CuO/CuBi2O4 heterojunction photocathode: High stability and current densities for solar water splitting

Global energy crisis escalates the emphasis on ways to find green and sustainable solutions. Photoelectrochemical (PEC) conversion is one of the key technologies to fulfill the energy demand by converting solar energy into chemical fuels. Binary copper oxides suffer from severe photocorrosion and ternary copper oxides such as copper bismuth oxide (CuBi2O4) exhibit poor charge separation and transfer. In this work, a composite consisting of CuO annealed at 450 °C and CBO electrodeposited for 5 min on top of it (CuO-450/CBO-5) showed the best performance with a positive shift of 0.2 V in onset potential, a high current density of −0.9 mA cm−2 at 0.1 V vs RHE and high stability over pure CuO. The systematic deposition of CBO on CuO leads to intimate contact between the two semiconductors wherein, CuO acts as a hole carrier and CBO accommodates the hydrogen evolution reaction (HER)

Nearly full-density pressureless sintering of AlCoCrFeNi-based high-entropy alloy powders

AlCoCrFeNi is among the promising high-entropy alloys (HEAs) that possess high strength with considerable ductility. Powder sintering is one of the competitive routes for the production of HEA powders. However, sintering of HEA powders under a pressureless condition is difficult. The present work aims to produce high-density components from mechanically alloyed AlCoCrFeNi HEA powders through the pressureless sintering method. Nearly full density was achieved at 1275 °C. Sintering was performed in the presence of a viscous phase in the temperature range of 1200–1250 °C, which was confirmed through differential scanning calorimetry and dilatometric measurements. This viscous phase was found have a Cr-rich composition, detected by interrupting the sintering and quenching of the sample. The powder initially contained the BCC phase with a small fraction of FCC and other phases. During sintering, a significant fraction of the FCC phase and nanosized B2 phase were formed. Sintered sample had a hardness of 679 ± 20 Hv

Heterogeneous interface-induced electrocatalytic efficiency boosting of bimetallic Cu/Zn selenides for stable water oxidation and oxygen reduction reactions

An increased emphasis on alternative energy technologies paves the way for the design and development of highly active, cost-effective electrocatalysts for application in water splitting and fuel cells. In lieu of this, we evaluated heterostructured copper selenide and zinc selenide enwrapped in carbon nanofibers (CZSe@C-450) as bifunctional electrocatalysts synthesized by electrospinning and selenization. CZSe@C-450 demonstrated superior electrochemical performance with a low overpotential of 260 mV at 10 mA cm(-2), high stability (1.2% loss in 12 hours and 9.9% loss in 50 hours) for oxygen evolution reaction, a half-wave potential (E-1/2) of 0.88 V, and high stability (14.35% loss in 50 hours) for oxygen reduction reaction. The enhanced performance is attributed to the formation of a heterogeneous phase boundary between copper selenide and zinc selenide, which increases both the built-in potential and local atomic disorder. The lattice mismatch/disorder reduces the surface energy and leads to the creation of an ample number of active sites that participate in both oxygen evolution and reduction reactions

Microstructure Dictates the Behavior of Plasmons in Nanostructured Ag-Cu Alloy Films

Surface plasmon (SP) resonances play a vital role in the efficient control of light-matter interaction at the nanoscale beyond the diffraction limit. Alloy plasmonics has opened new avenues for composition-dependent tuning of the plasmonic response. In this study, we demonstrate that phase separation in immiscible alloy systems can be used as an additional degree of freedom in conjunction with the composition to tune the plasmon behavior. The Ag-Cu alloy system is used as a model case to demonstrate the implications of phase separation and composition on both propagating and localized SPs. We use magnetron cosputtering to deposit a metastable FCC solid solution thin film with nanocrystalline grains. Subsequent annealing of the film at 400 °C leads to phase separation and grain growth. The annealed samples exhibit Ag-rich and Cu-rich phases with composition-dependent connectivity. Dispersion of propagating SPs in thin films shows a significant dependence on the composition and annealing conditions. Annealing of the alloy films leads to a strong decrease, by a factor of up to 20%, in the resonance widths of the propagating SPs which is due to a decrease in the imaginary part of the permittivity. Nanoapertures fabricated using focused ion beam (FIB) milling show strong scattering signatures for the metastable and annealed samples. Finally, we demonstrate the site-specific fabrication of nanoapertures in the Cu or Ag domains using ion-secondary electron imaging in FIB. The proposed approach for realizing complex bimetallic nanostructures can potentially be used for realizing multiplexed metasurfaces, active plasmonic platforms, plasmon enhanced catalysis, and site-specific multianalyte sensing. © 2022 American Chemical Society

Localized polymerization using single photon photoinitiators in two-photon process for fabricating subwavelength structures

Localized polymerization in subwavelength volumes using two photon dyes has now become a well established method for fabrication of nano structures. Unfortunately, the two photon absorption dyes used in such process are not only expensive but also proprietary. Lucirin TPO-L is an inexpensive, easily available single photon photoinitiator and has been used extensively for single photon absorption of UV light for polymerization. These polymerization volumes however are not localized and extend to micron size resolution having limited applications. We have exploited high quantum yield of radicals of Lucirin TPO-L for absorption of two photons to achieve localized polymerization in subwavelength volumes, much below the diffraction limit. Critical concentration (10 wt%) of Lucirin TPO-L in acrylate (Sartomer) was found optimal to achieve subwavelength localized polymerization and has been demonstrated by fabricating 2D/3D complex nanostructures and functional devices such as variable polymeric gratings using two photon processes. Systematic studies on influence of Lucirin TPO-L concentration on two photon polymerization of Sartomer show that resolution of the fabricated structures critically depends on loading of Lucirin TPO-L. This is expected to unleash the true potential of two photon polymerization for fabrication of complex polymeric nano devices at a larger scale. (C) 2017 Elsevier Ltd. All rights reserved

New insights on recovery and early recrystallization of ferrite-pearlite banded cold rolled high strength steels by high speed nanoindentation mapping

This work unravels structure-property correlations at the micrometer length scale during recovery and early recrystallization of a cold rolled high strength steel comprised of ferrite and pearlite. High resolution nano-indention mapping is used to measure the hardness of ferrite, pearlite and the transition zone between them, which correlates well with the local microstructure obtained from scanning and transmission electron microscopy. A clustering algorithm is used to determine the properties of the constituent microstructural features. The variation in the hardness of the phases with annealing temperature agrees well with the dislocation activity observed using Transmission Electron Microscopy (TEM) and a simple mechanism to reconcile the observations is presented. © 2020 Acta Materialia Inc

Insights on early recovery kinetics in ferrite - pearlite cold rolled high strength sheet steels

This study presents the results of temperature and composition dependent recovery behavior of ferrite-pearlite high strength steels. Annealing of cold rolled sheets at 300 °C with varying pearlite fractions results in an increase in hardness that scales with the pearlite content. In contrast, annealing at 500 °C results in a decrease in hardness, independent of pearlite content. By coupling complementary techniques such as high resolution nanoindentation mapping and electron microscopy (EBSD and TEM), microstructure-property correlations at the micrometer length scale are established to provide new insights on the driving force for temperature and composition dependent recovery kinetics. Simple recovery models are also discussed to complement the microstructural observations. Collectively, these results offer insights into the role of individual phases in the early recovery of ferrite-pearlite high strength steels that are critical for subsequent processing steps including inter-critical annealing. © 202

Extremely low thermal conductivity in BaSb2Se4: Synthesis, characterization, and DFT studies

We report the synthesis of black-colored crystals and a polycrystalline phase of BaSb2Se4 by high-temperature reaction of elements at 1173 ​K and 973 ​K, respectively. The X-ray diffraction studies show that it crystallizes in the monoclinic P21/c space group, and the structure is composed of one-dimensional stripes of ∞1[Sb2Se4]2− that are separated by the Ba2+ cations. The optical absorption study reveals the semiconducting nature (Eg ​= ​1.3(1) eV) of the polycrystalline BaSb2Se4 sample. A thermal conductivity (κ) study shows a gradual decrease of the κ-value from ∼0.39 ​W/mK to ∼0.29 ​W/mK on heating the polycrystalline sample from 300 ​K to 773 ​K. The DFT study of the electronic structure of BaSb2Se4 shows that the bandgap is indirect with a magnitude in the range of ∼1.0–1.6 ​eV depending on the choice of XC functional. The COHP analysis has been performed to investigate the relative strengths of chemical bonding between pertinent atoms in the BaSb2Se4 structure. © 2022 Elsevier Inc