bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the Interfacial Water Transfer on the Analysis of Dynamic Sorption and Desorption Experiments in Nafion® Membrane
Authors: Didierjean Sophie , Perrin Jean-Christophe , Xu Feina , Maranzana Gael , Mainka Julia , Lottin Olivier
Published: February 2020

Water sorption and desorption in Nafion
®
117 membranes in acid form were studied by means of dynamic experiments as a response of relative humidity steps from 20% to 80% using a balance IGASORP (Hiden Isochema Ltd) which allows the measurement of very small mass variations with an accuracy of about 1 mg. The recorded mass variations with time of the membrane samples were analyzed by means of the least squares method based on a model that takes into account a transfer resistance at the interface between the membrane and the surrounding humid gas [1]. As the diffusion time is small (the diffusion coefficient being large), the diffusive internal resistance can be neglected compared to the interfacial resistance so that the water content of the membrane can be assumed uniform, which was confirmed using NMR imaging [2]. The model predicts than the kinetics of sorption is much faster than the kinetics of desorption, and the comparisons with the experimental results show a good agreement and give the value of the corresponding mass transfer coefficients (Figure 1). These results also agree with the results reported by Satterfield and Benziger [3] and they contribute to the debate concerning the existence of an interfacial resistance as reported in the recent review of Weber et al. [4]. For the experimental conditions considered in this study, the membrane is in equilibrium with the humid gas at the interface but the main resistance to water transfer is located in the humid gas phase.

REFERENCES

C.W. Monroe, T. Romero,W. Merida, M. Eikerling, Journal of Membrane Science 324 (2008) 1-6

M. Klein, J.-C. Perrin, S. Leclerc, L. Guendouz, J. Dillet and O. Lottin, ECS Transactions, 58 (1) 283-289 (2013)

M.B. Satterfield and J.B. Benziger, Non-Fickian vapor sorption dynamics by Nafion membranes, J. Phys. Chem. B, 2008, 3693-3704

Weber et al. A critical review of modeling transport phenomena in polymer-electrolyte fuel cells. Journal of the electrochemical society, 161 (12), F1254-F1299 (2014)

Figure 1
Random and Triblock Copolymers with Phosphonium Cations for Alkaline Fuel Cells
Authors: Liu Ye , Zhang WenXu , Zhang Bingzi , Yang Yuan , Coughlin Bryan E , Yan Yushan , Liberatore Matthew W , Herring Andrew M
Published: February 2020

Comparing with well-studied proton exchange membrane fuel cells (PEMFCs), a strongly competitive candidate of alkaline fuel cell (AFC) by using anion exchange membrane (AEM) as solid electrolyte has been joined attention1,2 Researchers worldwide are searching for new AEM electrolytes met with both long operation life and sufficient ionic conductivity in order to realize good AFC performance.3,4

Block copolymers are expected with highly ordered morphology, which will have interesting influence on the water uptake as well as conductivity performance. In our study, we compare tris(2,4,6-trimethoxyphenyl) phosphonium functionalized AEMs with both triblock (Figure 1. (a)) and random (Figure 1. (b)) backbone structures. The reason investigating on the bulky phosphonium cation is that attaching electron-donating functional groups (2,4,6-trimethoxyphenyl) has been tested beneficial for improvement of the chemical stability based on our previous study.5Besides, based on exploration on water uptakes, morphologies, conductivities and transport properties, Insights on block and random copolymer structures impact on fuel cell performance are developed. A further understanding of correlations between hydration number/morphology and conductivity performance are investigated. In this study, water uptake and hydration number are measured through dynamic vapor sorption (DVS). Conductivities under different relative humidity are performed by electrochemical impedance spectroscopy (EIS). Water transportation is measured by pulsed field gradient NMR (PFGNMR) and anion transportation is calculated via Mitra equation based on conductivity result. Morphologies are obtained from small angle X-ray scattering (SAXS) and atomic force microscopy (AFM).

Reference

[1] J.R. Varcoe, P. Atanassov, D.R. Dekel, A.M. Herring, M.A. Hickner, P.A. Kohl, A.R. Kucernak, W.E. Mustain, K. Nijmeijer, K. Scott, Anion-exchange membranes in electrochemical energy systems, Energy & Environmental Science 7 (2014) 3135-3191.

[2] G. McLean, T. Niet, S. Prince-Richard, N. Djilali, An assessment of alkaline fuel cell technology, Int. J. Hydrogen Energy 27 (2002) 507-526.

[3] V. Neagu, I. Bunia, I. Plesca, Ionic polymers - VI. Chemical stability of strong base anion exchangers in aggressive media, Polym. Degrad. Stab. 70 (2000) 463-468.

[4] A.A. Zagorodni, D.L. Kotova, V.F. Selemenev, Infrared spectroscopy of ion exchange resins: chemical deterioration of the resins, React. Funct. Polym. 53 (2002) 157-171.

[5] Y. Liu, J. Wang, Y. Yang, T.M. Brenner, S. Seifert, Y. Yan, M.W. Liberatore, A.M. Herring, Anion Transport in a Chemically Stable, Sterically Bulky Α-C Modified Imidazolium Functionalized Anion Exchange Membrane. J. Phys. Chem. C 118 (2014) 15136-15145.

Figure 1
PEM Fuel Cells - Critical Power
Authors: Sookhoo Ryan
Published: February 2020

Critical applications demand a high reliability of power to ensure our safety, functionality and security.   Energy diversity is key to achieving a high quality of power where and when it is needed; hydrogen fuel cells are essential to accomplishing this.  As traditional technologies advance and cutting edge products are created, they demand reliable and safe hydrogen solutions to fill the energy gaps.  

Critical power applications require flexibility from the power generation mix of technologies, whenever and wherever needed.   Fuel cell systems offer competitive runtime with diesel generators while providing the same reliability as batteries.  Fuel cell systems can remain in standby for extended periods of time without any maintenance or impact to their fuel source, and can react when needed.  Further, fuel cells offer a competitive solution over incumbent technology, by providing higher reliability, durability, economic and environmental improvements.

We will discuss how Hydrogenics fuel cell technology and design innovations, are being adopted in aviation, mobility and underwater applications.
Method to Resolve Transport Distance for Oxygen Diffusion in the Land-Channel Geometry of a PEMFC
Authors: Shrivastava Udit N , Tajiri Kazuya
Published: February 2020

Abstract

Land-channel geometry is known to cause significant current density distribution in the land-channel direction of a PEMFC. Previously, many modeling studies and a few experimental studies have shown significant variation of current density in the land-channel direction such as [1-2]. There are two prime sources of such variation: (1) non-uniform transport distance for gas diffusion from channel to the catalyst layer, and (2) non-uniform transport distance for product water generated at catalyst layer to the channel. Baker et. al. defined a shape factor f (> 1)  that removes anisotropy originated from land-channel geometry and gas diffusion layer (GDL) properties to provide resultant thickness of fh where h is thickness of a GDL [3].

We present a method to evaluate local transport distance in the land-channel geometry of a PEMFC. A segmented cell is developed to measure current density and high frequency resistance distribution in land-channel direction at sub-millimeter resolution of 350 μm. In this study, 1 mm wide land and channel configuration and GDL without microporous layer is used. Limiting current analysis reported in literature [4] is utilized to measure local limiting current at given resolution and then transport resistances were estimated.

H. Ju. J. of Power Sources, 191, 259 (2009).

U.N. Shrivastava, K. Tajiri. J. of Electrochem. Soc., 162, F722 (2015).

D. R. Baker, D. A. Caulk, K. C. Neyerlin, and M. W. Murphy. J. of Electrochem. Soc., 156, B991 (2009).

J. St-Pierre, B. Wetton, G.-S. Kim, and K. Promislow, J. of Electrochem. Soc., 154, B186 (2007).
Development of a Durable Cathode Material for PEFC By Encapsulating of Pt Particles into Carbon Mesopores
Authors: Hayashi Akari , Minamida Yasuto , Kitamura Masahiko , Noda Zhiyun , Sasaki Kazunari
Published: February 2020

Electrocatalysts have an important role to determine the performance of PEFC, which is a promising energy device for our future sustainable society. For PEFC electrocatalysts, Pt particles are generally dispersed on carbon supports. Reduction of Pt active sites during the long-time use becomes a serious problem for practical use of PEFC. Pt particles have tendency to agglomerate, or dissolve and re-precipitate under the potential cycles, resulting in the growth of particles. We are focusing of suppressing such Pt particle growth and increasing the durability of electrocatalysts by encapsulating Pt into the nanochannnels of mesoposous carbon (MC). This idea comes from reducing Pt mobility on the curved surface comparing to the flat surface, which is also supported by theoretical study.1

Electrocatalysts were synthesized from platinum(II) acetylacetonate as a precursor by depositing ca. 30 wt% Pt on our original MC, which was made from the self-organization formaldehyde/resorcinol and Pluronic F127.2 The resulting electrocatalyst was named as Pt/MC and used as a cathode catalyst. For the anode, a standard Pt/Ketjen black catalysts (TEC10E50E, TKK Corp.) was used. Membrane electrode assemblies (MEAs) were prepared by spray-printing the dispersion containing a catalyst and Nafion ionomer on both sides of Nafion membrane. For the comparison, Pt was also deposited on commercial available Vulcan XC72 carbon black, named as Pt/V, and used as a cathode catalyst.

Current-voltage (IV) characteristics of MEAs were measured in this study. Then, ohmic loss, concentration loss, and overvoltage were further analyzed separately after ohmic resistance was found by impedance measurements. In order to evaluate durability of MEAs, accelerating degradation tests were performed using potential cycles between 0.6 and 1.0 V vs RHE, where dissolution and re-precipitation of Pt particles occur.3 When the change in overvoltage was compared, the overvoltage was lower for Pt/MC-MEA than Pt/VC-MEA in all the cases after 5000, 20000, and 40000 cycles. Therefore, encapsulation of Pt nanoparticles into carbon nanochannels successfully increased durability.

  Change in size of Pt particles before and after 40000 potential cycles was evaluated by both surface and transmitted images at the same position. As seen Figure 1, large particles seen in STEM image are mostly identified as staying on the MC surface observed from SEM image Therefore, the growth of Pt particles was found suppressed within the nanochannels, which is most likely due to reduced Pt mobility inside the nanochannels.

References

[1] A. Staykov et al., J. Phys. Chem. C, 118, 8907 (2014)

[2] A. Hayashi et al., Electrochim. Acta, 53(21) 6117 (2008)

[3] A. Ohma et al., ECS Trans., 41, 755 (2011)

Figure 1
Influence of Structural Effects on Platinum Electrodes in the Preferential Adsorption of CO and Methanol in Acid Media
Authors: Paulino Marcia Elizangela , Colmati Flavio , Gonzalez Ernesto Rafael
Published: February 2020

The complete methanol electro-oxidation on platinum single crystal electrodes produces CO2, H2O and 6 e- in acidic medium. However methanol adsorption is sensitive to the platinum surface orientation, showing different reactivity for different platinum crystallographic planes.

In this work, it was studied the preferential adsorption and oxidation of carbon monoxide (CO) and methanol in acid media on polycrystalline and low index planes of platinum single crystals.

 In the experimental procedure carbon monoxide was bubbled in methanol solution with the platinum electrode polarized at 0.1 V vs. RHE. Then, the potential was scanned from 0.1 to 0.8 or 1.0 V vs ERH depending on platinum single crystal electrode.

From Figure 1a the carbon monoxide oxidation occurs at potential above 0.6 V vs. RHE for all platinum surfaces.  Besides data from Figure 1b methanol oxidation on Pt(111), Pt(100) and polycrystalline platinum electrodes exhibited high potential, above 0.8 V (RHE).

After adsorption of carbon monoxide on platinum electrodes, on polycrystalline platinum and Pt(100) the peak maximum occurred at more positive potential compared with methanol reaction. In this case methanol oxidation only was promoted after carbon monoxide oxidation reaction. On Pt(100) and Pt(111) the adsorption of CO contributed to reduce the potential for methanol oxidation.

Thus, these experiments suggest that carbon monoxide competes with methanol for adsorption on platinum electrode. For polycrystalline Pt and Pt(110) single crystals, the mixture CO+CH3OH showed potential of oxidation larger than with pure reactants. On the other hand, on Pt (111) and Pt(100) the oxidation of methanol happens at potential above that for the mixture of methanol and carbon monoxide, so that, it is possible that the electrochemical reaction follows different pathways on these surfaces.

Figure 1. (a) first potential scan at platinum electrodes in 0.2 M CH3OH + 0.1M H2SO4, obtained at 10 mV s-1. Insert show CO peak between 0.2 – 0.4 V (RHE). (b) Potential peak maximum dependence for CO, CH3OH and CO + CH3OH oxidation.

Acknowledgedment:CNPq for financial support (process 150885/2012-1).

References

1. X.H. Xia, T. Iwasita, F. Ge, W.Vielstich, Electrochim. Acta. 41 (1996) 711.

2. N.P. Lebedeva, A. Rodes, J.M. Feliu, M.T.M. Koper, R.A. van Santen, J. Phys. Chem. B 106 (2002) 9863.

3. T.M.T. Housmans, M.T.M. Koper, J. Phys. Chem. B 107 (2003) 8557.

Figure 1
Effect of Pore Volume of Hydrophilic Microporous Layer (MPL) on PEFC Performance
Authors: Tanuma Toshihiro , Kawamoto Masako
Published: February 2020

The effect of the microporous layer (MPL) on membrane electrode assemblies (MEAs) has been investigated. The performance of an MEA employing an MPL with a larger pore volume was better under both 100%RH and 30%RH conditions.

We reported that the MEA using a hydrophilic MPL showed much better performance in a wide range of pressure and humidity conditions than that using a hydrophobic MPL (1, 2). The hydrophilic MPL consists of vapor-grown carbon fiber with a fiber diameter of 150 nm and ionomer. We applied our technique of preparing a carbon fiber dispersion to the fabrication of MPLs using carbon particles and carbon fibers with various fiber diameters. Properties of carbon materials and MPLs are shown in Table 1. The pore size distribution (Fig. 1) was measured using mercury intrusion porosimetry (Auto Pore IV 9500, Shimadzu Co.).

Figure 2 shows the surface SEM images of the MPLs: The MPL made of carbon black (Vulcan XC) has the smallest pore diameter (0.068 μm) and that made of carbon fiber (VGCF-H) has the largest pore diameter (0.77 μm). Although carbon fiber CF-X has the largest fiber diameter of 250 nm, the MPL made of it has a smaller pore volume. This is probably because fibers of CF-X are straight and longer than other carbon fibers, tending not to become tangled and form larger pores.

MEAs having an MPL made of four different carbon materials (Vulcan, 24PS, VGCF-H, and CF-X) were prepared, and polarization curves were measured under the conditions of 80 ºC, 100%RH & 30%RH. The estimated mass transfer loss based on the polarization curves (80 ºC, 100%RH) for the four MEAs are plotted against the pore volume of MPL in Fig. 3. The larger the pore volume of MPL, the smaller the mass transfer loss becomes. The MEA employing a hydrophilic MPL with a larger pore volume also showed higher cell voltage under the dry condition of 80 ºC, 30%RH.

It was found that the pores of the hydrophilic MPL play a crucial role in achieving excellent MEA performance, such as mitigating cathode flooding under the wet condition and high cell voltage under the dry condition by preventing the membrane from drying.

References

1. T. Tanuma and S. Kinoshita, Energy Procedia, 28, 12 (2012).

2. T. Tanuma and S. Kinoshita, J Electrochem Soc, 159, B150 (2012).

Figure 1
RE-Doped Ternary Sulfides ALnS2 (A = Rb, K, Na; Ln = La, Gd, Lu, Y) - a New Phosphor Family
Authors: Jary Vitezslav , Havlak Lubomir , Barta Jan , Mihokova Eva , Buryi Maksym , Rejman Martin , Nikl Martin
Published: February 2020

We have recently started to investigate structural, scintillation, luminescence and paramagnetic (in case of Eu2+ doping) properties of the unexplored family of rare earth (RE)-doped ternary sulfides of general formula ALnS2 (A = Rb, K, Na; Ln = La, Gd, Lu, Y), which show prospective application potential in the field of X-ray and solid state white LED phosphors. The X-ray diffraction (XRD) detected only a single crystalline phase of rhombohedral lattice system, except NaLaS2 which has cubic structure. Time-resolved luminescence spectroscopy, XRD and electron paramagnetic resonance were employed to understand the nature of Eu2+ emission centre in these sulfidic hosts and find correlation between structural and optical properties of these materials. Eu2+ and Ce3+ emission features are investigated in a broad temperature and concentration ranges and phenomenological modeling and delayed recombination decay measurements are used to understand better the Eu2+ excited state dynamics. Optical properties of ALnS2 doped by another RE ions are presented as well. Motivating figure 1 shows clear energy shift of the Eu2+ emission spectra maxima with different chemical compositions, peaking from 498 nm (RbLuS2) to 779 nm (NaGdS2).

Figure 1.
RT Radioluminescence spectra of Eu2+-doped ALnS2.
Water Splitting Semiconductor Photoanodes - a Comparative Study
Authors: Augustynski Jan
Published: February 2020

The long term stability is the critical issue that conditions application of semiconductor materials in photo-electrochemical water splitting devices. This is the reason why the choice of the semiconductors intended to operate as water oxidation photo-anodes is actually restricted to a few metal oxides. However, none among those materials, able to absorb a significant portion of solar light, exhibits band-edge energy levels that match those of hydrogen and oxygen evolution reactions. Neither tungsten trioxide, nor bismuth vanadate and still less hematite ferric oxide have the positions of the conduction band edges more negative than the H2 evolution potential, a condition necessary to perform unassisted water splitting. Consequently, continuing efforts are devoted to minimize the bias voltage required to perform visible light-driven photo-oxidation of water. These efforts include, among others, development of new electrocatalysts and incorporation into photo-anodes of plasmonic metal nanostructures that allow incoupling of light into the semiconductor films, by scattering from plasmonic nanostructures and/or resonant coupling of the plasmonic electromagnetic near field to the semiconductor. Recent advances regarding the most investigated photoanode materials: WO3 (Eg = 2.5 eV); BiVO4 (Eg = 2.4 eV) and hematite Fe2O3 (Eg = 2.2 eV) will be discussed.
Catalysts, Protection Layers, and Semiconductors: The Challenge of Interfacing
Authors: Chorkendorff Ib
Published: February 2020

Hydrogen is the simplest solar fuel to produce and in this presentation we shall give a short overview of the pros and cons of various tandem devices [1,2]. The large band gap semiconductor needs to be in front, but apart from that we can chose to have either the anode in front or back using either acid or alkaline conditions.  Since most relevant semiconductors are very prone to corrosion the advantage of using buried junctions and using protection layers offering shall be discussed [3-5]. In particular we shall show how doped TiO2 is a very generic protection layer for both the anode and the cathode [6]. Next we shall discuss the availability of various catalysts for being coupled to these protections layers and how their stability and amount needed may be evaluated [7, 8, 9].  Examples of half-cell reaction using protection layers for both cathode and anode will be discussed though some of recent examples both under both alkaline and acidic conditions. Notably NiOx promoted by iron is a material that is transparent, providing protection, and is a good catalyst for O2 evolution [10]. Si is a very good low band gap semiconductor and the optimal thickness of this in a tandem device will be discussed [11]. We have also recently started searching for large band gap semiconductors like III-V based or pervoskite materials and follow the same strategy by using protection layers and catalysts [12].  Finally if time allows we shall also discuss the possibility of making high energy density fuels by hydrogenation of CO2 instead of hydrogen evolution [13].

 

References

       [1]     A. B. Laursen et al., Energy & Environ. Science 5 5577 (2012)

       [2]     B. Seger et al. Energy & Environ. Science 7 2397 (2014)

       [3]     B. Seger, et al. Angew. Chem. Int. Ed., 51 9128 (2012)

       [4]     B. Seger, et al., JACS 135 1057 (2013)

       [5]     B. Seger, et al., J. Mater. Chem. A, 1 (47) 15089 (2013)

       [6]     B. Mai et al. Submitted (2015).

       [7]     R. Frydendal, et al. Chem.Elec.Chem 1 2075 (2014).

       [8]     E. A. Paoli, et al. Chemical Science, Chemical Science, 6 190 (2015)

       [9]     E. Kemppainen et al. In Preparation (2015)

    [10]     B. Mei, et al. J. Phys. Chem. Lett. 5 1948 (2014)

    [11]     B. Dowon et al. Energy & Environ. Sci. 8  650 (2015)

    [12]     M. Malizia, et al. J. Mater. Chem. A DOI: 10.1039/C4TA00752B (2014)

    [13]     A. Verdaguer-Casadevall et al. In Preparation (2015)
Emerging Semiconductor Materials for Direct Photoelectochemical Water Splitting
Authors: Sivula Kevin
Published: February 2020

High-efficiency solar-to-fuel energy conversion can be achieved using direct semiconductor-liquid junctions in a photoelectrochemical (PEC) device consisting of an n-type photoanode in tandem with a p-type photocathode. However, the development of high-performance, stable and inexpensive photoelectrodes are needed to make PEC devices economically viable. In this presentation an overview and the state-of-the-art of this technology including economic considerations is given. In addition, our group’s progress in the development of economically-prepared, high performance photoelectrodes will be discussed along with the application toward overall PEC water splitting tandem cells. Specifically, how the use of scalable solution-processing techniques (e.g. colloidal processing of nanoparticles or sol-gels) leads to limitations in charge transport and charge transfer in the resulting thin-film photoelectrode will be examined. Strategies to overcome these limitations such as using charge extraction buffer layers, catalysts, annealing/doping and nanoparticle self-assembly will be additionally presented. Materials of interest are delafossite CuFeO2, CZTS, CIGS, CdS, organic (conjugated) semiconductors and 2D-layered MoS2 and WSe2.
Metal Organic Framework Solar Cells: A New Class of Sensitized Light Harvesting Devices
Authors: Maza William A , Morris Amanda J
Published: February 2020

Metal organic frameworks (MOFs) are comprised of bidentate linker scaffolds and metal/metal clusters nodes oriented into a porous, three-dimensional, crystalline networks. Modification of MOFs either through incorporation or encapsulation of molecular light-harvesters impart photo-activity through the generation of molecular excited states. Excited state chemistry in MOFs has been utilized for sensing, photo-catalytic, and photovoltaic applications. Herein, we report the fabrication of MOF-sensitized solar cells (MOFSCs) and compare their photovoltaic properties to an analogous dye-sensitized solar cell (DSSC) construct. Importantly, we report the first MOFSC that outperforms a traditional DSSC, solidifying MOFSCs as a promising platform for photovoltaic assemblies. The structure of the modified MOFs and their energy transfer properties are explored in detail and these results are correlated to solar cell efficiency. Through these correlations, we have uncovered vital structure–function relationships for the development of future MOFSCs.
Metal Oxide Nanosurfaces and Hetero-Interfaces for Solar Harvesting Applications
Authors: Mathur Sanjay , Gonullu Yakup , Fischer Thomas
Published: February 2020

Metal oxide nanostructures with hetero-contacts and phase boundaries offer unique platform for designing materials architectures for solar harvesting applications. Besides the size and surface effects, the modulation of electronic behavior due to junction properties leads to modify surface states that promote higher efficiency. The growing possibilities of engineering nanostructures in various compositions (pure, doped, composites, heterostructures) and forms (particles, tubes, wires, films) has intensified the research on the integration of different functional material units in a single architecture to obtain new materials for solar energy harvesting application.

In this work we present the deposition and modification of semiconducting metal oxides and their multilayers (TiO2, Fe2O3 and TiO2/Fe2O3) for photoelectrochemical (PEC) hydrogen production. The deposition parameters for thin film creation were optimized with respect to the PEC performance of the resulting materials in both alkali solution and simulated seawater. The long-term performances of the metal oxide photoanodes were determined in alkali and seawater electrolyte, as well. The results presented that the multilayered TiO2/Fe2O3 photonanode yielded higher photocurrent density (ca 2mA at 1.23 V) with very stable conditions even after 1-week measurement.
Hexavalent Chromium Removal in Industrial Relevant Water Matrices Using Metal Oxide Photocatalysts
Authors: Chan Candace K.
Published: February 2020

Photocatalysis is an attractive treatment method for removing hexavalent chromium, Cr(VI), from water. Thus far, photocatalytic reduction of Cr(VI) has been investigated mostly using TiO2 photocatalysts in acidic water solutions. Here we investigate Cr(VI) removal using zinc oxide (ZnO), tungsten trioxide (WO3), and sodium tantalate (NaTaO3), metal oxides that display good activity for other photocatalytic reactions such as water splitting, as well as the P90 form of TiO2 . The efficiency for Cr(VI) removal using these photocatalysts was investigated in synthetic neutral and alkaline water, as well as in cooling tower blowdown water.

A few common industrial additives were examined and the improvement on Cr(VI) removal using NaTaO3 from high to low was: sodium sulfite > ammonium chloride > sodium formate. At neutral pH, citric acid was found to inhibit Cr(VI) reduction with NaTaO3. Sulfite alone could remove Cr(VI) by chemical reduction, but required large quantities in excess. The combination of sulfite and photocatalyst greatly improved the Cr(VI) removal. Cr(VI) removal using photocatalysts was only slightly affected by other constituents in cooling tower blowdown and had similar removal rates as those observed in pH 7 DI water. NaTaO3 was found to display the highest Cr(VI) removal rates on a photon basis at pH = 3 and in the presence of sodium sulfite, while ZnO and TiO2 showed the best performance in pH = 7 and cooling tower blowdown water.

Different regeneration protocols were applied to the used photocatalysts. The alkaline treatment was more effective for removing adsorbed Cr(III) compared to nitric acid treatment, but acid treated TiO2 had better subsequent Cr(VI) reduction capabilities due to surface modifications that enhanced Cr(VI) adsorption. Both acid regenerated TiO2 and NaTaO3 demonstrated comparable Cr(VI) reduction rates with the pristine forms, indicating that these photocatalysts could be stable during regeneration and recycled for multiple uses. These results show that large scale wastewater treatment using metal oxide photocatalysts to remove Cr(VI) may be possible.
Fuel Production from the Electroreduction of CO2
Authors: Co Anne C.
Published: February 2020

Introduction

Electrochemical reduction is a highly effective method for converting CO2 to CO, organic acids, low molecular weight hydrocarbons and alcohols.  Product distribution from the reduction of CO2 is highly dependent on the composition and preparation of the catalysts and reduction potential, as such, multiple reduction pathways are observed depending on the catalysts material and the preparation methods.

Copper and its alloys have been found to produce higher molecular weight hydrocarbons, such as ethylene, methanol and ethanol.  Here we demonstrate a high surface area Cu alloy catalysts that has a preferential selectivity towards the formation of C2 and C3 species.  This paper will also discuss our attempts to understand the mechanistic pathway using in-situ vibrational spectroscopy under reaction conditions.

Experimental

A copper/aluminum alloy was used as the starting material for producing a high surface area copper catalyst.  The aluminum was removed through an etching procedure in strong base. The resulting nanoporous copper was crushed and mixed with Nafion, a binding agent, then casted over a copper foil substrate.  Carbon dioxide electroreduction was performed by placing the catalyst in a specially designed flow cell. A bubbler in the cell was used to deliver CO2 to saturate the electrolyte, 0.1 M KHCO3, at a rate of 10 mL/min. The catalyst acts as the working electrode in this electrochemical cell. The product distribution from the electroreduction process was collected at a series of potentials. Gaseous products were identified and quantified using gas chromatography coupled with both mass spectrometry and a thermal conductivity detector.  Liquid products were analyzed using nuclear magnetic resonance.

The surface morphology and composition of the catalyst was characterized using scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS).  The SEM images show a rough surface that retains a porous structure before and after experiments. XPS studies incorporated depth profiling, and show that ruthenium from the surface of the material migrates to the bulk after electrolysis.
Atomic Layer Deposition of Epitaxial Iron Oxides for Photoelectrochemical Water Oxidation
Authors: Emery Jonathan D. , Schlepütz Christian M. , Guo Peijun , Riha Shannon C. , Chang Robert P.H. , Martinson Alex B.F.
Published: February 2020

Solar-to-hydrogen energy conversion is regarded as an integral component in the future renewable energy infrastructure. Photo-assisted electrochemical (PEC) water splitting remains one possible route towards a viable solar-to-hydrogen conversion technology. Of the candidate materials for PEC water splitting photoanodes, hematite (α-Fe2O3) remains one of the most promising semiconductors for the water oxidation half-reaction because of its suitable bandgap for solar absorption, its terrestrial abundance, and its stability in aqueous. However, α-Fe2O3 photoanodes still demonstrate relatively poor PEC behavior due to slow water-splitting kinetics, poor charge transport, and challenges in the fabrication of high-quality Fe2O3 nanostructures necessary for efficient PEC devices.

Here, we show how epitaxial atomic layer deposition (ALD) can allow for the control of Fe2O3 phase, enables directed crystal growth, and permits nanostructured epitaxy. First, we utilize a transparent conducting substrate, (tin-doped indium oxide, ITO) as an isomorphic template for the epitaxial stabilization of the rare bixbyite phase of iron oxide (β-Fe2O3) and explore the PEC water oxidation properties of this material. Then, we utilize the metastable nature of β-Fe2O3 to produce various epitaxial α-Fe2O3/ITO films via a topotactic phase transition. These epitaxial α-Fe2O3 films provide benefits over their polycrystalline counterparts, possibly due to their well-defined crystallite orientations and reduction in density of high-angle grain boundaries. Finally, we show that ALD enables epitaxy of α-Fe2O3 on the walls of ITO nanowires, thereby providing a route to high-quality core-shell nanostructures which orthogonalize light absorption and charge transport to interfaces.
Electrodeposited WO3 Film on Various Metal Substrates and Its Morphological Effect for Photoelectrochemical Water Splitting
Authors: Kang Soon Hyung
Published: February 2020

Metal oxides such as TiO2, WO3, ZnO, SnO2 etc. have widely investigated because of low cost, environmental friendliness, and the application to various energy related devices. In particular, WO3 having the energetic band gap of about 2.8 eV has the absorption of more visible light, the suitable position of conduction band to transfer the photogenerated electrons to the substrate, and the stable photoresponse in the strong acidic condition. Herein, we prepared the WO3 film by electrodeposition that provides the clean and reproducible technique. That is, a compact structured WO3 film with a thickness of 780 nm was prepared by facile electrodeposition at a constant potential of -0.47 V versus saturated Ag/AgCl electrode. For a nanoporous structured WO3 film, polystyrene (PS) beads with a size of 320 nm were used as the template, and the electrodeposition was performed under the same experimental conditions by varying the reaction time from 1 to 3 min to adjust the thickness of the depositing layer. The PS beads were completely removed from the template by the calcination at 450 °C for 3 h under air, affording inverse opal WO3 films with a pore size of 300 nm. For the inverse opal WO3 film with a thickness of 790 nm prepared by electrodeposition for 1 min, the highest photocurrent density (1.75 mA/cm2 at 1.5 V versus sat. Ag/AgCl) was achieved, followed by compact WO3, inverse opal WO3 (2 min), and inverse opal WO3 (3 min) films with photocurrent densities of 1.2, 0.74, and 0.35 mA/cm2, respectively. The further discussion on the morphological and crystalline properties of the prepared WO3 film was confirmed by a field emission scanning electron microscope and X-ray diffraction.
Preparation, Characterization and Photoelectrochemical Investigation of p-Type Nanostructured Cobalt Titanate
Authors: Farsi Hossein , Moghiminia Shokufeh , Raissi Heidar
Published: February 2020

Nanostructured CoTiO3 was prepared by a low temperature modified sol-gel method using tetraisopropylorthotitanate as the sourse of Ti, cobalt nitrate as the source of cobalt, ethylene glycol and ethanol and a calcination temperature of 550°C. X-ray differactometry and transmission electron microscopy were used for characterization of crystal structure and morphology of prepared materials. A crystallite size of 57 nm for cobalt titanate and a nanoparticle size smaller than 70 nm were obtained for prepared samples. The band gap of prepared nanostructured cobalt titanate was determined optically by UV-Vis diffuse reflectance spectroscopy. Using electrochemical impedance spectroscopy and Mott-Schottky analysis, the energy band structures of nanostructured CoTiO3 were determined and its cyclic voltammograms were interpreted in terms of its energy band structure.
Photoelectrochemical Treatment of Reject Brines from RO Plants
Authors: Rassoolkhani Alan , Nguyen Kevin , McKee Austin , Hemingway Monica , Tentinger Scott , Cheng Wei , Mubeen Syed
Published: February 2020

Water scarcity issues have forced nations to find new approaches to meet growing water demands. Most often, this involves harvesting lower quality or impaired water supplies as a source for drinking water.  For example, in sea water desalination along coastal communities and in land-locked urban centers there is growing reliance of wastewater recycling. Desalination techniques, such as Reverse Osmosis, are used to restore municipal and industrial wastewater to a quality suitable for beneficial reuse (including drinking).  This method to produce high quality water is energy intensive and produces large volumes of concentrated brine that challenge the widespread implementation of such technologies.  Here we report a photoelectrochemical process that is built on established chloralkali processes to explore alternative systems. In doing so we address important fundamental questions on water desalination using sunlight while also pointing to near-horizon applications in solar energy conversion.
Understanding Lithium Solvation in Ionic Liquids from First Principles Molecular Dynamics Simulations
Authors: Kachmar Ali , Carignano Marcelo A.
Published: February 2020

Ionic liquids are being considered as an alternative electrolyte for Li-ion batteries. The main reason behind this application is the non-flammability of many ionic liquids that will eliminate one of the major safety issues affecting this technology. In this particular case, we investigate the solvation of lithium (Li) in Ethylammonium Nitrate (EAN). The study relies on a combination of classical, and first principles molecular dynamics simulations using the Gromacs and CP2K software packages, respectively [1,2]. Starting with an existing force field we initially performed a classical simulation in order to obtain a molecular arrangement that was then used as the starting configuration for the first principles simulations. We found that the first principles results give a lower Li-Oxygen average coordination number when compared to recently reported classical simulations [3]. The issue of the discrepancy between classical and first principles predictions for the coordination has been already discussed in the literature for cations solvated in water [4,7]. In particular, our ab-initio simulations conclusively show that only three nitrate molecules solvate the lithium ion in a planar arrangement, namely, the Li ion is located on or very close to the plane defined by the three nitrogen atoms corresponding to nitrate molecules.

[1] http://www.gromacs.org

[2] CP2K, http://www.cp2k.org/

[3] Méndez-Morales, Trinidad and Carrete, Jesús and Cabeza, "scar and Russina, Olga and Triolo, Ales- sandro and Gallego, Luis J. and Varela, Luis M. J. Phys. Chem. B, 2014, 118, 761-770.

[4] Bakó, I. and Hutter, J. and Pálinkás, G. J. Chem. Phys, 2002, 117, 9838-9843.

[5] Bakó, I. and Hutter, J. and Pálinkás, G. J. Phys. Chem. A, 2006, 110, 2188-2194.

[6] Ikeda, T. and B, Mauro, T, Kiyoyuki J. Chem. Phys. 2007, 126, 034501-9.

[7] Ikeda, T. and B, Mauro J. Chem. Phy. 2012, 137, 041101-4.
Graphene Oxide Based Electrochemical Biosensor
Authors: Rodriguez-Silva Allen Armando , Movil-Cabrera Omar , Staser John A
Published: February 2020

Recent advancements in nanotechnology have shown that carbon allotropes, such as graphene oxide, are potential candidates for use on electrochemical biosensors. The emerging field of electrochemical sensors to detect biomolecules have become of great importance to the biomedical field due to the urgent need of point-of-care devices that can serve as early detection and prevention methods. Our research has focused on developing a monoclonal antibodies functionalized electrode using functionalized graphene oxide (GO) as its anchor. We have synthetized this electrode by utilizing two different polymers: one for GO functionalization, and another as the polymer matrix. Preliminary spectroscopy results have confirmed GO functionalization which have led us to believe that the use of this nanocomposite in an electrode will serve as potential anchor for biomolecules, such as antibodies, for targeting biomolecules in blood serum. The use of certain antibodies in the functionalization process allows us to target desired, specific biomolecules in blood serum which can potentially impact the way blood serum tests are performed in clinical laboratories. Continuous use of Fourier Transform Infrared (FTIR), and Raman Spectroscopy will serve as validation of electrode functionalization. Cyclic voltammetry will confirm the electrode effectiveness towards measurements of certain biomolecules concentrations.
Integration of Nanostructured Dielectrophoretic Device and Surface-Enhanced Raman Probe for Highly Sensitive and Rapid Pathogen Detection
Authors: Madiyar Foram , Bhana Saheel , Swisher Luxi , Huang Xiaohua , Culbertson Christopher , Li Jun
Published: February 2020

Rapid and highly sensitive is critical for food safety and environmental protection. To achieve this, it requires the combination of both novel sample handling techniques and extremely sensitive detection methods. In previous studies, we have demonstrated the effective capture and quick concentration of pathogenic particles such as viral and bacterial particles in a fluidic chip using dielectrophoresis (DEP) enhanced with the highly focused electric field at the tip of an embedded nanoelectrode array. This work reports a further development with a synergistic approach to the concentration, detection and kinetic monitoring of pathogens through the integration of the nanostructured DEP device with nanotag-labelled Surface Enhanced Raman Scattering (SERS) for specific bacterial identification. A nanoelectrode array made of embedded Vertically Aligned Carbon Nanofibers (VACNFs) at the bottom of a microfluidic chip is used to effectively capture and concentrate nanotag-labelled E. coli DHα5 cells into a 200 micron x 200 micron area at which the Raman laser probe is focused. The SERS nanotags are based on iron oxide-gold (IO-Au) core-shell nanoovals (NOVs) of ~50 nm in size, which are coated with QSY21 Raman reporters and attached to E. coli cells through specific antibodies. The combination of the greatly enhanced Raman signal by the SERS nanotags and the effective DEP concentration significantly improves the detection limit and speed. The SERS signal has been measured with both a confocal Raman microscope and a portable Raman probe during DEP capture, and has been fully validated with fluorescence microscopy measurements under all DEP conditions. The SERS measurements are sensitive enough to detect a single bacterium. A concentration detection limit as low as 210 cfu/mL using a portable Raman system has been obtained with a DEP capture time of only ~50 s. The detection has been validated in purified solutions as well as complex samples including chicken broth, soil solution and apple juice. These results demonstrate the potential to develop a compact portable system for rapid and highly sensitive detection of specific pathogens. Furthermore, the AC impedance can be used to monitor the pathogen capture with slightly higher detection limit. Such system is reusable, requires minimum sample preparation, and is ideal for field applications.
Enzyme Biosensor for Detection of Formaldehyde on Carbon Nanotube-Screen Printed Electrodes Modified with Pyrenyl Groups
Authors: Premaratne Gayan , Farias Sabrina , Krishnan Sadagopan
Published: February 2020

Formaldehyde has been recognized as a marker in diseases associated with kidneys, nerves and lungs. Our objective is to develop a novel, highly sensitive electrochemical amperometric enzyme biosensor for detection of low levels of formaldehyde. Our biosensor design involves CNTs-modified screen-printed electrodes (SPEs) with immobilized formaldehyde dehydrogenase (FDH). CNT-coated electrodes modified with non-covalently attached pyrenebutyric acid linkers were used to attach the FDH enzyme and achieve enhanced electron transfer and biosensing properties. The FDH catalyzed oxidation of formaldehyde, using NAD+ as the electron acceptor, yields formic acid and NADH. This was detected electrochemically using an electrochemical mediator in solution. Such electrochemical sensors upon further optimization are expected to be useful for diagnosing clinically relevant levels of small molecule disease markers and environment pollutants.

Acknowledgements: We are grateful for the financial support by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health under Award Number R15DK103386.
Electrochemical Sensors to Detect Heavy Metals and Carcinogenic Compounds: Inquiry-Based Modules to Meet Today's Interest
Authors: Lunsford Suzanne Kay , Spradlin Corrie , Sullivan Mary , Dobson Dolores , Hughes Miyong
Published: February 2020

The developments of novel electrochemical sensors to detect phenol (phenol derivatives) and heavy metals in solution have been a focus of our inquiry-based laboratory experiences.  Our students are engaged into the applications of Controlled Potential Electrolysis (CPE) to create a modified working electrode to detect the common contaminants such as phenols and heavy metals in solutions by electroanalytical techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square wave anodic stripping voltammetry (SWASV).   Additional analytical instrumentation skills were required through out these inquiry-based learning experiences to confirm the modified working electrodes (TiO2/ZrO2, Polymers and Carbon Nanotube, CNT) were electrochemically created by such instrumentation such as Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy and X-Ray Fluorescence.  The students content gains were assessed through out these lab modules according to the R.R. Hake’ method.  These content gains assessed will be discussed as well to exemplify the inquiry-based learning experiences of our undergraduate students experiences to meet the needs of todays workforce.
Sensor Research and Detection Technology for Efficient Water Usage and Security in Agriculture
Authors: KIM Dong-Joo
Published: February 2020

Agriculture is the world’s largest consumer of water. Currently, 70% of global freshwater consumption is for agriculture, corresponding to a volume of over 2,500 km3. Unfortunately, water usage in agriculture is often highly inefficient with only a fraction of the water effectively used in plant growth. The rest of the water is lost via soil drainage, evaporation or transpiration. By 2050, the world’s population is expected to exceed 7 billion. The United Nations estimates that total agricultural water consumption will increase by 19% to meet global food demand. Additionally, increasing demand to shift more of the water used in agriculture to higher-value urban and industrial purposes will place additional stress on water for agriculture. Irrigation is also energy intensive. For example, irrigation with groundwater can lead to energy costs in the range of $10 to 100/acre per year. In California alone, agricultural irrigation uses 10 billion kilowatt hours of electricity annually.

Water use efficiency in agriculture has been researched extensively. Conversion from traditional furrow irrigation to micro-irrigation methods has been shown to reduce irrigation needs by about 50% while improving yields. Unfortunately, present practice is less than ideal and often fails to collect all information necessary for cost effective management decisions. The utilization of above-ground irrigation systems has been shown to be effective, but a lack of adequate sensors for monitoring and control has led to non-optimal irrigation practices. Improving the efficient use of water resources still demands the development of new technologies that cost less and save energy by accurately assessing crop status for a given location, climate and soil conditions. 

Recently, advances in sensing and detection technologies as well as new approaches and protocols demonstrated potential for efficient irrigation control. Examples of the sensors include measurement of water efficiency, crop and soil-water conditions and evaluate food safety. Wireless sensor networks to transmit the measured information is also one of important technologies.  As efforts to address issues in agricultural monitoring, our research team has developed smart dipstick sensors to measure liquid conditions including surface tension, viscosity, temperature, water content and acidity. Smart trap to monitor invasive pests and environment has demonstrated the use of sensor systems for protecting crops. A remote, wireless magnetoelastic biosensor has also been focused on identifying the presence of various pathogens for enhancing food safety and security.

Sensor system and detection technology will enable targeted applications of water, fertilizer and pesticides to greatly reduce costs, improve producer profitability, and lead to a more sustainable agriculture. Efficient irrigation will also reduce environmental degradation while lowering energy usage in agriculture.