Non-precious metal electrocatalysts for hydrogen production in proton exchange membrane water electrolyzer

Kim, Hoyoung,Hwang, Eunkyoung,Park, Hyanjoo,Lee, Byung-Seok,Jang, Jong Hyun,Kim, Hyoung-Juhn,Ahn, Sang Hyun,Kim, Soo-Kil Elsevier BV 2017 Applied Catalysis B Vol.206 No.-

<P><B>Abstract</B></P> <P>Electrodeposited Cu<I> <SUB>x</SUB> </I>Mo<SUB>100− <I>x</I> </SUB> catalysts were prepared on a Ti substrate for the hydrogen evolution reaction (HER) in acidic medium. By varying the electrolyte composition for electrodeposition, the atomic concentration of the Cu<I> <SUB>x</SUB> </I>Mo<SUB>100− <I>x</I> </SUB> electrocatalysts could be controlled, and the Mo content ranged between 0.8 and 6.9%. In the first cyclic voltammetry scan in a 0.5M H<SUB>2</SUB>SO<SUB>4</SUB> electrolyte, the recorded HER current densities of the Cu<I> <SUB>x</SUB> </I>Mo<SUB>100− <I>x</I> </SUB> electrocatalysts at −0.50V<SUB>RHE</SUB> increased on increasing the Mo content to 3.8%; then, a further increase in Mo to 6.9% led to a saturation in the HER activity. The maximum value of the normalized current density with respect to the electrochemical surface area and the loading mass was found for the Cu<SUB>99.2</SUB>Mo<SUB>0.8</SUB> electrocatalyst. Characterization of the prepared catalysts revealed that the enhancement of catalytic activity originates from changes in the grain size and electronic structure. To operate a single cell of the proton exchange membrane water electrolyzer (PEMWE), we electrodeposited CuMo catalyst on carbon paper, and this was used as the cathode, while IrO<SUB>2</SUB> electrodeposited on carbon paper was used as the anode. The cell performance was normalized with respect to the metal mass loading and was found to be 3.4A/mg<SUB>metal</SUB> at 1.9V, a 2.2–10.8 times better catalyst cost-activity relationship compared to that of currently reported PEMWEs using Pt-based cathodes. Consequently, the results presented here show that non-noble metal cathodes can be used for PEMWE operation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cu<SUB>x</SUB>Mo<SUB>100−x</SUB> catalysts are prepared for hydrogen evolution reaction in acidic medium. </LI> <LI> Small amount of Mo enhances catalytic activity of Cu<SUB>x</SUB>Mo<SUB>100−x</SUB> catalysts. </LI> <LI> Water electrolyzer with non-precious catalyst demonstrates reasonable performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effectiveness of vegetation and sound wall-vegetation combination barriers on pollution dispersion from freeways under early morning conditions

Ranasinghe, Dilhara,Lee, Eon S.,Zhu, Yifang,Frausto-Vicencio, Isis,Choi, Wonsik,Sun, Wu,Mara, Steve,Seibt, Ulrike,Paulson, Suzanne E. Elsevier BV 2019 Science of the Total Environment Vol.658 No.-

<P><B>Abstract</B></P> <P>Pollutants in tailpipe emissions can be highly elevated around roadways, and in early mornings the pollution plume can extend hundreds of meters into surrounding neighborhoods. Solid sound walls and vegetation barriers are commonly used to mitigate noise, but they also help mitigate near-road air pollution. Here we assess the effectiveness of barriers consisting of vegetation only and of a combination of vegetation and a solid sound wall (combination barrier) in reducing pollution concentrations downwind of roads, under stable atmospheric stability and calm to light wind conditions. Because there was no practical (no barrier) control site in the area, we primarily compare the two barrier types to each other and explore the importance of atmospheric conditions. Using measurements collected with a mobile platform, we develop concentration decay profiles of ultrafine and fine particles, oxides of nitrogen (NO and NO<SUB>2</SUB>) and carbon monoxide downwind of a freeway in California with different barrier configurations and meteorological conditions. Diurnally averaged data collected with passive samplers indicate that pollution from morning rush hour has about equal impact as the entire remainder of the day, because of differences in atmospheric dispersion as the day progresses. Under calm and stable atmospheric conditions (wind speed <0.6 m/s); a vegetation-only barrier was more effective than a combination barrier with a total height that was somewhat lower than the vegetation-only barrier, by 10–24% in the first 160 m downwind. Under light winds (above ~ 0.6 but below 3 m/s) and stable conditions, the combination barrier was more effective than the vegetation barrier alone, by 6–33%, in the first 160 m from the barrier. The average particle size downwind of the vegetation-only barrier was larger than downwind of the combination barrier, indicating that particle deposition plays an important role in the reductions observed downwind of vegetation. Our results are consistent with the notion that at low wind speeds, vegetation acts as an effective barrier. Overall, adding vegetation alone or to an existing solid barrier results in lower downwind pollution concentrations, especially under low wind speeds when concentrations can be high.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Measurements were made around two barrier types under stable conditions. </LI> <LI> At higher wind speeds, the combination barrier was better than vegetation alone. </LI> <LI> Pollution reduction from vegetation was higher at low wind speeds. </LI> <LI> Deposition of particles onto even thin stands of trees is important. </LI> <LI> Pollution from a brief morning period equaled that from the remainder of the day. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Regulation of morphological, molecular and nutrient status in <i>Arabidopsis thaliana</i> seedlings in response to ZnO nanoparticles and Zn ion exposure

Nair, Prakash M. Gopalakrishnan,Chung, Ill Min Elsevier BV 2017 Science of the Total Environment Vol.575 No.-

<P><B>Abstract</B></P> <P>This study examined the mechanism of toxicity in <I>Arabidopsis thaliana</I> seedlings to zinc oxide nanoparticles (ZnO NPs) and zinc (Zn) ions. We subjected plants to different ZnO NPs and Zn ion concentrations (0, 20, 50, 100 and 200mg/L) and analyzed resulting morphological changes, transcriptional regulation of genes involved in Zn-homeostasis, macro- and microelement homeostasis, as well as auxin regulation. Except for 20mg/L, the fresh weight and primary root length was reduced after exposure to all other concentrations of Zn ion and ZnO NP concentrations. An increase in lateral root formation (19 and 32%) was observed after exposure to 20 and 50mg/L of Zn ions respectively; whereas 20mg/L ZnO NPs treatment triggered a 9% increase in lateral root formation. Both qualitative, using Zynpyr-1 fluorescent probe and quantitative analysis revealed Zn uptake and translocation from roots to shoots after Zn ion exposure. However, ZnO NPs-treated seedlings resulted in no root to shoot translocation and Zn accumulation was mainly located in root tips, primary-lateral root junctions and root- shoot junctions. The macronutrients viz. P (1.34mg/kg DW), K (13.29mg/kg DW), S (1.29mg/kg DW) and micronutrients Cu (0.004mg/kg DW) and Fe (0.345mg/kg DW) contents were highly decreased as a result of exposure to 200mg/L of Zn ions. Similarly, the highest reduction of P (2.30mg/kg DW), K (6.36mg/kg DW), S (2.63mg/kg DW) and Cu (0.004mg/kg DW) was observed after exposure to 200mg/L of ZnO NPs. Gene regulation studies indicated the transcriptional modulation of various genes involved in Zn, macro- and micro nutrient homeostasis as well as hormone regulation. Taken together, it was observed that the mechanism of toxicity of Zn ions and ZnO NPs were different. These findings will help to design safer strategies for the application of ZnO NPs as plant fertilizer without compromising the morphological and nutritional qualities as well as for the future phytoremediation purposes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ZnO NPs and Zn ions induced morphological changes in <I>Arabidopsis thaliana</I>. </LI> <LI> Changes in roots system architecture was observed. </LI> <LI> Modulated the expression of metal homeostasis and hormone regulation genes </LI> <LI> Changed macro- and micro-nutrient contents </LI> <LI> Provides insights for future application of ZnO NPs as fertilizer. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Urea additives for reduction of hydration heat in cement composites

Elsevier BV 2017 Construction and Building Materials Vol.156 No.-

<P><B>Abstract</B></P> <P>This study evaluates the feasibility of using urea in cement composites, as a means to reduce the heat generated from the hydration of cement. The performed experimental evaluation uses several different test and analysis techniques: calorimetric tests, X-ray diffraction, scanning electron microscopy, mercury intrusion porosimetry, and compressive strength tests. To avoid the potential difficulties related with the increase in the solution volume, an alternative mix design is proposed, which can produce concrete with mechanical properties—including the compressive strength—that are equal to or better than the traditional control mix, while simultaneously preserving the outstanding temperature reduction capabilities of urea.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Dissolving urea in water reduces the solution temperature abruptly and drastically. </LI> <LI> Mixing urea in cement composites can reduce the hydration-generated heat. </LI> <LI> The effects of urea mixing on structure and strength were assessed experimentally. </LI> <LI> The compressive strength and pore features of conventional mixes can be preserved. </LI> </UL> </P>

Design of active Pt on TiO₂ based nanofibrous cathode for superior PEMFC performance and durability at high temperature

Ji, Yunseong,Cho, Yong il,Jeon, Yukwon,Lee, Chanmin,Park, Dae-Hwan,Shul, Yong-Gun Elsevier BV 2017 Applied Catalysis B Vol.204 No.-

<P><B>Abstract</B></P> <P>Oxygen reduction reaction (ORR) activity and stability of the cathode catalyst are important issues for practical applications, which should be even considered for the materials in high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). To improve these properties, modification of the catalyst electronic structure and finding durable supports can be a good approach. In this study, we synthesized a noble nanofibrous composite electrode which consist of carbon nanotube (CNT)-winded Pt/TiO<SUB>2</SUB> nanofiber (CNT-Pt/TiO<SUB>2</SUB>). Our approach takes advantages of the electrochemical conductivity of CNF as well as better stability from the corrosion resistivity of TiO<SUB>2</SUB> and strong metal-support interaction (SMSI) between the Pt nanoparticles and TiO<SUB>2</SUB> nanofibers for less Pt dissolution. We also found that the Pt electronic state can be changed by an interaction with neighbouring CNT and TiO<SUB>2</SUB>, resulting a decrease of Pt d-band vacancy for enhanced catalytic activity. Furthermore, nanofibrous structure with a unique 3D pore structure provides higher surface area for additional improvements of the mass transfer. These results reveal that the CNT-Pt/TiO<SUB>2</SUB> nanofiber based electrode shows enhanced performance with the maximum power density of 567mWcm<SUP>−2</SUP> compare to commercial Pt/C (461mWcm<SUP>−2</SUP>) with a significant durability at harsh conditions of 120°C and RH 40%.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CNT-Pt/TiO<SUB>2</SUB> has exceptional performance and stability at HT-PEMFCs cell test. </LI> <LI> Inorganic–carbon composite shows synergistic effects for good ORR activity. </LI> <LI> CNT and TiO<SUB>2</SUB> cause a charge transfer phenomena offering more electrons to platinum. </LI> <LI> Interconnected nanofibrous catalyst has well organized paths for better transport. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Variability of pCO₂ in surface waters and development of prediction model

Chung, Sewoong,Park, Hyungseok,Yoo, Jisu Elsevier BV 2018 Science of the Total Environment Vol.622 No.-

<P><B>Abstract</B></P> <P>Inland waters are substantial sources of atmospheric carbon, but relevant data are rare in Asian monsoon regions including Korea. Emissions of CO<SUB>2</SUB> to the atmosphere depend largely on the partial pressure of CO<SUB>2</SUB> (pCO<SUB>2</SUB>) in water; however, measured pCO<SUB>2</SUB> data are scarce and calculated pCO<SUB>2</SUB> can show large uncertainty. This study had three objectives: 1) to examine the spatial variability of pCO<SUB>2</SUB> in diverse surface water systems in Korea; 2) to compare pCO<SUB>2</SUB> calculated using pH-total alkalinity (Alk) and pH-dissolved inorganic carbon (DIC) with pCO<SUB>2</SUB> measured by an in situ submersible nondispersive infrared detector; and 3) to characterize the major environmental variables determining the variation of pCO<SUB>2</SUB> based on physical, chemical, and biological data collected concomitantly. Of 30 samples, 80% were found supersaturated in CO<SUB>2</SUB> with respect to the overlying atmosphere. Calculated pCO<SUB>2</SUB> using pH-Alk and pH-DIC showed weak prediction capability and large variations with respect to measured pCO<SUB>2</SUB>. Error analysis indicated that calculated pCO<SUB>2</SUB> is highly sensitive to the accuracy of pH measurements, particularly at low pH. Stepwise multiple linear regression (MLR) and random forest (RF) techniques were implemented to develop the most parsimonious model based on 10 potential predictor variables (pH, Alk, DIC, Uw, Cond, Turb, COD, DOC, TOC, Chla) by optimizing model performance. The RF model showed better performance than the MLR model, and the most parsimonious RF model (pH, Turb, Uw, Chla) improved pCO<SUB>2</SUB> prediction capability considerably compared with the simple calculation approach, reducing the RMSE from 527–544 to 105μatm at the study sites.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Spatial variations of pCO<SUB>2</SUB> were provided with concomitant environmental factors. </LI> <LI> Biases between calculated pCO<SUB>2</SUB> and in situ NDIR measurements were evaluated. </LI> <LI> Calculated pCO<SUB>2</SUB> is highly sensitive to pH measurements, particularly at low pH. </LI> <LI> Environmental factors determining the spatial variability of pCO<SUB>2</SUB> were elucidated. </LI> <LI> pCO<SUB>2</SUB> was predicted properly by the parsimonious RF model (pH, Turb, Uw, Chla). </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Enhancing the oxidation resistance of graphite by applying an SiC coat with crack healing at an elevated temperature

Park, J.W.,Kim, E.S.,Kim, J.U.,Kim, Y.,Windes, W.E. Elsevier BV * North-Holland 2016 Applied Surface Science Vol.378 No.-

The potential of reducing the oxidation of the supporting graphite components during normal and/or accident conditions in the Very High Temperature Reactor (VHTR) design has been studied. In this work efforts have been made to slow the oxidation process of the graphite with a thin SiC coating (~10μm). Upon heating at≥1173K in air, the spallations and cracks were formed in the dense columnar structured SiC coating layer grown on the graphite with a functionally gradient electron beam physical vapor deposition (EB-PVD. In accordance with the formations of these defects, the sample was vigorously oxidized, leaving only the SiC coating layer. Then, efforts were made to heal the surface defects using additional EB-PVD with ion beam bombardment and chemical vapor deposition (CVD). The EB-PVD did not effectively heal the cracks. But, the CVD was more appropriate for crack healing, likely due to its excellent crack line filling capability with a high density and high aspect ratio. It took~34min for the 20% weight loss of the CVD crack healed sample in the oxidation test with annealing at 1173K, while it took~8min for the EB-PVD coated sample, which means it took ~4 times longer at 1173K for the same weight reduction in this experimental set-up.

Linear analysis of signal and noise characteristics of a nonlinear CMOS active-pixel detector for mammography

Yun, Seungman,Kim, Ho Kyung,Han, Jong Chul,Kam, Soohwa,Youn, Hanbean,Cunningham, Ian A. Elsevier BV * North-Holland 2017 Nuclear Instruments & Methods in Physics Research. Vol. No.

<P><B>Abstract</B></P> <P>The imaging properties of a complementary metal-oxide-semiconductor (CMOS) active-pixel photodiode array coupled to a thin gadolinium-based granular phosphor screen with a fiber-optic faceplate are investigated. It is shown that this system has a nonlinear response at low detector exposure levels (<10mR), resulting in an over-estimation of the detective quantum efficiency (DQE) by a factor of two in some cases. Errors in performance metrics on this scale make it difficult to compare new technologies with established systems and predict performance benchmarks that can be achieved in practice and help understand performance bottlenecks. It is shown the CMOS response is described by a power-law model that can be used to linearize image data. Linearization removed an unexpected dependence of the DQE on detector exposure level.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A nonlinear response of a CMOS detector at low exposure levels can overestimate DQE. </LI> <LI> A power-law form can model the response of a CMOS detector at low exposure levels, and can be used to linearize image data. </LI> <LI> Performance evaluation of nonlinear imaging systems must incorporate adequate linearizations. </LI> </UL> </P>

Strength and toughness of hybrid steel and glass fiber-reinforced sulfur polymer composites

Gwon, Seongwoo,Kim, Seungpil,Ahn, Eunjong,Kim, Chanyoung,Shin, Myoungsu Elsevier BV 2019 Construction and Building Materials Vol.228 No.-

<P><B>Abstract</B></P> <P>In this study, we investigated the effects of microfibers on the compressive and flexural behaviors of modified sulfur composites. Dicyclopentadiene-modified sulfur was used as the binder in the sulfur composites. Fifteen mix cases were tested by varying the volumetric ratios of steel and electric chemical resistant glass fibers. Fly ash (35% by volume) was included to not only increase strength and workability, but also ensure fiber dispersibility in the matrix. A non-contact displacement measurement technique, digital image correlation, was used in flexure tests to monitor the development of high strain zones and microcracks. The effect of fiber dosage on the porosity of sulfur composites was analyzed by quantifying the pore volume and size distribution through mercury intrusion porosimetry. The test results confirmed that the hybrid use of steel and glass fibers with a volume ratio of up to 4% was effective in improving the flexural stress-deflection response. The post-peak toughness ratio in flexure increased as the volume of microfibers increased. In addition, the total volume of hybrid microfibers generally had a positive correlation with the flexural strength. In contrast, the compressive strength of hybrid fiber-reinforced sulfur composites was more dependent on the portion of steel fibers than glass fibers.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The behaviors of microfiber-reinforced modified sulfur composites were investigated. </LI> <LI> The hybrid of steel and glass fibers was effective in improving flexural response. </LI> <LI> The post-peak toughness ratio in flexure increased according to more microfibers. </LI> <LI> The total volume of microfibers had a positive correlation with flexural strength. </LI> <LI> The compressive strength of sulfur composites was more dependent on steel fibers. </LI> </UL> </P>

Transformation of methylparaben during water chlorination: Effects of bromide and dissolved organic matter on reaction kinetics and transformation pathways

Yoom, Hoonsik,Shin, Jaedon,Ra, Jiwoon,Son, Heejong,Ryu, Dongchoon,Kim, Changwon,Lee, Yunho Elsevier BV 2018 Science of the Total Environment Vol.634 No.-

<P><B>Abstract</B></P> <P>The reaction kinetics, products, and pathways of methylparaben (MeP) during water chlorination with and without bromide (Br<SUP>−</SUP>) were investigated to better understand the fate of parabens in chlorinated waters. During the chlorination of MeP-spiked waters without Br<SUP>−</SUP>, MeP was transformed into mono-Cl-MeP and di-Cl-MeP with apparent second-order rate constants (<I>k</I> <SUB>app</SUB>) of 64M<SUP>−1</SUP> s<SUP>−1</SUP> and 243M<SUP>−1</SUP> s<SUP>−1</SUP> at pH7, respectively, while further chlorination of di-Cl-MeP was relatively slower (<I>k</I> <SUB>app</SUB> =1.3M<SUP>−1</SUP> s<SUP>−1</SUP> at pH7). With increasing Br<SUP>−</SUP> concentration, brominated MePs, such as mono-Br-MeP, Br-Cl-MeP, and di-Br-MeP, became major transformation products. The di-halogenated MePs (di-Cl-MeP, Br,Cl-MeP, and di-Br-MeP) showed relatively low reactivity to chlorine at pH7 (<I>k</I> <SUB>app</SUB> =1.3–4.6M<SUP>−1</SUP> s<SUP>−1</SUP>) and bromine (<I>k</I> <SUB>app</SUB> =32–71M<SUP>−1</SUP> s<SUP>−1</SUP>), which explains the observed high stability of di-halogenated MePs in chlorinated waters. With increasing pH from 7 to 8.5, the transformation of di-halogenated MePs was further slowed due to the decreasing reactivity of di-MePs to chlorine. The formation of the di-halogenated MePs and their further transformation become considerably faster at Br<SUP>−</SUP> concentrations higher than 0.5μM (40μg/L). Nonetheless, the accelerating effect of Br<SUP>−</SUP> diminishes in the presence of dissolved organic matter (DOM) extract (Suwannee River humic acid (SRHA)) due to a more rapid consumption of bromine by DOM than chlorine. The effect of Br<SUP>−</SUP> on the fate of MeP was less in the tested real water matrices, possibly due to a more rapid bromine consumption by the real water DOM compared to SRHA. A kinetic model was developed based on the determined species-specific second-order rate constants for chlorination/bromination of MeP and its chlorinated and brominated MePs and the transformation pathway information, which could reasonably simulate the transformation of MePs during the chlorination of water in the presence of Br<SUP>−</SUP> and selected DOM.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Transformation kinetics and pathways of methylparaben during chlorination are studied. </LI> <LI> Second-order rate constants for chlorine/bromine with methylparabens are reported. </LI> <LI> Brominated methylparabens are dominant over chlorinated ones with increasing bromide. </LI> <LI> Bromide effect on methylparaben transformation diminishes by dissolved organic matter. </LI> <LI> The developed kinetic model can simulate the paraben transformation in chlorination. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>