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Cobalt oxide (Co3O4) serves as a promising electrocatalyst for oxygen evolution reactions (OER) in water-electrolytic hydrogen production. For more practical applications, advances in dry-deposition processes for the high-throughput fabrication of such Co3O4 electrocatalysts are needed. In this work, a thermal metal–organic deposition (MOD) technique is developed to form Co3O4 deposits on microscale-diameter carbon fibers constituting a carbon fiber paper (CFP) substrate for high-efficiency OER electrocatalyst applications. The Co3O4 electrocatalysts are deposited while uniformly covering the surface of individual carbon fibers in the reaction temperature range from 400 to 800 °C under an ambient Ar atmosphere. It is found that the microstructure of deposits is dependent on the reaction temperature. The Co3O4 electrocatalysts prepared at 500 °C and over exhibit values of 355–384 mV in overpotential (η10) required to reach a current density of 10 mA cm−2 and 70–79 mV dec−1 in Tafel slope, measured in 1 M KOH aqueous solution. As a result, it is highlighted that the improved crystallinity of the Co3O4 electrocatalyst with the increased reaction temperature leads to an enhancement in electrode-level OER activity with the high electrochemically active surface area (ECSA), low charge transfer resistance (Rct), and low η10, due to the enhanced electrical conductivity. On the other hand, it is found that the inherent catalytic activity of the surface sites of the Co3O4, represented by the turnover frequency (TOF), decreases with reaction temperature due to the high-temperature sintering effect. This work provides the groundwork for the high-throughput fabrication and rational design of high-performance electrocatalysts.

In this study, the advanced chemical vapor transport (CVT) method in combination with the quenching effect is introduced for creating molybdenum oxide nanoparticle arrays, composed of the hierarchical structure of fine nanoparticles (NPs), which are vertically grown with a homogeneous coverage on the individual carbon fibers of carbon fiber paper (CFP) substrates. The obtained molybdenum oxide NPs hold a metastable high-temperature γ-Mo4O11 phase along with a stable α-MoO3 phase by the quenching effect. Furthermore, such a quenching effect forms thinner and smaller nanoparticle aggregates by suppressing the growth and coalescence of primary particles. The molybdenum oxide nanoparticle aggregates are prepared using two different types of precursors: MoO3 and a 1:1 (mol/mol) mixture of MoO3 and activated carbon. The results characterized using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy show that the relative amount of α-MoO3 to γ-Mo4O11 within the prepared NPs is dependent on the precursor type; a lower amount of α-MoO3 to γ-Mo4O11 is obtained in the NPs prepared using the mixed precursor of MoO3 and carbon. This processing–structure landscape study can serve as the groundwork for the development of high-performance nanomaterials in various electronic and catalytic applications.

Herein, we report high electrocatalytic activity of monoclinic VO2 (M1 phase) for the oxygen evolution reaction (OER) for the first time. The single-phase VO2 (M1) nanoparticles are prepared in the form of uniformly covering the surface of individual carbon fibers constituting a carbon fiber paper (CFP). The VO2 nanoparticles reveal the metal-insulator phase transition at ca. 65 °C (heating) and 62 °C (cooling) with low thermal hysteresis, indicating a high concentration of structural defect which is considered a grain boundary among VO2 nanoparticles with some particle coalescence. Consequently, the VO2/CFP shows a high electrocatalytic OER activity with the lowest η10 (350 mV) and Tafel slope (46 mV/dec) values in a 1 M aqueous solution of KOH as compared to those of the vacuum annealed V2O5 and the hydrothermally grown VO2 (M1), α-V2O5, and γ′-V2O5. The catalytically active site is considered V4+ components and V4+/5+ redox couples in VO2. The oxidation state of V4+ is revealed to be more favorable to the OER catalysis compared to that of V5+ in vanadium oxide through comparative studies. Furthermore, the amount of V5+ component is found to be increased on the surface of VO2 catalyst during the OER, giving rise to the performance degradation. This work suggests V4+ and its redox couple as a novel active component for the OER in metal-oxide electrocatalysts.

The electrocatalytic water electrolysis is the most eco-friendly technique for hydrogen generation, which is governed by the electrode reaction kinetics involving cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) in common alkaline electrolytes. Cobalt oxide (Co _3 O _4 ) and related compounds are the most efficient OER catalysts, replacing the noble metals. In this work, the surface oxidations of the cobalt carbonate (Co(CO _3 ) _0.5 OH·0.11H _2 O) and Co _3 O _4 nanowires during the OER are carefully investigated by contrasting the polarization curves, Tafel plots, and x-ray photoelectron spectroscopy (XPS) spectra, before and after the 1000th cyclic voltammetry (CV) cycling in 1 M KOH alkaline solution. The overpotentials required to reach a current density ( j ) of 20 mA cm ^−2 ( η _20 ) are estimated to be 313 mV for the 300 °C-calcined Co _3 O _4 , 350 mV for the 400 °C-calcined Co _3 O _4 , 365 mV for the 500 °C-calcined Co _3 O _4 , and 373 mV for the cobalt carbonate (Co(CO _3 ) _0.5 OH·0.11H _2 O). The Tafel slope of cobalt carbonate (Co(CO _3 ) _0.5 OH·0.11H _2 O) nanowires is the highest at 93 mV dec ^−1 , while it is measured to be 57 mV dec ^−1 for the 300 °C-calcined Co _3 O _4 , 47 mV dec ^−1 for the 400 °C-calcined Co _3 O _4 , and 79 mV dec ^−1 for the 500 °C-calcined Co _3 O _4 . As a result, the oxidation from Co ^2+ to Co ^3+ within Co _3 O _4 during the OER is detected, which improves the OER activity. On the other hand, the formation of cobalt hydoxide is found on the surface of the Co _3 O _4 nanowires during the OER in alkaline solution, which decreases the OER activity. For the surface oxidation of the cobalt carbonate (Co(CO _3 ) _0.5 OH·0.11H _2 O) nanowires, the increase in the amounts of Co ^3+ and oxygen vacancy and the formation of O-C-O and carbonates are found, which highly enhance the OER activity. These findings indicate that the surface redox kinetics during the electrocatalytic reactions should be considered important in order to enhance the electrocatalytic activity, and furthermore can provide insight into future challenges in designing advanced electrocatalysts.

Here, single-phase Mn2O3 and Mn3O4 films are successfully fabricated by a facile solution process based on metal-organic decomposition (MOD), for the first time. A formulated manganese 2-ethylhexanoate solution was used as an MOD precursor for the preparation of manganese oxide films. The difference in thermal decomposition behavior of precursor solution in air and inert atmospheres was observed, indicating that the calcination atmosphere is the main factor for controlling the valence of manganese oxide films. Significantly, the solution-coated films on substrates are found to be transformed into single-phase Mn2O3 and Mn3O4 films when they are calcinated under air and inert atmosphere, respectively. The film crystallinity was improved with increasing calcination temperature for both Mn2O3 and Mn3O4 films. In particular, it is noted that the grains of Mn2O3 film were somewhat linearly grown in air, while those of Mn3O4 film exhibited the drastic growth in Ar with an increase of calcination temperature.

This paper describes a methodology for implementing the state estimation and enhancing the accuracy in large-scale power systems that partially depend on variable renewable energy resources. To determine the actual states of electricity grids, including those of wind and solar power systems, the proposed state estimation method adopts a fast-decoupled weighted least square approach based on the architecture of application common database. Renewable energy modeling is considered on the basis of the point of data acquisition, the type of renewable energy, and the voltage level of the bus-connected renewable energy. Moreover, the proposed algorithm performs accurate bad data processing using inner and outer functions. The inner function is applied to the largest normalized residue method to process the bad data detection, identification and adjustment. While the outer function is analyzed whether the identified bad measurements exceed the condition of Kirchhoff’s current law. In addition, to decrease the topology and measurement errors associated with transformers, a connectivity model is proposed for transformers that use switching devices, and a transformer error processing technique is proposed using a simple heuristic method. To verify the performance of the proposed methodology, we performed comprehensive tests based on a modified IEEE 18-bus test system and a large-scale power system that utilizes renewable energy.

Here, it is found that the incorporation of rGO into (Sn _0.5 Ti _0.5 )O _2 solid solution suppresses spinodal decomposition via two characteristic routes. First, the addition of rGO to the solid solution leads to the compositional change from (Sn _0.5 Ti _0.5 )O _2 to (Sn _0.1 Ti _0.9 )O _2 moving out of the miscibility gap at SnO _2 -TiO _2 phase diagram, which suppresses spinodal decomposition. The results indicate that addition of rGO promotes reduction and evaporation of SnO _2 during heat treatment. Secondly, the incorporation of rGO is found to produce the solid solution with lower Sn and Ti valences and more oxygen vacancies, which can also suppress spinodal decomposition.

This paper proposes an advanced continuous voltage control method that implements multiple-point control to ensure peak power system performance. Most control schemes utilize generators to regulate the pilot point voltage of a control area. However, exact control of a single pilot point is difficult because of the influence of adjacent areas in a meshed power system. To address this challenge, the proposed method accesses multiple pilot points to mitigate the effects of the neighboring area. In simulations of the Korean power system, the proposed control scheme offered a considerable improvement in performance when compared with the conventional, currently implemented voltage control system.

In this paper, a method to estimate ice loads as a function of the buttock angle of an icebreaker is presented with respect to polycrystalline freshwater ice. Ice model tests for different buttock angles and impact velocities are carried out to investigate ice pressure loads and tendencies of ice pressure loads in terms of failure modes. Experimental devices were fabricated with an idealized icebreaker bow shape, and medium-scale ice specimens were used. A dry-drop machine with a freefall system was used, and four pressure sensors were installed at the bottom to estimate ice pressure loads. An estimation equation was suggested on the basis of the test results. We analyzed the estimation equation for design ice loads of the International Association of Classification Societies (IACS) classification rules. We suggest an estimation equation considering the relation between ice load, buttock angle, and velocity by modifying the equations given in the IACS classification rules.

Organic metal halide perovskites have rapidly emerged as among the leading candidates for the next generation of photovoltaic and light-emitting devices. The band gap, exciton binding energy, and absorption cross-section of these materials are tunable to some extent by compositional variation. Dimensional confinement represents an attractive alternative to compositional variation for tuning these properties via quantum confinement close to the Böhr radius. While the stabilization of few-layered nanoplatelets of methylammonium lead bromide has recently been demonstrated, mechanistic understanding of synthetic parameters resulting in dimensional confinement remains to be developed. Here we show that the layer thickness can be precisely modulated as a function of the chain length and concentration of the added alkylammonium cations. Surface capping ligands bind preferentially to sheets of corner sharing PbBr6 octahedra and thereby buffer the extent of supersaturation of monomeric units enabling precise modulation of the layer-by-layer growth of 2D nanoplatelets. Crystal growth can be confined to yield nanoplatelets with tunable unit cell thickness spanning between one and six layers, which allows for precise tuning of the emissive properties of 2D perovskite nanoplatelets in the range of 430-520 nm depending on the layer thickness. The results suggest a generalizable strategy for tuning the layer thickness of these materials as a function of the alkyl chain length of the ligands. [ABSTRACT FROM AUTHOR]

Thenucleation and growth behavior of Cu nanoparticles during thermalheating of Cu(II) complex inks for printed Cu metallization were investigated,particularly focusing on the effects of the amine concentration onthe microstructure evolution and electrical conductivity. Herein,the dual effects of hexylamine as a reducing agent dissociating thecarboxyl group from the precursor and a capping agent hindering thesubsequent growth of Cu nuclei were confirmed. On the basis of suchdual effects of amine, the sufficient complexation of the Cu(II) precursorwith a high amine concentration in the ink led to the single-routegrowth of Cu nanoparticles during thermal heating, which resultedin the dense film with a narrow particle size distribution exhibitinga high electrical conductivity. The electrical conductivity of thefilm could be further enhanced by a reducing atmosphere with formicacid. Significantly, the understanding of the ink chemistry and thenucleation and growth kinetics in the metal ion complex or metal–organicdecomposition (MOD) ink can provide the design rules for the formulationof the solution-type inks to control the microstructure of printedmetallization. [ABSTRACT FROM AUTHOR]

A Ga-In-Zn-O thin-film transistor with double-gate structure is reported. Enhancement-mode operation that is essential to the constitution of a low-power digital circuitry is easily achieved when the upper and lower gate electrodes are tied together. The saturation mobility and the subthreshold swing are improved from 3.65 cm2/(V · s) and 0.44 V/dec to 18.9 cm2/(V · s) and 0.14 V/dec, respectively, compared with the single-gate structure. We can modulate the threshold voltage of either gate by adjusting the bias on the other gate. [ABSTRACT FROM AUTHOR]