bluuebunny/crossref_metadata_2025_split 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.
(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).
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
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