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The compositional space of high-entropy-alloy nanoparticles (HEA NPs) significantly expands the diversity of the materials library. Every atom in HEA NPs has a different elemental coordination environment, which requires knowledge of the local electronic structure at an atomic level. However, such structure has not been disclosed experimentally or theoretically. We synthesized HEA NPs composed of all eight noble-metal-group elements (NM-HEA) for the first time. Their electronic structure was revealed by hard X-ray photoelectron spectroscopy and density function theory calculations with NP models. The NM-HEA NPs have a lower degeneracy in energy level compared with the monometallic NPs, which is a common feature of HEA NPs. The local density of states (LDOS) of every surface atom was first revealed. Some atoms of the same constituent element in HEA NPs have different LDOS profiles, whereas atoms of other elements have similar LDOS profiles. In other words, one atom in HEA loses its elemental identity and it may be possible to create an ideal LDOS by adjusting the neighboring atoms. The tendency of the electronic structure change was shown by supervised learning. The NM-HEA NPs showed 10.8-times higher intrinsic activity for hydrogen evolution reaction than commercial Pt/C, which is one of the best catalysts.

We evaluated the role of raw-material features for machine-learning prediction of the flux crystal growth of Al2O3 in MoO3 based on 185 types of growth trials.

Millimeter-sized K2Ti2O5 single crystals were grown from a KCl–KOH mixed flux using a flux-evaporation assisted method. H2O was found to be the best solvent for the liquid exfoliation of K2Ti2O5 crystals.

A multiple pre-doping system with a looser structure displays small fractional volume expansion.

Unique features of alloy nanoparticles (NPs) originate from the configuration of elements within NPs; solid solution and segregated configurations show different properties even with the same overa...

There is significant unexplored potential when it comes to combining different elements. As such, computational science is looking into how combinations can be explored within cyberspace, enabling theoretical work to be conducted at impressive speeds. Professor Michihisa Koyama, Research Initiative for Supra-Materials, Shinshu University, Japan, is working to predict the catalytic activity of combined elements by employing an approach that involves a digital transformation of materials science. He and his team are developing cyber technologies to explore the infinite material space of nanoparticles, which involves the use of first-principles calculations based on quantum mechanics, as well as real system calculations. In their nanoparticle investigations, the researchers divide the real system of nanoparticles into three: super atoms, clusters and nanoparticles. Koyama and the team have been successful in their use of experimental science to synthesise nanoparticles and predict catalytic activity. The researchers believe that by 2030, they will have material development examples driven by their work.

Solid-solution alloy nanoparticles (NPs) comprising Pd and Ru, which are immiscible in the bulk state, have been synthesised and show excellent catalytic performance. To date, most studies have evaluated the stability of alloy NPs at 0 K only. Because the thermodynamic stability of Pd-Ru alloy NPs may differ from that of the alloy in the bulk state, the stable configuration of the NPs must be evaluated under a finite temperature. Such stability evaluations are critical for developing the durable NPs as catalysts. Therefore, the thermodynamic stability of Pd-Ru alloy NPs was analysed using density functional theory (DFT), supervised learning (SL), and Wang-Landau sampling. We calculated the excess energy of Pd-Ru alloy NPs, which depends on their composition, structure, NP size, adatom type, and defects, and applied SL to all models. The excess energies of the Pd-Ru alloy NPs expressed by structural information, such as the surface-to-volume ratio, correlated with those calculated using DFT. Wang-Landau sampling based on the energy estimated by SL gave the thermodynamic stability of Pd-Ru alloy NPs with a stable configuration under a finite temperature. The solid-solution atomic configuration was subdivided into partially mixed configurations in the surface layer or in the core of the NPs, which is different from the bulk state. The partially mixed configuration was determined by the overall composition and surface properties. The findings from the combined method could contribute to a better understanding of the alloy-NP stability and their application in catalysis.

We studied the adsorption energies of the NO species on face-centered-cubic M405-nanoparticles (NPs) (M = Rh, Pd, Ag, Ir, or Pt) using density functional theory calculations. Various adsorption sit...

Testing the stretching frequency shift of adsorbed CO has been a popular tool to evaluate the chemical property change of catalysts. We demonstrated first-principles models to reveal the mechanism of oxides effect on the frequency shift of CO on the Ni catalysts. Our calculations show that higher coverage of CO molecules leads to blue frequency shift, and there is negligible frequency shift when co-adsorbed with Al2O3 species and red frequency shift when co-adsorbed with ZrO2 or CeO2 species, which are consistent with the experimental literatures. The frequency shift is conformed to be proportional to the charge transfer amount of the π back-donation from Ni to the π⁎ orbital of CO molecule. The frequency shift direction is not determined by whether the oxide species is an electron acceptor or donor when adsorbed on Ni surface, but by how the oxide species affects the electrons on t2g and eg orbitals of the Ni atom under the CO molecule. The redistribution between t2g and eg orbitals induces the decreasing or increasing back-donation when a CO molecule co-adsorbed with the CO molecules or CeO2 species.

The massive implementation of renewable energy requires sophisticated assessments considering the combination of feasible technology options. In this study, a techno-economic analysis was conducted for hydrogen production from photovoltaic power generation (PV) utilizing a battery-assisted electrolyzer. The installed capacity of each component technology was optimized for the wide range of unit costs of electricity from the PV, battery, and proton-exchange membrane electrolyzer. Leveling of PV output by battery, the necessary capacity of electrolyzer is suppressed and the operating ratio of electrolyzer increases. The battery-assist will result in a lower hydrogen production cost when the benefit associated with the smaller capacity and higher operation ratio of the electrolyzer exceeds the necessary investment for battery installation. The results from this study indicated the cost of hydrogen as low as 17 to 27 JPY/Nm3 using a combination of technologies and the achievement of ambitious individual cost targets for batteries, PV, and electrolyzers.

The energy targets of the Sustainable Development Goals (SDGs) call for both a reduction of total energy use and an increase in the share of renewables as part of the total consumed energy. With the emergence of Renewable Energy Systems (RES) on a local scale there is still little research on the efficiency of actual micro-grids on building scale, let alone on how their functioning relates to reaching the energy targets of the SDGs. Here it is shown how an expected degree of decrease in renewable energy generation from solar panels, combined with a failure to anticipate intensifying building energy needs, can impede reaching the SDGs’ energy targets on the local level. When examining a building scale micro-grid, not only had solar panel performance decreased by twice the expected average, but building energy use had doubled by 156-203%, and thereby the share of renewable energy of total energy use has decreased by 29-47%, depending on the season. This indicates that in order to reach the SDG energy targets, it is important that newly designed building, as well as community Energy Management Systems, do not merely account for current energy users, but accommodate increasing RES concurrent to increasing energy demand.

Based on the concept of density of states (DOS) engineering, we theoretically designed a pseudo-Tc material (Mo–Ru alloy) and investigated its electronic structure, phase stability and catalytic activity by using density functional theory. Through comparing the DOS shape, peak distribution, and DOS area differences between Tc and the Mo–Ru alloy, we noticed that bcc-Mo8Ru8 and hcp-Mo8Ru8 had the most similar electronic structures to Tc. The excess energies after entropy correction of hcp-Mo8Ru8 and bcc-Mo8Ru8 are stable when the temperature is up to 765 and 745 K, respectively. These results provided the possibility of pseudo-Tc alloy (hcp-Mo8Ru8 and bcc-Mo8Ru8) synthesis. Finally, according to reaction coordinate analysis, the similar catalytic activity between hcp-Mo8Ru8 and Tc have been demonstrated in CO oxidation and N2 dissociation. In N2 dissociation, Tc has a suitable ratio of transition state (TS) barrier to reaction energy which make Tc an efficient catalyst for NH3 synthesis, in addition to our designed pseudo-Tc (hcp-MoRu) because of the similar electronic structures. Our finding provides valuable insight into materials and catalyst design.

The oxidation of carbon monoxide (CO) over PdRu solid solution nanoparticles was studied by the combined theoretical and experimental approaches. In this work, CO and O adsorptions on PdRu alloy surface models were theoretically investigated to understand the kinetics of CO oxidation reaction. It was found that CO adsorption on Pd atom in the PdRu alloy surfaces is weaker than on monometallic surfaces. From the experiment, reaction order of CO on the PdRu surface was observed to be smaller than that on Pd surface. While, the positive first order with respect to O2 obtained for both Pd and PdRu alloy surfaces. Catalytic reaction mechanism is discussed on the basis of both theoretical and experimental observations.

Hybrid materials composed of metal nanoparticles and metal-organic frameworks have attracted attention for various applications because of the synergistic functionality between their constituent materials. Interfacial interaction is expected however the mechanism remains ambiguous. Here we report the valence bands of palladium nanocubes covered by copper(II) 1, 3, 5-benzenetricarboxylate (HKUST-1), denoted as Pd@HKUST-1, and the charge transfer from the palladium nanocubes to HKUST-1 at the Pd/HKUST-1 interface is investigated quantitatively. Interfacial density of states are different from those of internal constituents and imply that the Cu-O group in HKUST-1 acts as a charge accepter. The role of Cu-O group in charge transfer behaviour is also observed experimentally. Finally, we reveal the charge transfer mechanism from the Pd 4d bands to the Cu 3d (4sp) - O 2p hybridization bands of HKUST-1 at the Pd/HKUST-1 interface, which explains the enhanced hydrogen storage capacity in Pd@HKUST-1., Pd-MOFハイブリッド材料の界面電子状態と水素貯蔵特性の関係の定量的な解析に成功 --電子約0.4個分の電荷移動が約2倍の特性向上に寄与 新規ハイブリッド材料開発の促進が期待--. 京都大学プレスリリース. 2018-10-11.

The performance of a solid oxide fuel cell based on BaTiO3 anode improves when H2 and CH4 containing H2S are employed as fuels. In this work, density functional theory calculations were conducted to reveal the origin behind this boost in performance. Our calculations predicted that the sulfidation of the BaTiO3(001) surfaces is possible via different reaction pathways. For the hydrogen oxidation reaction, the presence of sulfur led to the formation of different molecular entities; thus alternative sequences of elementary steps for the reaction to proceed came to light, and no significant detrimental effect was noticed on the adsorption of the species involved. On the other hand, for the methane sequential dissociation, no detrimental effect on the methane activation and the promoted scission of some C–H bonds may be responsible for the mentioned boost in performance.

We have analyzed the crucial factors that stabilize face-centered cubic (fcc) ruthenium nanoparticles (Ru-NPs) using the density functional theory method. We calculated the cohesive energy of the decahedral fcc, icosahedral fcc, truncated octahedral fcc, and hexagonal close-packed (hcp) Ru-NPs with between 55 and 1557 atoms. The cohesive energy of the icosahedral fcc Ru-NPs became closer to that of the hcp Ru-NPs with decreasing number of atoms, i.e., particle size. This characteristic is mainly caused by the high coordination number of the icosahedral fcc Ru-NP and the negative twin boundary energy for fcc {111}. On the other hand, the d-band center of Ru atoms in the surface layer of icosahedral fcc Ru-NPs is less negative than those of the other structures. This characteristic is caused by the longer interatomic distance between Ru atoms in the surface layer of the icosahedral fcc Ru-NP. Together with the structural stability, the icosahedral fcc structure shows a unique electronic structure compared w...

A one-dimensional microkinetic model combining H and O migration mechanisms is used to simulate the surface diffusion, chemical and charge-transfer reactions near the triple phase boundary of the Ni/YSZ patterned anode. A number of parameter sets are exhaustively examined in the microkinetic schemes to obtain a proper set for the explanation of experimental observations. We find a set of parameters free from unphysical fitting parameters, and can explain a large activity gap of patterned anodes reported in literature. From our simulation, we found that the lower activity patterned anode is kinetically governed by both H and O migration across the triple phase boundary, while the higher activity patterned anodes are governed by the O migration.

We analyzed theoretically the hydrogen absorption properties and kinetics into Pd nanocubes coated with copper(II) 1,3,5-benzenetricarboxylate (HKUST-1), which is a type of metal–organic framework, using density functional theory. We prepared an interface model consisting of the Pd(100) surface and Cu-edged HKUST-1 structure and calculated the hydrogen adsorption and absorption energies in a Pd nanocube model. To discuss the kinetics of the hydrogen absorption, we also evaluated the hydrogen diffusion barrier near the interface. Compared with bare Pd, the hydrogen diffusion barrier from the surface to the subsurface decreased. We found that the adsorption of HKUST-1 on the Pd nanocube leads to chemical and steric effects for the diffusion rate increase of hydrogen. As a chemical effect, hydrogen adsorption was destabilized by the change of electronic structure of the Pd surface because of the atomic charge displacement between the Pd and Cu atoms in HKUST-1. As a steric effect, a new hydrogen diffusion pa...

Introduction Doped lanthanum cobaltite and its derivatives are used as cathode materials in solid oxide fuel cell (SOFC). For a high catalytic activity, the improvement of properties governing the cathode performance is important. It is generally regarded that one of the important factors is the electronic structure of cathode material. Recently, the influence of the lattice strain on the kinetics of the oxygen reduction reaction (ORR) was reported [1]. In addition, the heterostructured oxide interface ((La,Sr)2CoO4±δ/La1-xSrxCoO3-δ (LSC)) and thin-film heterostructure interface (La0.6Sr0.4Co0.2Fe0.8O3-δ/gadolinium-doped CeO2 (GDC)) enhanced the surface oxygen exchange kinetics and ORR activity [2,3]. These results indicate the possibility that the structural change near interface changes the electronic structure of cathode materials. Detailed understandings of electronic structure of doped lanthanum cobaltite near the interface is important to design the high catalytic cathode materials. In this study, we analyzed the stability of oxygen vacancy in LSC of LSC/GDC interface by using the density functional theory (DFT) calculation. Computational Details We used LaO-terminated (001) surface of cubic LaCoO3 crystal structure. Half of La atoms were substituted by Sr atoms in LaO layers in LSC slab model (La6Sr6Co8O28). As a surface of CeO2, we used (111) surface model (Ce14O28) from the surface stability. GDC surface model was prepared based on the previous DFT calculation [4]. The interface of LSC and GDC was modeled from CoO2-terminated LSC(001) and GDC(110) surfaces. The initial spin configuration of Co3+ ion was set as intermediate spin state. GGA-PAW potentials were applied with cutoff energy of 600 eV and 1×1×1 k-points. We employed GGA+U to improve the description of Co 3d and Ce 4f electrons. All DFT calculations were performed by using VASP. Results and Discussion We first analyzed the charge distribution near LSC/GDC interface. In case of LSC/CeO2 interface, the electron transferred from CeO2 to LSC. We clearly observed the larger electron transfer from GDC to LSC. These results indicate that the LSC region near CeO2 or GDC interface shows the negatively charged structure. We analyzed the oxygen vacancy formation energy in LSC. The oxygen vacancy formation energy from surface at LSC/GDC interface was more stable than that of LSC model. Although the oxygen vacancy formation energy from 2ndlayer in LSC model was stable, unstable oxygen vacancy formation energy was obtained in the LSC/GDC interface model. One of the reasons of oxygen vacancy formation energy difference between LSC and LSC/GDC interface is an effect of electron transfer from GDC to LSC. The atomic position change at interface is also influenced the oxygen vacancy formation energy. To see the relation between oxygen vacancy formation energy and distance from interface, we prepared larger LSC/GDC interface models. Details are discussed in the presentation. Acknowledgement This work was supported by CREST, Japan Science and Technology Agency. All calculations were performed on the HA8000 computer systems in Research Institute for Information Technology, Kyushu University. The activities of Advanced Automotive Research Collaborative Laboratory in Hiroshima University are supported by Mazda Corporation. The activities of INAMORI Frontier Research Center in Kyushu University are supported by Kyocera Corporation. References [1] N. Tsvetkov, Q. Li, and B. Yildiz, ACS Nano, 9, 1613 (2015). [2] D. Lee, Y. Lee, W. T. Hong, M. D. Biegalski, D. Morgan, and Y. Shao-Horn, J. Mater. Chem. A, 27, 7910 (2015). [3] E. M. Hopper, E. Perret, B. J. Ingram, H. You, K. Chang, P. M. Baldo, P. H. Fuoss, and J. A. Eastman, J. Phys. Chem. C, 119, 19915 (2015). [4] X. Aparicio-Anglès, A. Roldan, and N. H. de Leeuw, Chem. Mater., 27, 7910 (2015).

The electrode performance in solid oxide fuel cell depends both on electrode materials and microstructure. Therefore, it is important to breakdown the complexity of multi-physics in the porous electrode into processes in different scales. To clarify the multi-physics toward better electrode design, the use of both the advanced measurement and the simulation techniques is inevitable. For this purpose, we have taken the combined top-down and bottom-up approaches. In this manuscript, we discuss the practical issues in multi-scale, multi-physics simulation, focusing on the local activity of Ni-YSZ anode.

Understanding the electrode kinetics in solid oxide fuel cells is important to realize the highly efficient system. Doped lanthanum cobaltite and its derivatives are used as cathode materials in solid oxide fuel cell. As results of considerable number of studies, it is generally accepted that the dissociative adsorption of oxygen at the cathode surface is one of the rate-determining steps. Toward the rational design of cathode materials, we discuss how the electronic structure affects the surface kinetics of doped cobaltite in this study. We focus on La0.5Sr0.5CoO3-δ (LSC) as cathode material and discuss the properties (001) surface with LaO termination based on density functional theory method. We investigated the oxygen adsorption energy and vacancy formation energy by changing the spin states of Co in LSC. The calculated properties are discussed in the context of the kinetic process of oxygen reduction at LSC surface together with future perspectives.

In this paper, we describe, first, the present status and the tasks toward the future of energy systems in Japan from the viewpoint of 3E+S. 3E+S means energy security, environmental conservation, economic efficiency, and safety. Second, we describe the future energy society in 2030 and 2050, respectively. We introduce a large picture of the total energy system considering the energy resources, conversion, transportation, storage, consumption, control, and system architecture. For the image of 2030, the Japanese government has already announced the middle-term (2030) energy demand and supply on July 16, 2015. For 2050, we assume three cases regarding the renewable energy installations: the status quo of 2030 covering 22–24% of the total consumption, and 50 and 100% of the total consumption. In the last section, we describe smart technologies to support the envisioned society in 2030 and 2050. We also introduce the reference architecture model. To achieve 80% reduction of greenhouse gas (GHG) emission in 2050, the innovations at the consumer side, such as the large-scale renewable energy resources and storage installations, utilization of electrified vehicles, distributed energy management systems including virtual power plants, and system integration, will become very important in addition to innovations at the supply side. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Abstract While Pt-nanoparticles supported on SnO2 exhibit improved durability, a substantial detriment is observed on the Pt-nanoparticles’ activity toward the oxygen reduction reaction. A density functional theory method is used to calculate isolated, SnO2- and graphene-supported Pt-nanoparticles. Work function difference between the Pt-nanoparticles and SnO2 leads to electron donation from the nanoparticles to the support, making the outer-shell atoms of the supported nanoparticles more positively charged compared to unsupported nanoparticles. From an electrostatic point of view, nucleophilic species tend to interact more stably with less negatively charged Pt atoms blocking the active sites for the reaction to occur, which can explain the low activity of Pt-nanoparticles supported on SnO2. Introducing oxygen vacancies and Nb dopants on SnO2 decreases the support work function, which not only reduces the charge transferred from the Pt-nanoparticles to the support but also reverses the direction of the electrons flow making the surface Pt atoms more negatively charged. A similar effect is observed when using graphene, which has a lower work function than Pt. Thus, the blocking of the active sites by nucleophilic species decreases, hence increasing the activity. These results provide a clue to improve the activity by modifying the support work function and by selecting a support material with an appropriate work function to control the charge of the nanoparticle’s surface atoms. Graphic abstract

The triple phase boundary (TPB) of metal, oxide, and gas phases in the anode of solid oxide fuel cells plays an important role in determining their performance. Here we explore the TPB structures from two aspects: atomic-resolution microscopy observation and reaction dynamics simulation. Experimentally, two distinct structures are found with different contact angles of metal/oxide interfaces, metal surfaces, and pore opening sizes, which have not previously been adopted in simulations. Reaction dynamics simulations are performed using realistic models for the hydrogen oxidation reaction (HOR) at the TPB, based on extensive development of reactive force field parameters. As a result, the activity of different structures towards HOR is clarified, and a higher activity is obtained on the TPB with smaller pore opening size. Three HOR pathways are identified: two types of hydrogen diffusion processes, and one type of oxygen migration process which is a new pathway. The triple phase boundary structure in solid-oxide fuel cells largely determines the thermodynamics and kinetics of electrochemical processes therein. Here the authors use atomic-resolution microscopy and reaction dynamics simulation to reveal three discrete hydrogen oxidation reaction pathways.

The implementation of energy systems and technologies has been incentivized by the assessment of various aspects, including social and economic acceptance and sharing rational technology targets. In this study, battery-assisted hydrogen production systems were analyzed with regard to their environmental and techno-economic aspects. The costs of hydrogen production were minimized by the capacity optimization of the system components based on different development levels of contained technologies. The cost minimization indicated the upper limit of battery cost for reducing hydrogen cost. The relation with the cost of electrolyzer can be formulated in some assumptions. Greenhouse gas emissions and the abiotic resource depletion of cost-minimized systems were also analyzed. The performance of battery-assisted hydrogen production on unit cost and greenhouse gas emission may be high enough to be competitive with other hydrogen production or fossil fuel use. In contrast, the environmental impact of this system on the abiotic resource depletion is too large to be environmentally competitive to other options. Technology and system improvements such as metal recycling are important factors for the system.