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The reversibility of structural change in a bimetallic catalyst during the chemical reaction is an essential factor to determine the catalytic stability. Herein, we investigate the surface modulation of three Pt−Ni bimetallic alloy nanoparticle compositions (Pt3Ni1, Pt1Ni1, and Pt1Ni3) under alternating redox cycles. We validate trends in the structural change of the three compositions of Pt−Ni nanoparticles via spectroscopic/microscopic investigations at bulk and atomic levels. Pt‐rich Pt−Ni nanoparticles exhibited higher reversibility in structural change during the repeated redox cycles. On the contrary, Ni‐rich Pt−Ni nanoparticles showed irreversible structural changes, leading to the segregation and separation of Ni species from the alloy, which could deactivate the catalysts. This work demonstrates the reversibility of structural dynamics in alloy catalysts depending on their composition, providing fundamental insights for developing ideal bimetallic catalysts. [ABSTRACT FROM AUTHOR]

Direct methane protonic ceramic fuel cells are promising electrochemical devices that address the technical and economic challenges of conventional ceramic fuel cells. However, Ni, a catalyst of protonic ceramic fuel cells exhibits sluggish reaction kinetics for CH4 conversion and a low tolerance against carbon-coking, limiting its wider applications. Herein, we introduce a self-assembled Ni-Rh bimetallic catalyst that exhibits a significantly high CH4 conversion and carbon-coking tolerance. It enables direct methane protonic ceramic fuel cells to operate with a high maximum power density of ~0.50 W·cm−2 at 500 °C, surpassing all other previously reported values from direct methane protonic ceramic fuel cells and even solid oxide fuel cells. Moreover, it allows stable operation with a degradation rate of 0.02%·h−1 at 500 °C over 500 h, which is ~20-fold lower than that of conventional protonic ceramic fuel cells (0.4%·h−1). High-resolution in-situ surface characterization techniques reveal that high-water interaction on the Ni-Rh surface facilitates the carbon cleaning process, enabling sustainable long-term operation. Direct methane protonic ceramic fuel cells are promising electrochemical energy conversion devices. However, their performance and stability remain challenging. Here, the authors develop a self-assembled Ni-Rh bimetallic catalyst which shows great enhancements in power output and long-term operational sustainability. [ABSTRACT FROM AUTHOR]

Orbital anisotropy at interfaces in magnetic heterostructures has been key to pioneering spin–orbit‐related phenomena. However, modulating the interface's electronic structure to make it abnormally asymmetric has been challenging because of lack of appropriate methods. Here, the authors report that low‐energy proton irradiation achieves a strong level of inversion asymmetry and unusual strain at interfaces in [Co/Pd] superlattices through nondestructive, selective removal of oxygen from Co3O4/Pd superlattices during irradiation. Structural investigations corroborate that progressive reduction of Co3O4 into Co establishes pseudomorphic growth with sharp interfaces and atypically large tensile stress. The normal component of orbital to spin magnetic moment at the interface is the largest among those observed in layered Co systems, which is associated with giant orbital anisotropy theoretically confirmed, and resulting very large interfacial magnetic anisotropy is observed. All results attribute not only to giant orbital anisotropy but to enhanced interfacial spin–orbit coupling owing to the pseudomorphic nature at the interface. They are strongly supported by the observation of reversal of polarity of temperature‐dependent Anomalous Hall signal, a signature of Berry phase. This work suggests that establishing both giant orbital anisotropy and strong spin–orbit coupling at the interface is key to exploring spintronic devices with new functionalities. [ABSTRACT FROM AUTHOR]

Oxygen‐redox‐based cathode materials for sodium‐ion batteries (SIBs) have attracted considerable attention in recent years owing to the possibility of delivering additional capacity in the high‐voltage region. However, they still suffer from not only fast capacity fading but also poor rate capability. Herein, P2‐Na0.75[Li0.15Ni0.15Mn0.7]O2 is introduced, an oxygen‐redox‐based layered oxide cathode material for SIBs. The effect of Ni doping on the electrochemical performance is investigated by comparison with Ni‐free P2‐Na0.67[Li0.22Mn0.78]O2. The Na0.75[Li0.15Ni0.15Mn0.7]O2 delivers a specific capacity of ≈160 mAh g−1 in the voltage region of 1.5–4.6 V at 0.1 C in Na cells. Combined experiments (galvanostatic cycling, neutron powder diffraction, X‐ray absorption spectroscopy, X‐ray photoelectron spectroscopy, and nuclear magnetic resonance (7Li NMR)) and theoretical studies (density functional theory calculations) confirm that Ni substitution not only increases the operating voltage and decreases voltage hysteresis but also improves the cycling stability by reducing Li migration from transition metal to Na layers. This research demonstrates the effect of Li and Ni co‐doping in P2‐type layered materials and suggests a new strategy of using Mn‐rich cathode materials via oxygen redox with optimization of doping elements for SIBs. [ABSTRACT FROM AUTHOR]

In spite of great application potential as transparent n-type oxides with high electrical mobility at room temperature, threading dislocations (TDs) often found in the (Ba,La)SnO3 (BLSO) films can limit their intrinsic properties so that their role in the physical properties of BLSO films need to be properly understood. The electrical properties and electronic structure of BLSO films grown on SrTiO3 (001) (STO) and BaSnO3 (001) (BSO) substrates are comparatively studied to investigate the effect of the TDs. In the BLSO/STO films with TD density of ~1.32 × 1011 cm−2, n-type carrier density ne and electron mobility are significantly reduced, as compared with the BLSO/BSO films with nearly no TDs. This indicates that TDs play the role of scattering-centers as well as acceptor-centers to reduce n-type carriers. Moreover, in the BLSO/STO films, both binding energies of an Sn 3d core level and a valence band maximum are reduced, being qualitatively consistent with the Fermi level shift with the reduced n-type carriers. However, the reduced binding energies of the Sn 3d core level and the valence band maximum are clearly different as 0.39 and 0.19 eV, respectively, suggesting that the band gap renormalization preexisting in proportion to ne is further suppressed to restore the band gap in the BLSO/STO films with the TDs. [ABSTRACT FROM AUTHOR]

Abstract: Multilayer transition metal dichalcogenides (TMDs) potentially provide opportunities for large‐area electronics, including flexible displays and wearable sensors. However, most TMDs suffer from a Schottky barrier (SB) and nonuniform defects, which severely limit their electrical performances. Here, a novel chemical doping scheme is presented using poly‐(diketopyrrolopyrrole‐terthiophene) (PDPP3T) to compensate the defects and SB of multilayer molybdenum diselenide (MoSe2), exhibiting greatly enhanced electrical characteristics, including on‐current (≈2000‐fold higher) and photoresponsivity (≈10‐fold larger) over the baseline MoSe2 device. Based on comprehensive analysis using X‐ray photoelectron spectroscopy, grazing incidence wide‐angle X‐ray diffraction, atomic force microscopy, and near‐edge X‐ray absorption of fine structure, it is shown that two mechanisms (dipole‐induced and charge‐transfer doping effects) account for such enhancements in the multilayer MoSe2 device. The methodical generality of the strong n‐doping behavior of multilayer MoSe2 is further demonstrated by applying thiophene instead of PDPP3T. [ABSTRACT FROM AUTHOR]

It is reported on the allocation effects of branched alkyl chains, when used as solubility and ordering enhancers of the conjugated donor-accepter (D-A) copolymer backbones, on the ordering and π-π overlapping of the copolymers, that drastically affect the electrical properties of organic field-effect transistors (OFETs). Triisopropylsilylethynyl-benzo[1,2-b:4,5-b′]dithiophene (TIPSBDT) and diketopyrrolopyrrole (DPP)-based copolymers, which have two linear alkyl spacers (methylene (C1) or butylene (C4)) between the DPP and side-substituent (C10H21) CH(C8H17)-, are synthesized by Suzuki cross-coupling. These copolymer films are spun cast onto a polymer-treated SiO2 dielectric surface, and some are further thermally annealed. The longer spacer, C4, is found to efficiently enhance the coplanarity and conjugation of the D-A backbone, while the C1 does not. The resulting C4-bridged TIPSBDTDPP-based copolymer readily develops a superior π-extended layer on the dielectric surface; the edge-on chains with randomly oriented side chains can be closely packed with a short π-planar distance (d(010)) of 3.57 Å. Its properties are superior to those of the short spacer C1 system with d(010) ≈3.93 Å. The C4-bridged TIPSBDT-DPP copolymer films yield a field-effect mobility up to 1.2 cm² V-1 s-1 in OFETs, 12 times as higher than that of the C1 spacer system. [ABSTRACT FROM AUTHOR]

Here, a novel strategy is reported to develop polymer field effect transistors using ethanol, propanol, and butanol-the most environmentally benign solvent except water-as processing solvents. From such environmentally benign processes, for the first time high-mobility (>1 cm2 V−1 s−1) polymer field effect transistors are demonstrated. These mobility values realized from 'really green solvents' exceed those of conventional hydrogenated amorphous silicon semiconductors. To achieve this 1) stable sub-microparticles of conjugated polymers dispersed in alcohols are fabricated, 2) an aldehyde-assisted surface tension-depression methodology is developed to successfully form thin films from alcohol, and 3) the structural information of alcohol-dispersed sub-microparticles of semiconducting polymers is carefully characterized. [ABSTRACT FROM AUTHOR]

A donor-acceptor (D-A) semiconducting copolymer, PDPP-TVT-29, comprising a diketopyrrolopyrrole (DPP) derivative with long, linear, space-separated alkyl side-chains and thiophene vinylene thiophene (TVT) for organic field-effect transistors (OFETs) can form highly π-conjugated structures with an edge-on molecular orientation in an as-spun film. In particular, the layerlike conjugated film morphologies can be developed via short-term thermal annealing above 150°C for 10 min. The strong intermolecular interaction, originating from the fused DPP and D-A interaction, leads to the spontaneous self-assembly of polymer chains within close proximity (with π-overlap distance of 3.55 Å) and forms unexpectedly long-range π-conjugation, which is favorable for both intra- and intermolecular charge transport. Unlike intergranular nanorods in the as-spun film, well-conjugated layers in the 200°C-annealed film can yield more efficient charge-transport pathways. The granular morphology of the as-spun PDPP-TVT-29 film produces a field-effect mobility (μFET) of 1.39 cm2 V-1 s-1 in an OFET based on a polymer-treated SiO 2 dielectric, while the 27-Å-step layered morphology in the 200°C-annealed films shows high μFET values of up to 3.7 cm2 V-1 s-1 . [ABSTRACT FROM AUTHOR]

We report on a new class of microliter-scale solution processes for fabricating highly uniform and large-area transistor arrays with extremely low consumption of semiconducting polymers. These processes are accomplished by applying a vertical phase separation of polymers with an environmentally benign solvent, a random copolymerization strategy between two highly conductive repeating units, and a meniscus-dragging deposition technique. The successful realization of these three processes, as confirmed by the structural and morphological in-depth characterizations, has enabled the fabrication of high-performance polymeric field-effect transistors that were uniformly distributed, without a single failure, on a 4 inch wafer using only 40 μg of semiconducting polymers. The resulting transistor arrays showed an average mobility of 0.28 cm2 V−1 s−1, with a low standard deviation of 0.04, as well as ultra-uniform near-zero threshold voltages. Our simple strategy shows great promise for fabricating large-scale organic electronic devices in the future using a truly low-cost process. [ABSTRACT FROM AUTHOR]

The influence of Ni vacancies on the chemistry and electronic structure of NiO thin films was investigated using X-ray absorption spectroscopy and extended X-ray absorption fine structure analysis. Changes in the electronic structures upon partial oxidation are mainly addressed. It is strongly suggested that the hole carriers are mostly delocalized on oxygen sites while localized holes coexist at both Ni and O sites. Such delocalized carriers are found to be depleted by capping with a thin n-type TiO2 layer. This suggests that the defect states can be healed effectively by the TiO2 capping and its density can be tuned for functionality as a base p-type oxide material. The relationship with threshold resistive switching behavior is also discussed. [ABSTRACT FROM AUTHOR]

Electronic structures of spinel oxides FeT2O4 (T = V, Cr) have been investigated by employing soft x-ray magnetic circular dichroism (XMCD) and soft x-ray absorption spectroscopy (XAS). XAS reveals that Cr and V ions are trivalent, and that Fe ions are nearly divalent in FeT2O4 (T = V, Cr). Finite XMCD signals are observed in FeV2O4 at T = 80 K, while they are very weak in FeCr2O4. XMCD shows that Fe spins are antiparallel to V and Cr spins, with the V and Cr spins being canted from Fe spins, which suggests a Yafet-Kittel type triangular spin configuration in FeT2O4 (T = V, Cr). [ABSTRACT FROM AUTHOR]

A high‐rate of oxygen redox assisted by cobalt in layered sodium‐based compounds is achieved. The rationally designed Na0.6[Mg0.2Mn0.6Co0.2]O2 exhibits outstanding electrode performance, delivering a discharge capacity of 214 mAh g−1 (26 mA g−1) with capacity retention of 87% after 100 cycles. High rate performance is also achieved at 7C (1.82 A g−1) with a capacity of 107 mAh g−1. Surprisingly, the Na0.6[Mg0.2Mn0.6Co0.2]O2 compound is able to deliver capacity for 1000 cycles at 5C (at 1.3 A g−1), retaining 72% of its initial capacity of 108 mAh g−1. X‐ray absorption spectroscopy analysis of the O K‐edge indicates the oxygen‐redox species (O2−/1−) is active during cycling. First‐principles calculations show that the addition of Co reduces the bandgap energy from ≈2.65 to ≈0.61 eV and that overlapping of the Co 3d and O 2p orbitals facilitates facile electron transfer, enabling the long‐term reversibility of the oxygen redox, even at high rates. To the best of the authors' knowledge, this is the first report on high‐rate oxygen redox in sodium‐based cathode materials, and it is believed that the findings will open a new pathway for the use of oxygen‐redox‐based materials for sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

The multiscale chemomechanical interplay in lithium‐ion batteries builds up mechanical stress, provokes morphological breakdown, and leads to state of charge heterogeneity. Quantifying the interplay in complex composite electrodes with multiscale resolution constitutes a frontier challenge in precisely diagnosing the fading mechanism of batteries. In this study, hard X‐ray phase contrast tomography, capable of nanoprobing thousands of active particles at once, enables an unprecedented statistical analysis of the chemomechanical transformation of composite electrodes under fast charging conditions. The damage heterogeneity is demonstrated to prevail at all length scales, which stems from the unbalanced electron conduction and ionic diffusion, and collectively leads to the nonuniform utilization of active particles spatially and temporally. This study highlights that the statistical mapping of the chemomechanical transformation offers a diagnostic method for the particles utilization and fading, hence could improve electrode formulation for fast‐charging batteries. [ABSTRACT FROM AUTHOR]