bluuebunny/crossref_metadata_2025 huggingface dataset:
The Choice of Substrate Material and Electrodeposition of High Purity Niobium Coatings
Authors: Dubrovskiy Anton R. , Okunev Maxim A. , Makarova Olga V. , Kuznetsov Sergey A.
Published: February 2020

The interaction of different materials with the NaCl-KCl-NaF(10 wt.%)-K2NbF7(8 wt.%)-Nb melt was investigated. As substrate materials the ceramic, beryllium and carbopyroceram of different shape (spheres, cylinders, parallelepipeds) were chosen. The time of the experiments was varied from 10 minutes to 12 hours. The spherical ceramic samples were coated with protective molybdenum film by magnetron sputtering. Porous area of these films was at an average 200 μm2. After the experiment (exposition time 10 min) the exfoliation of molybdenum film was observed due to interaction of the substrate with the melt and the porous area was increased in to 27 times. The XRD data showed niobium oxides formation such as NbO, Nb4O5, NbO2 on the ceramic surface. The same XRD data were obtained for the samples without protective films. The beryllium samples regardless of the shape and the presence of the protective films were dissolved in the niobium containing melt due to more negative electrode potential comparing with niobium one. The carbopyroceram samples were exposed in the melt during 3 and 12 hours. After 3 hours of exposition, no changes of XRD data and weight of samples were found, but after 12 hours, XRD data indicated the formation of niobium carbide (NbC) of insignificant thickness. On the base obtained results, the carbopyroceram was chosen as a perspective material for electrodeposition of high purity niobium coatings because it not corrodes in the niobium containing melt.

The electrolyte mentioned above was used for niobium coatings electrodeposition on carbopyroceram spheres. Due a spherical shape of substrates, a special form of the cathode should be used for plating of samples by niobium in molten salts. In the present study construction of the cathode was developed. It consists of two parts: top part is fixed, bottom part is rotating by digital controlled stirrer. Construction of the cathode provides the electrical contact in random point of the sample. Due to such contact a uniform coatings were obtained. The optimal regimes (temperature, current density, time of electrolysis and rotation speed of the cathode) for electrodeposition of smooth uniform niobium coatings with the thickness up to 50 µm on carbopyroceram spheres were found. Purity of the coatings was determined by spectral quantitative analysis. The impurity content is given below (ppm): Mn < 2.0; Mg < 3.0; Si < 10; Fe = 2.3; Ni < 5.0; Pb < 5.0; Sn < 5.0; Ti < 10; Al < 5.0; Co < 10; Mo < 10; Ca < 10; Zr < 20; V< 3.0; Cu ≤ 10; Cr < 5.0.
Red-Ox Reactions in Ionic Liquids and Their Impact on Electrodeposition of Metals and Alloys
Authors: Freydina Evgeniya , Abbott Joshua G.
Published: February 2020

Electrodeposition from ionic liquids has some significant benefits over aqueous electrolytes in that there are no side reactions associated with the presence of water and oxygen. Metal deposits can be plated without deleterious oxides or hydrogen inclusions, which may cause a loss of mechanical and corrosion resistance properties. However, these benefits come with practical limitations and implications.

In the absence of water, there are fewer restrictions on the nature of ionic metal species that can exist in the electrolyte. In some ionic liquids, multivalent metals like niobium or vanadium may have several stable oxidation states under the same conditions. Ions with high valencies can react with low valent species to form ions of intermediate oxidation states. They can also comproportionate with freshly electrodeposited metal, dissolving it back into the bath in a low valent state.

In the case of alloy deposition, two or more metallic ions with different reduction potentials are dissolved in the electrolyte. The initial oxidation states of the metals in the system may change spontaneously if a red-ox reaction between different ions is possible. The resulting species may be insoluble or otherwise not suitable for the electrodeposition. The more positive ion can be reduced to the metallic state and precipitate out of solution. This makes some metals incompatible with each other in the electrolyte and limits the combinations of alloying elements.

Options for anodic reaction during electrodeposition from ionic liquids are usually limited to the dissolution of sacrificial anodes. Without oxygen or water, the surface of the anode remains free of a passivating oxide layer and therefore remains very chemically active. Ions with more positive reduction potentials will attack the anode and this reaction may continue until all of the more positive ions in the bath have been reduced.

Water-sensitive ionic liquids, in particular chloroaluminates, may also have H+ ions present as a result of reactions with traces of moisture. The protons can participate in the oxidation of some ions, forming hydrogen gas that eventually leaves the system.

Examples of red-ox reactions in selected ionic liquid electrolytes are discussed, as well as some proposed methods of taking these processes into account.
(Invited) Electrochemical Soft Devices
Authors: Takada Kazutake
Published: February 2020

There has been a great deal of researches to add functionalities to soft materials with intent to develop intelligent device, as they are potential candidates for bio-mimic materials. Our group has been developing functional devices by introducing redox active species and groups to polymer gels. We have employed gels because they are known to show abrupt volume change, which can be used as a driving force of the devices. A variety of stimuli has been used as trigger of changes in volume of the gel, including light, temperature, pH, ionic strength, voltage/potential, and magnetic field. Electric potential has been one of the most widely used stimulus since it can easily be controlled. The devices we have developed can be operated at low potential of a few volts, which depend on the redox species used. Further, since they are mainly composed of polymer gels, they can easily be downsized. I will present some of our representative devices, electrochemical actuators and an electrochemical micro pump.

The electrochemical actuator consists of two poly(acrylic acid) gel films which sandwich a polyimide film (5 mm x 25 mm x 12.5 μm thick or 1.5 mm x 3 mm x 12.5 μm thick) coated with Au layers on both sides. It is driven by changes in the volume of the gel induced by redox reaction of p-hydroquinone (QH2)/p-benzoquinone (BQ). The oxidation of QH2 results in decrease in pH, which gives rise to collapse of the gel, whereas the reduction of BQ causes expansion. The Au film electrodes on both sides of the actuator are used as two electrodes setup. Thus, when the oxidation takes place at one electrode, the reduction does on the other electrode at the opposite side at the same time. In a solution of 5 mM QH2 and 5 mM BQ containing 1 x 10-4 M NaClO4the actuator bent to left (anode) side at 1.3 V, and bent to right side after the reversal of the polarity (Fig. 1). The actuator showed repeated stretching/bending at least 400 cycles (Fig. 2). Further, it was able to actuate after 6 times of repeated drying/wetting of the gel.

The electrochemical micropump consists of poly(acrylic acid) gel containing Cu2+ serving as a piston and a Au pipe (1 mm i.d. x 14 mm length) serving as cylinder. It discharges and charges liquid at a level of a few hundred of picoliter per second upon expansion and contraction of the gel induced by reduction and oxidation of the copper, respectively. The pump discharged and charged equal volumes of 3.5 ml water under potentiostatic control at –1.1 V vs. Ag/AgCl and at +0.8 V for 3 h each, showing excellent reversibility. Under galvanostatic control the volumes expelled and taken were nearly controlled with the charge at steady states with flow rates of 3 x 10 pl s–1 for the discharging and 1.6 x 102 pl s–1 for the charging.

Figure 1
Electrochemical Characterization of Au(111)| EMMImNTf2 and Au(111)|2,2Bipyridine+EMMImNTf2 Interfaces
Authors: Siinor Liis , Siimenson Carolin , Doneux Thomas , Buess-Herman Claudine
Published: February 2020

Room temperature ionic liquids (RTILs) are non-conventional electrolytes that have been under intensive investigation in recent years. Due to their unique physical properties they are interesting media to study at fundamental level and in novel electrochemical devices. [1-4]

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods were used to characterize the electrochemical behavior of 1-ethyl-2,3-dimethyl imidazolium bis(trifluoromethanesulfonyl)imide (EMMImNTf2) in the presence of 2,2′-bipyridine (2,2’-BP) at a Au(111) electrode. All the experiments were carried out in a nitrogen controlled atmosphere in a glove-box.

CV method was used to determine the region of ideal polarizability (ΔE) and to evaluate the electrochemical characteristics of both systems under investigation. The capacitance (C) vs. potential (E) curves were measured using electrochemical impedance at a fixed ac frequency (113 Hz). Capacitance values depend on the composition of the electrolyte (i.e. addition of 2,2’-BP) as well as on the applied potential. At more positive E values C depends noticeably on the chemical composition of the electrolyte i.e. C values are lower in the mixture than those measured in pure EMMImNTf2 at E > – 0.1 V. This effect is caused by the adsorption of 2,2′-BP molecules at the electrode surface. This is also confirmed by phase angle values, which are lower than − 80° for Au(111)|2,2’-BP + BMMImNTf2 in a wide range of frequencies. Only at low frequency values (f < 1 Hz) mixed kinetic processes (adsorption, diffusion and partial charge transfer) were observed.

The shape and values of C
s- E curves, which were calculated from Nyquist plots at several ac frequencies (C
s
= (Z''i2πf)−1), depend strongly on the ac frequency and potential applied on the system. C
s values are higher at lower frequencies and more negative electrode potentials. We attribute this to a pseudocapacitive behavior linked to the adsorption/desorption of 2,2’-BP at these potentials. Investigating the adsorption of organic additives is a strategy to contribute to a better understanding of metal|RTILs interfaces.

Acknowledgments:

This project is supported by a FNRS (BE) grant (PDR n°T.0090.13).

References:

[1] S. Vanderaspoilden et al., Electrochim. Acta, 2015, 162, 156-162.

[2] P. Pikma et al., Electrochem. Commun., 2015, 61, 61-65.

[3] A. Lahiri et al., J. Phys. Chem. C, 2015, 119 (29), 16734–16742.

[4] T. Tooming et al., J. Power Sources, 2015, 280, 667-677.
Understanding Inclusion Mechanisms and Effects in Hardened Gold Electrodeposits
Authors: Perez Carlos R. , Pillars Jamin Ryan , Hollowell Andrew E , Arrington Christian L. , Yelton W. Graham
Published: February 2020

Gold electroplating, now over two centuries old(1), remains a mainstay of the electronic industry, where the good electrical and mechanical properties of hard gold in particular make for excellent contacts. Electrodeposited gold is hardened by the incorporation of minute amounts of inclusions, both metallic and non-metallic, which affect the microstructure of the growing film as well as its final surface(2). As previously demonstrated(3), the main contributor to hardening is the inclusions’ effect on decreasing grain size. In addition to the metal inclusions, carbon-containing by-products of the electroplating bath, particularly AuCN and CN-complexed cobalt have been found, affecting both hardness and wear resistance(4).

In our work, we aim to better understand the inclusion mechanism in cobalt-hardened gold in particular, and by extension that of other additions such as nickel, and the resulting microstructure and properties. We will electrodeposit gold with systematically varying bath compositions under several deposition conditions, while measuring the nucleation rate using Tafel plots, and characterize the resulting films in terms of microstructure, hardness and wear resistance. The effect of thermal aging on the inclusion profile will be studied by Auger electron spectroscopy.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

1. Kohl PA. Electrodeposition of gold. In: Schlesinger M, Paunovic M, editors. Modern Electroplating, Fifth Edition. New York, NY, USA: Wiley; 2000. p. 201-25.

2. Okinaka Y. Significance of inclusions in electroplated gold films for electronics applications. Gold bulletin. 2000;33(4):117-27.

3. Lo CC, Augis JA, Pinnel MR. Hardening mechanisms of hard gold. Journal of Applied Physics. 1979;50(11):6887-91.

4. DeDonker R, Vanhumbeeck J. Cobalt in gold electrodeposits. Transactions of the Institute of Metal Finishing. 1985;63:59.
Electrochemical Nitrate Reduction at Sn-Modified Single Crystalline Metal Electrodes
Authors: Yagi Ichizo , Okui Manabu , Kato Masaru
Published: February 2020

Sn-modified Pt, Pd and PtPd alloy electrodes have been known as the most active electrode for the electrochemical reduction of nitrate, which becomes abandant in ground water and industrial drain water. However, these electrodes were usually polycrystalline and the research at well-defined electrode surfaces were required to understand the reaction mechanism and the nature of reaction sites. In the present study, we prepared Sn-modified Pt(111) and Pd(111) electrodes to investigate the nitrate reduction in acidic solution. Pd-doped Pt(111) electrodes are also prepared. The coverage dependences of Sn at single crystalline electrodes on the activity toward nitrate reduction have been estimated by CV in detail. For Pt(111) and Pd(111), the oxidation induced alloying between Sn and the substrate, which was confirmed by XPS measurements, caused enhancement in the electrochemical activity toward nitrate reduction.
Modelling the Electrochemical Interface: Applications to CO2 Reduction
Authors: Chan Karen
Published: February 2020

The electroreduction of CO2 has the potential to store energy from intermittent renewable sources and to produce carbon-neutral fuels and chemicals [1, 2]. In recent years, theoretical studies of CO2 reduction have usually applied the computational hydrogen electrode model, which allows for the determination of the energies of reaction intermediates without explicitly treating the potential and the ions in solution [3]. In this talk, I will briefly review the application of this approach to CO2 reduction: the determination of lowest free energy pathways and correlation of theoretical activity volcanoes with experimental onset potentials  [4, 5], and the computational screening of new catalysts [6].  I will then focus on recent developments in the explicit treatment of the electrochemical interface [7], required for an understanding of charge transfer barriers, kinetics, and selectivity.  I will discuss the scaling of CO2 reduction barriers,  field effects,  C-C coupling [8], and the integration of these effects into microkinetic models.

Whipple, D. T. & Kenis, P. J. a. Prospects of CO 2 Utilization via Direct Heteroge- neous Electrochemical Reduction. J. Phys. Chem. Lett. 1, 3451–3458 (Dec. 2010).

Graves, C., Ebbesen, S. D., Mogensen, M. & Lackner, K. S. Sustainable hydrocarbon fuels by recycling CO 2 and H 2 O with renewable or nuclear energy. Renewable and Sustainable Energy Reviews 15, 1–23 (2011).

Nørskov, J. K., Rossmeisl, J., Logadottir, A., Lindqvist, L., Kitchin, J. R., Bligaard, T. & Jónsson, H. Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode. J. Phys. Chem. B 108, 17886–17892 (Nov. 2004).

Shi, C., Hansen, H. a., Lausche, A. C. & Nørskov, J. K. Trends in electrochemical CO2 reduction activity for open and close-packed metal surfaces. Phys. Chem. Chem. Phys. 16, 4720–7 (Mar. 2014).

Kuhl, K. P., Hatsukade, T., Cave, E. R., Abram, D. N., Kibsgaard, J. & Thomas, F. Electrocatalytic conversion of carbon dioxide to methane and methanol on transition metal surfaces (2014).

Chan, K., Tsai, C., Hansen, H. A. & Nørskov, J. K. Molybdenum sulfides and selenides as possible electrocatalysts for CO2 reduction. ChemCatChem 6, 1899–1905 (2014).

Chan, K. & Nørskov, J. K. Electrochemical Barriers Made Simple. J. Phys. Chem. Lett. 2663–2668 (2015).

Montoya, J. H., Shi, C., Chan, K. & Nørskov, J. K. Theoretical Insights into a CO Dimerization Mechanism in CO2 Electroreduction. The journal of physical chemistry letters 6, 2032–2037 (2015).
Electrochemical Carbon Dioxide Reduction to Hydrocarbons with a Nickel-Gallium Thin Film Catalyst at Low Overpotentials
Authors: Francis Sonja A , Torelli Daniel A , Crompton J Chance , Javier Alnald , Thompson Jonathan R , Brunschwig Bruce S , Soriaga Manuel P. , Lewis Nathan S.
Published: February 2020

We present bimetallic Ni-Ga thin films as new electro-catalysts for the conversion of carbon dioxide into methane, ethylene and ethane at low overpotentials in aqueous media. Three different phases of Ni-Ga (NiGa, Ni3Ga and Ni5Ga3) were prepared by drop casting, and tested for CO2 reduction activity in aqueous carbonate electrolytes acidified to pH 6.8 with 1 atm CO2. CH4, C2H4 and C2H6 are detected at potentials as anodic as -0.48V vs RHE, representing some of the lowest onset potentials for C2-product formation reported to date. Carbon monoxide reduction over the Ni-Ga thin films also resulted in the formation of CH4, C2H4 and C2H6 with similar Faradaic efficiencies, consistent with a CO2 reduction mechanism that involves a CO intermediate. Theoretically, hydrocarbon formation over single element transition metal surfaces is governed by scaling relations, where the binding energy of intermediates like adsorbed CO and adsorbed CHO are coupled. This coupling typically manifests experimentally in high overpotentials for CO2 reduction on the transition metals. The low overpotentials we observe for CO2 reduction on the bimetallic Ni-Ga are suggested to arise from the material not being governed by such scaling relations.
Design of Photonic and Plasmonic Materials for Photocatalytic CO2 Reduction
Authors: Gaulding E. Ashley , Sharp Ian D. , Toma Francesca M.
Published: February 2020

This work explores the effects of photonic structuring and localized surface plasmon resonance (LSPR) and on CO2 reduction reactions (CO2RR). We design photonic crystals where the photonic bandgap is tuned by changing the periodicity of the inverse opal cavities. The photonic bandgap of an inverse opal structure can be tuned by the material and pore size/periodicity. These photonic properties control how the incoming light is reflected and refracted within the material. We investigate a variety of photonic crystal materials, such as metal oxides, by infilling the voids of an opal template of polystyrene (PS) spheres to obtain an inverse opal photonic crystal by subsequently removing the PS spheres.

Similarly, the LSPR can be tuned in metal or degeneratively doped semiconductor nanoparticles by tuning the size, shape, and material composition. This increases absorption near the resonance peak. Additionally, hot carriers can be generated as the LSPR decays, providing the potential to access kinetic pathways normally difficult for desired products in CO2RR chemistry. Since we can tune the photonic bandgap simply by changing the size of the PS spheres in the template, we can investigate how matching the photonic bandgap with the plasmonic resonance of a metal particle affects CO2 reduction. We then study the effects of combining both of these physics phenomena on chemical transformation and selectivity in CO2 reduction. From this basis, one could potentially tune CO2RR processes to a desired hydrocarbon fuel product.

We use a combination of SEM, TEM, and XRD to analyze the morphological structure and crystallinity of our materials as well as material composition via EDX. Surface analysis of our structures is done using XPS. We characterize the films’ optical properties, monitoring shifts in the photonic bandgap and LSPR, via UV-Vis-NIR spectroscopy. We monitor CO2 reduction products using in line GC for gas products and NMR for liquid products.
(Invited) Titania-Silica Mesoporous Materials for Solar Hydrogen Evolution
Authors: Koodali Ranjit T
Published: February 2020

The looming energy crisis has prompted intense research into the identification and development of materials that can effectively split water to generate hydrogen that may be used as an energy carrier or used to produce chemicals, i.e. solar fuels. Among the various semiconductor photocatalysts identified and developed, titania based materials continue to attract the attention of researchers because of its excellent photostability, ease of preparation, and cost-effectiveness. In this regard titania supported silica systems provide an ideal platform to explore the photocatalytic water splitting reaction. This is because the physico-chemical properties of the silica support can be easily modulated and varied to allow for effective and well dispersion of titania nanoclusters that are spatially isolated. These spatially isolated titania moieties intrinsically exhibit higher activities compared to bulk titanium dioxide semiconductors because of favorable conduction band edges for production of hydrogen. The choice of the silica support is also a crucial factor that needs to be considered in the design of such artificial photoredox systems.
(Invited) Photo-Electro-Chemical Water Splitting and the Making of Renewable Chemicals
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]. Finally if time allows we shall also discuss the possibility of making high energy density fuels by hydrogenation of CO2 instead of hydrogen evolution [12]. We shall here show how we can investigate the recent ethanol synthesis on oxygen derived Cu found by Kanan et al. and show how acetaldehyde seems to be an important intermediate [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. J. Phys. Chem. C 119 15019 (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. Energy & Environmental Science, 8 2991 (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] A. Verdaguer-Casadevall et al. J. Am. Chem. Soc. 137  9808 (2015)

[13] E. Bertheussen et al. Angew. Chem. Int. Ed. 55 1450 (2016)
(Invited) Charge Carrier Dynamics and Origin of Instability of Organo-Metal Perovskite Films and Quantum Dots
Authors: Zhang Jin Z
Published: February 2020

Organo-metal perovskites are highly promising materials for photovoltaic applications, yet their degradation due to factors such as light, moisture, and oxygen remains a significant problem and the mechanism behind is not yet well understood. We have studied the degradation mechanism of methylammonium lead iodide (MAPbI3) perovskite films subjected to light in a dry environment from a structural perspective. The effect of mesoporous titanium dioxide (mp-TiO2) layer, commonly used in device applications, on the degradation is also investigated. The perovskite structural change was investigated using XRD, UV-Vis absorption spectroscopy, Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, and Fourier Transform Infrared (FT-IR) spectroscopy. The mp-TiO2 plays a significant role in the degradation rate of the perovskite film. Our results indicate that the first step in the light-induced degradation process is the deprotonation of the methylammonium cations, which results in the evaporation of HI and CH3NH2 molecules leaving unreacted PbI2 behind. This is further supported by ultrafast dynamics studies of charge carriers using femtosecond transient absorption spectroscopy.

In addition, have synthesized various organo-metal perovskite quantum dots (PQDs) and used them as a model system to understand the origin of the materials instability. We have found the photogenerated electrons and holes can cause material degradation through redox reactions that damage the ammonium ions acting as localized trap sites, which is likely the origin of instability from light. We also found that species that are likely to react with or extract the protons from the ammonium ions will cause degradation, such as water or alcoholic solvents. Therefore, a more acidic environment is desired for better stability. Based on this understanding, we have designed new strategy to passivate the surface of PQDs using branched ligands to improve stability. The new insight gained from our studies is also important for developing new perovskite materials for solar cell and other applications such as LEDs and sensors.
(Invited) Plasmonic Photocatalysts for Extending Light Harvesting Range and Enhancing Charge Separation
Authors: Wu Nianqiang (Nick)
Published: February 2020

This talk shows how to use plasmonic metal nanostructures as the photosensitizers to extend the light absorption spectral range and enhancing the charge separation in the semiconductor. The plasmonic enhancement mechanism will be discussed. The principle for designing efficient metal-semiconductor heterojunctions will be elaborated. The solar water splitting by the plasmonic metal-semiconductor heterojunctions will be demonstrated.
(Invited) In Situ Synchrotron x-Ray Spectroscopic Studies of Energy Materials
Authors: Dong Chung-Li
Published: February 2020

Global warming and climate change make gradual shortage of energy resources. An epoch of renewable energy is dawning and material scientists are devoted to search the advanced energy materials and solutions for the future global energy problem. The novel material for renewable and sustainable energy that has great efficiency of energy conversion/generation/storage is the most pressing challenge. In several important energy relevant materials such as artificial photosynthesis, nanostructural catalysts, and smart thin films, the change of atomic and electronic structures near the interfacial region during the reaction deliver the fundamental comprehension of the physical and chemical properties of a material. Look into these interfacial phenomena provides the decisive information to better engineer the material and thus control its performance. Synchrotron x-ray spectroscopies, including x-ray absorption and x-ray emission spectroscopies can be employed to explore the local unoccupied and occupied electronic states. Use of in situ/in operando techniques, determination of the modulations of atomic/electronic structures in the energy materials under its operational condition now becomes achievable. This presentation will report the emerging in situ/in operando characterizations on energy relevant materials by synchrotron x-ray spectroscopy. A few of recent investigations of atomic/electronic structure of energy materials will be presented. In addition, a new facilities comprised of in situ XAS, XES, RIXS and STXM will be briefly introduced.
(Invited) Insight into Polyoxometalate-Induced Catalysis at Semiconducting Oxides
Authors: Solarska Renata , Augustynski Jan
Published: February 2020

One of the major limitations in photoelectrochemical water splitting with use of semiconducting oxide is their sluggish surface water oxidation kinetics. Identification of a molecular oxygen evolution catalysts active especially in highly corrosive media is not a trivial case. N-type mesoporous tungsten trioxide, WO3, is one of few stable semiconductor materials able to photo-electrochemically split water under solar light irradiation but it’s operational acidic environment restricts use of any catalyst to the precious metals. In an attempt to overcome this limitation, Keggin‐type polyoxometalate, [PW12O40]3− and [PMo12O40]3−, anions have been employed to act as highly effective oxygen evolution reaction molecular catalysts in photoelectrochemical water splitting devices. This the first example of oxidatively stable in acid media non noble metal water splitting catalyst. Combined with semitransparent Na‐doped nanoporous WO3 film photoanode, they allow achieving under simulated AM 1.5G sunlight exceptionally high water oxidation photocurrent of 4.5 mA cm−2 at 1.1 V versus reversible hydrogen electrode. The surface and structure modifications of a WO3 photoanode which led to this performance, in parallel with the mechanism of the enhancement will be presented and discussed in details.

M. Sarnowska, K. Bienkowski, R. Solarska, P. Barczuk, J.Augustynski; Highly Efficient and Stable Solar Water Splitting at (Na)WO3 Photoanodes in Acidic Electrolyte Assisted by Non-noble Metal Oxygen Evolution Catalyst; Advanced Energy Materials 10.1002/aenm201600526
Photoelectrochemical Hydrogen Production Using Inverted Perovskite Solar Cell
Authors: Ilhwan Oh , Jihun Han
Published: February 2020

Solar water splitting based on organic metal halide (OMH) perovskite materials is reported. The inverted configuration functions as photocathode and provides more benign reductive environment than harsh oxidative environment of photoanode. But the water still penetrated in this photocathode. So the polymer additive in PCBM as top layer was used as a protective layer. Here, we fabricate perovskite-based photocathode consisting of TCO / HTM / OMH perovskite / PCBM : polymer additive / catalyst, which provides stable photoelectrode for solar water splitting.
Structural Design of Graphitic Carbon-Nitride Photocatalysts for Boosting Hydrogen Production from Water Decomposition
Authors: Huang Yu-Jie , Wu Kwun-Han , Teng Hsisheng
Published: February 2020

Melem-based two-dimensional (2D) conjugated polymer, graphitic carbon nitride (g-C3N4), has been demonstrated to be a promising material for photo-driven water splitting due to its unique electronic band structure and good photochemical stability.1 The search for suitable precursors is an important issue regarding the synthesis of active g-C3N4. Commonly used precursors are nitrogen-rich compounds containing pre-bounded triple or double C-N core structure, such as cyanamide, dicyandiamide, melamine, and urea. 2

g-C3N4 synthesized from urea is active in hydrogen production, which is attributable to the resulting sheet-like structure.3 The 2D carbon nitride polymer offers many technical options to engineer the molecular structure, electronic structure, and texture for promoting the performance of water splitting. Methods that have been applied to modify the carbon-nitride photocatalysts include dye sensitization, copolymerization, hybridization, hard-templating fabrication, loading with cocatalysts (e.g., Pt, RuO2, NiO is effective for hydrogen evolution while PtOx, Co is effective for oxygen evolution), and doping with metal (e.g., Fe, Zn, Cu) or non-metal (e.g., S, B, P, I) atoms.4

The present study develops a novel method to synthesize a melem/g-C3N4 hybrid photocatalyst through temperature-programmed ammonia treatment. This treatment regulates the crystalline phase of g-C3N4 and reproduces melem fragments, which is the building blocks of g-C3N4. The hybridized melem/g-C3N4 structure facilitates separation of photo-generated charges and therefore exhibits excellent performance in hydrogen production from photocatalytic water decomposition. We have evaluated the photocatalytic activities of this melem/g-C3N4 catalyst in an assay of photocatalytic hydrogen evolution from water under visible light irradiation, by using Pt and triethanolamine as the cocatalyst and sacrificial reagent, respectively. The hydrogen evolution quantum yield is unprecedented for photocatalytic reactions using g-C3N4-based catalysts.

References

X. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J. M. Carlsson, K. Domen, M. Antonietti., Nat. Mater. 8 (2009), 76−82.

(a) F. Dong, Y. Sun, L. Wu, M. Fu, Z. Wu., Catal. Sci. Technol. 2 (2012), 1332-1335. (b) J. Liu, T. Zhang, Z. Wang, G. Dawson, W. Chen, J. Master. Chem., 21 (2011), 14398-14401.

G. Zhang, Z. A. Lan, L. Lin, S. Lin, X. Wang, Chem. Sci., 10.1039/c5sc04572j .

G. Zhang, M. Zhang, X. Ye, X. Qiu, S. Lin, X. Wang, Adv. Mater., 26 (2014), 805-809.

Acknowledgments: This research was supported by the Ministry of Science and Technology, Taiwan (104-2221-E-006-231-MY3, 104-2221-E-006-234-MY3, 105-3113-E-006-005, and 104-3113-E-006-011-CC2), and by the Ministry of Education, Taiwan, The Aim for the Top University Project to the National Cheng Kung University.
High Efficiency Photoelectrochemical Water Splitting Using Graphene/GaN Nanowire Photoelectrode
Authors: Ha Jun-Seok , Bae Hyojung , Min Jung-Wook , Seo Dong-Ju , Ryo Hokyun , Lee Hyo-Jong , Lee Dong-Seon , Lee Yong-Tak , Lee Sang Hyun
Published: February 2020

GaN based photoelectrode with a nanowire structure have been studied due to superior performance of water splitting ability. Self‐organized GaN nano‐rod on silicon has been demonstrated, and a direct growth via vapour–liquid–solid using metal particle as a catalyst has been reported. Nonowire structure has benefit with short minority carrier diffusion lengths and large surface-to-volume ratio. It allows minor carrier to easily reach to surface without recombination, so that water splitting ability could be increased. However, this structure has photocorrosion problem. For solving this problem, we covered graphene material on the tips of nanowires as a passivation layer. Graphene has been known to have excellent mechanical, thermal, optical, and electrical properties.

For these reasons, we studied the photoelectrochemical water splitting properties of graphene coated GaN nanowire (graphene/GaN nanowire) photoelectrode. GaN nanowire sample without graphene was used for the reference. The GaN nanowire structures were grown on n-type Si(111) substrates using radio-frequency plasma-assisted molecular beam epitaxy. The graphene was grown by chemical vapor deposition method and exfoliated to surface of GaN nanowire. As a result, compared with non-coated GaN nanowire sample, the graphene/GaN nanowire phoeoelectrode showed higher photocurrent density. Also, we could know that it has much higher photocurrent stability. We will present the results and the reasons for higher efficiency and stability of this graphene coated GaN nanowire sample at this conference.

Reference

[1] Allon I. Hochbaum, and Peidong Yang, Chem. Rev., 110 (2010) 527–546

[2] B. AlOtaibi, M. Harati, S. Fan, S. Zhao, H. P. T. Nguyer, M. G. Kibiria, and Z. Mi, Nanotechnology, 24 (2013) 175401
Quasi-Solid Electrolytes Comprising Cobalt Complexes for Efficient and Durable Dye-Sensitized Solar Cells
Authors: Kim So-Eun , Kim Do-Hyeong , Kang Moon-Sung
Published: February 2020

There has been much attention towards dye-sensitized solar cells (DSSCs) for the past decades due to their attractive features such as reasonable energy conversion efficiency and low energy production cost. Even though a respectable energy conversion efficiency (~12%) has been achieved for photovoltaic cells employing organic liquid electrolyte that consists of I-/I3
- redox couples and volatile solvent (e.g. acetonitrile), the leakage and evaporation of liquid solvent from such cells has been suggested as the one of the critical factors limiting the long-term stability of the DSSC. Moreover, the use of I-/I3
- redox couples limits the energy conversion and even causes some problems such as the metal corrosion and visible light absorption etc. Recently, cobalt complexes (e.g. [Co(bpy)3]2+/3+, bpy=2,2’-bipyridine) have been suggested as one of the most promising candidates for replacing conventional I-/I3
- redox shuttles owing to their high voltage characteristics. Although a high energy efficiency exceeding 12% was reported by employing liquid electrolyte that consists of cobalt complex redox mediator and volatile solvent, the use of volatile liquid solvent cannot ensure the long-term stability of the DSSCs. In this work, therefore, novel quasi-solid electrolytes (QSEs) including cobalt complexes as redox couples have been developed for efficient and long-term stable DSSCs. The physicochemical properties of QSEs were adjusted by selecting proper solvent and functional additives (for improving cobalt complex solubility and cation transference number etc.). Polyethers with polar groups and polymers without polar groups were used as the polymer additives for the gelation of the liquid electrolytes with various blending ratios. The DSSC employing the QSEs showed the respectable energy conversion efficiency comparable with those of the DSSCs with liquid electrolytes. After the thermal aging tests, it was also proven that the long-term stability of the DSSC employing the QSE is much better than that of the cell filled with volatile liquid electrolyte. (This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Korea government (MSIP) (2015R1A1A1A05001486).)
Hieratical Cu2SnS3 (CTS) Nanostructure As a Highly Efficient Visible Light Photocatalyst for CO2 Reduction to Solar Fuels
Authors: Shown Indrajit , Chang H. S. , Tai Yian , Chen Li-Chyong , Chen Kuei-Hsien
Published: February 2020

The conversion of greenhouse CO2 gas into value added chemicals using solar energy or photocurrent derived from visible light is known as artificial photosynthesis. Recently, the production of solar fuel through artificial photosynthesis has been gained tremendous attention due to their fascinating potential in environmental and energy-related application. In CO2 photoreduction technology, the major challenge is the low efficiency of the photocatalyst. Several wide band gap and hybrids carbonaceous materials have been demonstrated as photocatalyst for CO2 reduction. However, in real application these photocatalyst materials are far away from the actual 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. Last few years several metal sulfides like MoS2, CuS, Cu2S, ZnS and their composite have been attracted considerable attention as a photocatalyst due to their good optical property, high absorption coefficient. However, the application of these perfect semiconductors for photocatalytic CO2 reduction to solar fuels may be limited due to their high interfacial electron-hole recombination process. Recently, Cu-Sn-S ternary semiconductor system has been attracted for its potential contribution as a light absorber layer in photovoltaic application. Cu2SnS3 (CTS) is a ternary p-type semiconductor with a high absorption coefficient. The observed optical band edge of CTS is around 1.4 eV, nearly ideal for solar-energy harvesting. In this study, CTS nanostructure has been demonstrated as a photocatalyst for photocatalytic CO2 reduction to solar fuels under visible light. The ternary CTS nanostructure was obtained from the hydrothermal process and characterized by XRD, Raman spectroscopy, UV-Vis spectroscopy and SEM technique. The photocatalytic activity of the CTS nanostructure hybrid with different S composition was measured in the gas phase CO2 photoreduction under visible-light irradiation. Ethanol has been found to be major product as a high selectivity and efficiency from the photocatalytic CO2 reduction. The observed ethanol formation rate is around 5.6 μmol/g-cat.hr. Detailed investigation on the optimum phase composition, its nanoarchitectures and possible mechanism for the selective solar fuel generation will be discussed.

References

Nanoscale, 5, 262, (2013)

Nano letters, 14, 6097, (2014)
Fabrication of a Monolithic Heterostructured c-Si/BiVO4 Core-Shell Photoanode for Unassisted Solar Water Splitting
Authors: Chakthranont Pongkarn , Hellstern Thomas R , McEnaney Joshua M , Jaramillo Thomas F
Published: February 2020

Photoelectrochemical (PEC) water splitting is a promising way of storing solar energy in hydrogen, which can be used as a carbon-free fuel or a chemical feed stock. A tandem-junction PEC device offers a high theoretical solar-to-hydrogen (STH) efficiency due to the additive voltages across two photoabsorbers and the better utilization of the solar spectrum. Modeling STH efficiency as a function of band gap for a tandem device shows that over 20% STH can be achieved with band gaps of 1.2 and 1.8 eV.1 One promising photoabsorber material combination is c-Si paired with a metal oxide, especially BiVO4. In addition to the appropriate band structure alignment of both semiconductors, c-Si and BiVO4 are low cost, earth abundant, and industrially scalable. However, the key challenges for these materials are the instability of c-Si in aqueous environment and the poor electronic properties of BiVO4, a common limitation for most metal oxides. Hence, only a very few c-Si/metal oxide systems have been demonstrated for unassisted water splitting.2

In this work, we present the fabrication of a monolithic heterostructured c-Si/BiVO4 core-shell tandem based monolithic device capable of performing spontaneous water splitting without any precious metal. The wafer scaled device architecture was prepared by (1) nanostructuring of the d c-Si substrate to serve as both a bottom absorber and a scaffold to improve the charge separation of BiVO4; (2) tuning the c-Si p-n junction depth to maximize the device photovoltage; (3) engineering the SnO2 interfacial layer to passivate the c-Si/BiVO4 interface and protect the c-Si p-n junction; (4) conformally coating a BiVO4 thin film on the nanostructured Si; and (5) decorating the c-Si and BiVO4surfaces with both oxygen and a hydrogen evolution catalysts.

(1) Seitz, L. C.; Chen, Z.; Forman, A. J.; Pinaud, B. A.; Benck, J. D.; Jaramillo, T. F. ChemSusChem
2014,
7(5), 1372-1385.

(2) (a) Shaner, M. R.; Fountaine, K. T.; Ardo, S.; Coridan, R. H.; Atwater, H. A.; Lewis, N. S. Energy Environ. Sci.
2014,
7 (2), 779-790; (b) Liu, C.; Tang, J.; Chen, H. M.; Liu, B.; Yang, P. Nano Lett.
2013,
13 (6), 2989-2992; (c) Xu, P.; Feng, J.; Fang, T.; Zhao, X.; Li, Z.; Zou, Z. RSC Adv.
2016,
6 (12), 9905-9910.
Modification of Electronic States at Surface of Photocatalysts for Enhanced Photoelectrochemical Water Oxidation
Authors: Park Jong Hyeok , Jeong Myung Jin
Published: February 2020

We report the effect of chemical reduction of bismuth vanadate (BiVO4) photoelectrdoe by lithium-based strongly basic solution. Lithium dissolved in ethylenediamine anhydrous rapidly reduces the bismuth vanadate films with momentary immersion in the solution. This chemical reduction could form oxygen vacancies and these defects act as shallow donors for bismuth vanadate and increase the donor densities without trapping. Electrochemical impedance measurements showed that the donor densities of bismuth vanadate films were significantly enhanced. Photoelectrochemical water splitting performance was improved as well with photocurrent increase. The enhanced photoactivities were attributed to increased donor densities of reduced bismuth vanadate, which have effects on the charge transport.
Electrochemical Modification of Boron-Doped Diamond with Cu2O Nanoparticles for Photocatalytic Applications
Authors: Hasan Maksudul , Mavrokefalos Christos K. , Rohan James F. , Foord John S.
Published: February 2020

It is generally accepted that one of the main challenges facing our planet today is the human interfered climate change and its inseparable link to our global society’s present and future needs. Solar energy is doubtless one of the most attractive ways to deal with these issues. Water splitting by artificial photosynthesis is a favourable means of converting solar energy into transportable and end user chemical energy. Two of the major issues that remain unresolved in artificial photosynthesis are first to find a visible light absorber earth abundant semiconductor and second a robust substrate. Additionally, photon to current conversion efficiency of the current state-of-the-art semiconductor is far below the theoretical value due to undesirable charge carrier recombination loses. Cuprous oxide (Cu2O) is a naturally occurring p-type metal oxide semiconductor, is abundant and promisingly possesses a suitable band gap (2.0 eV) and energy band position that enable it to absorb solar light in the visible spectrum to produce hydrogen gas without external bias. However, Cu2O suffers from rapid charge carrier recombination losses and self-photocorrosion when comes in contact with water under illumination. The use of bimetallic alloys or core-shell metals in nanoparticle format is beneficial in two ways; protecting semiconductor from self-photo corrosion and providing short diffusion paths for electron-hole pairs enabling fast transfer to the respective redox reaction sites. Boron-doped diamond (BDD) is a potential substrate in the field of electrocatalysis due to its plethora of advantages such as wide potential window, low background current, resistance to fouling and electrocorrosion as well as its availability at a low cost when grown by chemical vapour deposition (CVD).

In this work, the electrochemical modification of oxygen terminated boron doped diamond (OBDD) electrodes decorated with NiO-Cu2O nanoparticles is described. The method involves the electrodeposition of Cu2O nanoparticles on OBDD from a surfactant-free electrolyte followed by a thin coating of NiO onto Cu2O nanoparticles (Fig. 1a). The electrochemical experimental data showed that electronic effects due to the bimetallic catalysts led to higher photocurrent densities in comparison with Cu2O nanoparticles alone (Fig. 1b). In order to understand the morphology, dispersity and size of the nanoparticles, deposits were characterised by high resolution scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).

Figure 1 (a) SEM image of NiO-Cu2O modified OBDD electrode and (b) Linear-sweep voltammograms of the photoelectrochemical response of Cu2O and NiO-Cu2O modified OBDD electrodes, respectively under chopped light (100 mW cm-2 and on-off frequency 0.2 Hz) at a scan rate of 10 mV s-1 in 0.1 M Na2SO4 (pH 6.2).

Figure 1
Photocatalytic Hydrogen Production with Zn-Based Photocatalyst
Authors: Kaneco Satoshi , Katsumata Hideyuki , Suzuki Tohru
Published: February 2020

THe photocatalytic hydrogen production with Zn-based photocatalyts was investigated.