Simultaneous Improvements in Performance and Durability of an Octahedral PtNix/C Electrocatalyst for Next-Generation Fuel Cells by Continuous, Compressive, and Concave Pt Skin Layers

Simultaneous improvements in oxygen reduction reaction (ORR) activity and long-term durability of Pt-based cathode catalysts are indispensable for the development of next-generation polymer electrolyte fuel cells but are still a major dilemma. We present a robust octahedral core–shell PtNix/C electrocatalyst with high ORR performance (mass activity and surface specific activity 6.8–16.9 and 20.3–24.0 times larger than those of Pt/C, respectively) and durability (negligible loss after 10000 accelerated durability test (ADT) cycles). The key factors of the robust octahedral nanostructure (core–shell Pt73Ni27/C) responsible for the remarkable activity and durability were found to be three continuous Pt skin layers with 2.0–3.6% compressive strain, concave facet arrangements (concave defects and high coordination), a symmetric Pt/Ni distribution, and a Pt67Ni33 intermetallic core, as found by STEM-EDS, in situ XAFS, XPS, etc. The robust core–shell Pt73Ni27/C was produced by the partial release of the stress, Pt/Ni rearrangement, and dimension reduction of an as-synthesized octahedral Pt50Ni50/C with 3.6–6.7% compressive Pt skin layers by Ni leaching during the activation process. The present results on the tailored synthesis of the PtNix structure and composition and the better control of the robust catalytic architecture renew the current knowledge and viewpoint for instability of octahedral PtNix/C samples to provide a new insight into the development of next-generation PEFC cathode catalysts

Biomimetic design of an α-ketoacylphosphonium-based light-activated oxygenation auxiliary

The biomimetic design of a transition metal complex based on the iron(IV)-oxo porphyrin π-cation radical species in cytochrome P450 enzymes has been studied extensively. Herein, we translate the functions of this iron(IV)-oxo porphyrin π-cation radical species to an α-ketoacyl phosphonium species comprised of non-metal atoms and utilize it as a light-activated oxygenation auxiliary for ortho-selective oxygenation of anilines. Visible light irradiation converts the α-ketoacyl phosphonium species to the excited state, which acts as a transiently generated oxidant. The intramolecular nature of the process ensures high regioselectivity and chemoselectivity. The auxiliary is easily removable. A one-pot protocol is also described

Key Structural Transformations and Kinetics of Pt Nanoparticles in PEFC Pt/C Electrocatalysts by a Simultaneous Operando Time-Resolved QXAFS–XRD Technique

This account article treats with the key structural transformations and kinetics of Pt nanoparticles in Pt/C cathode catalysts under transient voltage operations (0.4 VRHE→1.4 VRHE→0.4 VRHE) by simultaneous operando time-resolved QXAFS–XRD measurements, summarizing and analyzing our previous kinetic data in more detail and discussing on the key reaction steps and rate constants for the performance and durability of polymer electrolyte fuel cells (PEFC). The time-resolved QXAFS–XRD measurements were conducted at each acquisition time of 20 ms, while measuring the current/charge of the PEFC. The rate constants for the transient responses of Pt valence, CN(Pt–O) (CN: coordination number), CN(Pt–Pt), and Pt metallic-phase core size under the transient voltage operations were determined by the combined time-resolved QXAFS‒XRD technique. The relationship of the structural kinetics with the performance and durability of the PEFC Pt/C was also documented as key issues for the development of next-generation PEFCs. The present account emphasizes the time-resolved QXAFS and XRD techniques to be a powerful technique to analyze directly the structural and electronic change of metal nanoparticles inside PEFC under the operating conditions

Nonfullerene Acceptors Bearing Spiro‐Substituted Bithiophene Units in Organic Solar Cells: Tuning the Frontier Molecular Orbital Distribution to Reduce Exciton Binding Energy

Wang Kai, Jinnai Seihou, Urakami Takumi, et al. Nonfullerene Acceptors Bearing Spiro‐Substituted Bithiophene Units in Organic Solar Cells: Tuning the Frontier Molecular Orbital Distribution to Reduce Exciton Binding Energy. Angewandte Chemie International Edition, e202412691 (2024); https://doi.org/10.1002/anie.202412691.The development of nonfullerene acceptors (NFAs), represented by ITIC, has contributed to improving the power conversion efficiency (PCE) of organic solar cells (OSCs). Although tuning the electronic structures to reduce the exciton binding energy (Eb) is considered to promote photocharge generation, a rational molecular design for NFAs has not been established. In this study, we designed and developed two ITIC-based NFAs bearing spiro-substituted bithiophene or biphenyl units (named SpiroT-DCI and SpiroF-DCI) to tune the frontier molecular orbital (FMO) distribution of NFAs. While the highest occupied molecular orbitals (HOMOs) of SpiroF-DCI and ITIC are delocalized in the main π-conjugated framework, the HOMO of SpiroT-DCI is distributed on the bithiophene unit. Reflecting this difference, SpiroT-DCI exhibits a smaller Eb than either SpiroF-DCI or ITIC, and exhibits greater external quantum efficiency in single-component OSCs. Furthermore, SpiroT-DCI shows improved PCEs for bulk-heterojunction OSCs with a donor of PBDB-T, compared with that of either SpiroT-DCI or ITIC. Time-resolved spectroscopy measurements show that the photo-induced intermolecular charge separation is effective even in pristine SpiroT-DCI films. This study highlights the introduction of spiro-substituted bithiophene units that are effective in tuning the FMOs of ITIC, which is desirable for reducing the Eb and improving the PCE in OSCs

Transcriptome Profiling of Lotus japonicus Roots During Arbuscular Mycorrhiza Development and Comparison with that of Nodulation

To better understand the molecular responses of plants to arbuscular mycorrhizal (AM) fungi, we analyzed the differential gene expression patterns of Lotus japonicus, a model legume, with the aid of a large-scale cDNA macroarray. Experiments were carried out considering the effects of contaminating microorganisms in the soil inoculants. When the colonization by AM fungi, i.e. Glomus mosseae and Gigaspora margarita, was well established, four cysteine protease genes were induced. In situ hybridization revealed that these cysteine protease genes were specifically expressed in arbuscule-containing inner cortical cells of AM roots. On the other hand, phenylpropanoid biosynthesis-related genes for phenylalanine ammonia-lyase (PAL), chalcone synthase, etc. were repressed in the later stage, although they were moderately up-regulated on the initial association with the AM fungus. Real-time RT–PCR experiments supported the array experiments. To further confirm the characteristic expression, a PAL promoter was fused with a reporter gene and introduced into L. japonicus, and then the transformants were grown with a commercial inoculum of G. mosseae. The reporter activity was augmented throughout the roots due to the presence of contaminating microorganisms in the inoculum. Interestingly, G. mosseae only colonized where the reporter activity was low. Comparison of the transcriptome profiles of AM roots and nitrogen-fixing root nodules formed with Mesorhizobium loti indicated that the PAL genes and other phenylpropanoid biosynthesis-related genes were similarly repressed in the two organs

Observation of Degradation of Pt and Carbon Support in Polymer Electrolyte Fuel Cell Using Combined Nano-X-ray Absorption Fine Structure and Transmission Electron Microscopy Techniques

It is hard to directly visualize spectroscopic and atomic–nanoscopic information on the degraded Pt/C cathode layer inside polymer electrolyte fuel cell (PEFC). However, it is mandatory to understand the preferential area, sequence, and relationship of the degradations of Pt nanoparticles and carbon support in the Pt/C cathode layer by directly observing the Pt/C cathode catalyst for the development of next-generation PEFC cathode catalysts. Here, the spectroscopic, chemical, and morphological visualization of the degradation of Pt/C cathode electrocatalysts in PEFC was performed successfully by a same-view combination technique of nano-X-ray absorption fine structure (XAFS) and transmission electron microscopy (TEM)/scanning TEM–energy-dispersive spectrometry (EDS) under a humid N2 atmosphere. The same-view nano-XAFS and TEM/STEM–EDS imaging of the Pt/C cathode of PEFC after triangular-wave 1.0–1.5 VRHE (startup/shutdown) accelerated durability test (tri-ADT) cycles elucidated the site-selective area, sequence, and relationship of the degradations of Pt nanoparticles and carbon support in the Pt/C cathode layer. The 10 tri-ADT cycles caused a carbon corrosion to reduce the carbon size preferentially in the boundary regions of the cathode layer with both electrolyte and holes/cracks, accompanied with detachment of Pt nanoparticles from the degraded carbon. After the decrease in the carbon size to less than 8 nm by the 20 tri-ADT cycles, Pt nanoparticles around the extremely corroded carbon areas were found to transform and dissolve into oxidized Pt2+–O4 species

Effects of zinc deficiency/zinc supplementation on ammonia metabolism in patients with decompensated liver cirrhosis.

Hepatic encephalopathy is one of the major complications in decompensated liver cirrhosis. The current study was conducted to clarify the mechanisms of zinc deficiency in liver cirrhosis and its involvement in hepatic encephalopathy via ammonia metabolism. Ten patients each with compensated or decompensated liver cirrhosis and 11 healthy volunteers were enrolled in the study. Serum zinc levels and its daily urinary excretion were measured, an oral zinc-tolerance test was performed to examine zinc malabsorption, and the effects of diuretics on zinc excretion and of zinc supplementation on ammonia metabolism in the skeletal muscle were studied. The mean serum zinc levels in patients with decompensated liver cirrhosis were found to be significantly lower than the levels in controls and patients with compensated liver cirrhosis. The serum zinc levels were inversely correlated with blood ammonia in the fasting state. In the oral zinc-tolerance test, the percent increase in serum zinc levels 120 and 180 min after ingestion was less in cirrhotic patients than in controls. A diuretic administration resulted in a significant reduction in serum zinc levels. An increased uptake of ammonia by and an increased release of glutamine from leg skeletal muscle after oral supplementation of zinc sulfate were evident. Taken together, zinc deficiency in decompensated cirrhotic patients appears to be due to low absorption and to high urinary excretion, for which excessive diuretic administration is, in part, responsible, and zinc supplementation might play an important role in the prevention of hepatic encephalopathy by activating glutamine synthetase.</p

Confined Single Alkali Metal Ion Platform in a Zeolite Pore for Concerted Benzene C–H Activation to Phenol Catalysis

The well-known cumene process via an explosive cumene hydroperoxide intermediate in liquid phase currently employed for phenol production is energy-intensive and not environmentally friendly. Therefore, there is a demand for an alternative single-step gas-phase catalysis process. According to the conventional catalysis concept, selective oxidation reactions are promoted by redox catalysts and not by acid–base catalysts. In general, alkali and alkaline earth metal ions cannot activate each of benzene, O2, and N2O when they adsorb separately. However, we observed an unprecedented catalysis of single alkali and alkaline earth metal ion sites incorporated into zeolite pores for the selective oxidation of benzene to phenol with N2O and O2 + NH3, thereby providing a single-site catalytic platform with high selectivity. Among alkali and alkaline earth metal ions, single Cs+ and Rb+ sites with ion diameters of >300 pm in the pores of β-zeolites exhibited remarkable selectivity for benzene C–H activation to phenol catalysis in a concerted reaction pathway

Operando Imaging of Ce Radical Scavengers in a Practical Polymer Electrolyte Fuel Cell by 3D Fluorescence CT–XAFS and Depth-Profiling Nano-XAFS–SEM/EDS Techniques

There is little information on the spatial distribution, migration, and valence of Ce species doped as an efficient radical scavenger in a practical polymer electrolyte fuel cell (PEFC) for commercial fuel cell vehicles (FCVs) closely related to a severe reliability issue for long-term PEFC operation. An in situ three-dimensional fluorescence computed tomography–X-ray absorption fine structure (CT–XAFS) imaging technique and an in situ same-view nano-XAFS–scanning electron microscopy (SEM)/energy-dispersive spectrometry (EDS) combination technique were applied for the first time to perform operando spatial visualization and depth-profiling analysis of Ce radical scavengers in a practical PEFC of Toyota MIRAI FCV under PEFC operating conditions. Using these in situ techniques, we successfully visualized and analyzed the domain, density, valence, and migration of Ce scavengers that were heterogeneously distributed in the components of PEFC, such as anode microporous layer, anode catalyst layer, polymer electrolyte membrane (PEM), cathode catalyst layer, and cathode microporous layer. The average Ce valence states in the whole PEFC and PEM were 3.9+ and 3.4+, respectively, and the Ce³⁺/Ce⁴⁺ ratios in the PEM under H₂ (anode)–N₂ (cathode) at an open-circuit voltage (OCV), H₂–air at 0.2 A cm⁻², and H₂–air at 0.0 A cm⁻² were 70 ± 5:30 ± 5%, as estimated by both in situ fluorescence CT–X-ray absorption near-edge spectroscopy (XANES) and nano-XANES–SEM/EDS techniques. The Ce³⁺ migration rates in the electrolyte membrane toward the anode and cathode electrodes ranged from 0.3 to 3.8 μm h⁻¹, depending on the PEFC operating conditions. Faster Ce³⁺ migration was not observed with voltage transient response processes by highly time-resolved (100 ms) and spatially resolved (200 nm) nano-XANES imaging. Ce³⁺ ions were suggested to be coordinated with both Nafion sulfonate (Nf_sul) groups and water to form [Ce(Nf_sul)_x(H₂O)_y]³⁺. The Ce migration behavior may also be affected by the spatial density of Ce, interactions of Ce with Nafion, thickness and states of the PEM, and H₂O convection, in addition to the PEFC operating conditions. The unprecedented operando imaging of Ce radical scavengers in the practical PEFCs by both in situ three-dimensional (3D) fluorescence CT–XAFS imaging and in situ depth-profiling nano-XAFS–SEM/EDS techniques yields intriguing insights into the spatial distribution, chemical states, and behavior of Ce scavengers under the working conditions for the development of next-generation PEFCs with high long-term reliability and durability