bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of TiS2 by OS Process in CaCl2 Melt
Authors: Suzuki Nobuyoshi , Tanaka M , Noguchi H , Natsui S , Kikuchi T , Suzuki Ryosuke O.
Published: February 2020

Kroll process is composed a few independent thermal processes and consumes huge energy to produce metal Ti. OS process produces reductant Ca continuously in the molten salts and reduces directly Ti oxides to obtain metal Ti, which may become energy saving [1]. However, it is necessary to electrolyze for long time because the reduction speed is slow. To avoid severe problems in oxide reduction, we select TiS2 as raw material. Sulfur locates just below oxygen at periodic table, and many chemical properties are similar with oxygen. In addition, metallic Ti does not dissolve sulfur according to Ti-S binary phase diagram. Therefore, the step for sulfur removal from Ti-S solid solution can be skipped and a high quality of Ti is expected to be formed more quickly. A dry synthesis of TiS2 from TiO2[2] can be combined with the studied processes to recycle sulfur.

The purpose of this work is to examine the feasibility of thermochemical and electrochemical reduction of TiS2 by the electrolysis in the molten CaCl2to establish the new metal Ti manufacturing process.

Figure shows the results by the OS process at 1173 K in CaCl2-0.5mol% CaS melt. Concentration of sulfur decreased significantly at early stage. 0.043 mass %S was achieved when the stoichiometric charge Q0 was supplied, and 0.01 mass %S was achieved when Q = 4Q0 was supplied. Only Ti was identified by XRD at Q ≥ Q0. In stoichiometry, metal Ti and lower oxide were identified but no lower sulfide could be found.

The electrolysis rate could be improved when the larger amount of CaS is dissolved. However, concentration of residual sulfur in Ti increased as the addition of CaS increased.

In conclusion, 0.01mass%S could be obtained by the OS process. Addition of CaS could improve reduction rate, but impurity in Ti increased. It is possible to remove sulfur from Ti-S system, and the usage of Ti sulfide opens a new process of titanium refining process. Kroll process needs three steps to manufacture metal Ti, chlorinating, reduction by Mg, and electrolysis of MgCl2, while this new process needs only two steps, sulfide formation, and reduction by Ca. The authors desire the higher efficiency and energy saving using our proposal.

R
eferences

[1] R.O. Suzuki, K. Teranuma and K. Ono, Metall. Mater. Trans B, 34B, [6] 287 (2003).

[2] S.Hirai, M.Ohta, S.Satoh, and T.Kuzuta, Acta Materialia60 (2012) 7232-7240

Acknowledgements: This work was partly supported by the "Innovative Structural Materials Project (ISMA, Future Pioneering Projects)” and KOBE STEEL, LTD. The authors thank Prof. S. Hirai at Muroran Institute of Technology for discussion.

Figure 1
Probing Ionic Liquid/Electrode Interfaces by Hyperspectral Imaging
Authors: Malik Muhammad Kasim , Chrestenson Jacob R , Parr Daniel , Gray David , Mitiku H , Kahila Thomas , Malinowski Aleksander , Sánchez José , Haverhals Luke M.
Published: February 2020

We will present data for experiments that probe structure and dynamics at ionic liquid (IL) and ionic liquid-based (IL-based) systems with electrode interfaces. IL-based electrolytes have been investigated for applications ranging from energy conversion devices (e.g., capacitors, batteries, fuel cells, and solar cells) to sensors. Fundamental characterizations of IL-based electrolyte/electrode systems can contribute toward engineered progress for these enterprises since adsorbed species and their associated interfacial dynamics play critical roles in determining device efficiencies. Our studies utilize surface enhanced infrared absorption (SEIRA) spectroscopy. In particular, we demonstrate hyperspectral imaging at an attenuated total reflectance crystal that has been modified with a nanostructured gold electrode. Imaging experiments characterize interfacial structure and dynamics between several ionic liquid media (compositions) at the electrode surface simultaneously during electrochemical perturbation. Our initial spectral imaging studies explore ILs composed of imidazolium-based cations with alkylsulfate, tetrafluoroborate, thiocyanate, dicyanamide, and bis(trifluoromethylsulfonyl)imide anions.
Self-Assembled Multilayer Structures of Imidazolium Based Ionic Liquids at Mica Interfaces Are Induced By Confinement and the Presence of Water
Authors: Cheng Hsiu-Wei , Dienemann Jan-Niklas , Stock Philipp , Merola Claudia , Chen Ying-Ju , Valtiner Markus
Published: February 2020

Tuning chemical structure and molecular layering of ionic liquids (IL) at solid interfaces offers leverage to design performance of ILs in emerging technologies including super-capacitors, heterogeneous catalysis or lubrication. Recent experimental interpretations suggest that ILs containing cations with long hydrophobic tails form well-ordered bilayers at interfaces. Here we demonstrate that interfacial bilayer formation is insignificant and not an intrinsic quality of hydrophobic ILs. In contrast, bilayer formation is triggered by boundary conditions including confinement and humidity present in the IL. Therefore, we performed force versus distance profiles using atomic force microscopy and the surface forces apparatus. Our results support models of disperse low-density bilayer formation in confined situations, and at high surface charging in the presence of water. Conversely, interfacial structuring of long-chain ILs in dry environments and at low surface charging is disordered and bulk structuring also dominates interface structures in confinement. Our results demonstrate that boundary conditions such as charging, confinement and the presence of impurities drive structure formation of ILs at interfaces, while at low surface charge solvophobic interactions have a much weaker influence on interface structuring than generally believed. These results have important implications for understanding solid/IL interfaces and clarify previous interpretations.
(Invited) Green Composites from Cellulose, Wool, Hair and Chicken Feather. Synthesis, Structure and Antimicrobial Property
Authors: Tran Chieu d
Published: February 2020

Novel composites between cellulose (CEL) and keratin (KER) from three different sources (wool, hair and chicken feather) were successfully synthesized in a simpleone-step process in which butylmethylimidazolium chloride (BMIm+Cl-), an ionic liquid, was used as the sole solvent.  The method is green and recyclable because [BMIm+Cl-] used was recovered for reuse.  Spectroscopy (FTIR, XRD) and imaging (SEM) results confirm that CEL and KER remain chemically intact and homogeneously distributed in the composites. KER retains some of its secondary structure in the composites.  Interestingly, the minor differences in the structure of KER in wool, hair and feather produced pronounced differences in the conformation of their corresponding composites with wool has the highest α-helix content and feather has the lowest content. These results correlate well with mechanical and antimicrobial properties of the composites.  Specifically, adding CEL into KER substantially improves mechanical strength of all three composites ([CEL+wool], [CEL+hair] and [CEL+feather].  The fact that feather has the lowest content of α-helix (and wool has the highest) enables the [CEL+ feather] composite to have strongest mechanical strength  (and [CEL+wool] composite has the weakest strength). All three composites exhibit antibacterial activity against MRSA.  The antibacterial property is due not to CEL but to the protein and strongly depends on the type of the keratin, namely, the bactericidal effect is strongest for feather and weakest for wool.
Mechanism of the Electrochemical Oxidation of Ammonia over Platinum: An in Situ attenuated Total Reflection Infrared Study
Authors: Katayama Yu , Okanishi Takeou , Muroyama Hiroki , Matsui Toshiaki , Eguchi Koichi
Published: February 2020

The recent development of anion exchange membranes (AEMs) has increased the potential and the importance of ammonia as a fuel for anion exchange membrane fuel cells (AEMFCs). Although the reaction mechanism for the electrochemical ammonia oxidation over Pt electrode has been extensively studied, there is no report on the detection of the prospected intermediates and/or the poisoning species on Pt electrode.

In this study, the electro-oxidation of ammonia over Pt electrode in alkaline aqueous solutions was studied by in situ attenuated total reflection infrared (ATR-IR) spectroscopy. In the presence of NH3, the band ascribable to the HNH bending mode of adsorbed NH3 was confirmed at 1662−1674 cm−1 in the potential range of 0.1−1.1 V. The intensity of this band decreased continuously with a rise in potential, indicating the oxidative consumption of adsorbed ammonia. In response to this behavior, the band at 1269 cm−1 appeared alternatively above 0.2 V, and its intensity reached the local maximal value at ca. 0.4 V. Note that this potential of ca. 0.4 V agreed well with the onset potential of ammonia oxidation, ca. 0.45 V, in the linear sweep voltammogram. This 1269 cm−1 band was assigned to the NH2 wagging mode of N2H4, which was one of the active intermediates, N2H
x

+

y

,ad (x = 1 or 2, y = 1 or 2), according to the mechanism proposed by Gerischer and Mauerer. To the best of our knowledge, this is the first report for the detection of N2H4 as a reaction intermediate over Pt electrode. Furthermore, the formation of bridged NO was also observed above the onset potential of ammonia oxidation, ca. 0.5 V. Such adsorbed NO species probably inhibit the electrochemical reaction due to the occupation of reaction sites at higher potential.

Figure 1
Lanthanide Voltammetry: Electrocatalysis and Electrochemistry in Acetonitrile
Authors: Rathuwadu Nadeesha , Knoche Krysti L. , Leddy Johna
Published: February 2020

An electrochemical method has been developed to allow voltammetric interrogation of lanthanides in common organic, electrochemical solvents [1, 2]. Lanthanide electrochemistry was enabled in acetonitrile at an ion exchange polymer (Nafion) modified platinum electrode with triflate ligands. Under these conditions, formal potentials of the lanthanides are shifted into the potential window of acetonitrile and voltammetry is enabled.

Here, voltammetry of lanthanides on the benchtop and evidence of electrocatalysis of reactions important in energy and environment are presented.

For several lanthanide triflate complexes, the voltammetry is reviewed. For five lanthanides, two reductions are observed under cyclic voltammetric conditions. For each lanthanide triflate complex, LN(OTf)3 where LN is a lanthanide, two well resolved reduction waves are observed. The first is for LN3+ to LN2+. The second wave about a volt negative of the first is for reduction of the LN(II) triflate. Under cyclic voltammetric conditions, the reverse sweep to positive potentials is less well resolved. The mechanistic path for the LN(OTf)3 is considered.

Electrochemical reactions of small molecule, ubiquitous species play important roles in energy and the environment. This includes the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), carbon dioxide reduction, and the chemistry of other organic species that contain one carbon, such as methanol, formic acid, formaldehyde, and carbon monoxide. Many of these reactions are kinetically limited. ORR limits performance of many fuel cell and air batteries. Increased rates of HER facilitate energy generation. The sequence of single carbon species both maps the thermodynamic advantages of organic electrochemical fuels and identifies the dominant kinetic limitations of their exploitation in practical, low temperature electrochemical energy systems. Carbon dioxide is the highest oxidation state of carbon and so the focus of study for reduction to regenerate fuels and value added products as well as to remediate greenhouse gases. Voltammetry undertaken in the presence of some of these species will be presented. For example, there is clear cyclic voltammetric evidence of increased rates of oxygen reduction in acetonitrile when lanthanide triflates are present in solution and the Nafion film on the electrode.

References

[1] Krysti L. Knoche, Ph.D., University of Iowa, 2014.

[2] J. Leddy and K. L. Knoche, “Lanthanide Electrochemistry,” Published U.S. Patent Application, 12 November 2015, 20150322581-A1.
(Invited) Molecular Hydrogen-Evolution Electrocatalysts for Dye-Sensitized Solar Fuels
Authors: Wu Yiying
Published: February 2020

Proton reduction is one of the most fundamental and important reactions in nature. MoS2 edges have been identified as the active sites for hydrogen evolution reaction (HER) electrocatalysis. Designing molecular mimics of MoS2 edge sites is an attractive strategy to understand the underlying catalytic mechanism of different edge sites and improve their activities. Herein I will discuss our recent progress in this aspect. The first example is a dimeric molecular analog [Mo2S12]2-, as the smallest unit possessing both the terminal and bridging disulfide ligands. Our electrochemical tests show that [Mo2S12]2- is a superior heterogeneous HER catalyst under acidic conditions. Computations suggest that the bridging disulfide ligand of [Mo2S12]2- exhibits a hydrogen adsorption free energy near zero (-0.05 eV). The second example is a group of compounds with the general formular of MoO(S2)2bpy. By varying substitution on the bpy ligand, we demonstrate the induction effect on the S—S ligand, thereby tuning the rate constants for HER and overpotentials. We have studied homogenous electrocatalytic hydrogen production performance metrics of three catalysts with different bipyridine substitutions. By varying the electron-donating abilities, we present the first demonstration of using the ligand to tune catalytic properties of the S—S bond in molecular MoS2 edge site mimics. These works can shed light on the relationship between structure and electrocatalytic activity of molecular MoS2 catalysts and thus is of broad importance from catalytic hydrogen production to biological enzyme functions. Lastly, I will discuss how to integrate the molecular catalysts into dye-sensitized photoeletrochemical platforms for solar hydrogen production.
Effects of TiO2 nanoparticle Size on Solar-to-Hydrogen Efficiency in Photoelectrochemical Cells
Authors: Bonning Bo , Salimijazi Farshid , Shirvanian Pezhman
Published: February 2020

The photocatalytic splitting of water into oxygen and hydrogen using solar light is a promising clean and renewable source for hydrogen fuel1. Metal-oxides are one type of material that researchers are studying to overcome this scientific challenge. TiO2 is one of the most studied and promising photocatalysts. This is due to TiO2 having a band gap with edge positions that makes it capable of splitting water. However, due to its large band gap (3.0-3.3eV) hindering its ability to utilize portions of the solar spectrum, TiO2 has a low solar-to-hydrogen efficiency2. Therefore, steps have been made to improve this material. Going to nanoscale has shown to have potential, but research comparing different sized nanoparticles hasn’t been as prevalent as other methods, such as doping. Having smaller particle size, particularly in the lower nanometer range, can give materials unique properties that could increase photoactivity3. Some properties, such as quantum confinement, aren’t as beneficial for large band gap materials like TiO2. When a material reaches a small enough size, quantum confinement effects take over, changing the electrochemical properties. One of these properties is the band gap energy, which increases as particle size decreases4. Therefore, it is imperative to find a particle size that gives a material the most optimal balance of these effects, leading to a material with the highest water splitting efficiency. The purpose of this study was to test the differences in efficiencies, such as solar-to-hydrogen efficiency (STH), of TiO2 for decreasing nanoparticle size. Nanoparticle sizes ranging from 100 nm down to 5 nm were tested using photoelectrochemical(PEC) measurements. It was our prediction that smaller particle size will result in an overall increase in photoactivity, as per other literature3, and therefore a higher solar-to-hydrogen efficiency (STH). The process of putting together the working electrode, as well as procedure and results of experiments, will be discussed.

 References

[1] Marschall, R. (2014). Semiconductor composites: strategies for enhancing charge carrier separation to improve photocatalytic activity. Advanced Functional Materials, 24(17), 2421-2440.

[2] Khan, S. U., Al-Shahry, M., & Ingler, W. B. (2002). Efficient photochemical water splitting by a chemically modified n-TiO2. science, 297(5590), 2243-2245.

[3] Almquist, C. B., & Biswas, P. (2002). Role of synthesis method and particle size of nanostructured TiO 2 on its photoactivity. Journal of Catalysis,212(2), 145-156.

[4] Alivisatos, A. P. (1996). Semiconductor clusters, nanocrystals, and quantum dots. Science, 271(5251), 933.
Photocatalytic Degradation of Phenolic Compounds in Presence Electrogenearated O3 and or H2O2
Authors: Al-Kandari Halema Ali , Abdullah Aboubakr Moustafa , Al-Kandari Shekhah Ali , Mohamed Ahmed meslam
Published: February 2020

A Graphene oxide (GO) was prepared using modified Hummer`s method starting from graphite. GO was impregnated on commercial nanoparticles P25 TiO2 (GOTi) or WO3. After that, reduced GOTi or GOWO3 was obtained by hydrothermal reduction. The photocatalysis behavior of as-prepared catalysts were tested towards the phenolic compounds degradation and compared against commercial P25 TiO2 in presence and absence of in-situ electrochemically generated ozone. The SiO2/Ti300nm/Pt100nm/TiOx100nm/SnOx500nm electrode was used to produce ozone electrochemically. Table 1 showed that the photocatalytic degradation rate constant of phenol on RGOTi under Xe illumination in presence of H2O2 and electrochemically generated ozone is the better than TiO2.

Table 1: Rate constant data in min-1 of phenol (20 mg L-1) on Ti and RGOTi under 150 Xe illuminations in absence and absence of 70 µL H2O2 and Ozone

Xe
Xe + H2O2

Xe + O3

Xe + H2O2 + O3

Ti
RGOTi
Ti
RGOTi
Ti
RGOTi
Ti
RGOTi

0.0214
0.0226
0.0296
0.032
0.0257
0.0262
0.0375
0.0615
Fabrication of WO3/BiVO4 p-n Junction Photoanode for Efficient Solar Water Splitting
Authors: Seo Hyungtak , Kalanur Shankara S.
Published: February 2020

Photo-electrochemical (PEC) water splitting for hydrogen production is one of the most attractive renewable energy technologies as it directly converts solar energy to chemical energy. And hence, it could play a central role in hydrogen-based energy economy of future. Efficient photo-catalytic water splitting requires effective generation, separation and transfer of photo-induced charge carriers that can hardly be achieved simultaneously in a single material. Hence, using single inorganic semiconductors faces a limitation and leads to decrease in overall efficiency of the PEC. Therefore, p–n junction photo-anodes can be very effective as they can facilitate the separation of the photo-generated electron–hole pairs. In this work, a p–n junction having n type WO3 and p type BiVO4 photo-anode has been designed and fabricated. This junction dramatically showed higher photocurrent density compared to individual WO3 and BiVO4 electrodes. We achieve one the highest photocurrent of 4.2 mA/cm2 at an potential of 1.23 V versus a reversible hydrogen electrode (RHE) under simulated sunlight without an added catalyst. In the composite WO3/BiVO4 film a shifted quasi-Fermi level results, due to electronic equilibration between the two materials. The better performance of WO3/BiVO4 hetero-junction electrodes is thus a consequence of the electron injection from BiVO4 into WO3, Thin layer (5 nm) of amorphous TiO2 was deposited on the photo-anode using electrochemical deposition. The deposition was noticed to be uniform and complete on the photo-anode and increases the photo-stability of the photo-anode for longer times. The strategies for constructing such kind of hetero-junctions are well applicable to other dual bandgap photo-anodes.
(Invited) Hybrid Photocatalysts Consisting of Metal Complexes and Semiconductors for CO2 Reduction
Authors: Ishitani Osamu
Published: February 2020

Both the problems of the global warming and shortage of the fossil resources have brought about great interest in photochemical utilization of CO2 with solar energy. Efficient photocatalysts for CO2 reduction must be necessary for development of such an important technology.

We have developed novel types of photocatalytic systems using metal complexes and/or semiconductors as a photocatalyst. I will focus on the following systems in my presentation.

(1)
Architecture of supramolecular photocatalysts driven with visible light, which can efficiently reduce CO2 selectively to CO or HCOOH.

1-10

(2)
Z-scheme type photocatalysts by using hybrids composed with the supramolecular photocatalyst and a semiconductor, which can reduce CO2 with methanol as an electron donor.11-14

(3)
Photoelectrochemical systems with metal-complex photocatalyt adsorbed on p-type semiconductor electrodes, which can reduce CO2 with water as an electron donor.15

 

References:

[1].
Gholamkhass, B.; Mametsuka, H.; Koike, K.; Tanabe, T.; Furue, M.; Ishitani, O. Inorg. Chem. 2005, 44, 2326.

[2].
Sato, S.; Koike, K.; Inoue, H.; Ishitani, O. Photochem. Photobiol. Sci. 2007, 6, 454.

[3].
Koike, K.; Naito, S.; Sato, S.; Tamaki, Y.; Ishitani, O. J Photochem. Photobiol. A: Chem. 2009, 207, 109.

[4].
Tamaki, Y.; Watanabe, K.; Koike, K.; Inoue, H.; Morimoto, T.; Ishitani, O. Faraday Discuss. 2012, 155, 115.

[5].
Tamaki, Y.; Morimoto, T.; Koike, K.; Ishitani, O. Proc. Natl. Acad. Sci. USA 2012, 109, 15673.

[6].
Tamaki, Y.; Koike, K.; Morimoto, T.; Yamazaki, Y.; Ishitani, O. Inorg. Chem. 2013, 52, 11902.

[7].
Tamaki, Y.; Koike, K.; Morimoto, T.; Ishitani, O. J. Catal. 2013, 304, 22.

[8].
Tamaki, Y.; Koike, K.; Ishitani, O. Chemical Science 2015, 6, 7213

[9].
Tamaki, Y.; Koike, K.; Ishitani, O. Chemical Science 2015, 6, 7213.

[10].
Nakada, A.; Koike, K.; Maeda, K.; Ishitani, O. Green Chemistry 2016, 18, 139.

[11].
Sekizawa, K.; Maeda, K.; Domen, K.; Koike, K.; Ishitani, O. J. Am. Chem. Soc. 2013, 135, 4596.

[12].
Yoshitomi, F.; Sekizawa, K.; Maeda, K.; Ishitani, O. ACS Appl. Mater. Interfaces 2015, 7, 13092.

[13].
Nakada, A.; Nakashima, T.; Sekizawa, K.; Maeda, K.; Ishitani, O. Chemical Science 2016 in press (DOI 10.1039/C6SC00586A).

[14].
Kuriki, R.; Matsunaga, H.; Nakashima, T.; Wada, K.; Yamakata, A.; Ishitani, O.; Maeda, K. J. Am. Chem. Soc. in press (DOI 10.1021/jacs.6b01997).

[15].
Sahara, G.; Abe, R.; Higashi, M.; Morikawa, T.; Maeda, K.; Ueda, Y.; Ishitani, O. Chem. Commun. 2015, 51, 10722.

Figure 1
(Invited) Development of Photocatalytic and Photoelectrochemical CO2 Reduction System
Authors: Ohno Teruhisa , Kamimura Sunao
Published: February 2020

Morphology controlled brookite TiO2 nanorod having brookite phase was developed. Exposed crystal surfaces play different roles such as oxidation and reduction, respectively.  These properties are a great advantageous for multi-electron reaction such as CO2 reduction. We also investigated the co-catalysts loading effects for improving CO2 reduction.  The maim product for CO2 reduction was methanol The photocatalytic activates of brookite TiO2 nanorods loaded with Ag or Rh were about 10 times higher than that of brookite TiO2 without co-catalysts loading.  The apparent quantum efficiency of the reaction reached to about 3 % under UV light. 

            We had also developed g-C3N4/WO3 nanocomposite photocatalysts for CO2reduction to generate methanol, CO, CH4, and formic acid under visible light   Among the several kinds of products, methanol was obtained as a main product. Co-catalysts loading effect such as Ag, Au had been also investigated. The reaction mechanism was investigated by using double beam pohtoacoustic spectroscopy.

            Several kinds of photoelectrochemical systems for CO2 reduction by using B-doped g-C3N4, CuCrO2, Cu3Nb2O8 photocatalysts electrodes had been developed in order to separate the products such as CO, methanol, etc..  The photocurrent responses for CO2 reduction using the g-C3N4 electrodes improved by Boron doping and co-catalysts coating such as Au, Ag, Rh etc on the surface of the electrodes.  The main product of this photoelectronchemical system was ethanol. The photocurrent responses of CuCrO2 and Cu3Nb2O8 electrodes were about 10-30 times higher than that of the Boron doped g-C3N4 coted with Rh photoelectrode.  The detailed discussion of these results will be presented at the presentation.

            We had also developed CZTS (Cu2ZnSnS4) photoelectrode covered by ZnS, CdS or In2S3 for CO2 reduction.  ZnS, CdS or In2S3 played a role for an electron correction layer and protection layer.  The photocurrent response for H+ reduction and CO2 reduction was drastically improved by covering CdS or In2S3 thin layer.  Faraday efficiency of H2, CO evolution and HCOOH generation are about 60, 1.5, and 2.5 %, respectively.  The effects of CdS, In2S3, and metals co-catalyst loading will be discussed.
(Invited) Stand-Alone Photoreduction of Carbon Dioxide on Copper Oxide Nanowires Powered By WO3/Dye Dual Absorber
Authors: Nath Narayan Chandra Deb , Choi Seung Yo , Park Hyunwoong , Lee Jae-Joon
Published: February 2020

A photoelectrochemical cell, composed of WO3/dye-sensitized solar cell (WO3/DSSC) and copper oxide (CuxO, where x = 1 and 2) nanowires as a dual absorber photoanode and cathode, respectively, is demonstrated as a stand-alone device for CO2 photoreduction to CO, H2 and formate. The single-absorber cell of a WO3 photoanode and CuxO nanowire cathode couple (WO3-CuxO) required the minimum overpotential of ~0.7 V to drive CO2 photoreduction. For the unassisted or stand-alone CO2 photoreduction, a DSSC was coupled to the WO3-CuxO system to construct a dual-absorber cell (WO3/DSSC-CuxO). In the dual-absorber cell, the long-wave band (λ > ca. 500 nm) passed through the semi-transparent WO3 film was absorbed by the dye-sensitized TiO2 electrode of DSSC. The WO3/DSSC-CuxO showed a potential gain of ~0.7 V, which resulted in the CO2 photoreduction successfully without supply of any external potential. In this stand-alone system, the primary CO2 conversion product is CO with solar-to-chemical energy efficiency of ~2.5% while H2 and formate are obtained with the energy efficiencies of 0.7% and 0.25%, respectively, in 5 h.
(Invited) SnS2 Nanostructure As a Highly Efficient Photocatalyst for CO2 Reduction to Solar Fuels
Authors: Chen Kuei-Hsien , Chen Li-Chyong , Shown Indrajit
Published: February 2020

Photocatalytic CO2 reduction to solar fuels by artificial photosynthesis is an attractive and effective research area to solve the energy crisis as well as anthropogenic greenhouse emission problems from CO2 emission. In the past several years, many significant efforts have been applied to develop an efficient photocatalyst for the CO2 reduction to hydrocarbons. Among the entire reported photocatalyst several semiconductor materials together with carbonaceous hybrid materials GO, g-C3N4, TiO2/rGO, MoS2/rGO and Cu-GO have been reported as a promising photocatalyst for CO2 reduction to solar fuels conversion because of their comparatively low cost, low toxicity and photocorrosion resistance. However, wide bad gap semiconductor photocatalysts are not enough to use for practical application due to their limited visible light absorption. The promising prospect of these materials is far away from the commercial requirement due to the low quantum efficiency and lack of selectivity. Thus, it is a great challenge to develop a potential low-cost photocatalyst for a high CO2 reduction efficiency and produce desire solar fuel under visible light.

Since the discovery of graphene, two-dimensional (2D) layered transition metal dichalcogenides (TMDs) nanostructure are playing an important role in the various applications due to their crystal structure, a wide range of chemical compositions and optoelectronic properties. The wide range of electronic properties of TMD semiconductor materials is also promising for catalysis due to their strong correlation between electronic and catalytic properties. Last few years, several narrow band gap metal sulfides such as CdS, PbS, CdSe, MoS2 have been introduced as a photocatalyst or a co-catalyst together with another wide-band gap semiconductor for photocatalytic reaction under visible light. Although CdS and PbS contains sufficient potential characteristics as a photocatalyst, however, they explored less as a commercial photocatalyst due to the toxicity problem of Cd and Pb. Therefore, it's highly desirable to explore non toxic narrow bandgap metal sulfide for photocatalytic CO2 reduction. Among various, metal sulfides SnS2 is one of the narrow bandgap nontoxic semiconductor associate with dichalcogenide family. Recently, it has been attracted for its potential applications as a light absorber layer for desensitized solar cell, gas sensing, energy storage and conversion. SnS2 possesses CdI2 crystal structure, consisting sandwiched S-Sn-S layers bounded by weak van der Waals's interaction. The strong intra- and weak inter-layer inter-actions induce the high anisotropy of 2D SnS2. SnS2 is an n-type semiconductor with a narrow bandgap around 2.2-2.4 eV at room temperature, and high quantum yield, thus it shows several benefits to be a good photocatalyst behavior under visible light. The details photocatalytic performance, high quantum yield and selectivity of solar chemicals will be discussed.
Interface Engineering in Inorganic Hybrid Structures Towards Improved Photocatalysis
Authors: Xiong Yujie
Published: February 2020

Designing new photocatalytic materials for improving photoconversion efficiency is a promising route to alleviate the steadily worsening environmental issues and energy crisis.  Despite the invention of a large number of catalytic materials with well-defined structures, their overall efficiency in photocatalysis is still quite limited as the three key steps - light harvesting, charge generation and separation, and charge transfer to surface for redox reactions - have not been substantially improved.  To improve each step in the complex process, there is a major trend to develop materials based on inorganic hybrid structures.  In this case, interface engineering holds the promise for boosting the overall efficiency, given the key roles of interface structures in charge and energy transfer.  In this talk, I will demonstrate several different approaches to designing inorganic hybrid structures with improved photocatalytic performance via interface engineering.  The typical demonstrations include semiconductor-plasmonics systems for broad-spectrum light harvesting, metal-semiconductor interfaces for improved charge separation, semiconductor-MOF (metal-organic framework) configurations for activated surface reactions.  It is anticipated that this series of works open a new window to rationally designing inorganic hybrid materials for photo-induced applications.

References:

(1) Bai, S.; Yang, L.; Wang, C.; Lin, Y.; Lu, J.; Jiang, J. and Xiong, Y.*, Angew. Chem. Int. Ed. 54, 14810-14814 (2015).

(2) Bai, S.; Jiang, J.; Zhang, Q. and Xiong, Y.*, Chem. Soc. Rev. 44, 2893-2939 (2015).

(3) Bai, S.; Li, X.; Kong, Q.; Long, R.; Wang, C.; Jiang, J. and Xiong, Y.*, Adv. Mater. 27, 3444-3452 (2015).

(4) Bai, S.; Ge, J.; Wang, L.; Gong, M.; Deng, M.; Kong, Q.; Song, L.; Jiang, J.;* Zhang, Q.;* Luo, Y.; Xie, Y. and Xiong, Y.*, Adv. Mater. 26, 5689-5695 (2014).

(5) Li, R.; Hu, J.; Deng, M.; Wang, H.; Wang, X.; Hu, Y.; Jiang, H. L.; Jiang, J.;* Zhang, Q.;* Xie, Y. and Xiong, Y.*, Adv. Mater. 26, 4783-4788 (2014).
Kinetic Study on Multielectron-Transfer Mechanism for Flake-Ball-Shaped Bismuth-Tungstate Photocatalyst
Authors: Hori Haruna , Takashima Mai , Takase Mai , Ohtani Bunsho
Published: February 2020

It has been reported that flake ball (FB)-shaped particulate bismuth tungstate (Bi2WO6: BTO) particles prepared by hydrothermal method exhibit photocatalytic activity for oxidative decomposition of organic compounds comparable to that of a commercial titania photocatalyst, while the activity for methanol dehydrogenation is relatively low even with platinum-loaded ones [1]. These facts suggest that two (or four)-electron transfer to the surface-adsorbed oxygen (O2), requiring more anodic potential of electrons in photocatalyst particles, happens in FB-BTO, but no report on the evidence for the multielectron-transfer mechanism have been published. In this study, light-intensity dependence of the rate of acetic-acid decomposition was investigated to obtain kinetic evidence for the multielectron transfer.

FB-BTO, composed of particles of spherical assembly of BTO flakes, was prepared following the previous report [1]. As-prepared FB, its ball-milled samples (L and H) and their 773 K-calcined samples (500FB, 500L and 500H) were used for decomposition of acetic acid in aerobic aqueous suspensions under monochromatic photoirradiation by (A) a diffraction grating-type illuminator (Jasco CRM-FD; maximum 10 mW) or (B) a 365-nm UV-LED (maximum 320 mW).

Figure 1 shows order (n) of light-intensity dependences at four wavelengths (irradiation A) calculated by assuming; r = a × I
n (r: rate, a: constant and I: light intensity). Except for the samples L and H at 380 and 410 nm, BTO showed almost first-order light-intensity dependences at wavelengths between 320 and 410 nm. With the higher intensity irradiation (irradiation B), the order was decreased to ca. 0.5 order for FB and L as shown in Fig. 2. As has been reported previously, photocatalytic acetic-acid decomposition proceeds through radical-chain mechanism with an alkyl peroxy radical as a chain carrier when titania was used as a photocatalyst, and the order of light-intensity dependence was ca. 0.5 [2]. The above-mentioned first-order light-intensity dependence for the most BTO samples can be interpreted by combination of second-order dependence for the accumulation of two electrons to reduce O2 and 0.5-order dependence owing to the radical-chain mechanism. Difference in folding points of plots in Fig. 2 between FB and L was observed; a folding point for FB was appreciably lower than that of L. One of the possible reasons for this difference is that the probability of the second-photon absorption by one photon-absorbed FB particle within its lifetime is higher than that of L particle owing to larger volume of FB particles.

[1] F. Amano, K. Nogami, R. Abe, B. Ohtani, J. Phys. Chem. C. 112, 9320 (2008).

[2] T. Torimoto, Y. Aburakawa, Y. Kawahara, S. Ikeda, and B. Ohtani, Chem. Phys. Lett., 392, 220 (2004).

Figure 1
In Situ ATR-FTIR Investigation of the Effects of H2o and D2o Adsorption on the TiO2 Surface
Authors: Bahnemann Detlef Werner , Belhadj Hamza , Robertson Peter
Published: February 2020

Surface hydroxyl groups on TiO2 play an important role for the photoinduced hydrophilicity as well as for photocatalytic reactions. Adsorbed species such as water and organic compounds are expected to affect the hydroxyl group behaviour on the TiO2 surface, however, their influences have to date not been clearly determined. Herein, a detailed investigation of H2O and D2O adsorption on the TiO2 surface (anatase) in the dark and under UV(A) irradiation is reported using ATR-FTIR spectroscopy. The adsorption and photocatalytic degradation of acetate on the TiO2 surface was also investigated in H2O and D2O. Adsorption of H2O with different ratios of D2O revealed an isotopic exchange reaction occurring on the surface of TiO2 in the dark. This isotopic exchange leads to a change in the behaviour of acetate with the intensity of the OH bending band between the carboxylate and the OH group at 900 cm-1 decreasing and ultimately disappearing in the dark.

Upon illumination with UV(A) light both, OH and OD groups are formed, which in turn increase the hydrophilicity of the TiO2 surface. The amount of OH and OD groups was found to increase in the presence of molecular oxygen. This increase is most likely caused by the photoadsorption of H2O and D2O due to photoinduced charge transfer processes [1]. On the other hand, the investigations show that during UV(A) irradiation the acetate molecules can adsorb again on the TiO2 surface which is explained by an increased surface area due to a de-aggregation of the particles agglomerates [2]. Based upon the observed correlation between the carboxylate and the OH and/or OD groups at neutral pH (pH ≈ pHzpc) it is obvious that acetate preferentially adsorbs on the positively charged anatase in a monodentate structure. As an in-situ technique, ATR-FTIR studies provide evidence of the adsorption behaviour of water and D2O on TiO2 surfaces thus yielding new insights into the mechanism of photoinduced hydrophilicity and of photocatalytic reactions.
Efficiently Charge Transfer Promoted By Dual Vacancies Overlayer for Water Oxidation of WO3 Photoanode
Authors: Ma Ming , Park Jong Hyeok
Published: February 2020

Alleviating charge recombination at electrode/electrolyte interface by introducing a passivation overlayer is regarded as an efficient approach to improve photoelectrochemical (PEC) water oxidation. Here, we report a dual vacancies WO3 overlayer by reductive agent Li-EDA (lithium dissolved in ethylene diamine) that dramatically improves the PEC performance of the mesoporous WO3 photoanode. In comparison to the pristine mesoporous WO3 photoanodes, the interconnected WO3 nanoparticles surrounded by a 2~2.5 nm dual vacancies WO3 layer shows 2.4 times of the photocurrent density and a markedly cathodic shift of the onset potential. The enhancement of the PEC activity is mainly attributed to the facilitative effect on interface charge transfer through the dual vacancies WO3 layer. While, the dual vacancies WO3 layer, in-situ formed on WO3 nanoparticles, could significantly increase its charge carrier density, which is superior to passivation-dominant overlayer. These findings elucidate a simple and effective strategy, which can provide a new direction to get dramatic improvement on water oxidation of photoanode.
Quinone Based Conducting Redox Polymers for Electric Energy Storage
Authors: Huang Hao , Karlsson Christoffer , Gogoll Adolf , Strømme Maria , Sjödin Martin
Published: February 2020

Conducting redox polymers (CRP), consisting of conducing polymer (CP) and a redox active pendant group (PG) covalently linked to the CP backbone, have been suggested as electrode materials for secondary batteries. This type of material could provide an alternative to inorganic electrode materials and is favorable because of its renewability and sustainability (figure 1). Redox active organic compounds have previously been used as electrode materials for secondary batteries. However, due to the dissolution of many interesting compounds in common battery electrolytes, they suffer from poor recyclability and, in addition, the limited conductivity in these materials requires addition of substantial amounts of conductivity additives in the electrode formulation. By introducing a CP as backbone, not only the dissolution issue is solved, but also the conductivity will be greatly improved.

In our studies, we choose polypyrrole as CP, and p-benzoquinone as PG. Polypyrrole has been extensively studied and the electrochemistry and charge transport in this system is well understood. The corresponding knowledge of charge transport in CRPs is however to a large extent lacking. With the aid of temperature dependent in-situ conductivity measurements during the polymer doping process, mechanistic information on the charge transfer in quinone-based CRPs was investigated. Additionally, by varying the link between the two subunits the effect of linker on the performance of the materials was studied. With assistance of various in situ techniques, such as in situ conductivity measurement, in situ ATR-FTIR, EQCM, the interaction between the CP and PG was probed. It was found that the choice of linker has a substantial impact on the charge transport properties of the material. The insight gained from investigating the interaction between these two subunits will benefit further molecular variation of quinone-based electrode materials for secondary batteries.

Figure 1
Building Stable Radical Cations for Non-Aqueous Redox Flow Batteries
Authors: Zhang Lu , Shkrob Ilya A , Brogden Wes , Duan Wentao , Wei Xiaoliang , Assary Rajeev , Cheng Lei , Curtiss Larry , Brushett Fikile R. , Thompson Levi T
Published: February 2020

E-mail: luzhang@anl.gov, shkrob@anl.gov

Abstract:

In advanced electrical grids of the future, electrochemically rechargeable fluids of high energy density could capture the power generated from intermittent sources like solar and wind. To meet this outstanding technological demand there is a need to understand the fundamental limits and interplay of electrochemical potential, stability, and solubility in low-weight redox-active molecules, among which, stability is the crucial factor for determining the real cycling performance. 1
,
2

The derivatives of 1,4-dimethoxybenzene are thus far the best performing catholyte molecules and have been intensively studied for non-aqueous redox flow batteries (NRFBs). However, most of these molecules have been found by trial and error, and the structural factors that determine durability of their radical cations (and even the nature of reactions controlling the life times of these radical cations) are insufficiently understood. In this report, an exploratory study focusing on the correlation between molecular symmetry and electrochemical stability was conducted. As shown in Fig 1, we examined a large selection of previously reported stable redox molecules3-5seeking for the root causes of the radical cation stability. By comparing their cycling performance, we observed that symmetric molecules are more likely to be stable than asymmetric ones. We rationalize this connection through the effect of symmetry on fragmentation (e.g., deprotonation) of a conformationally frozen radical cation. In asymmetric radical cations, the extra positive charge residing on the functional groups is unevenly distributed between them, causing more rapid fragmentation in the more positively charged groups. Following this observation, we have designed and synthesized several novel structures that are expected to be exceptionally stable redox molecules.

Figure 1. Molecular Structures for Redox Active compounds. The Symmetry Group and Estimated Dipole Moments (in Debye) are indicated in the Parentheses.

 

(1) Wei, X.; Xu, W.; Huang, J.; Zhang, L.; Walter, E.; Lawrence , C.; Vijayakumar, M.; Henderson, W. A.; Liu, T.; Cosimbescu, L.; Li, B.; Sprenkle, V.; Wang, W. Angewandte Chemie International Edition
2015, 54, 8684.

(2) Wei, X.; Cosimbescu, L.; Xu, W.; Hu, J. Z.; Vijayakumar, M.; Feng, J.; Hu, M. Y.; Deng, X.; Xiao, J.; Liu, J.; Sprenkle, V.; Wang, W. Adv. Energy Mater.
2015, 5, 10.1002/aenm.201570002.

(3) Huang, J.; Cheng, L.; Assary, R. S.; Wang, P.; Xue, Z.; Burrell, A. K.; Curtiss, L. A.; Zhang, L. Adv. Energy Mater.
2015, 5, 1401782.

(4) Zhang, L.; Zhang, Z.; Redfern, P. C.; Curtiss, L. A.; Amine, K. Energy & Environ. Sci.
2012, 5, 8204.

(5) Zhang, Z.; Zhang, L.; Schlueter, J. A.; Redfern, P. C.; Curtiss, L.; Amine, K. J. Power Sources
2010, 195, 4957.

Figure 1
The Gamma-V2O5 phase: A High Voltage Cathode Material for Sodium-Ion Batteries
Authors: Safrany-Renard Marianne , Baddour-Hadjean Rita , Muller-Bouvet Diane , Pereira-Ramos Jean-Pierre
Published: February 2020

The growing interest in the Na-ion batteries is justified by cost and availability of sodium resources combined with an insertion chemistry close to the lithium one. While α-V2O5 was one of the first example of Li intercalation compounds only a few works report Na insertion into that layered host lattice. We recently reported sodium insertion into the so called α-V2O5 with a capacity of 120 mAh/g at a low voltage of 1.6V [1]. In this work a new sodium insertion compound is prepared by the chemical oxidation of the γ-LiV2O5 using NO2BF4 as oxidizing agent. One sodium ion per mole of γ’-V2O5 can be reversibly inserted at a remarkably high potential of 3.3V against 1.6V in the usual α-V2O5 (figure 1). The γ’-V2O5 electrode can deliver a reversible and stable capacity of 145 mAh/g at C/60 and 50°C and 125 mAh/g at C/20. An excellent capacity retention is also demonstrated at RT with 80 mAh/g recovered after 100 cycles at C/20. A two phases mechanism involving the γ’-V2O5 / γ-NaV2O5 system is evidenced from XRD and Raman spectroscopy experiments. The structural features of the fully sodiated γ-NaV2O5 phase with an usual expansion of the interlayer spacing (+2Å/compared to γ’-V2O5) are solved. These results reveal that the γ’-V2O5constitutes a new competitive cathode material for the reversible intercalation of sodium ions.

 Reference

[1] D. Muller-Bouvet, R. Baddour-Hadjean, M. Tanabe, L.T.N. Huynh, M.L.P. Le, J.P. Pereira-Ramos

Electrochemically formed α’-NaV2O5 : A new sodium intercalation compound

Electrochimica Acta2015, Vol. 176 (2015) 586-593

doi : 10.1016/j.electacta.2015.07.030

Figure 1
(Invited) Li-S Battery and Beyond Systems: Composite Cathodes, Li Anodes and Prospects
Authors: Guo Yu-Guo
Published: February 2020

Rechargeable Li metal batteries including Li-S, and Li-O2 batteries have become attractive candidates for the next-generation rechargeable electrochemical energy storage systems with high-energy densities because of their high theoretical energy densities and cost effectiveness. Here, we report our recent progress in Li-S and Li-Se batteries including S-C and Se-C composite cathodes, Li metal anodes, and the electrode/electrolyte interfaces. In contrast to the extensive studies of the electrochemical behavior of conventional cyclic S8 molecules in Li-S batteries, there has been hardly any investigation of the electrochemistry of S chains. Here we use S chains encapsulated in single- and double-walled carbon nanotubes as a model system and report the electrochemical behavior of 1D S chains in Li-S batteries. In addition, rational design of S-C composite cathodes with high sulfur loading and remarkable electrochemical properties will also be reported. On lithium metal anode we show that a 3D current collector with a submicron skeleton and high electroactive surface area can significantly improve the electrochemical deposition behavior of Li. Li anode is accommodated in the 3D structure without uncontrollable Li dendrites. We also demonstrate that an artiﬁcial SEI layer with high Young’s modulus can restrain Li dendrite growth and reduce the side reaction between Li metal and the organic electrolyte.

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