bluuebunny/crossref_metadata_2025_split huggingface dataset:
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
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)
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.
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.