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>

Synergistic combination of bandgap-modified carbon nitride and WO₃ for visible light-induced oxidation of arsenite accelerated by in-situ Fenton reaction

Moon, Gun-hee,Kim, Sujeong,Cho, Young-Jin,Lim, Jonghun,Kim, Dong-hyo,Choi, Wonyong Elsevier BV 2017 Applied Catalysis B Vol.218 No.-

<P><B>Abstract</B></P> <P>Photocatalytic oxidation of arsenite (As(III)) to arsenate (As(V)) using non-toxic semiconductor materials has been considered as an environmentally-benign pretreatment process of arsenic contaminated waters, but poor visible light activity hinders the practical applications utilizing solar light. In this study, we designed a ternary photocatalytic system consisting of modified carbon nitride (mCN), WO<SUB>3</SUB>, and Fe<SUP>3+</SUP> for efficient oxidation of As(III) which was done by using <I>in-situ</I> generated H<SUB>2</SUB>O<SUB>2</SUB> as a Fenton reagent under visible light (λ>420nm). While superoxide anion and H<SUB>2</SUB>O<SUB>2</SUB> were effectively produced via the reduction of dissolved O<SUB>2</SUB> by mCN, WO<SUB>3</SUB> regenerated Fe<SUP>2+</SUP> from Fe<SUP>3+</SUP>, which activated <I>in-situ</I> generated H<SUB>2</SUB>O<SUB>2</SUB> for Fenton process. The overall photocatalytic oxidation activity of As(III) was optimized at a specific mixing ratio of catalysts (mCN:WO<SUB>3</SUB> =60:40) where there is an optimal balance between the conduction band electron transfer to dissolved O<SUB>2</SUB> (to produce H<SUB>2</SUB>O<SUB>2</SUB> on mCN) and the competing electron transfer to Fe<SUP>3+</SUP> (to regenerate Fe<SUP>2+</SUP> on WO<SUB>3</SUB>). The ternary combination enabled the simultaneous participation of superoxide anions, hydroxyl radicals, and holes to complete the oxidation of 500μM As(III) within 90min with 1.0g/L catalyst and 70μM Fe<SUP>3+</SUP> and that of 10μM As(III) within 60min with a tenth amount of catalyst (0.1g/L) and Fe<SUP>3+</SUP> (7μM) under visible light without requiring noble metal catalysts and chemical additives. The process consists of earth abundant elements only (C, N, O, W, and Fe) and operates with utilizing visible light photons and dissolved O<SUB>2</SUB> only, which is eco-friendly and cost effective.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A synergistic combination of bandgap-modified carbon nitride (mCN) and WO<SUB>3</SUB> coupled with ferric ions is proposed. </LI> <LI> <I>In-situ</I> formed H<SUB>2</SUB>O<SUB>2</SUB> and its activation by Fe<SUP>2+</SUP> highly accelerates the photocatalytic arsenic oxidation under visible light. </LI> <LI> H<SUB>2</SUB>O<SUB>2</SUB> is produced mainly by mCN part and the regenerative cycle of Fe<SUP>3+</SUP>/Fe<SUP>2+</SUP> is mainly driven by the WO<SUB>3</SUB> part. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Recyclable patterning of silver nanowire percolated network for fabrication of flexible transparent electrode

Yoo, Byungwook,Kim, Youngmin,Han, Chul Jong,Oh, Min Suk,Kim, Jong-Woong Elsevier BV * North-Holland 2018 Applied Surface Science Vol.429 No.-

<P><B>Abstract</B></P> <P>Recent studies have revealed that silver nanowires (AgNWs) are a promising material for highly flexible transparent electrodes. Here we introduce a novel photoinduced recyclable approach to AgNW patterning to overcome the issue of loss of material during fabrication of AgNW patterns, which is a leading factor in the high fabrication costs of AgNW-based electrodes. Our patterning scheme involves the selective irradiation of an AgNW/polymer composite with high-intensity pulsed light, followed by immersion of the sample in a liquid and an ultrasonication treatment. The nanowires that detach during sonication could be recycled, and the recycled AgNWs achieved comparable performance to that of pristine AgNWs. The recycled AgNWs were also superior to commercial indium tin oxide films and other competing materials. We successfully demonstrated a high performance transparent heater by employing the recyclable patterning method and recycled AgNWs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Silver nanowire networks were used for transparent conducting electrodes. </LI> <LI> Pulsed irradiation allowed patterned adhesion of silver nanowires to PET. </LI> <LI> Non-adhering silver nanowires were removed by ultrasonication and recycled. </LI> <LI> Recycled silver nanowires were used to fabricate a flexible, transparent heater. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Synthesis of two-dimensional MoS₂/graphene heterostructure by atomic layer deposition using MoF₆ precursor

Kim, Youngjun,Choi, Daeguen,Woo, Whang Je,Lee, Jae Bok,Ryu, Gyeong Hee,Lim, Jun Hyung,Lee, Sunhee,Lee, Zonghoon,Im, Seongil,Ahn, Jong-Hyun,Kim, Woo-Hee,Park, Jusang,Kim, Hyungjun Elsevier BV * North-Holland 2019 Applied Surface Science Vol.494 No.-

<P><B>Abstract</B></P> <P>The effective synthesis of two-dimensional (2D) heterostructures is essential for their use in electronic devices. In this study, by using atomic layer deposition (ALD), 2D transition metal dichalcogenide (TMD) heterostructures were grown by a halide precursor. This study shows the growth characteristics of the fluoride precursor compared to the chloride precursor used for the synthesis of the TMD on the graphene layer and the other TMD layer. Additionally, a carbonyl precursor was used for comparison with the halide precursor in terms of the thermal stability. From these experiments, the fluoride precursor was adequate for synthesizing on the graphene, however, was inappropriate for the TMD/TMD heterostructure because of its etching characteristic. Meanwhile, the chloride precursor was appropriate for the TMD/TMD heterostructure, even for a low binding energy with the substrate, but was inadequate in forming the TMD/graphene heterostructure, even if the ALD cycle increased. Through our experiments, we show, for the first time, that there exists a suitable halide precursor for a 2D layer for a substrate.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Synthesis of two-dimensional MoS<SUB>2</SUB> synthesized by MoF<SUB>6</SUB> precursor using atomic layer deposition </LI> <LI> MoF<SUB>6</SUB> is suitable for MoS<SUB>2</SUB>/graphene heterostructure </LI> <LI> Chloride precursor is suitable for transition metal dichalcogenide based heterostructure </LI> <LI> Different precursors are suitable depending on the substrate when forming the heterostructure in the atomic layer deposition </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

On CCE graphs of doubly partial orders

Kim, Seog-Jin,Kim, Suh-Ryung,Rho, Yoomi Elsevier BV, North-Holland 2007 Discrete Applied Mathematics Vol.155 No.8

<P><B>Abstract</B></P><P>Let <I>D</I> be a digraph. The competition-common enemy graph (CCE graph) of <I>D</I> has the same set of vertices as <I>D</I> and an edge between vertices <I>u</I> and v if and only if there are vertices w and <I>x</I> in <I>D</I> such that (w,u), (w,v), (u,x), and (v,x) are arcs of <I>D</I>. We call a graph a CCE graph if it is the CCE graph of some digraph. In this paper, we show that if the CCE graph of a doubly partial order does not contain <SUB>C4</SUB> as an induced subgraph, it is an interval graph. We also show that any interval graph together with enough isolated vertices is the CCE graph of some doubly partial order.</P>

Identification of environmental determinants for spatio-temporal patterns of norovirus outbreaks in Korea using a geographic information system and binary response models

Kim, Jin Hwi,Lee, Dong Hoon,Joo, Yongsung,Zoh, Kyung Duk,Ko, Gwangpyo,Kang, Joo-Hyon Elsevier BV 2016 Science of the Total Environment Vol.569 No.-

<P><B>Abstract</B></P> <P>Although norovirus outbreaks are well-recognized to have strong winter seasonality relevant to low temperature and humidity, the role of artificial human-made features within geographical areas in norovirus outbreaks has rarely been studied. The aim of this study is to assess the natural and human-made environmental factors favoring the occurrence of norovirus outbreaks using nationwide surveillance data. We used a geographic information system and binary response models to examine whether the norovirus outbreaks are spatially patterned and whether these patterns are associated with specific environmental variables including service levels of water supply and sanitation systems and land-use types. The results showed that small-scale low-tech local sewage treatment plants and winter sports areas were statistically significant factors favoring norovirus outbreaks. Compactness of the land development also affected the occurrence of norovirus outbreaks; transportation, water, and forest land-uses were less favored for effective transmission of norovirus, while commercial areas were associated with an increased rate of norovirus outbreaks. We observed associations of norovirus outbreaks with various outcomes of human activities, including discharge of poorly treated sewage, overcrowding of people during winter season, and compactness of land development, which might help prioritize target regions and strategies for the management of norovirus outbreaks.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A GIS and binary response models were used to predict norovirus outbreaks' patterns. </LI> <LI> Strong winter seasonality of norovirus outbreaks was confirmed. </LI> <LI> Local sewage treatment plants favored norovirus outbreaks. </LI> <LI> Compactness of the land development affected the occurrence of norovirus outbreaks. </LI> <LI> Overcrowding of people and cold temperature synergistically increased norovirus outbreaks. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Homogeneous photoconversion of seawater uranium using copper and iron mixed-oxide semiconductor electrodes

Lee, Seunghoon,Kang, Unseock,Piao, Guangxia,Kim, Soonhyun,Han, Dong Suk,Park, Hyunwoong Elsevier BV 2017 Applied Catalysis B Vol.207 No.-

<P><B>Abstract</B></P> <P>Sunlight-driven conversion of hexavalent uranium (U(VI)) in seawater is achieved with mixed p-type CuO and CuFeO<SUB>2</SUB> (CuO/CuFeO<SUB>2</SUB>) photocatalyst film electrodes synthesized <I>via</I> electrodeposition (ED) of Cu(II) and Fe(III), followed by annealing in air. The mixed photocatalysts exhibit a double-layer configuration with crystalline structures of CuO and CuFeO<SUB>2</SUB>. On irradiation of the CuO/CuFeO<SUB>2</SUB> electrodes (held at −0.5V vs. SCE) with solar simulated light (air mass 1.5; 100mWcm<SUP>−2</SUP>), the U(VI) concentration decreases with time, while the total amount of uranium in solution does not change. This indicates that virtually all conversion reactions of U(VI) occur in the bulk solution, while surface reactions are limited due to insignificant adsorption of U(VI). U(VI) conversion leads to the mixed production of lower oxidation states U<SUP>4+</SUP>, U<SUP>14/3+</SUP>, and U<SUP>16/3+</SUP> at a ratio of 42:28:30, with an overall Faradaic efficiency of ∼98%. The kinetics and induction time for U(VI) conversion are significantly influenced by the conditions of photocatalyst synthesis (CuO/CuFeO<SUB>2</SUB>, CuO, and CuFeO<SUB>2</SUB>; ED times of 2–4h), the applied potential value (−0.4, −0.5, and −0.6V vs. SCE), and the seawater condition (air-equilibrated vs. N<SUB>2</SUB>-purged; pH 3–10.4). Based on the obtained results, O<SUB>2</SUB> is proposed to play a key role in shuttling photogenerated electrons between the electrodes and U(VI). In addition, the existence of an induction time is discussed in terms of material and reaction pathway.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sunlight-driven conversion of U(VI) in seawater is achieved with mixed CuO and CuFeO<SUB>2</SUB>. </LI> <LI> U(VI) is photoelectrochemically reduced with a Faradaic efficiency of ∼98%. </LI> <LI> Virtually all conversion reactions of U(VI) occur in the bulk solution. </LI> <LI> Induction times are present in uranium conversion. </LI> <LI> O<SUB>2</SUB> acts as an electron shuttle between electrodes and U(VI). </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Associations between urinary phthalate metabolites and bisphenol A levels, and serum thyroid hormones among the Korean adult population - Korean National Environmental Health Survey (KoNEHS) 2012–2014

Park, Choonghee,Choi, Wookhee,Hwang, Moonyoung,Lee, Youngmee,Kim, Suejin,Yu, Seungdo,Lee, Inae,Paek, Domyung,Choi, Kyungho Elsevier BV 2017 Science of the Total Environment Vol.584 No.-

<P><B>Abstract</B></P> <P><B>Background</B></P> <P>Phthalates and bisphenol A (BPA) have been used extensively in many consumer products, resulting in widespread exposure in the general population. Studies have suggested associations between exposure to phthalates and BPA, and serum thyroid hormone levels, but confirmation on larger human populations is warranted.</P> <P><B>Methods</B></P> <P>Data obtained from nationally representative Korean adults (n=6003) recruited for the second round of the Korean National Environmental Health Survey (KoNEHS), 2012–2014, were employed. Three di-(2-ethylhexyl) phthalate (DEHP) metabolites, along with benzyl-butyl phthalate (BBzP) and di-butyl phthalate (DBP) metabolites, and BPA were measured in subjects' urine. Thyroxine (T4), total triiodothyronine (T3), and thyroid-stimulating hormone (TSH) were measured in serum. The associations between urinary phthalates or BPA and thyroid hormone levels were determined.</P> <P><B>Results</B></P> <P>Urinary phthalate metabolites were generally associated with lowered total T4 or T3, or increased TSH levels in serum. Interquartile range (IQR) increases of mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), and mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) were associated with a 3.7% increase of TSH, and a 1.7% decrease of total T4 levels, respectively. When grouped by sex, urinary MEHHP levels were inversely associated with T4 only among males. Among females, mono-benzyl phthalate (MBzP) and mono-<I>n</I>-butyl phthalate (MnBP) levels were inversely associated with TSH and T3, respectively. In addition, negative association between BPA and TSH was observed.</P> <P><B>Conclusions</B></P> <P>Several phthalates and BPA exposures were associated with altered circulatory thyroid hormone levels among general Korean adult population. Considering the importance of thyroid hormones, public health implications of such alteration warrant further studies.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Phthalates and bisphenol A were associated with thyroid hormones in Korean adults. </LI> <LI> DEHP metabolites were positively associated with TSH but negatively with total T4. </LI> <LI> Negative associations were found between BPA and TSH, and MnBP and total T3. </LI> <LI> Consequences of thyroid disruption warrant further investigations. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

ZnO supported Au/Pd bimetallic nanocomposites for plasmon improved photocatalytic activity for methylene blue degradation under visible light irradiation

Lee, Seung Jun,Jung, Hyeon Jin,Koutavarapu, Ravindranadh,Lee, Seung Heon,Arumugam, Malathi,Kim, Ju Hyun,Choi, Myong Yong Elsevier BV * North-Holland 2019 Applied Surface Science Vol.496 No.-

<P><B>Abstract</B></P> <P>Recently, photocatalysis has attracted great attention due to its potential applications in the environmental sector. Visible light driven metal–semiconductor photocatalysts with efficient light absorption, high charge separation, enhanced surface plasmon resonance, and utilized active sites have emerged as promising materials for the degradation of organic pollutants. Here, plasmonic ZnO/Au/Pd nanocomposites, with various concentrations of Au (5, 10, and 15 wt%) and 5 wt% of Pd nanoparticles (NPs) were prepared by a facile and eco–friendly three–step pulsed laser ablation in liquid and photodeposition technique without utilizing any surfactants or capping agents to enhance the photocatalytic performance under visible light illumination. The plasmonic properties of Au NPs and an excellent trapping of photogenerated electrons on the surface of Pd led to the improved photocatalytic activity (PCA). The as-prepared ZnO/Au/Pd nanocomposites were characterized by numerous spectroscopic and microscopic techniques, and the results confirmed the fabrication of Au and Pd NPs homogeneously decorated on the surface of ZnO nanospheres. The effect of plasmon improved photocatalytic activity of the ZnO/Au/Pd photocatalysts was investigated by the degradation of methylene blue dye under visible light illumination. The optimum ZnO/Au/Pd nanocomposite was ca. 5.4 times more efficient at degrading methylene blue than pure ZnO. This exceptional improvement of photocatalytic activity for the ZnO/Au/Pd catalysts was due to the enhanced surface plasmon resonance effect of the Au NPs under visible light illumination, and the deposited Pd NPs assisted as an electron storage chamber for the degradation of methylene blue, thus, enabling the separation of charge carriers. Based on the experimental results, a possible photocatalytic mechanism for the degradation of methylene blue catalyzed by the ZnO/Au/Pd nanocomposite was proposed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ZnO/Au/Pd catalyst prepared by pulsed laser ablation and photodeposition technique. </LI> <LI> Facile and eco-friendly technique without utilizing surfactants or capping agents. </LI> <LI> Plasmon improved photocatalytic performance of the ZnO/Au/Pd photocatalysts. </LI> <LI> Photocatalytic degradation of methylene blue under visible light illumination. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Several polynomials associated with the harmonic numbers

Cheon, G.-S.,Hwang, S.-G.,Lee, S.-G. Elsevier BV, North-Holland 2007 Discrete Applied Mathematics Vol.155 No.18

We develop polynomials in z@?C for which some generalized harmonic numbers are special cases at z=0. By using the Riordan array method, we explore interesting relationships between these polynomials, the generalized Stirling polynomials, the Bernoulli polynomials, the Cauchy polynomials and the Norlund polynomials.