching of catalyst-coated Nafion membrane led to a decrease in membrane resistance and an improvement in mass transport, which resulted in enhanced device performance.

Anti-inflammatory Potential of Quercetin-3-O-ß-D-("2"-galloyl)-glucopyranoside and Quercetin Isolated from Diospyros kaki calyx via Suppression of MAP Signaling Molecules in LPS-induced RAW 264.7 Macrophages.

Diospyros kaki (DK) contains an abundance of flavonoids and has been used in folk medicine in Korea for centuries. Here, we report for the first time the anti-inflammatory activities of Quercetin (QCT) and Quercetin 3-O-ß-("2"-galloyl)-glucopyranoside (Q32G) isolated from DK. We have determine the no cytotoxicity of Q32G and QCT against RAW 264.7 cells up to concentration of 50 µM. QCT and Q32G demonstrated potent anti-inflammatory activities by reducing expression of nitric oxide (NO), tumor necrosis factor (TNF)-α, interleukin (IL)-1ß, IL-6 inducible NO synthase (iNOS), cyclooxygenase (COX)-2, and mitogen-activated protein kinase (MAPKs) in mouse RAW 264.7 macrophages activated with lipopolysaccharide (LPS). Both QCT or Q32G could decrease cellular protein levels of COX-2 and iNOS as well as secreted protein levels of NO, PGE2 , and cytokines (TNF-α, IL-1ß, and IL-6) in culture medium of LPS-stimulated RAW 264.7 macrophages. Immunoblot analysis showed that QCT and Q32G suppressed LPS-induced MAP kinase pathway proteins p-p38, ERK, and JNK. This study revealed that QCT and Q32G have anti-inflammatory potential, however Q32G possess comparable activity as that of QCT and could be use as adjuvant to treat inflammatory diseases.