bluuebunny/crossref_metadata_2025 huggingface dataset:
Epitaxially Grown Pt and Pt-Ir Thin Films: Effect of the Deposition Conditions on the Electro-Oxidation of Ammonia
Authors: Sacré Nicolas , Hufnagel Gregor , Garbarino Sebastien , Ruediger Andreas , Roué Lionel , Guay Daniel
Published: February 2020

Ammonia (NH3) is a highly toxic gas, a major environmental pollutant, and a potential fuel for fuel cells. Thus, the electrooxidation of NH3 has important applications in NH3 safety sensors, NH3 decontamination in wastewater and power production. However, on most electrode materials, NH3 oxidation reaction proceeds with a high overpotential, low current density, and rapid poisoning rate. Better electrocatalysts for this reaction would lower the NH3 detection threshold in sensors, increase the rate of NH3 removal for decontamination, and boost power of NH3 fuel cells.

Platinum is the electrocatalyst that shows the highest current density at the lowest overpotential for catalyzing the oxidation of NH3 to N2. The electrooxidation of NH3 on Pt is further complicated by the fact that the reaction rate strongly depends on the metal surface structure. In alkaline medium, the electrooxidation of ammonia on Pt occurs almost exclusively on surface sites with (100) symmetry, especially on wide terraces. Accordingly, the preferred way to study the effect of alloying Pt with other elements would be to rely on a series of mixed Pt-M alloy single crystals with the appropriate (100) surface termination. However, the preparation of single-crystals is difficult. In the case of Pt-Ir, the situation is even more complicated since the Pt-Ir binary phase diagram shows that Pt and Ir are barely miscible at temperature below 1000°C, which could translate into insurmountable technical difficulty in the preparation of Pt-M alloy single crystals.

In recent years, Pulsed Laser Deposition (PLD) has emerged as an effective method for preparing thin films with preferential orientation and kinetically stable alloys. In this work, we will study the influence of different deposition parameters (composition, temperature and thickness) on the electro-oxidation of ammonia. To achieve this, a combination of X-ray diffraction (ϴ - 2ϴ scans, rocking curves and pole figures) and atomic force microscopy will be used to get information about the surface organisation and the length of the terraces. Then, electrochemical measurements will be performed to confirm the preferential (100) surface orientation and evaluate the electrochemical performances of the various films for the oxidation of NH3.

It will be shown that the current for the electro-oxidation of NH3 varies with the Pt content and the thickness of the film (see Fig. 1). For the thinnest films, the role of Ir atoms in helping the formation of large (100) terraces will be emphasized.

Figure 1 Variation of the current density for the electro-oxidation of NH3 with respect to the Pt content. The data were collected from the current at 0.71 V vs RHE during cyclic voltammetry (20 mV.s-1) in 0.1M NaOH + 0.1M NH3.

Figure 1
(Invited) Engineering Bismuth-Based Ternary Oxide Thin Films for Photoelectrochemical Water Oxidation
Authors: Ng Yun Hau , Amal Rose
Published: February 2020

Bismuth based ternary oxide powders (such as BiVO4, Bi2WO6 and Bi2MoO6) have been reported to be active for oxidation of organic substances and water under visible light. In general, these materials have sufficient absorption within the solar spectrum and stability against photocorrosion. The preparation of bismuth based ternary oxide is inexpensive, environmentally benign and can be made using a number of different facile methods. In this presentation, we investigate the performance of these bismuth based ternary oxides in photoelectrochemical water splitting. A few aspects will be highlighted to substantiate the differences when they were employed in photocatalytic water splitting or through photoelectrochemical means. It is generally acknowledged that surface area and crystallinity of photocatalysts are critical factors regulating performances in powder-type suspension reactions. When they were made into thin film, quality of the contact between bismuth based ternary oxides and the charge collecting substrate becomes another crucial factor. In this work, we also discuss a few strategies formulated to directly synthesise these ternary oxide thin films without having the powder oxide as the intermediate.

BiVO4, Bi2WO6 and Bi2MoO6 thin films are synthesised in this work. BiVO4 with controlled exposed facet is engineered to study the dynamic of charge interactions between their respective facets. It is revealed that a balance of charge transfer and charge trapping are occurring to govern the overall performance of BiVO4. From that point of view, specific interface is engineered to boost the higher charge transfer efficiency, for example, by using graphene as electron mediator. Bi2WO6 and Bi2MoO6 thin films are synthesised by a direct conversion of anodised WO3 and MoO3 films. The adhesion of the resultant Bi2WO6 and Bi2MoO6 on the substrate is highly stable. With the control of synthesis parameter, a concentration gradient can be introduced to form the composite of Bi2WO6-WO3 and Bi2MoO6-MoO3 with desired composition. With the favourable band alignment in this composite material, an improved activity in photoelectrochemical water oxidation is observed.
(Keynote) Electrochemical and Molecular Approaches for Artificial Photosynthesis
Authors: Yoon Kyung Byung
Published: February 2020

The ultimate goal of artificial photosynthesis research is to develop methods to produce carbon-based gaseous and liquid fuels such as carbon monoxide, methane, and methanol from carbon dioxide and water using solar energy as the energy source. In particular for the methods to be commercially viable the overall costs for the production processes should be low enough so that the processes can compete with the current fossil fuel based processes. The fastest and the most feasible approach would be to combine solar cells and electrochemistry. In other words to electrochemically reduce CO2 to CO, CH4, C2H4, and alcohols such as methanol, ethanol, propanol, and others using the electricity produced by solar cells. For this, to be economically feasible, two electrode systems should be used, the electrochemical reaction should be stable for months, and the electrical energy to chemical energy conversion efficiency (ECCE) should be over high (>70%). Our recent results arising from our efforts to address the above issues will be presented. Another simplest strategy to commercialize artificial photosynthesis is to develop artificial molecular enzymes which can carry out artificial photosynthesis by merely dissolving them into the water pool placed under the sunlight. To make this strategy to be feasible the effective molecular water oxidation catalysts and CO2 reduction catalysts should be developed and the molecular system consisting of a water oxidation catalyst, a photopump (photosensitizer), and a CO2 reduction catalyst should be developed. Our recent efforts to address this issue will also be presented.
(Invited) Understanding the Chemistry of Photocatalytic Processes
Authors: Bahnemann Detlef Werner , Hakki Amer , Schneider Jenny
Published: February 2020

Any enhancement of the efficiency of the utilization of photogenerated charge carriers on the surface of photocatalysts requires an enhanced understanding of the entire photocatalytic process. The reduction potentials of most substrates, as well as those of the intermediates formed during the photocatalytic reaction(s), are well known; nevertheless, it is essential to realize that thermodynamic properties may change upon the adsorption of these molecules at the photocatalyst surface. Therefore, a detailed understanding of the processes occurring on the photocatalyst surface before, during, and after light absorption is of utmost importance. On the other hand, the charge carriers generated upon light absorption that survive recombination and reach the semiconductor surface may suffer surface recombination processes or recombination via an electron shuttle mechanism (Z scheme deactivation mechanism), thus reducing the total efficiency of the photocatalytic system. Moreover, since the overall efficiency of a photocatalytic process will be determined by the efficiency of the slowest reaction step it is crucial to know whether this is the reductive or oxidative half-reactions. Besides the obvious one-electron transfer steps these reactions entail in particular multi-electron transfer processes, e.g. , the four-electron oxidation of water or the eight-electron reduction of CO2. Hence, this lecture provides some necessary tools for the understanding and the development of the photocatalytic reaction mechanism.
(Invited) Materials and Systems for Stand-Alone Solar Water Splitting
Authors: Lee Jae Sung
Published: February 2020

Sunlight is a clean, renewable and abundant energy source on the earth. Its conversion to hydrogen has been considered an ideal solution to counter the depletion and environmental problems of fossil fuels. Photoelectrochemical (PEC) water splitting is an ideal technology for the purpose, since H2 could be produced directly from abundant and renewable water and solar light from the process. The key to the technology is photoelectrodes made of small band gap semiconductors of photocatalytic properties. The materials should have high efficiency, high stability, and low cost. In addition of the discovery of new materials, the structure and morphology of the known materials could be controlled to enhance the performance of the photoelectrodes. In this presentation, the concepts of materials design and their examples are proposed for efficient photoelectrodes of PEC cells for visible light water splitting.

About 400 semiconductor solids are known to have photocatalytic activity for water splitting. Yet there is no single material that could satisfy all the requirements for desired photocatalysts: i) suitable band gap energy (1.7 eV< Eg < 2.3 eV) for high efficiency, ii) proper band position for reduction and/or oxidation of water, iii) long-term stability in aqueous solutions, iv) low cost, v) high crystallinity, and vi) high conductivity. Hence, in the selection of photocatalytic materials, we better start from intrinsically stable materials made of earth-abundant elements.  The band bap energy is also the primary consideration to absorb ample amount of solar energy of wide wavelength spectrum. It sets the limit of theoretically maximum efficiency and it could also be extended by band engineering techniques.

Upon selection of the candidate materials, we can also modify the materials for full utilization their potentials. The main path of efficiency loss in PEC water splitting process is recombination of photoelectrons and holes. We discuss the material designs including i) p-n heterojunction photoanodes for effective electron-hole separation, ii) electron highway to facilitate interparticle electron transfer, iii) metal or anion doping to improve conductivity of the semiconductor and to extend the range of light absorption, iv) one-dimensional nanomaterials to secure a short hole diffusion distance and vectoral electron transfer, and v) loading co-catalysts for faci;e charge separation. High efficiency has been demonstrated for all these examples due to efficient electron-hole separation. Modern material processing techniques have been explored to materialize these concepts.
(Invited) Hydrogen Evolution from Water Using Modified Chalcogenide Photocathodes
Authors: Ikeda Shigeru , Jiang Feng , Shen Qing , Nose Yoshitaro , Harada Takashi
Published: February 2020

Copper chalcopyrite semiconductors of Cu(In,Ga)(S,Se)2 include a wide range of compounds that are of interest for photoelectrochemical (PEC) water splitting due to their band gaps in the range of 1.0 eV to 2.5 eV by varying the alloy ratio. The conduction band of the compounds is also well positioned above the reduction potential of water, enabling them to be used as photocathodes for H2 generation. Two of important factors required for photocathodes of PEC water splitting are photocurrent (photocurrent density) and onset potential (photovoltage), i.e., photocathodes having positive onset potentials coupled with high photocurrents are promised in order to induce water splitting by using a tandem system without applied bias energy. For chalcopyrite materials applied to the photocathode part, this can be achieved through band engineering by altering the composition of the alloy.

In this study, wide-gap Cu(In,Ga)S2 (CIGS) films with various amounts of Ga were fabricated using spray pyrolysis followed by sulfurization. Photoelectrochemical water splitting properties of photocathodes based on these films were evaluated after modification with a CdS layer and Pt nanoparticles. Both photocurrent densities and onset potentials of the photocathodes were gradually improved by increase in the amount of Ga in the CIGS films up to a Ga/(In+Ga) ratio of 0.25 using 0.1 M Na2SO4 (pH 9) as an electrolyte under illumination of simulated sunlight (AM 1.5G). Further inclusion of Ga in the CIGS film was detrimental for both photocurrent density and onset potential. The maximum photocurrent density of 6.8 mA cm-2 (at 0 V vs. RHE) and the highest photocurrent onset potential of 0.84 V vs. RHE were obtained by using such photocathode. Achievements of a relatively wide interface band gap of the CIGS/CdS heterointerface and formation of relatively large grains in the CIGS with Ga/(In+Ga) ratio of 0.25 were likely to be responsible for such superior water reduction properties. The preliminary result of band engineering via replacement of Cu with Ag in the Cu(In,Ga)(S,Se)2 system in relation with its application as photocathode also will be presented.
Effect of Adding TiO2 Nanoparticles in AC-Operated Electrochemiluminescencent Device Using Ruthenium(II) Complex
Authors: Tsuneyasu Shota , Ichihara Kazuki , Nakamura Kazuki , Kobayashi Norihisa
Published: February 2020

Electrochemiluminescence (ECL) is a phenomenon in which light is emitted from the excited state of a redox-active material generated by electrochemical reactions. Among light-emitting device, ECL devices have various advantages in terms of structure and ease of fabrication, and therefore, they are expected as next generation emitting devices. Concerning to the ECL device, we have reported the improvement of emission response, ECL intensity and stability of the ECL device by employing alternating current (AC)-driven method.[1] Nevertheless, we found that the ECL intensity and long-term stability of the system were not enough, and improvement should be required for practical use.

In terms of improving the ECL intensity, several researchers have reported that the brightness of the Ru(bpy)3
2+-based ECL could be improved by adding metal oxide nanoparticles (NPs) into the ECL solution. However, the underlying mechanisms of the enhancements were not clarified.[2], [3] The purpose of this study is to elucidate the mechanism of this ECL enhancement. We first investigated the change in the ECL intensity and long-term stability of the ECL device upon addition of the TiO2 NPs to the Ru(bpy)3
2+-based ECL solution. With the addition of the TiO2 NPs into the solution, the emission luminescence of the ECL device increased to 165 cd/m2, which was 1.4 times higher than the device without the addition of TiO2 NPs (120 cd/m2). Without the TiO2 NPs, the half-life time of the ECL device was ~250 s, in contrast to that of the ECL device with the TiO2 NPs, which was expended by a factor of 4 to ~1000 s. Thus, the ECL intensity and long-term stability of the device were greatly improved by adding TiO2 NPs in the Ru(bpy)3
2+-based ECL solution.

To reveal the influence of the TiO2 NPs on achieving the high emission luminescence and long-term stability, we measured the optical and electrochemical properties of the Ru(bpy)3
2+-based ECL solution in detail. Increases in the photoluminescence for Ru(bpy)3
2+ were observed by adding the TiO2 NPs. This indicated that the suppression of the radiationless quenching of the excited states would improve the ECL intensity. In terms of the long-term stability, electron transfer between the Ru(bpy)3
2+ and TiO2 NPs was suggested by the detailed electrochemical measurements. Electron transfer occurred from the reduced species of Ru(bpy)3
2+ to the TiO2 NPs, and subsequently, from the TiO2 NPs to the oxidized species of Ru(bpy)3
2+. This kind of electron transfer is thought to improve the balance between the redox reactions in the ECL device, leading to long-term stability.

 Reference

[1] T. Nobeshima et al., J. Mater.
Chem., 20, 10630 (2010).

[2] N. Itoh, J. Electrochem. Soc.,
156, J37 (2009).

[3] N. Itoh, Matrials, 3, 3729 (2010).
Novel Light-Emitting Electrochemical Transistor Using Ruthenium Complex
Authors: Aoki Atsushi , Nakano Tomoyuki
Published: February 2020

Recently, organic light-emitting transistors (OLETs) which combined organic light-emitting diodes (OLEDs) with organic thin film transistors (OTFTs) have being intensively investigated for application to display. They can control light emission by the gate voltage. So far, we have investigated light-emitting electrochemical cells (LECs) and electrochemical transistors (ECTs) independently. LECs have some advantages about a simple device structure and usage of air-stable metal cathode compared to OLEDs. ECTs also have unique features for lower driving gate voltage than that of OTFTs because the electrochemical doping becomes easier for the formation of the electric double layer in the ECTs. Therefore, a novel concept for the light-emitting electrochemical transistor (LECT) which consists of the light-emitting electrochemical cell (LEC) and the electrochemical transistor (ECT) was introduced. To aim at constructing LECT, four-electrode electrochemical system using interdigitated array (IDA) electrodes was employed to demonstrate the concept of LECT in solution. Cyclic voltammetric (CV) measurement was carried out in acetonitrile solution containing Ru(bpy)3(PF6)2 as redox species and a chemiluminescent material. We confirmed that the light emission was controlled at the electrode potential difference between both fingers of IDA electrodes as source and drain electrodes of the transistor and reference/counter electrodes as gate electrode. The light emission was observed at the electrogenerated chemiluminescent condition where the excited state Ru(II) was produced on the gap distance by the electron exchange reaction of Ru(I) and Ru(III) produced at both fingers of IDA electrodes, respectively. If the electrode potential would be shifted to anodic or cathodic directions, whether Ru(I) or Ru(III) would be not produced, the light emission disappear even at the same bias voltage between the source and drain electrodes (VDS) where the light emission is possible. If VDS is not enough to produce Ru(I) and Ru(III), the light emission does not occur. If VDS is enough to produce Ru(I) and Ru(III) in the diffusion limited condition, the light emission becomes steady state intensity. Therefore, we demonstrated that the light emission can be controlled by VDS and the gate electrode potential in the LECT. We also confirmed that current behavior flowed between source and drain electrodes shows bipolar transistor characteristics. We are now trying to solidify the LECT system in solution to realize LECT device.
Shortening Response Time of Light-Emitting Electrochemical Cell By Addition of Ionic Liquid into Iridium Complex Film
Authors: Kubo Takayuki , Aoki Atsushi
Published: February 2020

Light-emitting electrochemical cells (LECs) are single layer electroluminescent devices consisting of a luminescent material. A large number of LECs using Iridium(Ⅲ) as the metal core to emit various color variations have been evaluated recently. However, there are many problems about performance or stability. We have aimed the improvement of the performance and stability of LECs using Ir complex. So, we have synthesized yellow emission ionic transition-metal complex, Ir(ppy)2(dtbbpy)NTf2. The resulting product is confirmed by 1H NMR. The absorption and emission spectra of Ir(ppy)2(dtbbpy)NTf2 in acetonitrile solution at room temperature were measured. The absorption bands were observed in the range of 230-350 nm assigned to spin-allowed π-π* and in the range of 350-500 nm assigned to spin-forbidden MLCT, LLCT, LC transitions. The emission peak was observed at 558 nm using an excitation wavelength of 420 nm. The redox behavior was characterized by cyclic voltammetry. We fabricated light-emitting electrochemical cell using Ir(ppy)2(dtbbpy)NTf2. Electrogenerated chemiluminescence peak was observed at 556nm indicating yellow emission. Addition of ionic liquid, (1-butyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide) into Ir(ppy)2(dtbbpy)NTf2 film in the mixing weight ratio of 4:1 makes response time decreased dramatically. And electroluminescence layer thickness was controlled by adjusting the concentration of Ir(ppy)2(dtbbpy)NTf2 in acetonitrile solution to shorten response time.
Photoelectrochemical Hydrogen Production By Water Splitting over Dual-Functionally Modified Oxide: P-Type N-Doped Ta2O5 Photocathode Active Under Visible Light Irradiation
Authors: Suzuki Tomiko M. , Saeki Shu , Sekizawa Keita , Kitazumi Kousuke , Takahashi Naoko , Morikawa Takeshi
Published: February 2020

It is widely accepted that photocatalytic hydrogen generation by water splitting and carbon dioxide recycling by reductive reaction are promising technologies as clean energy generation in the future. To this end, lots of semiconductor materials which can be activated under visible light irradiation have been developed to date. Recently, our group developed a dual-functional modified N-doped Ta2O5 (N-Ta2O5) that absorbs visible light at wavelengths below 520 nm (Eg = 2.4 eV) by forming a new energy state in which the N 2p is above the O 2p in the bandgap [1, 2]. The N-doping also changed its photoresponse from n-type to p-type conduction due to formation of acceptor level by N, and also resulted in a highly negative location of the conduction band minimum (E
CBM = -1.3 V vs NHE) originated from surface dipole effect [1, 3]. Depending on the much negative E
CBM, a highly selective visible light-induced reduction of CO2 to HCOOH was achieved by employing N-Ta2O5 linked with a ruthenium complex catalyst in acetonitrile (MeCN)/triethanolamine (TEOA) [4, 5]. These characters as a semiconductor are completely different from those of conventional tantalum pentoxide (Ta2O5, Eg = 4.0 eV, = -0.4 V vs NHE) and tantalum oxynitride (TaON, Eg = 2.4 eV, = -0.3 V vs NHE) [6], which exhibit anodic photoresponses.

In this paper, we demonstrate H2 evolution over N-Ta2O5 by water splitting in aqueous solution under visible light irradiation.

Although the surface of N-Ta2O5 was found to be almost inert for hydrogen production by water splitting, photocathodic current over N-Ta2O5 films under visible light irradiation (λ ≥ 410 nm) was highly enhanced by surface modification with Pt, Rh or Au. Loading with either Pt or Rh greatly enhanced the H2 evolution rate in an aqueous solution, increasing the rates by two orders of magnitude compared to that over unmodified N-Ta2O5 for both photoelectorodes and nanoscaled powders. At this moment, the conversion efficiency was low as 0.15 % at 400 nm. However, the dual functional modification of Ta2O5 by the single element doping of N was clarified to be as a new approach to facilitate the reductive reaction for energy conversion.

This finding should assist in the future development of highly efficient photocatalysts for solar energy conversion by photoelectrochemistry by N doping into oxide semiconductor materials.

[references]

[1] T. Morikawa, et al., Appl. Phys. Lett., 96(2010) 142111.

[2] T. M. Suzuki, et al., J. Mater. Chem., 22(2012) 24584.

[3] R. Jinnouchi, et al., J. Phys. Chem. C., DOI : 10.1021/acs.jpcc.5b06932.

[4] S. Sato, et al., Angew.
Chem. Int. Ed., 49(2010) 5101.

[5] T. M. Suzuki, et al., Chem. Commun., 47(2011) 8673.

[6] K. Domen, et al., J. Phys. Chem. B., 107 (2003) 1798.
Mixed Valence Tin Oxide Sn3O4: A Visible-Light Driven Semiconductor for Photocatalytic Water Splitting Under Visible Light Irradiation
Authors: Tanabe Toyokazu , Hashimoto Masanari , Tanikawa Tatsuhiro , Gunji Takao , Kaneko Shingo , Ohsaka Takeo , Matsumoto Futoshi
Published: February 2020

Water splitting using a particle photocatalyst with visible light has attracted interest, because this will realize efficient conversion of the solar energy to hydrogen fuels for sustainable energy managements. Many water-splitting photocatalysts, such as metal-doped oxides, metal-(oxy)nitrides, and metal-oxysulfides, exhibit water reduction and oxidation ability when absorbing visible light. However, in such water-splitting photocatalysts, solely doping and/or replacement of foreign element at host material has been attempted to prepare visible-light-driven photocatalysts. The doping and/or replacement induces defect sites and charge imbalance into photocatalyst, resulting in the formation of recombination centers between excited electron and holes, in return to create new valence state. Therefore, the development of new native visible-light-sensitive photocatalyst for water splitting without doping of foreign elements is a major challenge for photocatalyst research.

Herein, we report that an undoped metal oxide, Sn3O4, can efficiently catalyze Hydrogen (H2)-evolution in the presence of a sacrifice agent and, furthermore, can split water to H2 and O2 under irradiation of visible light by two-step photoexcitation (Z-scheme) systems using Sn3O4 as H2-evolving photocatalyst, combined with an appropriate O2-evolving photocatalyst in the presence of iodate/iodide (IO3
−/I−) as an electron mediator.

We prepared nanocrystals of Sn3O4 by hydrothermal synthesis using sodium citrate as a ligand [1]. The Sn3O4 significantly catalyzed hydrogen evolution in aqueous solution in the presence of sacrifice agent under irradiation of visible light (λ>420nm), even without Pt co-catalyst. Pt co-catalyst was critical for Sn3O4 material to exhibit higher photocatalytic activity, so far in this study. The apparent quantum yield was 0.2% for high purity Sn3O4 and 1.5% for Pt loaded-Sn3O4, competitive to that of visible-light-sensitive doped metal oxide and (oxy)nitrides photocatalyst. Simultaneous evolution of H2 and O2 was attempted by using Sn3O4 as H2-evolving photocatalyst, combined with an appropriate O2-evolving photocatalyst (BiVO4, WO3 etc.,). By employing the appropriate combination of Sn3O4 and the redox couple (IO3
−/I−), simultaneous evolution of H2 and O2 stably proceeded with higher rates.

[1] M. Maidhily, T. Tanabe, et al., ACS Appl. Mater. Interfaces 2014, 6, 3790.
(Keynote) Visible Light Photocatalysts Based on Interfacial Charge Transfer
Authors: Hashimoto Kazuhito
Published: February 2020

Indoor air quality is an important health and safety factor due to its influences on population health and wellbeing. The air levels of volatile organic compounds (VOCs) are of particular concern because these harmful chemicals cause a wide range of human health problems, including sick house syndrome. Infectious pathogens are also frequently encountered in our daily environment and can adversely impact human health. As a promising solution for environmental remediation, photocatalytic oxidation using semiconductors has attracted considerable attention. However, because most efficient photocatalysts are wide band-gap semiconductors, such as TiO2, which are only activated by ultraviolet (UV) light irradiation, they have been limited to outdoor applications. As indoor light sources contains low levels (below several µW/cm2 in white light fluorescent light) or no UV light (white incandescent light and white light emission diodes [LEDs]), it is highly desirable to develop visible-light-sensitive photocatalysts for indoor environmental purification applications.

Recently we demonstrated that the surface modification of TiO2 with Cu(II) or Fe(III) nanoclusters increases the visible-light-sensitivity of the resulted material without inducing impurity levels in the band gap. In the case of Cu(II) nanocluster-grafted TiO2 (Cu(II)-TiO2), electrons in the valence band (VB) of TiO2 are excited to the Cu(II) nanoclusters under visible-light irradiation through an interfacial charge transfer (IFCT) process. The introduction of excited electrons into the Cu(II) nanoclusters leads to the formation of Cu(I) species, which efficiently reduce oxygen molecules. During the IFCT process, holes with strong oxidative power for the decomposition of organic compounds are generated in the deep VB of TiO2. Thus, nanocluster-modified TiO2 is a promising material for visible-light-sensitive photocatalytic applications.

In this lecture, I will review our studies on the IFCT-based TiO2 visible light sensitive photocatalysts and also show the results of their demonstration tests obtained in some public spaces such as airports and hospitals.

 

References

1. J. Am. Chem. Soc. 2007, 129, 9596. 2. Chem. Phys. Lett., 2008, 457, 202.

3. J. Phys. Chem. C., 2009, 113, 10761. 4. J. Am. Chem. Soc. 2010, 132, 6899.

5. J. Am. Chem. Soc. 2010, 132, 15259. 6. Chem. Mater. 2011, 23, 5282.

7. J. Phys. Chem. C 2009, 113, 10761. 8. J. Hazard. Mater. 2012, 235-236, 265.

9. ACS Nano 2012, 6, 1609. 10. J. Am. Chem. Soc. 2013, 135, 10064.

11. J. Mater. Chem. A 2014, 2, 13571. 12. ACS Nano 2014, 8, 7229.
(Invited) Regulating the CO-Reduction Product Distribution by the Atomic-Level Structural Modification of the Cu Electrode Surface
Authors: Kim Youn-Geun , Baricuatro Jack Hess , Javier Alnald , Soriaga Manuel P.
Published: February 2020

Cu catalyzes the electrochemical reduction of CO2 or CO to an assortment of products, a behavior that is a detriment when only one reduced compound is desired. The present article provides an example in which, through the atomic-level control of the structure of the Cu electrode surface, the yield distribution is regulated to generate only one product. The reaction investigated was the preferential reduction of CO to C2H5OH on Cu at a low overpotential in alkaline solution. Experimental measurements combined operando electrochemical scanning tunneling microscopy (OECSTM) and differential electrochemical mass spectrometry (DEMS). An atomically ordered Cu(100) surface, prepared from either a single crystal or by Cu(pc)-to-Cu(100) reconstruction, did not produce ethanol. When the surfaces were subjected to monolayer-limited Cu↔Cu2O cycles, only the reconstructed surface underwent an additional structural transformation that spawned the selective production of ethanol at an overpotential 645 mV lower than that which generates multiple products. OECSTM indicated transformation to an ordered stepped surface, Cu(S)-[3(100)×(111)], or Cu(511). The non-selective, multiple-product Cu-catalyzed reduction of CO had thus been regulated to yield only one hydrocarbon compound by an atomic-level structural modification of the electrode surface.

Figure 1
Electrochemical Stability of Bipyridylimino Isoindoline Metal Complexes As Multi-Electron Anolyte Materials for Non-Aqueous Redox Flow Batteries
Authors: Laramie Sydney M , Sevov Christo S , Sanford Melanie S , Thompson Levi T
Published: February 2020

The development of grid scale energy storage will facilitate the integration of intermittent renewable electricity sources, such as wind and solar, into the grid. However, available technologies are limited by high cost or location dependence. Non-aqueous redox flow batteries (NAqRFBs) offer a scalable, non-geographically limited technology with the potential to provide a low cost, high energy density solution to the energy storage problem. Despite these promising attributes, the limited solubility and stability of current NAqRFB active species hinders implementation. In this work we explored a series of metal complexes of tridentate bipyridylimino isoindoline (BPI) ligands as anolyte materials for NAqRFBs. The goal was to evaluate the electrochemical stability of this class of materials and identify trends between the metal center and stability. Each complex exhibits 2 quasi-reversible redox events at -1.73 V and -1.83 V vs. Ag/Ag+. Bulk electrolysis through these 2 couples was used to quantify the electrochemical stability of each material and the following trend was identified: Co(BPI)2 = Ni(BPI)2 = Fe(BPI)2 > Zn(BPI)2 = Mg(BPI)2 > Mn(BPI)2. Co(BPI)2, Ni(BPI)2 and Fe(BPI)2 were all identified to be highly stable with no capacity fade observed over 50 cycles. This high stability is attributed to the tridentate, anionic ligand structure, which affords a stronger bond between the ligand and the metal center. Extended cycling experiments revealed that Ni(BPI)2 is stable through 2 negative electron transfers for over 200 cycles. Zn(BPI)2 and Mg(BPI)2 were both moderately stable as they have full valence shells while the instability of Mn(BPI)2 is attributed to rapid ligand exchange kinetics, which is common for Mn MCCs. For each of the unstable materials, post-cycling analysis revealed that ligand shedding is a prominent degradation mechanism. The developed stability trends can be used to guide the exploration and design of future NAqRFB active species to aid in the identification of electrochemically stable materials. Since solubility is also a concern, ligand functionalizations were identified that successfully enhanced the solubility of Ni(BPI)2 by three orders of magnitude, up to a maximum solubility of 0.7 M in acetonitrile. In conclusion, BPI MCCs exhibit remarkable stability, along with relatively high solubility, and we present the first demonstration of a stable 2 electron transfer for NAqRFB applications. These complexes can be paired with a suitable catholyte material to achieve a stable, high energy density, multi-electron transfer NAqRFB.
Studies of Earth Abundant Metal Complexes for Near Neutral Aqueous Redox Flow Battery (RFB) for Grid Storage
Authors: Nagasubramanian Ganesan , Allcorn Eric , Ingersoll David
Published: February 2020

Among the many options available for Large-Scale Grid Energy Storage, Redox Flow Batteries (RFB) are leading candidates because of the decoupled design of power and energy1 which offers tremendous design flexibility and modularity. As part of the Department of Energy’s Office of Electricity (OE) energy storage program at Sandia National Laboratories, we are investigating earth abundant transition metal coordination complexes for aqueous redox flow batteries at close to pH 7. The aqueous-based systems offer complete freedom from the thermal instabilities that plague non-aqueous systems, such as lithium-ion. Furthermore, the use of neutral pH electrolytes engenders intrinsic safety and low/no corrosion, unlike the highly corrosive and toxic electrolytes used for the vanadium redox flow battery or the zinc-bromine systems. In this abstract we discuss the electrochemical properties of some of the complexes under development, and the performance of full cells containing the optimized redox couples will be presented at the meeting.

Performance of Fe(2+)(tris-BPY)Cl2-0.4M Na2SO4

We have performed dc and ac voltammetry to characterize a number of iron coordination complexes, and Figure 1 shows the dc voltammetry curves at a 10 mV/s scan rate of one of these. As seen, the peak separation is ~60 mV, close to the theoretical value. We have also performed DC voltammetry at different scan rates up to 200 mV/s, and the peak separation varies between 60 and 64 mV which clearly demonstrate highly reversible behavior as well. Additionally, this couple exhibits higher redox voltage which will assure a RFB with a higher cell voltage and energy when appropriately configured with another redox couple.

Figure 2 shows a plot of redox peak potentials vs. square root of scan rate. The linear increase of peak value vs. square root of san rate indicates that this couple is highly reversible. We also performed AC voltammetry, which is more sensitive than the DC measurement, just to make sure that there are no other redox peaks buried around the solvent decomposition voltage. We observed only one reversible peak (Figure 3) which corroborates the DC measurement. Similar observations were observed for other couples and will be described in detail at the meeting.

Reference: B. Dunn, B., H. Kamath, H. & Tarascon, J.-M. “Electrical energy storage for the grid: a battery of choices” Science 334, 928–935(2011).

Acknowledgment: Sandia 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-AC04-94AL 85000. The authors would like to thank Dr. Imre Gyuk of the DOE Office of Electricity for the support.

Figure 1
Impact of Solvent Co-Intercalation in Cathodes: A Study on Mg-Xerogel V2O5
Authors: Gautam Gopalakrishnan Sai , Canepa Pieremanuele , Richards Will , Malik Rahul , Ceder Gerbrand
Published: February 2020

The electrochemical performance of several known Li- and Na-ion cathode materials can be influenced by the presence of specific solvents, such as water, either in the electrolyte or the electrodes. Indeed co-intercalation of solvent molecules, along with the redox active ions, is an approach to potentially impact the voltage and mobility with which cation species intercalate into electrodes in energy storage systems. While Multi-valent (MV) ion intercalation batteries that replace the Li+ with a MV cation, such as Mg2+, provide a pragmatic approach to improve upon the energy densities of current cutting-edge Li-ion batteries, several cathode hosts suffer from sluggish MV ion mobility within the cathode structure. One of the approaches that has been deployed to mitigate poor MV ion migration so far, specifically in layered oxide cathodes such as Xerogel-V2O5, is to introduce solvent molecules (water) in the structure that electrostatically shield the high positive charge density around MV ions and lower the local structural distortions. However, the role of water during the process of Mg2+ (or MV) intercalation is not well known yet, specifically if the structural water in the cathode “shuttles” along with the Mg2+ ion or stays in the structure during Mg-cycling.

In this study, we use first-principles calculations combined with the framework of grand potential phase diagrams to gain insight into the thermodynamics of Mg-water co-intercalation into Xerogel-V2O5. Based on our calculations, we find that Mg-water shuttling depends heavily on the water concentration of the electrolyte, ranging from full co-intercalation in wet to none in superdry electrolytes. Also, the Mg insertion voltages depend on the activity of water in the electrolyte in regimes where water shuttles with the Mg2+, leading to important consequences in the design of electrodes and electrolytes. We believe that this study can be further extended to other complex solvent-electrode pairs to develop a general understanding of the phenomenon of solvent co-intercalation.
Modeling Electrode/Electrolyte Interactions in Magnesium Batteries
Authors: Lowe Jeffrey S , Siegel Donald J
Published: February 2020

Many recent investigations have focused on multivalent metallic anodes, such as magnesium, as a potential improvement on state-of-the art Li-ion batteries which use intercalation anodes. Magnesium is of interest due to its high theoretical volumetric energy density, abundance, and safety. However, knowledge of phenomena such as side reactions occurring at the Mg electrode/electrolyte interface is limited. For instance, experimental studies have shown evidence of electrolyte decomposition on the surface of magnesium electrodes. In addition, whether or not a solid electrolyte interphase, similar to the one found in lithium batteries, forms in magnesium batteries remains an open question. In this work we employ electronic structure calculations on three low-energy model surface compositions of a magnesium anode in order to calculate the energy landscapes for the most likely electrolyte degradation pathways. We identified candidate low-energy electrolyte adsorption configurations using classical Monte Carlo techniques coupled with density functional theory; subsequent decomposition reaction barriers were evaluated with the nudged elastic band method. We found that adsorption energies, decomposition products, and reaction energy barriers were highly dependent on the model surface composition. Our results give an indication of the factors that control electrolyte stability, and assist in pinpointing promising electrode and electrolyte compositions.
Studies of New Rechargeable Mg-Ion Battery Using Boron-Hydrogen Based Electrolytes
Authors: Aso Hikaru , Tutusaus Oscar , Arthur Timothy S. , Mohtadi Rana
Published: February 2020

Mg-ion battery is one of the most promising candidates for a post Li-ion battery due to its high capacity, improved safety and potentially reduced cost. However, since the metallic Mg-anode is prone to passivation by electrolytes, we need to carefully use appropriate electrolytes which have high stability to the Mg metal. For example, common anions such as ClO4
-, BF4
- or TFSI- decompose on the Mg surface resulting in a highly resistive layer that partially or fully blocks Mg-ion transport. Although organo and chloride based reagents were found to be compatible with Mg metal, they still have severe issues such as highly corrosive nature and low Mg-ion transference number.1) We have been pioneering the development of a new class of electrolytes based on a novel design strategy and offering halogen free and non-corrosive boron-hydrogen salts, which can also improve the transport and solubility properties.2)

Another serious challenge facing Mg battery technologies is the limited choice of cathode materials due to the difficulty to reversibly intercalate divalent Mg-ion in host structures analogues to those used in Li-ion batteries such as transition metal oxides.3)Therefore, we have been studying alternative cathode chemistries beyond the intercalation types. The inertness and stability of the MMC electrolyte allow us to examine these new cathodes where fast and stable charge/discharge cycles can be performed with a relatively fine coulombic efficiency. In this presentation, we will unveil these new results and also show detailed mechanisms towards understanding the battery performance.

[1] J. Wook Choi, D. Aurbach, doi:10.1038/natrevmats.2016.13, Nature Reviews Materials, 2016

[2] a) R. Mohtadi, M. Matsui, T. S. Arthur, S.-J. Hwang, Angew. Chem. Int. Ed.
2012, 51, 9780 –9783; b) T. J. Carter, R. Mohtadi, T. S. Arthur, F. Mizuno, R. Zhang, S. Shirai, J. W. Kampf, Angew. Chem. Int. Ed.
2014, 53, 3173-3177; c) O. Tutusaus, R. Mohtadi, ChemElectroChem.
2015, 1, 51-57 d) O. Tutusaus, R. Mohtadi, T. Arthur. F. Mizuno, Angew. Chem. Int. Ed.
2015, 27, 8011-8015

[3] a) H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour, D. Aurbach, Energy Environ. Sci. 2013, 6, 2265-2279; b) R. Mohtadi, F. Mizuno Beilstein J. Nanotechnol. 2014, 5, 1291–1311
Investigation of the Electrochemical Oxygen Reduction Reaction in Non-Aqueous, Magnesium-Ion-Containing Electrolytes for Magnesium Air Batteries
Authors: Fischer Philipp , Schwarz Rainer Martin , Pejic Marijana , Marinaro Mario , Wachtler Mario , Jörissen Ludwig
Published: February 2020

Secondary magnesium-air batteries (MAB) hold great promise for cheap and highly dense energy storage as needed in automobiles and portable devices. While magnesium-ion-batteries1 and primary magnesium-air-batteries (magnesium air fuel cells, aqueous electrolyte)2 do already exist, there are difficulties in the development of the secondary magnesium air battery.

In principal, the work which was done on the Lithium-air-batteries (LAB) should also be usable in MABs. Therefore, in this work the system Mg(ClO4)2 + DMSO, first proposed by Shiga et al.3, was investigated. The equivalent electrolyte for LABs (LiClO4 + DMSO) is proven to work4.

It is shown that the oxygen reduction reaction (ORR) takes place (see Figure 1) within the stability window of the electrolyte and the electrochemical behavior of the system is discussed when using gold, platinum and glassy carbon as electrodes. It is shown that the ORR is not reversible and that passivating films are formed.

By using a change-disk-RRDE-setup, we could investigate those films with IR, Raman, XPS, SEM and EDX. It was possible to trace the electrolyte components (S-O-groups and Cl-O groups) on the surface and a quantitative analysis proves that oxygen is mainly contributing to the composition and structure of the surface film. The resulting decomposition products on the respective electrodes and a probable pathway of reaction are presented.

Acknowledgments

This work has been funded by the German Federal Ministry of Education and Research (BMBF) under the project “Mg-Air”, under the reference 03EK3027C.

References

1. H. D. Yoo et al., Energy Environ. Sci., 6, 2265 (2013)

2. I. C. Blake, J. Electrochem. Soc., 99, 202C–203C (1952)

3. T. Shiga, Y. Hase, Y. Kato, M. Inoue, and K. Takechi, Chem. Commun. (Camb)., 49, 9152–4 (2013)

4. M. M. Ottakam Thotiyl et al., Nat. Mater., 12, 1050–6 (2013)

Figures

Figure 1 Cyclic voltammograms of a 5mm diameter platinum disk (mirror polished) in 0.5 M Mg(ClO4)2 / DMSO electrolyte solution, argon saturated (red) and oxygen saturated (blue). Scan speed: 10 mV s-1

Figure 1
Low-Cost Modular Battery Fabrication System Based on 3D-Printed Parts and Microcontrollers
Authors: Kim Andrew , Raj Abhishek , Epstein Lindsay , Biswas Shaurjo , Steingart Daniel A
Published: February 2020

Integrating energy storage into clothing would enable wearable electronics of a more comfortable form factor and weight distribution compared to traditional rigid cells. Work on LTO vs LCO systems by previous groups have demonstrated the material system’s ability to be flexed or produced with scalable methods. In this work we report a low-cost automated fabrication setup to produce flexible LTO/LCO batteries on carbon fiber substrates.

The modular thread-coating system reported here takes advantage of cheap Arduino microcontrollers and 3D printed structures for a highly customizable design allowing for rapid prototyping of different material systems. In this particular setup, a stepper motor pulls a fiber through a series of 3D-printed stages where the fiber substrate is subjected to slurry deposition, washing, heating or packaging to produce a functional LTO/LCO battery.

The modular system serves as a useful intermediary between initial lab scale research— in which artisanal manual skills are often required from the researcher— and the industrial production process— in which automation and high throughput are paramount. The modular intermediary allows one to mimic mass production at a lab scale to identify challenges and solutions to scaling up a battery architecture for wide use.