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>

Hydrogen production from formic acid dehydrogenation over Pd/C catalysts: Effect of metal and support properties on the catalytic performance

Jeon, Hyo-jin,Chung, Young-Min Elsevier BV 2017 Applied Catalysis B Vol.210 No.-

<P><B>Abstract</B></P> <P>While formic acid dehydrogenation has become one of the most promising strategies for hydrogen storage, the crucial factors for realizing an efficient catalyst remain controversial. In this study, a range of Pd/C catalysts were systematically prepared by adopting either diverse metal deposition methods or different acid treatments, and the resulting catalysts were used for formic acid dehydrogenation under ambient conditions without additives. The volcano-type dependence of the activity on the Pd particle size, rate enhancement over Pd with smaller [111]/[200] ratios, and superior activity of Pd<SUP>0</SUP> or Pd<SUP>0</SUP>/Pd(OH)<SUB>2</SUB> mixture to Pd<SUP>2+</SUP> clearly indicate that not only the particle size but also the surface structure or electronic states of active metal would be of prime importance to promote the reaction. Moreover, another volcano relation between the activity and the pH of a reaction solution determined by the functional groups of an acid-treated support obviously suggests that the catalytic activity is very sensitive to pH, and that a neutral reaction solution is preferred to maximize the catalytic performance. The unprecedented critical effect of a support on the catalytic performance may be rationalized in terms of two factors: (i) recombination of the formate ion with a proton and/or delay of formic acid deprotonation by excess protons in an acidic solution; (ii) competitive adsorption between the formate and hydroxyl ions in a basic solution. Therefore, tuning the nature of a support to achieve a balance between the two competitive factors is important to enhance the catalytic performance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A range of Pd/C catalysts were prepared adopting different methods, and applied to formic acid dehydrogenation. </LI> <LI> The catalytic performance strongly depended on the physicochemical properties of active metal and acid-treated support. </LI> <LI> Particle size, surface structure, and electronic states of Pd were important to promote the reaction. </LI> <LI> The pH of a reaction medium determined by the functional groups of an acid-treated support exerted large influence on the catalytic activity. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Impact of future urban growth on regional climate changes in the Seoul Metropolitan Area, Korea

Kim, H.,Kim, Y.K.,Song, S.K.,Lee, H.W. Elsevier BV 2016 Science of the Total Environment Vol.571 No.-

The influence of changes in future urban growth (e.g., land use changes) on the future climate variability in the Seoul metropolitan area (SMA), Korea was evaluated using the WRF model and an urban growth model (SLEUTH). The land use changes in the study area were simulated using the SLEUTH model under three different urban growth scenarios: (1) current development trends scenario (SC 1), (2) managed development scenario (SC 2) and (3) ecological development scenario (SC 3). The maximum difference in the ratio of urban growth between SC 1 and SC 3 (SC 1 - SC 3) for 50years (2000-2050) was approximately 6.72%, leading to the largest differences (0.01<SUP>o</SUP>C and 0.03ms<SUP>-1</SUP>, respectively) in the mean air temperature at 2m (T2) and wind speed at 10m (WS10). From WRF-SLEUTH modeling, the effects of future urban growth (or future land use changes) in the SMA are expected to result in increases in the spatial mean T2 and WS10 of up to 1.15<SUP>o</SUP>C and 0.03ms<SUP>-1</SUP>, respectively, possibly due to thermal circulation caused by the thermal differences between urban and rural regions.

Crystalline beryllium oxide on Si (100) deposited using E-beam evaporator and thermal oxidation

Yoon, Seonno,Lee, Seung Min,Yum, Jung Hwan,Bielawski, Christopher W.,Lee, Hi-Deok,Oh, Jungwoo Elsevier BV * North-Holland 2019 Applied Surface Science Vol.479 No.-

<P><B>Abstract</B></P> <P>The growth characteristics and electrical properties of thin films of crystalline beryllium oxide (BeO) on Si (100) substrates grown using electron beam evaporation (EBE) are described. To expand the commercial viability of BeO, a combination of EBE with thermal oxidation was optimized to facilitate its use in nanoscale semiconductor devices. The surfaces of the EBE BeO films were found to be smooth with limited quantities of native oxides or metal silicates, as determined using atomic force measurements and X-ray photoelectron spectroscopy, respectively. Moreover, high-resolution transmission electron microscopy revealed that the films were highly crystalline. Excellent insulator properties, including a dielectric constant of 6.77 and a breakdown voltage of 8.3 MV/cm, were deduced from a series of capacitance–voltage and leakage current measurements. Reflection electron energy loss spectroscopy and ultraviolet photoelectron spectroscopy indicated that the films exhibited a high band gap of 8.6 eV and a high conduction band offset of 3.43 eV. Collectively, these results indicate that EBE BeO films hold promise for use as electrical insulators in Si CMOS and nanoscale device applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Crystalline BeO film on Si (100) was deposited using E-beam evaporator and thermal oxidation. </LI> <LI> Excellent insulator properties, including a dielectric constant of 6.77 and a breakdown voltage of 8.3 MV/cm were deduced. </LI> <LI> Band alignment of EBE BeO/Si was analyzed by REELS and UPS. </LI> <LI> BeO/Si exhibits a very high CBO value (3.43 eV). </LI> <LI> Physical details of the band structure provide a good basis for applying EBE BeO to Si(100) MOSFETs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Electrical bistabilities and memory mechanisms of nonvolatile organic bistable devices based on exfoliated muscovite-type mica nanoparticle/poly(methylmethacrylate) nanocomposites

Lim, Won Gyu,Lee, Dea Uk,Na, Han Gil,Kim, Hyoun Woo,Kim, Tae Whan Elsevier BV * North-Holland 2018 Applied Surface Science Vol.432 No.2

<P><B>Abstract</B></P> <P>Organic bistable devices (OBDs) with exfoliated mica nanoparticles (NPs) embedded into an insulating poly(methylmethacrylate) (PMMA) layer were fabricated by using a spin-coating method. Current–voltage (I–V) curves for the Al/PMMA/exfoliated mica NP/PMMA/indium-tin-oxide/glass devices at 300K showed a clockwise current hysteresis behavior due to the existence of the exfoliated muscovite-type mica NPs, which is an essential feature for bistable devices. Write-read-erase-read data showed that the OBDs had rewritable nonvolatile memories and an endurance number of ON/OFF switching for the OBDs of 10<SUP>2</SUP> cycles. An ON/OFF ratio of 1×10<SUP>3</SUP> was maintained for retention times larger than 1×10<SUP>4</SUP> s. The memory mechanisms of the fabricated OBDs were described by using the trapping and the tunneling processes within a PMMA active layer containing exfoliated muscovite-type mica NPs on the basis of the energy band diagram and the I–V curves.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Organic bistable devices (OBDs) with exfoliated mica NPs embedded into an insulating PMMA layer were fabricated. </LI> <LI> Current–voltage curves for the devices showed a bistability with an ON/OFF ratio of 1×10<SUP>3</SUP>. </LI> <LI> ON and the OFF states for the devices endured for 10<SUP>2</SUP> cycles. </LI> <LI> ON/OFF ratio of 1×10<SUP>3</SUP> was maintained for retention times larger than 1×10<SUP>4</SUP> s. </LI> <LI> Memory mechanisms for the devices were attributed to the F-N tunneling process. </LI> </UL> </P>

Core-shell fibrous stem cell carriers incorporating osteogenic nanoparticulate cues for bone tissue engineering

Olmos Buitrago, J.,Perez, R.A.,El-Fiqi, A.,Singh, R.K.,Kim, J.H.,Kim, H.W. Elsevier BV 2015 ACTA BIOMATERIALIA Vol.28 No.-

Moldable hydrogels that incorporate stem cells hold great promise for tissue engineering. They secure the encapsulated cells for required periods while allowing a permeable exchange of nutrients and gas with the surroundings. Core-shell fibrous structured hydrogel system represents these properties relevant to stem cell delivery and defect-adjustable tissue engineering. A designed dual concentric nozzle is used to simultaneously deposit collagen and alginate with a core-shell structured continuous fiber form in the ionic calcium bath. We aimed to impart extrinsic osteogenic cues in the nanoparticulate form, i.e., bioactive glass nanoparticles (BGn), inside the alginate shell, while encapsulating rat mesenchymal stem cells in the collagen core. Ionic measurement in aqueous solution indicated a continuous release of calcium ions from the BGn-added and -free scaffolds, whereas silicon was only released from the BGn-containing scaffolds. The presence of BGn allowed higher number of cells to migrate into the scaffolds when implanted in subcutaneous tissues of rat. Cell viability was preserved in the presence of the BGn, with no significant differences noticed from the control. The presence of BGn enhanced the osteogenic differentiation of the encapsulated rat mesenchymal stem cells, presenting higher levels of alkaline phosphatase activity as well as bone related genes, including collagen type I, bone sialoprotein and osteocalcin. Taken together, the incorporated BGn potentiated the capacity of the core-shell fibrous hydrogel system to deliver stem cells targeting bone tissue engineering.

Thermoresponsive nanospheres with independent dual drug release profiles for the treatment of osteoarthritis

Kang, M.L.,Kim, J.E.,Im, G.I. Elsevier BV 2016 Acta Biomaterialia: structure-property-function re Vol.39 No.-

Dual drug delivery of drugs with different therapeutic effects in a single system is an effective way to treat a disease. One of the main challenges in dual drug delivery is to control the release behavior of each drug independently. In this study, we devised thermo-responsive polymeric nanospheres that can provide simultaneous and independent dual drug delivery in the response to temperature change. The nanospheres based on chitosan oligosaccharide conjugated pluronic F127 grafting carboxyl group were synthesized to deliver kartogenin (KGN) and diclofenac (DCF) in a single system. To achieve the dual drug release, KGN was covalently cross-linked to the outer part of the nanosphere, and DCF was loaded into the inner core of the nanosphere. The nanospheres demonstrated immediate release of DCF and sustained release of KGN, which were independently controlled by temperature change. The nanospheres treated with cold temperature effectively suppressed lipopolysaccharide-induced inflammation in chondrocytes and macrophage-like cells. The nanospheres also induced chondrogenic differentiation of mesenchymal stem cells, which was further enhanced by cold shock treatment. Bioluminescence of the fluorescence-labeled nanospheres was significantly increased after cold treatment in vivo. The nanospheres suppressed the progression of osteoarthritis in treated rats, which was further enhanced by cold treatment. The nanospheres also reduced cyclooxygenase-2 expression in the serum and synovial membrane of treated rats, which were further decreased with cold treatment. These results suggest that the thermo-responsive nanospheres provide dual-function therapeutics possessing anti-inflammatory and chondroprotective effects which can be enhanced by cold treatment. Statement of Significance: We developed thermo-responsive nanospheres that can provide a useful dual-function of suppressing the inflammation and promoting chondrogenesis in the treatment of osteoarthritis. For a dual delivery system to be effective, the release behavior of each drug should be independently controlled to optimize their desired therapeutic effects. We employed rapid release of diclofenac for acute anti-inflammatory effects, and sustained release of kartogenin, a newly found molecule, for chondrogenic effects in this polymeric nanospheres. This nanosphere demonstrated immediate release of diclofenac and sustained release of kartogenin, which were independently controlled by temperature change. The effectiveness of this system to subside inflammation and regenerate cartilage in osteoarthritis was successful demonstrated through in vitro and in vivo experiments in this study. We think that this study will add a new concept to current body of knowledge in the field of drug delivery and treatment of osteoarthritis.

Zwitterionic mesoporous nanoparticles with a bioresponsive gatekeeper for cancer therapy

Khatoon, S.,Han, H.S.,Lee, M.,Lee, H.,Jung, D.W.,Thambi, T.,Ikram, M.,Kang, Y.M.,Yi, G.R.,Park, J.H. Elsevier BV 2016 ACTA BIOMATERIALIA Vol.40 No.-

To enhance cellular uptake and site-specific drug release in the tumor microenvironment, zwitterionic mesoporous silica nanoparticles (Z-MSN) were prepared by introducing a bioresponsive gatekeeper composed of negatively charged carboxylic groups and positively charged quaternary amine groups. When these Z-MSN encountered a mildly acidic environment, their surface charge readily switched from negative to positive by cleavage of an acid-labile maleic amide linkage, thus allowing for effective cellular uptake into tumor tissue. Doxorubicin (DOX) encapsulated in Z-MSN was not significantly released in physiological conditions (pH 7.4), whereas the release rate of DOX remarkably increased in mildly acidic conditions through disintegration of the gatekeeper. The antitumor efficacy of DOX-loaded Z-MSN (DOX-Z-MSN) was evaluated after their systemic administration to tumor-bearing mice. Compared to free DOX and DOX-loaded MSN without the gatekeeper, DOX-Z-MSN exhibited much higher antitumor efficacy in vivo. Overall, these results demonstrated that the hydrophilic negative surface of Z-MSN, with their closed gate, allowed for their effective accumulation in tumor tissue after systemic administration, and that their charge-swapping and gate-opening in the tumor environment enhanced their cellular uptake and drug release rate simultaneously, implying a highly promising potential for development of Z-MSN as a drug carrier for cancer therapy. Statement of Significance: In an attempt to address the issues of enhanced cellular uptake and site-specific drug release of nanoparticles, we herein report on zwitterionic MSN (Z-MSN) with a pH-responsive gatekeeper which can be internalized into cancer cells via switching their surface charge from negative, in physiological conditions, to positive, in the tumor microenvironment. We hypothesized that the hydrophilic negative surface of Z-MSN with a closed gate allows for their accumulation into tumor tissue after systemic administration, whereas their charge-swapping and gate-opening in the tumor environment enhance cellular uptake and drug release rate simultaneously. Overall, Z-MSN constitute a promising drug delivery carrier for cancer therapy.

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>

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.