The effect of porous structures on the electrocatalytic activity of N-doped carbon is studied by using electrochemical analysis techniques and the result is applied to synthesize highly active and ...stable Fe–N–C catalyst for oxygen reduction reaction (ORR). We developed synthetic procedures to prepare three types of N-doped carbon model catalysts that are designed for systematic comparison of the porous structures. The difference in their catalytic activity is investigated in relation to the surface area and the electrochemical parameters. We found that macro- and mesoporous structures contribute to different stages of the reaction kinetics. The catalytic activity is further enhanced by loading the optimized amount of Fe to prepare Fe–N–C catalyst. In both N-doped carbon and Fe–N–C catalysts, the hierarchical porous structure improved electrocatalytic performance in acidic and alkaline media. The optimized catalyst exhibits one of the best ORR performance in alkaline medium with excellent long-term stability in anion exchange membrane fuel cell and accelerated durability test. Our study establishes a basis for rationale design of the porous carbon structure for electrocatalytic applications.
This paper proposes a new bidirectional buck-boost converter, which is a key component in a photovoltaic and energy storage system (ESS). Conventional bidirectional buck-boost converters for ESSs ...operate in discontinuous conduction mode (DCM) to achieve zero-voltage switching turn-ON for switches. However, operation in DCM causes high ripples in the output voltage and current, as well as low power-conversion efficiency. To improve the performance of the conventional converter, the proposed converter has a new combined structure of a cascaded buck-boost converter and an auxiliary capacitor. The combined structure of the proposed converter reduces the output current ripple by providing a current path and the efficiency is increased. A prototype was built and tested to verify the effectiveness of the converter. The proposed converter has a maximum efficiency of 98%, less than 5.14 V p.p of output voltage ripple, and less than 7.12 A p.p of output current ripple. These results were obtained at an input voltage of 160 V, switching frequency of 45 kHz, output voltage of 80-320 V, and output power of 16-160 W. The experimental results show that the proposed converter has improved performance compared to the conventional converter.
Demands for ultrahigh strength in structural materials have been steadily increasing in response to environmental issues. Maraging alloys offer a high tensile strength and fracture toughness through ...a reduction of lattice defects and formation of intermetallic precipitates. The semi-coherent precipitates are crucial for exhibiting ultrahigh strength; however, they still result in limited work hardening and uniform ductility. Here, we demonstrate a strategy involving deformable semi-coherent precipitates and their dynamic phase transformation based on a narrow stability gap between two kinds of ordered phases. In a model medium-entropy alloy, the matrix precipitate acts as a dislocation barrier and also dislocation glide media; the grain-boundary precipitate further contributes to a significant work-hardening via dynamic precipitate transformation into the type of matrix precipitate. This combination results in a twofold enhancement of strength and uniform ductility, thus suggesting a promising alloy design concept for enhanced mechanical properties in developing various ultrastrong metallic materials.
Using molecular dynamics simulations, we characterized the generation and evolution of radiation-induced point defects in the CoCrFeMnNi high-entropy alloy (HEA), to compare it with pure Ni and pure ...Fe. The generation of primary point defects was investigated by a cascade simulation at 773 K and the evolution of point defect clusters by a defect evolution simulation using 1 at% defect-containing samples. The numbers of residual defects after cascade and surviving defects after evolution in the CoCrFeMnNi HEA are smaller than those in pure Ni and pure Fe. The defect clusters appearing in the CoCrFeMnNi HEA after the defect evolution are unstable because of the alloy complexity. The origin of the slower radiation damage accumulation and the higher radiation damage tolerance in the CoCrFeMnNi HEA is discussed.
Solution‐processed transition metal oxides (TMOs) prepared from complex ion precursors are developed as promising scalable interfacial layers for non‐fullerene organic photovoltaics (OPVs); however, ...challenges remain in achieving defect‐free and highly oriented metal‐oxygen networks without post‐deposition treatments due to the presence of residual organic metal‐binding ligands in films. Herein, the novel strategy that the problematic organic metal‐binding ligands in TMO precursors can be successfully eliminated by an anion‐induced catalytic reaction (ACR) at room temperature is demonstrated, in which the low‐level anions induce electron redistribution and instability of TMO precursors, expediting binding ligand removal during the hydrolysis reaction. The subsequent condensation process facilitates a dimensionally confined and continuous metal‐oxygen network with a 20‐fold increase in electrical conductivity (from 8.4 × 10−4 to 1.8 × 10−2 S m−1) and superior work function tunability (from 5.1 to 5.3 eV) compared to the pristine film. The ACR‐derived TMO thin film on top of a ternary PBDB‐TF:Y6:PC71BM photoactive layer enables an inverted device configuration with improved efficiency of 17.6%, as well as enhanced stability over 70% of the initial efficiency for up to 100 h AM 1.5G illumination.
A room temperature sol‐gel processed MoOx is developed for highly efficient and stable inverted organic photovoltaics via an anion‐induced catalytic reaction (ACR). The ACR‐derived MoOx thin film exhibits a defect‐free and highly oriented metal‐oxygen network without post‐treatment, enabling outstanding physical and electrical properties on top of the organic photoactive layer.
Combining an electrochemically stable material onto the surface of a catalyst can improve the durability of a transition metal catalyst, and enable the catalyst to operate stably at high current ...density. Herein, the contribution of the N‐doped carbon shell (NCS) to the electrochemical properties is evaluated by comparing the characteristics of the Ni3Fe@NCS catalyst with the N‐doped carbon shell, and the Ni3Fe catalyst. The synthesized Ni3Fe@NCS catalyst has a distinct overpotential difference from the Ni3Fe catalyst (ηOER = 468.8 mV, ηHER = 462.2 mV) at (200 and −200) mA cm−2 in 1 m KOH. In stability test at (10 and −10) mA cm−2, the Ni3Fe@NCS catalyst showed a stability of (95.47 and 99.6)%, while the Ni3Fe catalyst showed a stability of (72.4 and 95.9)%, respectively. In addition, the in situ X‐ray Absorption Near Edge Spectroscopy (XANES) results show that redox reaction appeared in the Ni3Fe catalyst by applying voltages of (1.7 and −0.48) V. The decomposition of nickel and iron due to the redox reaction is detected as a high ppm concentration in the Ni3Fe catalyst through Inductively Coupled Plasma Optical Emission Spectroscopy (ICP−OES) analysis. This work presents the strategy and design of a next‐generation electrochemical catalyst to improve the electrocatalytic properties and stability.
Forming N‐doped carbon shells on the catalyst surface is a promising method to improve the stability of electrochemical catalysts. Additionally, the carbon shell suppresses the phase change of the transition metal catalyst, significantly reducing the amount of catalyst dissolved in the electrolyte. This study demonstrates the role of the carbon shell as a strategy to maintain durability and catalytic properties.
Compared to nanostructured platinum (Pt) catalysts, ordered Pt-based intermetallic nanoparticles supported on a carbon substrate exhibit much enhanced catalytic performance, especially in fuel cell ...electrocatalysis. However, direct synthesis of homogeneous intermetallic alloy nanocatalysts on carbonaceous supports with high loading is still challenging. Herein, we report a novel synthetic strategy to directly produce highly dispersed MPt alloy nanoparticles (M = Fe, Co, or Ni) on various carbon supports with high catalyst loading. Importantly, a unique bimetallic compound, composed of M(bpy)32+ cation (bpy = 2,2′-bipyridine) and PtCl62– anion, evenly decomposes on carbon surface and forms uniformly sized intermetallic nanoparticles with a nitrogen-doped carbon protection layer. The excellent oxygen reduction reaction (ORR) activity and stability of the representative reduced graphene oxide (rGO)-supported L10-FePt catalyst (37 wt %-FePt/rGO), exhibiting 18.8 times higher specific activity than commercial Pt/C catalyst without degradation over 20 000 cycles, well demonstrate the effectiveness of our synthetic approach toward uniformly alloyed nanoparticles with high homogeneity.
Here, novel medium-entropy alloys with chemical compositions of Co17.5Cr12.5Fe55Ni10Mo4C1 and Co17.5Cr12.5Fe55Ni10Mo3C2 (at%) exhibiting excellent tensile properties at both room and liquid nitrogen ...temperatures have been developed. Precipitation of carbides changes the chemical composition and phase stability of the matrix, resulting in the controlled deformation-induced martensitic transformation from face-centered cubic to body-centered cubic of the alloys. The carbide precipitation, lattice distortion, and martensitic transformation led the alloy to have ultra-high yield strength of ~1 GPa and ultimate tensile strength of ~2 GPa with extra work hardening at liquid nitrogen temperature.
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Sarcopenia and adipopenia have prognostic significance in cancer. Analysis of a single abdominal computed tomography (CT) section at the third lumbar vertebra has been widely adopted for this ...purpose. The approach using a single section at the first lumbar vertebra level (L1) may extend clinical viability. We evaluated the prognostic value of sarcopenia and adipopenia assessed using a CT section at L1 in acute myeloid leukemia (AML). Data from 96 patients with available imaging were retrospectively reviewed. Patients with sarcopenia (37.5%) had significantly worse overall survival (OS) (median 17.8 months vs. not reached,
p
= 0.038) and treatment-related mortality (TRM) (22.2% vs. 3.0%,
p
= 0.0019) than those without. Subcutaneous adipopenia (51.0%) was significantly associated with inferior OS (median 17.9 months vs. not reached,
p
= 0.0011), progression-free survival (PFS) (median 6.2 months vs. not reached,
p
= 0.004), and TRM (16.3% vs. 4%,
p
= 0.024). Visceral adipopenia (30.2%) was associated with poor OS (12.7 vs. 31.7 months,
p
= 0.0055) and PFS (3.7 vs. 31.7 months,
p
= 0.003). Multivariable analyses found sarcopenia, subcutaneous adipopenia and visceral adipopenia were significant negative prognostic factors for OS. Sarcopenia and adipopenia assessed using a single CT section at the L1 level are useful in predicting the prognosis of AML.
Here, a new strategy for designing heterogeneous medium-entropy alloys with light-weight and excellent mechanical properties is proposed. Alx(CuFeMn)100-x (x = 0, 7.5, and 15 at%) alloys were ...developed by utilizing the immiscible nature of Cu–Fe alloys. The microstructures of the alloys show phase separation into Cu-rich and Fe-rich regions, and the addition of Al transforms the crystal structure from dual face-centered cubic to face-centered cubic and body-centered cubic. Phase separation of the microstructure into two domains enables further dissolution of Al into the matrix. The alloys exhibit high strength because of solid solution strengthening and hetero-deformation induced strengthening caused by heterogeneous microstructures. The presence of nano-scale twins and essential partially recrystallized microstructures also enhances the strength of the alloys. This new type of medium-entropy alloys is expected to expand the design window in physical metallurgy.
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