Toshiyuki Mori

Intermediate-temperature solid oxide fuel cells (IT-SOFCs) have attracted attention due to their potential to overcome the trade-off between the performance and lifetime of SOFC devices. However, the guiding principle for effective material design, which can reduce operating temperatures and overcome performance decreases caused by excessive overpotential on the anode surface, has not been clearly established. In the present work, we studied the reported Schottky anomaly, which has been observed exclusively in yttria-stabilized zirconia (YSZ). To investigate this phenomenon, a small amount (less than 1200 ppm) of trivalent cations (Rh³⁺ or Fe³⁺), chemically similar to Y³⁺ in Y₂O₃, was doped onto the YSZ surface in the anode layer. Then, the current density observed from the SOFC device at 973 K was found to be nine-times higher than the SOFC device with an undoped anode. The surface first-principles calculations in the present work indicate that this performance enhancement is caused by the delocalized electrons induced by trivalent cation doping in the vicinity of the three-phase boundary and the promotion of surface oxygen diffusion in YSZ. Based on all experimental data, the effective material design guiding principle was obtained for utilizing the unique physical property of YSZ for applications such as IT-SOFCs.

A Pt-nanocoated layer (thickness of approx. 10-20 nm) with Pt-O-Ce bonds was created through the water radiolysis reaction on a CeO _x nanowire (NW), which was induced by electron beam irradiation to the mixed suspension of K₂PtCl₄ aqueous solution and the CeO _x NW. In turn, when Pt-nanocoated CeO _x NW/C (Pt/C ratio = 0.2) was used in the cathode layer of a membrane electrode assembly (MEA), both an improved fuel cell performance and stability were achieved. The fuel cell performance observed for the MEA using Pt-nanocoated CeO _x NW/C with Pt-O-Ce bonds, which was prepared using the electron beam irradiation method, improved and maintained its performance (observed cell potential of approximately 0.8 V at 100 mW cm^-2) from 30 to 140 h after the start of operation. In addition, the activation overpotential at 100 mA cm^-2 (0.17 V) obtained for MEA using Pt-nanocoated CeO _x NW/C was approximately half of the value at 100 mA cm^-2 (0.35 V) of MEA using a standard Pt/C cathode. In contrast, the fuel cell performance (0.775 V at 100 mW cm^-2 after 80 h of operation) of MEA using a nanosized Pt-loaded CeO _x NW (Pt/C = 0.2), which was prepared using the conventional chemical reduction method, was lower than that of MEA using a Pt-nanocoated CeO _x /C cathode and showed reduction after 80 h of operation. It is considered why the nanocoated layer having Pt-O-Ce bonds heterogeneously formed on the surface of the CeO _x NW and the bare CeO₂ surface consisting of Ce⁴⁺ cations would become unstable in an acidic atmosphere. Furthermore, when a conventional low-amount Pt/C cathode (Pt/C = 0.04) was used as the cathode layer of the MEA, its stable performance could not be measured after 80 h of operation as a result of flooding caused by a lowering of electrocatalytic activity on the Pt/C cathode in the MEA. In contrast, a low-amount Pt-nanocoated CeO _x NW (Pt/C = 0.04) could maintain a low activation overpotential (0.22 V at 100 mA cm^-2) of MEA at the same operation time. Our surface first-principles modeling indicates that the high quality and stable performance observed for the Pt-nanocoated CeO _x NW cathode of MEA can be attributed to the formation of a homogeneous electric double layer on the sample. Since the MEA performance can be improved by examining a more effective method of electron beam irradiation to all surfaces of the sample, the present work result shows the usefulness of the electron beam irradiation method in preparing active surfaces. In addition, the quantum beam technology such as the electron beam irradiation method was shown to be useful for increasing both performance and stability of fuel cells.

Acenes and azaacenes lie at the core of molecular materials’ applications due to their important optical and electronic features. A critical aspect is provided by their heteroatom multiplicity, which can strongly affect their properties. Here we report pyrazinacenes containing the dihydro-decaazapentacene and dihydro-octaazatetracene chromophores and compare their properties/functions as a model case at an oxidizing metal substrate. We find a distinguished, oxidation-state-dependent conformational adaptation and self-assembly behaviour and discuss the analogies and differences of planar benzo-substituted decaazapentacene and octaazatetracene forms. Our broad experimental and theoretical study reveals that decaazapentacene is stable against oxidation but unstable against reduction, which is in contrast to pentacene, its C–H only analogue. Decaazapentacenes studied here combine a planar molecular backbone with conformationally flexible substituents. They provide a rich model case to understand the properties of a redox-switchable π-electronic system in solution and at interfaces. Pyrazinacenes represent an unusual class of redox-active chromophores.

To develop the state‐of‐the‐art polymer membrane fuel cells. Both maximization of oxygen reduction reaction (ORR) activity on Pt cathode and minimization of Pt content in the cathode are required. For this challenge, the defect interface on oxide support was modified by proton beam irradiation method. Pt‐CeO _x nanowire/C (Pt/C = 0.02) was fabricated using the proton beam irradiation method. Since the radical density generated by proton beam irradiation is two orders of magnitude greater than that of electron beam irradiation, the CeO _x nanowire surface was fully converted to a thin layer of Pt‐O‐Ce bonds under proton beam irradiation. The ORR activity observed for fabricated sample with above active surface layer was higher than that of conventional Pt/C (Pt/C = 0.2) and comparable to that of Pt‐CeO _x nanowire/C (Pt/C = 0.2) fabricated by conventional methods. From the combination of microanalysis characterization and surface atomistic simulation, we concluded that the Pt‐O‐Ce bond was formed on defect‐rich regions of the CeO _x nanowire and this leads to a maximized ORR activity on the fabricated sample. Based on all experimental data, it is concluded that the surface modification of CeO _x nanowire support using proton beam irradiation is useful for a lowering the Pt content of the cathode with high ORR activity.

Solid oxide fuel cells (SOFCs) are clean and efficient power sources for generating electricity using air and a variety of fuels. In the case of SOFCs, there is a global trend in decreasing the operating temperatures to enhance the lifetime durability and to reduce the overall cost (e.g., to use the stainless steel in stack cells of SOFCs). To make a good balance between high power generation efficiency and operation durability of SOFCs, the intermediate temperature (i.e. 400 to 700 ℃) SOFCs (IT-SOFCs) have been developed. However, the conventional IT-SOFC devices and systems cannot meet the energy market demands and environmental requirements. To overcome this situation, the 'state-of-the-art' IT-SOFCs with the quality of exceeding limits of conventional IT-SOFCs should be further developed. In order to develop the 'state-of-the-art' next generation IT-SOFCs, the design of interfaces in IT-SOFC devices is the key challenge. As a consequence, the authors introduce an interactive new research style strategy to see realization of GREEN innovation in the present prospective review. We believe that the fusion of fabrication, characterization and modelling based on microanalysis data provides us with a great opportunity to see the GREEN innovation in the field of R & D of the 'state-of-the-art' next generation IT-SOFC devices and systems. And it is expected that the present prospective review will inspire the challenging spirit of scientists and engineers who are interested in this GREEN innovation.

Developing highly efficient biomimetic catalysts that directly use O2 as terminal oxidant to dehydrogenate and monoxygenate substrates with high selectivity under mild conditions has long been pursued but rarely achieved yet. Herein, we report that heterogeneous Fe-N-C, which is commonly used as electrocatalyst for oxygen reduction reaction, had unusual biomimetic catalytic activity in both dehydrogenation and monoxygenation of a series of organic molecules (~100% selectivity) by direct using O2. The Fe-Nx center was verified to be the active site that reductively activated O2 by spontaneous generating specific reactive oxygen species (1O2, O2•−, and H2O2). Aided by these ROS, under physiological conditions, the Fe-N-C was further successfully exampled to kill proliferative lung cancer cells. Fe-N-C had several striking superior features with respect to natural enzymes, classical heterogeneous nanozymes, and homogeneous artificial enzymes in capable of working in harsh conditions (extreme pH and high temperature), ease of separation and recycling, and direct use of O2. It would open up a new vista of Fe-N-C as an artificial enzyme in biomimetic catalysis ranging from fundamental simulation of oxidase/oxygenase metabolism to industrial oxidation processes, and to disease treatment.

Invited for this month's cover is the group of Prof. Dr. Toshiyuki Mori at National Institute for Materials Science (NIMS), Japan. The front cover picture shows the formation of new active sites on Ni in the anode of a solid oxide fuel cell (SOFC), which displays high performance at intermediate temperature. The combination of processing route design, microanalysis, and surface atomistic simulation provides us with a new design paradigm for fabrication of high‐performance SOFCs. Read the full text of the article at 10.1002/cplu.201800170.

In recent years, the lowering of the operation temperature of solid oxide fuel cells (SOFCs) has attracted much attention owing to the trade‐off between the best performance and the life span of SOFCs. For this challenge, new active sites on the Ni surfaces in a Nickel–Yttria‐Stabilized Zirconia (Ni‐YSZ) cermet anode of SOFCs have been created by deposition of trace amounts of platinum oxide (PtO_x) followed by an activation step of the anode at 1073 K in a hydrogen flow. The internal resistance (IR) free value (185 mA cm⁻² at 0.8 V) observed for the single cell with an anode sputtered with a trace amount of PtO_x (Pt content in anode: from 9 to 91 ppm) at 973 K is conspicuously higher than that of a similar single cell with a nonsputtered cermet anode (85 mA cm⁻²) at 0.8 V and 1073 K. Transmission electron microscopy microanalysis shows that the defect structure is formed on a partially oxidized Ni surface by active Pt species. Also, surface atomistic simulation on NiO (111) predicts the formation of Frenkel defect clusters with Pt cations, which partially cover the Ni surface. The formation of Frenkel defect clusters on the partially oxidized Ni surface (i.e., creation of new active sites for formation of water molecules) promotes the anode reaction, resulting in improvements in the anode performance of SOFC single cells at 973 K. Design of the aforementioned new active sites on Ni through sputtering of trace amounts of PtO_x provides a great opportunity for “radical innovation” in the design of intermediate‐temperature SOFCs.