Highly active and stable surface structure for oxygen evolution reaction originating from balanced dissolution and strong connectivity in BaIrO3 solid solutions.

Catalysts for the oxygen evolution reaction (OER) are receiving great interest since OER remains the bottleneck of water electrolyzers for hydrogen production. Especially, OER in acidic solutions is crucial since it produces high current densities and avoids precipitation of carbonates. However, even the acid stable iridates undergo severe dissolution during the OER. BaIrO3 has the strongest IrO6 connectivity and stable surface structure, yet it suffers from lattice collapse after OER cycling, making it difficult to improve the OER durability. In the present study, we have successfully developed an OER catalyst with both high intrinsic activity and stability under acidic conditions by preventing the lattice collapse after repeated OER cycling. Specifically, we find that the substitution of Ir-site with Mn for BaIrO3 in combination with OER cycling leads to a remarkable activity enhancement by a factor of 28 and an overall improvement in stability. This dual enhancement of OER performance was accomplished by the novel strategy of slightly increasing the Ir-dissolution and balancing the elemental dissolution in BaIr1-x Mn x O3 to reconstruct a rigid surface with BaIrO3-type structure. More importantly, the mass activity for BaIr0.8Mn0.2O3 reached ∼73 times of that for IrO2, making it a sustainable and promising OER catalyst for energy conversion technologies.

Effects of A-site Cations in Quadruple Perovskite Ruthenates on Oxygen Evolution Catalysis in Acidic Aqueous Solutions.

The quadruple perovskite ruthenate CaCu3 Ru4 O12 is more active and stable than the benchmark catalyst RuO2 in the oxygen evolution reaction (OER) in acidic aqueous solutions, where many oxide-based catalysts are dissolved. Studies on the crystal structures of quadruple perovskite ruthenates are rare, and the origin of OER activity or stability from a structural aspect has not been clarified in detail. This presents the need to study the effects of cations at the A site of quadruple perovskite ruthenates ACu3 Ru4 O12 (A = Ca, Sr, La, Nd, and Ce) on the OER catalytic activity and stability in acidic aqueous solutions. CaCu3 Ru4 O12 has the highest activity and stability among all quadruple perovskite samples. The type of cation at the A site changes the average Cu and Ru valence states, and the plot of OER activity versus the average Cu valence number shows a volcano-type relationship. In addition, stability increases with a decrease in Ru-O bond length. This research provides a good design principle for OER catalysts with high activity and stability in severely acidic aqueous solutions.

Electrochemical deposition of amorphous cobalt oxides for oxygen evolution catalysis.

The oxygen evolution reaction (OER) is crucial in water splitting for hydrogen production. However, its high over-potential and sluggish kinetics cause an additional energy loss and hinder its practical application. The cobalt spinel oxide Co3O4 exhibits a high catalytic activity for the OER in alkaline solutions. However, the activity requires further enhancement to meet the industrial demand for hydrogen production. This paper presents an electrochemical deposition method to obtain cobalt oxides with a controllable crystallinity on carbon paper (CP). Usually, cobalt oxides grown on CP have a Co3O4 spinel oxide structure. The self-supported Co3O4/CP exhibited a considerable catalytic activity for the OER. When a VS2 layer grown on the CP beforehand by a hydrothermal method was used as substrate, the deposited cobalt oxides were in an amorphous state, denoted as CoO x /VS2/CP, which exhibited a higher OER activity and better stability than those of Co3O4/CP. The enhancement in the catalytic activity was attributed to the mixture formation of different types of cobalt species, including Co3O4, CoO, Co(OH)2, and metallic Co, because of the reduction by VS2. We also clarify the significance of the crystallinity of cobalt oxides in the improvement in the OER activity. This process can also be applied to the direct formation of other types of self-supported oxide electrodes for OER catalysis.

Highly active postspinel-structured catalysts for oxygen evolution reaction.

The rational design principle of highly active catalysts for the oxygen evolution reaction (OER) is desired because of its versatility for energy-conversion applications. Postspinel-structured oxides, CaB 2O4 (B = Cr3+, Mn3+, and Fe3+), have exhibited higher OER activities than nominally isoelectronic conventional counterparts of perovskite oxides LaBO3 and spinel oxides ZnB 2O4. Electrochemical impedance spectroscopy reveals that the higher OER activities for CaB 2O4 series are attributed to the lower charge-transfer resistances. A density-functional-theory calculation proposes a novel mechanism associated with lattice oxygen pairing with adsorbed oxygen, demonstrating the lowest theoretical OER overpotential than other mechanisms examined in this study. This finding proposes a structure-driven design of electrocatalysts associated with a novel OER mechanism.

Metamagnetic Behavior in a Quadruple Perovskite Oxide.

A cubic quadruple perovskite oxide CeMn3Cr4O12 has been synthesized under high-pressure and high-temperature conditions of 8 GPa and 1273 K. The X-ray absorption spectroscopy reveals that the Ce ions are in a trivalent state, as represented by the ionic model of Ce3+Mn3+3Cr3+4O12. The magnetic study demonstrates three independent antiferromagnetic transitions attributed to Ce (∼10 K), Mn (46 K), and Cr (133 K) ions. Furthermore, a magnetic field-induced antiferromagnetic-to-ferromagnetic (metamagnetic) transition of Ce3+ 4f moments is observed at low temperatures below 20 K, exhibiting a rare example of metamagnetism in the Ce3+-oxides. This finding represents that the 3d-electron magnetic sublattices play a role in the metamagnetism of 4f-electron magnetic moments, demonstrating a new aspect of the 3d-4f complex electron systems.

Extended gate-type organic transistor functionalized by molecularly imprinted polymer for taurine detection.

Molecularly imprinted polymers (MIPs) are a fascinating technology for the sensitive and selective detection of target molecules. However, in most situations, the need for complicated and expensive analytical devices for reading the responses of MIPs greatly limits their applications. For exploring low-cost and easy-to-use applications of MIPs, herein we have developed a MIP-modified extended-gate type organic field-effect transistor (MIP-OFET). Taurine was selected as a demonstrative analyte due to its biological roles and utility as a nutrient. We explored the rational design of the novel MIP with the aid of density functional theory and wave function calculations and characterized the electrochemically synthesized MIP using differential pulse voltammetry and electrochemical impedance spectroscopy. The mechanism of taurine detection by the MIP-OFET can be explained by the changes in the surface potential of the MIP-functionalized extended-gate electrode accompanied with the capture of taurine. The detection limit of taurine in complete aqueous media was estimated to be 0.33 µM, which was lower or comparable to those calculated by high-performance liquid chromatography. Furthermore, taurine in a commercial drink without any extraction was also successfully detected using the fabricated MIP-OFET. This study would broaden the scope of the applications of MIP-OFETS as chemical sensors for on-site detection of various daily nutrients.

Spinel-Type MgMn2O4 Nanoplates with Vanadate Coating for a Positive Electrode of Magnesium Rechargeable Batteries.

Spinel-type MgMn2O4 nanoplates ∼10 nm thick were prepared as a positive electrode for magnesium rechargeable batteries by the transformation of metal hydroxide nanoplates. Homogeneous coating with a vanadate layer thinner than 3 nm was achieved on the spinel oxide nanoplates via coverage of the precursor and subsequent mild calcination. We found that the spinel oxide nanoplates with the homogeneous coating exhibit improved electrochemical properties, such as discharge potential, capacity, and cyclability, due to the enhanced insertion and extraction of magnesium ions and suppressed decomposition of electrolytes. The nanometric platy morphology of the spinel oxide and the vanadate coating act synergistically for the improvement of the electrochemical performance.

ZIF-Derived Co9-xNixS8 Nanoparticles Immobilized on N-Doped Carbons as Efficient Catalysts for High-Performance Zinc-Air Batteries.

Bimetallic sulfides have been attracting considerable attention because of their high catalytic activities for oxygen reduction reaction (ORR) and oxygen evolution reaction; thus, they are considered efficient catalysts for important energy conversion devices such as fuel cells and metal-air batteries. Here, the catalytic activity of a novel catalyst composed of Co9-xNixS8 nanoparticles immobilized on N-doped carbons (Co9-xNixS8/NC) is reported. The catalyst is synthesized using a Ni-adsorbed Co-Zn zeolitic imidazolate framework (ZIF) precursor (NiCoZn-ZIF). Because of the porous structure of ZIF and the high intrinsic activity of the bimetallic sulfide nanoparticles, the Co9-xNixS8/NC catalyst exhibits high half-wave potential 0.86 V versus reversible hydrogen electrode for ORR and outstanding bifunctional catalytic performance. When Co9-xNixS8/NC is applied as a cathode catalyst in zinc-air batteries, considerably higher power density of about 75 mW cm-2 and discharge voltage are achieved compared to those of batteries with commercial Pt/C and other ZIF-derived catalysts. The zinc-air battery with the Co9-xNixS8/NC catalyst shows a high cyclability more than 170 cycles for 60 h with almost negligible decline at 10 mA cm-2. Our work provides a new insight into the design of bimetallic sulfide composites with high catalytic activities.

Non-Fermi Liquids as Highly Active Oxygen Evolution Reaction Catalysts.

The oxygen evolution reaction (OER) plays a key role in emerging energy conversion technologies such as rechargeable metal-air batteries, and direct solar water splitting. Herein, a remarkably low overpotential of ≈150 mV at 10 mA cm-2disk in alkaline solutions using one of the non-Fermi liquids, Hg2Ru2O7, is reported. Hg2Ru2O7 displays a rapid increase in current density and excellent durability as an OER catalyst. This outstanding catalytic performance is realized through the coexistence of localized d-bands with the metallic state that is unique to non-Fermi liquids. The findings indicate that non-Fermi liquids could greatly improve the design of highly active OER catalysts.

Bifunctional Oxygen Reaction Catalysis of Quadruple Manganese Perovskites.

Bifunctional electrocatalysts for oxygen evolution/reduction reaction (OER/ORR) are desirable for the development of energy conversion technologies. It is discovered that the manganese quadruple perovskites CaMn7 O12 and LaMn7 O12 show bifunctional catalysis in the OER/ORR. A possible origin of the high OER activity is the unique surface structure through corner-shared planar MnO4 and octahedral MnO6 units to promote direct OO bond formations.

Covalency-reinforced oxygen evolution reaction catalyst.

The oxygen evolution reaction that occurs during water oxidation is of considerable importance as an essential energy conversion reaction for rechargeable metal-air batteries and direct solar water splitting. Cost-efficient ABO3 perovskites have been studied extensively because of their high activity for the oxygen evolution reaction; however, they lack stability, and an effective solution to this problem has not yet been demonstrated. Here we report that the Fe(4+)-based quadruple perovskite CaCu3Fe4O12 has high activity, which is comparable to or exceeding those of state-of-the-art catalysts such as Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) and the gold standard RuO2. The covalent bonding network incorporating multiple Cu(2+) and Fe(4+) transition metal ions significantly enhances the structural stability of CaCu3Fe4O12, which is key to achieving highly active long-life catalysts.

One-pot synthesis of silica-coated copper nanoparticles with high chemical and thermal stability.

With the recent development of nanotechnology, enhancement of the stability of nanomaterials is becoming ever more important for their practical applications. We studied the silica-coating of Cu nanoparticles and the enhanced stability of silica-coated Cu nanoparticles to oxidation. The metallic nanoparticles are easily oxidized and agglomerated compared with the bulk metals because the nanoparticles possess large specific surfaces. The Cu nanoparticle is one of the most difficult nanoparticles to be handled due to its absence of the oxidation stability. In the synthesis of silica-coated Cu nanoparticles via a sol-gel process using tetraethyl orthosilicate, the addition of NH3 as a catalyst of sol-gel reaction yielded homogeneous silica-coating. However, a large amount of Cu nanoparticles is instantly dissolved by forming complex ions in a NH3 solution during and before the silica-coating process. This is the difficulty in the silica-coating of Cu nanoparticles. In the present work, the dissolution behavior of Cu nanoparticles was electrochemically examined. This electrochemistry-based optimization of reducing power of a reaction bath enabled us to synthesize the silica-coated Cu nanoparticle via a consecutive liquid-phase reaction which requires only basic equipment and involves no separate centrifuging or extraction step. Cu nanoparticles coated by silica shells had the remarkable stability even in the presence of a strong oxidizing agent. Furthermore, we demonstrated that the highly stable Cu nanoparticles can be applied to a red pigment using a unique red color of Cu nanoparticles because of its surface plasmon resonance.

Intercalation and Push-Out Process with Spinel-to-Rocksalt Transition on Mg Insertion into Spinel Oxides in Magnesium Batteries.

On the basis of the similarity between spinel and rocksalt structures, it is shown that some spinel oxides (e.g., MgCo2O4, etc) can be cathode materials for Mg rechargeable batteries around 150 °C. The Mg insertion into spinel lattices occurs via "intercalation and push-out" process to form a rocksalt phase in the spinel mother phase. For example, by utilizing the valence change from Co(III) to Co(II) in MgCo2O4, Mg insertion occurs at a considerably high potential of about 2.9 V vs. Mg2+/Mg, and similarly it occurs around 2.3 V vs. Mg2+/Mg with the valence change from Mn(III) to Mn(II) in MgMn2O4, being comparable to the ab initio calculation. The feasibility of Mg insertion would depend on the phase stability of the counterpart rocksalt XO of MgO in Mg2X2O4 or MgX3O4 (X = Co, Fe, Mn, and Cr). In addition, the normal spinel MgMn2O4 and MgCr2O4 can be demagnesiated to some extent owing to the robust host structure of Mg1-xX2O4, where the Mg extraction/insertion potentials for MgMn2O4 and MgCr2O4 are both about 3.4 V vs. Mg2+/Mg. Especially, the former "intercalation and push-out" process would provide a safe and stable design of cathode materials for polyvalent cations.

Three-dimensional nanoelectrode by metal nanowire nonwoven clothes.

Metal nanowire nonwoven cloth (MNNC) is a metal sheet that has resulted from intertwined metal nanowires 100 nm in diameter with several dozen micrometers of length. Thus, it is a new metallic material having both a flexibility of the metal sheet and a large specific surface area of the nanowires. As an application that utilizes these properties, we propose a high-cyclability electrode for Li storage batteries, in which an active material is deposited or coated on MNNC. The proposed electrode can work without any binders, conductive additives, and current collectors, which might largely improve a practical gravimetric energy density. Huge electrode surfaces provide efficient ion/electron transports, and sufficient interspaces between the respective nanowires accommodate large volume expansions of the active material. To demonstrate these advantages, we have fabricated a NiO-covered nickel nanowire nonwoven cloth (NNNC) by electroless deposition under a magnetic field and annealing in air. The adequately annealed NNNC was shown to be an excellent conversion-type electrode that exhibits a quite high cyclability, 500 mAh/g at 1 C after 300 cycles, compared to that of a composite electrode consisting of NiO nanoparticles. Thus, the present design concept will contribute to a game-changing technology in future lithium ion battery (LIB) electrodes.

B-site deficiencies in A-site-ordered perovskite LaCu3Pt(3.75)O12.

An A-site-ordered perovskite LaCu3Pt(3.75)O12 was synthesized by replacing Ca(2+) with La(3+) in a cubic quadruple AA'3B4O12-type perovskite CaCu3Pt4O12 under high-pressure and high-temperature of 15 GPa and 1100 °C. In LaCu3Pt(3.75)O12, 1/16 of B-site cations are vacant to achieve charge balance. The B-site deficiencies were evidenced by crystal structure refinement using synchrotron X-ray powder diffraction, hard X-ray photoemission spectroscopy, and soft X-ray absorption spectroscopy, leading to the ionic model La(3+)Cu(2+)3Pt(4+)(3.75)O(2-)12. Magnetic susceptibility data for this compound indicated a spin-glass-like behavior below T(g) = 3.7 K, which is attributed to disturbance of the antiferromagnetic superexchange interaction by the B-site deficiencies.

Insufficient ability of Rac1b to perturb cystogenesis.

Rac1b is frequently expressed in a number of human cancer cells. It is still unclear, however, whether Rac1b causes morphological abnormalities in epithelial tissues. To investigate whether Rac1b induces morphological changes in 3-dimensional epithelial structures, we utilized an auxin-dependent protein expression system, which enabled us to rapidly induce and evaluate Rac1b function in MDCK (Madin-Darby Canine Kidney) cysts, a model for polarized epithelial structure. Cells carrying the wild-type Rac1, Rac1b and constitutively active Rac1V12 gene were morphologically indistinguishable from normal, when their coding proteins were not expressed. However, upon protein induction, Rac1V12, but not the wild-type Rac1 or Rac1b, significantly induced the luminal cell accumulation. Live cell imaging with cell cycle indicators showed that expression of Rac1V12, but not the wild-type Rac1 or Rac1b, promoted cell cycle progression. From these results, we concluded that the expression of Rac1b per se cannot induce cell proliferation. Rather, it is considered that Rac1b expression may participate in progression of malignancy.

Effect of subthalamic nucleus stimulation during exercise on the mesolimbocortical dopaminergic region in Parkinson's disease: a positron emission tomography study.

To elucidate the dynamic effects of deep brain stimulation (DBS) in the subthalamic nucleus (STN) during activity on the dopaminergic system, 12 PD patients who had STN-DBS operations at least 1 month prior, underwent two positron emission tomography scans during right-foot movement in DBS-off and DBS-on conditions. To quantify motor performance changes, the motion speed and mobility angle of the foot at the ankle were measured twice. Estimations of the binding potential of [(11)C]raclopride (BP(ND)) were based on the Logan plot method. Significant motor recovery was found in the DBS-on condition. The STN-DBS during exercise significantly reduced the [(11)C]raclopride BP(ND) in the caudate and the nucleus accumbens (NA), but not in the dorsal or ventral putamen. The magnitude of dopamine release in the NA correlated negatively with the magnitude of motor load, indicating that STN-DBS facilitated motor behavior more smoothly and at less expense to dopamine neurons in the region. The lack of dopamine release in the putamen and the significant dopamine release in the ventromedial striatum by STN-DBS during exercise indicated dopaminergic activation occurring in the motivational circuit during action, suggesting a compensatory functional activation of the motor loop from the nonmotor to the motor loop system.

Suppression of Rac1 activity at the apical membrane of MDCK cells is essential for cyst structure maintenance.

Using MDCK cells that constitutively express a Förster resonance energy transfer biosensor, we found that Rac1 activity is homogenous at the entire plasma membrane in early stages of cystogenesis, whereas in later stages Rac1 activity is higher at the lateral membrane than at the apical plasma membrane. If Rac1 is activated at the apical membrane in later stages, however, the monolayer cells move into the luminal space. In these cells, tight junctions are disrupted, accompanied by mislocalization of polarization markers and disorientation of cell division. These observations indicate that Rac1 suppression at the apical membrane is essential for the maintenance of cyst structure.

In vivo mesolimbic D2/3 receptor binding predicts posttherapeutic clinical responses in restless legs syndrome: a positron emission tomography study.

Although D2/3 agonists have been used as a first-line medication for idiopathic restless legs syndrome (iRLS), findings on D2/3 receptors have been inconsistent. Here, we aimed to clarify the contribution of D2/3 receptor function to the clinical symptoms of iRLS by comparing the binding potential (BP(ND)) of [(11)C]raclopride with clinical improvements after D2/3 stimulation by pramipexole. Eight drug-naïve, iRLS patients and eight age-matched healthy subjects were scanned with positron emission tomography (PET). After PET scans, all patients received pramipexole (0.125 mg) orally for 2 weeks. Patients were evaluated every day with several standardized clinical tests. The BP(ND) values were compared using regions of interest and voxel-based methods. Results showed that the mean magnitude of [(11)C]raclopride BP(ND) in the mesolimbic dopamine region (nucleus accumbens (NA) and caudate) was significantly lower in the iRLS group. No significant differences between groups were observed in the putamen. The NA [(11)C]raclopride BP(ND) levels correlated negatively with clinical severity scores and positively with the degree of posttreatment improvement in iRLS. The present results suggest that alterations in mesolimbic D2/3 receptor function reflect the pathophysiology of iRLS, and the baseline availability of D2/3 receptors may predict the clinical outcome after D2/3 agonist treatment.

Chimaerin suppresses Rac1 activation at the apical membrane to maintain the cyst structure.

Epithelial organs are made of a well-polarized monolayer of epithelial cells, and their morphology is maintained strictly for their proper functions. Previously, we showed that Rac1 activation is suppressed at the apical membrane in the mature organoid, and that such spatially biased Rac1 activity is required for the polarity maintenance. Here we identify Chimaerin, a GTPase activating protein for Rac1, as a suppressor of Rac1 activity at the apical membrane. Depletion of Chimaerin causes over-activation of Rac1 at the apical membrane in the presence of hepatocyte growth factor (HGF), followed by luminal cell accumulation. Importantly, Chimaerin depletion did not inhibit extension formation at the basal membrane. These observations suggest that Chimaerin functions as the apical-specific Rac1 GAP to maintain epithelial morphology.