Electrochemical conversion of carbon dioxide (CO2) to small organic fuels (e.g. formate, methanol, ethylene, ethanol) is touted as one of the most promising approaches for solving the problems of climate change and energy security. In this study, we report the highly efficient electrochemical reduction of CO2 using cuprous oxide (Cu2O) electrodes to produce ethylene (C2H4) primarily. During CO2 electrolysis using electrodeposited Cu2O on a carbon electrode, we observe the transformation of a compact metal oxide layer to a metal oxide structure with oxygen vacant sites at the bulk region. In contrast to previous studies, our results clearly indicate that Cu2O remains at the surface of the catalyst and it efficiently catalyzes the conversion process of CO2 at low overpotential, exhibiting a high selective faradaic efficiency of over 20% towards C2H4 formation even in long-term electrolysis.
Effectiveness of TiCl3 pre- and post-treatments on dye-sensitized solar cells (DSCs) and interfacial charge-transfer properties were investigated. It was confirmed that a yield of current collection was strongly dependent on the position of the TiCl3/electrolyte matrix in the DSC configuration. The interfacial charge-transfer properties were studied using thermionic emission-diffusion process and electrochemical impedance spectroscopy analysis. The TiCl3/electrolyte matrix was considered to be a three-dimensional quasi-photonic crystal with a photonic band gap, which reinforces electric field and facilitates current collection from the TiCl3/electrolyte matrix to the FTO by accelerating electron motion, whereas the potential barrier blocks current collection from the TiO2 bulk region to the FTO and decreases current.
The effect of reduction of visibility on crash occurrence has recently been a major concern. Although visibility detection systems can help to mitigate the increased hazard of limited-visibility, such systems are not widely implemented and many locations with no systems are experiencing considerable number of fatal crashes due to reduction in visibility caused by fog and inclement weather. On the other hand, airports' weather stations continuously monitor all climate parameters in real-time, and the gathered data may be utilized to mitigate the increased risk for the adjacent roadways. This study aims to examine the viability of using airport weather information in real-time road crash risk assessment in locations with recurrent fog problems. Bayesian logistic regression was utilized to link six years (2005-2010) of historical crash data to real-time weather information collected from eight airports in the State of Florida, roadway characteristics and aggregate traffic parameters. The results from this research indicate that real-time weather data collected from adjacent airports are good predictors to assess increased risk on highways.
Metal-air batteries continue to become attractive energy storage and conversion systems due to their high energy and power densities, safer chemistries, and economic viability. Semiconductor-air batteries - a term we first define here as metal-air batteries that use semiconductor anodes such as silicon (Si) and germanium (Ge) - have been introduced in recent years as new high-energy battery chemistries. In this paper, we describe the excellent doping-dependent discharge kinetics of p-type Ge anodes in a semiconductor-air cell employing a gelled KOH electrolyte. Owing to its Fermi level, n-type Ge is expected to have lower redox potential and better electronic conductivity, which could potentially lead to a higher operating voltage and better discharge kinetics. Nonetheless, discharge measurements demonstrated that this prediction is only valid at the low current regime and breaks down at the high current density region. The p-type Ge behaves extremely better at elevated currents, evident from the higher voltage, more power available, and larger practical energy density from a very long discharge time, possibly arising from the high overpotential for surface passivation. A primary semiconductor-air battery, powered by a flat p-type Ge as a multi-electron anode, exhibited an unprecedented full discharge capacity of 1302.5 mA h gGe(-1) (88% anode utilization efficiency), the highest among semiconductor-air cells, notably better than new metal-air cells with three-dimensional and nanostructured anodes, and at least two folds higher than commercial Zn-air and Al-air cells. We therefore suggest that this study be extended to doped-Si anodes, in order to pave the way for a deeper understanding on the discharge phenomena in alkaline metal-air conversion cells with semiconductor anodes for specific niche applications in the future.
Co oxides are known to be active and stable alternative anode electrocatalysts possessing the potential to replace the best performing but most expensive Ir and Ru oxides in alkaline water electrolysis. Of late, Co oxides loaded on various carbon supports have been reported as a way to outperform Ir or Ru catalysts by improving the utilization efficiency. In this study, we introduce Co and Fe nanoparticles embedded carbon nanofibers (CoFe-CNFs), fabricated through electrospinning and pyrolysis of a polymer mixed with Co and Fe precursors. This method is a facile route for simultaneously making Co and Fe nanoparticles as well as the stable accommodation of the CoFe nanoparticles in the carbon support. We demonstrate the potential of the CoFe-CNFs as active and stable electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. We conducted detailed physico-chemical characterizations to elucidate the effect of the CNFs on the OER activity and stability of the CoFe-CNFs. It is suggested that the CNFs are a medium in which OER-active CoFe alloy nanoparticles are formed homogeneously, and that carbon layers surrounding the nanoparticles are beneficial to the stability of the CoFe-CNFs in the OER.
Platinum (Pt) is the best electrocatalyst for the oxygen reduction reaction (ORR) in hydrogen fuel cells, but it is an extremely expensive resource. The successful development of a cost-effective non-Pt ORR electrocatalyst will be a breakthrough for the commercialization of hydrogen-air fuel cells. Ball milling has been used to incorporate metal and nitrogen precursors into micropores of carbon more effectively and in the direct nitrogen-doping of carbon under highly pressurized nitrogen gas in the process of the preparation of non-noble ORR catalysts. In this study, we first utilize ball milling to excavate the ORR active sites embedded in Fe-modified N-doped carbon nanofibers (Fe-N-CNFs) by pulverization. The facile ball-milling process resulted in a significant enhancement in the ORR activity and the selectivity of the Fe-N-CNFs owing to the higher exposure of the metal-based catalytically active sites. The degree of excavation of the Fe-based active sites in the Fe-N-CNFs for the ORR was investigated with cyclic voltammetry, X-ray photoelectron spectroscopy, and pore-size distribution analysis. We believe that this simple approach is useful to improve alternative ORR electrocatalysts up to the level necessary for practical applications.
In this article, we highlight the salient issues in the development of lithium-sulfur battery (LSB) cathodes, present different points of view in solving them, and argue, why in the future, functionalized graphene or graphene oxide might be the ultimate solution towards LSB commercialization. As shown by previous studies and also in our recent work, functionalized graphene and graphene oxide enhance the reversibility of the charge-discharge process by trapping polysulfides in the oxygen functional groups on the graphene surface, thus minimizing polysulfide dissolution. This will be helpful for the rational design of new cathode structures based on graphene for LSBs with minimal capacity fading, low extra cost, and without the unnecessary weight increase caused by metal/metal oxide additives.
Although octamer-binding transcription factor 4 (Oct-4) is one of the most intensively studied factors in mammalian development, no cellular genes capable of replacing Oct-4 function in embryonic stem (ES) cells have been found. Recent data show that nuclear receptor subfamily 5, group A, member 2 (Nr5a2) is able to replace Oct-4 function in the reprogramming process; however, it is unclear whether Nr5a2 can replace Oct-4 function in ES cells. In this study, the ability of Nr5a2 to maintain self-renewal and pluripotency in ES cells was investigated. Nr5a2 localized to the nucleus in ES cells, similarly to Oct-4. However, expression of Nr5a2 failed to rescue the stem cell phenotype or to maintain the self-renewal ability of ES cells. Furthermore, as compared with Oct-4-expressing ES cells, Nr5a2-expressing ES cells showed a reduced number of cells in S-phase, did not expand normally, and did not remain in an undifferentiated state. Ectopic expression of Nr5a2 in ES cells was not able to activate transcription of ES cell-specific genes, and gene expression profiling demonstrated differences between Nr5a2-expressing and Oct-4-expressing ES cells. In addition, Nr5a2-expressing ES cells were not able to form teratomas in nude mice. Taken together, these results strongly suggest that the gene regulation properties of Nr5a2 and Oct-4 and their abilities to confer self-renewal and pluripotency of ES cells differ. The present study provides strong evidence that Nr5a2 cannot replace Oct-4 function in ES cells.
We first report the successful synthesis of porous germanium with ordered hierarchical structures, via controlled etching, and show its performance as an anode in a new metal-air battery. Our experimental results demonstrate the potential use of porous germanium in a high power density Ge-air energy conversion cell, showing a stable long-term discharge profile at various current drains.
Carbon-supported Pd electrocatalyst is prepared by an improved aqueous impregnation method applying a reducing agent of HCHO and an acidic sedimentation promoter of HCl. We investigate the effect of a solution pH on the zeta potential of both Pd particles and carbon support. The opposite sign of zeta potential results in uniform dispersion of Pd on carbon surface without aggregation problem. TEM analysis shows that optimal solution pH of 4.27 adjusted by NaOH provides a mean particle diameter of 3.2 nm with narrow size distribution. Cyclic voltammograms indicate that home-made Pd/C catalyst exhibits significantly higher electrochemical active surface area and better stability compared with commercial 40 wt.% Pd/C in a formic acid oxidation.
Ultrasound (US) imaging is one of the most common biomedical imaging methods, due to the easy assessment and noninvasive way. For more precise and accurate US imaging, many contrast agents have been developed in a form of microbubbles composed of inner gas and shell materials. However, microbubbles showed undesirable short half-life under acoustic field during US imaging and insufficient in vivo stability in blood flow due to diffusion or bubble destruction. Therefore, the improvement of the half-life and stability of microbubbles under in vivo condition is highly needed for long-term in vivo US imaging. Herein, we developed rationally designed gas-generating polymeric microsphere (GGPM) that can produce microbubbles without encapsulation of gas for long-term and continuous US imaging. The poly(cholesteryl ?-butyrolactone-b-propylene oxide), poly(CB-PO), with carbonate side chains was synthesized as gas-generating polymer by ring-opening polymerization of cholestryl ?-butyrolactone (CB) and propylene oxide (PO). As optimal structure for intense US signal generation, porous GGPMs (p-GGPMs) with the average size about 3-5 ?m were prepared with poly(CB-PO) by double emulsion method. These p-GGPMs generated continuous US signals over 70 min, while the signals from Sonovue(®), a commercial US contrast agent were completely attenuated within 15 min. This long-term signal duration of p-GGPM was also reproduced when they were subcutaneously injected under the skin of mouse. Moreover, as advanced in vivo application, the fine US imaging of heart in rat was enabled by intravenous injection of p-GGPM. Therefore, these overall results showed the great potential of p-GGPM as gas-generating US contrast agent for in vivo biomedical imaging and diagnosis.
Organic contamination of water bodies in which benthic microbial fuel cells (benthic MFCs) are installed, and organic crossover from the anode to the cathode of membraneless MFCs, is a factor causing oxygen depletion and substrate loss in the cathode due to the growth of heterotrophic aerobic bacteria. This study examines the possible use of silver nanoparticles (AgNPs) as a cathodic catalyst for MFCs suffering from organic contamination and oxygen depletion. Four treated cathodes (AgNPs-coated, Pt/C-coated, Pt/C+AgNPs-coated, and plain graphite cathodes) were prepared and tested under high levels of organics loading. During operation (fed with 50 mM acetate), the AgNPs-coated system showed the highest DO concentration (0.8 mg/L) in the cathode area as well as the highest current (ranging from 0.04 to 0.12 mA). Based on these results, we concluded that (1) the growth of oxygen-consuming heterotrophic microbes could be inhibited by AgNPs, (2) the function of AgNPs as a bacterial growth inhibitor resulted in a greater increase of DO concentration in the cathode than the other tested cathode systems, (3) AgNPs could be applied as a cathode catalyst for oxygen reduction, and as a result (4) the MFC with the AgNPs-coated cathode led to the highest current generation among the tested MFCs.
Novel nanostructured gas filtering systems with TiO(2) thin films using atomic layer deposition (ALD) were developed for volatile organic compounds. A superior toluene adsorption efficiency was found for the nanostructured TiO(2) thin films.
We investigated the origin of the reactive surface of Pd catalysts during the electrocatalytic oxidation of formic acid. XPS analysis was the primary tool adapted to characterize the surface changes in Pd catalysts arising from interactions with formic acid. Pd catalysts showed fast deactivation, though their activity could be simply recovered by applying a reduction potential at which hydrogen evolution reaction can occur. XPS analysis revealed that the surface of Pd catalysts is significantly affected by interaction with formic acid, thus confirming that the surface coverage of oxygen species plays an important role in formic acid electrooxidation on the Pd catalysts. At the same time, mass transfer of formic acid also has an effect on the deactivation of Pd catalysts.
P-type thermoelectric bismuth telluride nanowires were fabricated by pulsed electrodeposition in anodic aluminium oxide (AAO) membranes. Subsequently, the nanowires were annealed at 423, 523 and 673 K in an inert atmosphere for 4 h. With increasing temperature, it was observed that the Te compound incongruently sublimates due to its high vapor pressure, leading to disproportionation (from Bi(2)Te(3) to Bi(4)Te(3)via Bi(4)Te(5)). The crystalline structure of the nanowires was then investigated using XRD and SAED, with nanowire compositions investigated using an EDX attached to a TEM. The crystallinity of the nanowires was found to be enhanced with increased annealing temperature, and nanowires annealed at 673 K were stably maintained in the Bi(4)Te(3) phase. Additionally, the Seebeck coefficient was determined and the thermopower of nanowires annealed at a temperature of 423 K was shown to be slightly enhanced. Significantly suppressed Seebeck values for annealing temperatures of 523 K and 673 K were also observed.
Interfacial resistances between the polymer electrolyte membrane (PEM) and catalyst layer (CL) in membrane-electrode assemblies (MEAs) have yet to be systematically examined in spite of its great importance on the fuel cell performance. In order to investigate ionic transport through the PEM/CL interface, the symmetrical impedance mode (SIM) was employed in which the same type of gas was injected (H(2)/H(2)). In this study, the ionic transport resistance at the interface was controlled by the additionally sprayed outer ionomer on the surface of each CL. Effectiveness of the outer ionomer on ionic transport at the interface was quantitatively explained by the reduced contact, proton hydration, and charge transport resistances in the SIM. To characterize the ionic transport resistance, the concept of total resistance (R(tot)) in the SIM was introduced, representing the overall ohmic loss due to proton transport in an MEA. This concept was successfully supported via an agreement of the interpretation and the linear correlation that was obtained between the admittance (1/R(tot)) and the performance of a fuel cell in the ohmic loss region. This correlation will enable researchers to predict the performance of a fuel cell under the influence of proton transport by examining the R(tot) in the SIM.
This paper describes an ultra-sensitive surface-based detection method using nanoparticle-enhanced surface plasmon resonance (SPR) for the detection of immunoglobulin E (IgE) proteins, which could potentially be used for the diagnosis of allergic diseases. Two different probes, anti-IgE and IgE specific aptamers, which can specifically interact with IgE at different epitopes were first investigated for their specific interaction with IgE using SPR. Langmuir adsorption coefficient (K(ads)) values were measured as 2.0(+/-0.22)x10(8)M(-1) and 2.2(+/-0.20)x10(8)M(-1) for IgE interactions with anti-IgE and IgE specific aptamers, respectively. The SPR detection limit of the simple adsorption of IgE onto either anti-IgE or IgE specific aptamers was found to be about 1nM. In order to improve the SPR detection signal for IgE, two different approaches utilizing surface formed sandwich complexes with biofunctionalized gold nanoparticles (Au-Nps) were designed and their detection performance were compared; the complexes were created via the adsorption of IgE onto (i) surface immobilized anti-IgE followed by the adsorption of IgE specific aptamer coated gold nanoparticles and (ii) IgE specific aptamer surface with the subsequent adsorption of anti-IgE coated gold nanoparticles. Both detection schemes were able to directly measure IgE at femtomolar concentrations.
We demonstrate a novel reference electrode material namely an organometallic silver complex e.g., silver (I) tetramethylbis(benzimidazolium) diiodide [1a] for both acid and alkaline electrolysis. The potential usage of the silver complex as a reference electrode with at least equal electrochemical capabilities compared to those of the conventional electrode materials (e.g., Hg/HgO in alkaline media and Ag/AgCl in acidic media) are also demonstrated using cyclic voltammetry. In addition, the well dispersed surface morphology and fine crystalinity of the silver complex is investigated using field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD).
A basic understanding of electrode structure and the characteristics of its components can be powerfully utilized in fuel cell applications such as direct formic acid fuel cell (DFAFC) system integration and HCOOH concentration controlled systems. There have been, thus, tremendous efforts made to elucidate theoretical aspects of electrochemical processes involving new anode catalysts and put them into practical effect on formic acid fuel cells. Herein, we highlight recent studies for better understanding of the underlying processes in DFAFC: (i) a systematic approach for developing cost-effective and stable anode catalysts and electrode structures that incorporate mass transport characteristics of HCOOH; (ii) a clear evaluation of the HCOOH crossover rate based on its physicochemical properties; and (iii) a theoretical assessment process of individual electrodes and related components during DFAFC operation using electrochemical impedance spectroscopy and a reversible hydrogen reference electrode, which can potentially detect subtle changes in the DFAFC mechanism and provide useful information pertaining to rate-limiting processes.
As global warming directly affects the ecosystems and humankind in the 21st century, attention and efforts are continuously being made to reduce the emission of greenhouse gases, especially carbon dioxide (CO2). In addition, there have been numerous efforts to electrochemically convert CO2 gas to small organic molecules (SOMs) and vice versa. Herein, we highlight recent advances made in the electrocatalytic recycling of CO2 and SOMs including (i) the overall trend of research activities made in this area, (ii) the relations between reduction conditions and products in the aqueous phase, (iii) the challenges in the use of gas diffusion electrodes for the continuous gas phase CO2 reduction, as well as (iv) the development of state of the art hybrid techniques for industrial applications. Perspectives geared to fully exploit the potential of zero-gap cells for CO2 reduction in the gaseous phase and the high applicability on a large scale are also presented. We envision that the hybrid system for CO2 reduction supported by sustainable solar, wind, and geothermal energies and waste heat will provide a long term reduction of greenhouse gas emissions and will allow for continued use of the abundant fossil fuels by industries and/or power plants but with zero emissions.
Capacitive deionization (CDI) for removal of water hardness was investigated for water softening applications. In order to examine the wettability and pore structure of the activated carbon cloth and composites electrodes, surface morphological and electrochemical characteristics were observed. The highly wettable electrode surface exhibited faster adsorption/desorption of ions in a continuous treatment system. In addition, the stack as well as unit cell operations were performed to investigate preferential removal of the hardness ions, showing higher selectivity of divalent ions rather than that of the monovalent ion. Interestingly, competitive substitution was observed in which the adsorbed Na ions were replaced by more strongly adsorptive Ca and Mg ions. The preferential removal of divalent ions was explained in terms of ion selectivity and pore characteristics in electrodes. Finally, optimal pore size and structure of carbon electrodes for efficient removal of divalent ions were extensively discussed.
Sequences and organization of the mitochondrial genome have been used as markers to investigate evolutionary history and relationships in many taxonomic groups. The rapidly increasing mitochondrial genome sequences from diverse insects provide ample opportunities to explore various global evolutionary questions in the superclass Hexapoda. To adequately support such questions, it is imperative to establish an informatics platform that facilitates the retrieval and utilization of available mitochondrial genome sequence data.
Indium tri(isopropoxide)-catalyzed Meerwein-Ponndorf-Verley reduction of aliphatic and aromatic aldehydes in 2-propanol gave selectively the corresponding primary alcohols in good to excellent yields at room temperature. A wide range of functional groups including alkene, ether, ketone, ester, nitrile, and nitro were tolerated under the optimum reaction conditions. Chemoselective reductions were also achieved not only between aromatic aldehyde, aromatic ketone, and epoxide but also between aliphatic aldehyde and alkene.
The application of biofunctionalized nanoparticles possessing various shapes and sizes for the enhanced surface plasmon resonance (SPR) detection of a protein biomarker at attomolar concentrations is described. Three different gold nanoparticle shapes (cubic cages, rods and quasi-spherical) with each possessing at least one dimension in the 40-50 nm range were systematically compared. Each nanoparticle (NP) was covalently functionalized with an antibody (anti-thrombin) and used as part of a sandwich assay in conjunction with a Au SPR chip modified with a DNA-aptamer probe specific to thrombin. The concentration of each NP-antibody conjugate solution was first optimized prior to establishing that the quasi-spherical nanoparticles resulted in the greatest enhancement in sensitivity with the detection of thrombin at concentrations as low as 1 aM. When nanorod and nanocage antibody conjugates were instead used, the minimum target concentrations detected were 10 aM (rods) and 1 fM (cages). This is a significant improvement (>10(3)) on previous NP-enhanced SPR studies utilizing smaller (~15 nm) gold NP conjugates and is attributed to the functionalization of both the NP and chip surfaces resulting in low nonspecific adsorption as well as a combination of density increases and plasmonic coupling inducing large shifts in the local refractive index at the chip surface upon nanoparticle adsorption.
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