CuInS2 Nanosheet Arrays with a MoS2 Heterojunction as a Photocathode for PEC Water Splitting

Developing cost-effective noble metal-free co-catalysts as alternatives to platinum group metals is an impeccable strategy to enhance photoelectrochemical (PEC) water splitting. In this report, we successfully fabricated CuInS2 nanosheet array-based photocathode modified with CdS and co-catalyst MoS2 in a green approach to improve water splitting under solar irradiation. The visible light absorption of the modified hybrid photocathode (CIS/CdS/MoS2) was significantly enhanced due to introducing CdS and MoS2. Photoluminescence, impedance spectroscopy, and Mott-Schottky analysis depicted improved separation of excited electron-hole pairs, minimized resistance of charge transfer, and increased excited-state charge carrier concentration, resulting in increased photocurrent. Typical results indicated that composite photoelectrodes delivered higher photocurrent (−1.75 mA/cm2 at 0 V vs RHE) and HC-STH conversion efficiency (0.42% at 0.49 V vs RHE) than those of CIS and CIS/CdS photoelectrodes. This improved PEC performance is accredited to the synergetic impact of CdS in charge generation and transfer and MoS2 as a cocatalyst with active surface sites for proton reduction. This study not only reveals the promising nature of CuInS2-based light absorber photocathodes for solar energy utilization but also recommends the use of MoS2 as a cocatalyst for the proton reduction reactions for widespread applications in solar to hydrogen conversion

Nanostructured Silicon–Carbon 3D Electrode Architectures for High-Performance Lithium-Ion Batteries

Silicon is an attractive anode material for lithium-ion batteries. However, silicon anodes have the issue of volume change, which causes pulverization and subsequently rapid capacity fade. Herein, we report organic binder and conducting diluent-free silicon–carbon 3D electrodes as anodes for lithium-ion batteries, where we replace the conventional copper (Cu) foil current collector with highly conductive carbon fibers (CFs) of 5–10 μm in diameter. We demonstrate here the petroleum pitch (P-pitch) which adequately coat between the CFs and Si-nanoparticles (NPs) between 700 and 1000 °C under argon atmosphere and forms uniform continuous layer of 6–14 nm thick coating along the exterior surfaces of Si-NPs and 3D CFs. The electrodes fabricate at 1000 °C deliver capacities in excess of 2000 mA h g–1 at C/10 and about 1000 mA h g–1 at 5 C rate for 250 cycles in half-cell configuration. Synergistic effect of carbon coating and 3D CF electrode architecture at 1000 °C improve the efficiency of the Si–C composite during long cycling. Full cells using Si–carbon composite electrode and Li1.2Ni0.15Mn0.55Co0.1O2-based cathode show high open-circuit voltage of >4 V and energy density of >500 W h kg–1. Replacement of organic binder and copper current collector by high-temperature binder P-pitch and CFs further enhances energy density per unit area of the electrode. It is believed that the study will open a new realm of possibility for the development of Li-ion cell having almost double the energy density of currently available Li-ion batteries that is suitable for electric vehicles

Corrosion behaviour of Nano-lamellar AlCrCoFeNi2.1 Eutectic High Entropy Alloy

High entropy alloys (HEAs) are an emerging class of alloys which have received massive research attention due to their excellent mechanical properties and are prime candidates for advanced structural applications. As a result, research in the field of HEAs has primarily focused on improving the mechanical and structural properties, while the electrochemical corrosion behaviour has seldom been studied. Recent developments in the area of HEAs has been the emergence of Eutectic High Entropy Alloys (EHEAs) (such as AlCoCrFeNi2.1) primarily developed to achieve a combination of high strength and ductility. Recent studies have shown that through a special thermomechanical processing route of cryo-rolling and annealing, AlCoCrFeNi2.1 achieves an extraordinary combination of strength and ductility and thus has a huge potential for commercialization. Nevertheless, for a commercial alloy, it is essential to have an in-depth understanding of the corrosion and degradation behaviour. Moreover, the nano-lamellar morphology makes this system highly prone to a localized corrosion attack. This study investigates the corrosion behaviour of AlCoCrFeNi2.1 EHEAs using immersion tests, electrochemical methods and a correlation between the microstructure and corrosion properties is carried out through scanning electron microscopy. From these studies, it is observed that the corrosion rate from immersion tests as well as electrochemical tests is of the order of 0.02 mm/y, which is considered as acceptable corrosion rate for metallic alloys. However, the microscopic investigations show that these alloys are prone to localized attack. Although this alloy tends to passivate, the passive layer on prolonged exposure to NaCl solution (over 15 days) is not adherent. Through polarisation experiments, the corrosion potential, corrosion current, passivation potential and passive layer resistance were determined and corresponding SEM-EDS analysis has been carried out. From the compositional analysis using EDS, it is observed that there is a preferential dissolution of Al over other alloying elements. In short, although AlCoCrFeNi2.1 EHEA shows a relatively low rate of dissolution/corrosion, it is prone to localized corrosion attack. Further research should focus on improving the resistance against localized corrosion using alloy and microstructural design pathways

Carbon soot nanoparticles derived from wasted rubber: An additive in lubricating oil for efficient friction and wear reduction

Spheroidal carbon particles are touted as excellent additives in lubricants for reduction in friction and wear. Herein 50–100 nm-sized spheroidal carbon soot particles with heliocentric graphitic layers are prepared by controlled decomposition of wasted rubber and subsequent heat-treatment of wasted rubber derived soot. Thermogravimetric analysis showed that the on-set degradation temperature of the soot particles was representative of a material constituted by amorphous and crystalline phases complementing well with x-ray diffraction studies. The soot particles are dispersed in an additive-free base oil (BO), and the soot particles added oil was used as a lubricant. At room temperature, a reduction in coefficient of friction (CoF) and wear scar diameter (WSD) of ~9% and 16.55% were recorded. At a higher temperature of 70 °C, a reduction in CoF and WSD of as high as 48.93% and 28.12% were recorded. Based on the observations, it is theorized that the soot particles acted like nano-bearings between the contacting surfaces producing a rolling effect that efficiently reduced friction and wear concerning the contacting surfaces. Also, the dispersion of soot particles improved the viscosity retention of BO at higher temperatures indicating its multifunctional ability. © 202

Development of ultrafine grained cobalt-free AlCrFe2Ni2 high entropy alloy with superior mechanical properties by thermo-mechanical processing

The microstructure and properties of cobalt-free cost-effective AlCrFe2Ni2 high entropy alloy (HEA) in the as-cast condition and after thermo-mechanical processing by severe cold-rolling and annealing were investigated in the present work. The as-cast HEA showed a heterogeneous microstructure consisting of relatively coarse lamellar and much finer intertwined regions. The coarse regions consisted of eutectic mixture of FCC and ordered B2 (along with minor BCC) phases. The FCC phase was enriched in Fe and Cr, while the B2 phase was found enriched in Ni and Al but depleted in Cr. The BCC/B2 phase in the as-cast material showed phase separation due to spinodal decomposition to two different B2 phases in the fine regions. The overall FCC phase and BCC/B2 phase fractions were ∼60% and 40%, respectively. Despite the complex microstructure, the presence of a high fraction of the ductile FCC phase rendered remarkable workability, allowing heavy cold-rolling up to 90% reduction in thickness. Heavy deformation resulted in the development of intriguing microstructural features such as folding and bending of the lamellae, local shearing, and finally, deformation-induced nanocrystallization of the FCC phase. However, the B2 phase retained the ordered structure even after 90% cold-rolling. Annealing at 800 °C resulted in the formation of an ultrafine microduplex structure with significant resistance to grain growth even up to an annealing temperature of 1200 °C. A high yield (∼880 MPa) and tensile strength (̴ 1100 MPa) coupled with appreciable elongation (∼10%) could be achieved after annealing at 800 °C. The tensile properties obtained were superior to the other cobalt-free HEAs, which indicate the promising application of the cobalt-free cost-effective AlCrFe2Ni2 HEA as an advanced structural material. © 2021 Elsevier B.V

Synthesis, characterization, and electronic structure of SrBi2S4

Black-colored crystals and a pure polycrystalline phase of SrBi2S4 were synthesized using the high-temperature sealed tube method. A single-crystal and powder X-ray diffraction studies established the crystal structure and phase purity of SrBi2S4, respectively. It crystallizes in the hexagonal C6h2 −P63/m (176) space group with lattice parameters of a ​= ​b ​= ​24.9335(6) Å and c ​= ​4.0946(1) Å. The structure is made up of three-dimensional 3∞ [Bi2S4]4− anionic framework with one-dimensional tunnels which are occupied by Sr atoms. The optical bandgap and temperature-dependent resistivity studies indicated semiconducting nature for polycrystalline SrBi2S4 in agreement with the theoretical DFT study. The thermal conductivity (κ) of a cold-pressed sintered disk of SrBi2S4 decreases on heating the sample. The κ values vary from ∼0.65 ​W/mK at 300 ​K to ∼0.55 ​W/mK at 773 ​K. The COHP analysis is performed to estimate the relative strength of chemical bonding between Bi–S and Sr–S pairs. © 2022 Elsevier Inc

Metal to insulator transition in Ba2Ge2Te5: Synthesis, crystal structure, resistivity, thermal conductivity, and electronic structure

A monophasic polycrystalline sample of Ba2Ge2Te5 has been synthesized for the first time using the sealed tube solid-state method. The Rietveld refinement of a polycrystalline Ba2Ge2Te5 and a single crystal X-ray diffraction study confirm that Ba2Ge2Te5 crystallizes in the orthorhombic polar C2v9-Pna21 space group. Each of the Ge atoms in the Ba2Ge2Te5 structure is covalently connected to one Ge and three Te atoms making one-dimensional (1D) chains of 1∞[Ge2Te5]4− that are separated by Ba2+ cations. The (Ba2+)2(Ge3+)2(Te2−)5 can be charge-balanced as per the Zintl-Klemm concept. A resistivity study of Ba2Ge2Te5 shows a metallic behavior till 18 K below which metal to insulator transition was observed. Thermal conductivity of Ba2Ge2Te5 was found to decrease gradually on heating the sample with a minimum of about 0.41 Wm–1K–1 at 773 K. The DFT studies predict semiconducting nature for Ba2Ge2Te5 with a narrow indirect bandgap of about 0.6 eV. © 2021 Elsevier Lt

Chalcogen dependent metal vacancies and disorder in Ba2Ln1−Mn2−S5 and Ba2−Ln1−Mn2−Se5 (Ln = Pr, Nd, and Gd) structures

Single crystals of six new non-stoichiometric quaternary chalcogenides with a general formula Ba2−δLn1−xMn2−yQ5 (Ln = Pr, Nd, and Gd; Q = S and Se) have been synthesized by the molten flux method. Single crystal X-ray diffraction (SCXRD) studies show that these compounds are isostructural and crystallize in the monoclinic space group C2/m with two formula units. These structures show occupational disorder at the metal sites, and the SCXRD refined compositions of these compounds are Ba2Pr0.88(1)Mn1.79(1)S5, Ba2Nd0.83(1)Mn1.89(1)S5, Ba2Gd0.82(1)Mn1.77(1)S5, Ba1.86(1)Pr0.61(1)Mn1.88(1)Se5, Ba1.90(1)Nd0.57(1)Mn1.93(1)Se5, and Ba1.88(1)Gd0.56(1)Mn1.95(1)Se5. The sulfide structures have split positions for Mn atoms with the concomitant occupational disorder at the Pr and Mn sites. In contrast, the selenide structures do not exhibit split Mn sites. The Ba sites in these selenides also show occupational disorder along with partially occupied Ln and Mn sites. The crystal structures of the selenides are comprised of [2∞Ln1−xMn2−ySe5]n− layers separated by Ba2+ cations. The Ln atoms in these sulfides and selenides are octahedrally coordinated with six Q atoms, and each Mn atom is bonded with four Q atoms forming a distorted tetrahedral geometry. The charge balancing in these structures is difficult due to the metal vacancies. The optical absorption study on the polycrystalline Ba1.88Gd0.56Mn1.95Se5 sample reveals a direct bandgap of 1.73(2) eV in agreement with the reddish color of the sample. The density functional calculations are performed to study the atomic and electronic structures of Ba1.88(1)Gd0.56(1)Mn1.95(1)Se5. © 2022 Elsevier B.V

A new non-stoichiometric quaternary sulfide Ba3.14(4)Sn0.61(1)Bi2.39(1)S8: Synthesis, crystal structure, physical properties, and electronic structure

We report the syntheses of single crystals and polycrystalline phase of a new quaternary sulfide, Ba3.14(4)Sn0.61(1)Bi2.39(1)S8, by the high-temperature sealed tube method. A single-crystal X-ray diffraction study established that the title compound is non-stoichiometric and crystallizes in the orthorhombic D2h16-Pnma space group with cell parameters of a ​= ​12.4479(7) Å, b ​= ​4.3140(2) Å, c ​= ​28.7860(17) Å, and Z ​= ​4. The crystal structure is composed of infinite chains of ∞1[Sn(1)0.61Bi(1)0.39S3]2.39− and ∞1[Bi(2)Bi(3)S5]4− stripes, which are separated by Ba2+ cations. The optical absorption study of the polycrystalline Ba3.2Sn0.6Bi2.4S8 sample showed a direct bandgap of 1.4(1) eV, indicating the semiconducting nature. The thermal conductivity study showed that polycrystalline Ba3.2Sn0.6Bi2.4S8 has an extremely low thermal conductivity of ∼0.30 ​W/mK at 773 ​K. The first-principles theoretical studies of electronic structure and nature of chemical bonding in Ba3Sn0.62Bi2.38S8 are performed within the framework of DFT. © 2022 Elsevier Inc