Unique Chiro-optical Properties of the Weakly-2D (R-/S-MBA)2CuBr4 Hybrid Material

We establish that the formally 0D (R-/S-MBA)2CuBr4, containing R-/S-α-methyl benzylamine (R-/S-MBA) connected to highly distorted CuBr4 tetrahedral units in alternating layers, possesses extraordinary chiro-optical properties. The concentration and path length-independent chiral anisotropy factor, gCD, for this compound is the highest in the orange-red part of the visible spectrum reported so far from any hybrid material, arising from a chirality transfer from the organic component to the inorganic layer through the extensive asymmetric hydrogen bonding network and electronic coupling, driving the CuBr4 tetrahedral units to follow the 21-screw axis. This sensitivity in the orange-red part of the visible spectrum is achieved by incorporating bromine in the copper coordination sphere, which significantly red-shifts the band edge absorption to ∼710 nm compared to ∼490 nm reported for the chloride analogue. DFT/TDDFT calculations allow us to understand the underlying electronic structure responsible for its remarkable optical properties. We find that this compound gets a partial 2D character, crucial for its broadband chiro-optical properties, arising from Cu-Br···Br-Cu interactions connecting the otherwise isolated CuBr4 units

A Novel and Sustainable Approach to Enhance the Li-Ion Storage Capability of Recycled Graphite Anode from Spent Lithium-Ion Batteries

The ubiquitous manufacturing of lithium-ion batteries (LIBs) due to high consumer demand produces inevitable e-waste that imposes severe environmental and resource sustainability challenges. In this work, the charge storage capability and Li-ion kinetics of the recovered water-leached graphite (WG) anode from spent LIBs are enhanced by using an optimized amount of recycled graphene nanoflakes (GNFs) as an additive. The WG@GNF anode exhibits an initial discharge capacity of 400 mAh g-1 at 0.5C with 88.5% capacity retention over 300 cycles. Besides, it delivers an average discharge capacity of 320 mAh g-1 at 500 mA g-1 over 1000 cycles, which is 1.5-2 times higher than that of WG. The sharp increase in electrochemical performance is due to the synergistic effects of Li-ion intercalation into the graphite layers and Li-ion adsorption into the surface functionalities of GNF. Density functional theory calculations reveal the role of functionalization behind the superior voltage profile of WG@GNF. Besides, the unique morphology of spherical graphite particles trapping into graphene nanoflakes provides mechanical stability over long-term cycling. This work explains an efficient strategy to upgrade the electrochemical compatibility of recovered graphite anode from spent LIBs toward next-generation high-energy-density LIBs

Phonon Analysis of 2D Organic‐Halide Perovskites in the Low‐ and Mid‐IR Region

Combining the characteristics of hybrid perovskites and layered materials, 2D Ruddlesden-Popper perovskites exhibit unique properties, some of which still require to be deeply understood. In this study, the vibrational signatures of such materials are analyzed by collecting experimental Raman spectra of four distinct compounds. Supported by density functional theory simulations, the role of the phenyl spacer single fluorination on the phonon modes of two similar yet different compounds, i.e., phenethylammonium lead iodide (PEAI) and 4-fluorophenethylammonium lead iodide (PEAI-F), is explained. In addition, this work analyzes some so-far unreported experimental Raman peaks in the 600-1100 cm(-1) range and discusses their origin in this class of 2D compounds. This work paves the way for a better design of novel compounds as well as for their exploitation in (opto)electronic applications

Microstructural and chemical changes after high temperature electrolysis in solid oxide electrolysis cell

Degradation of solid oxide electrolysis cell is probably the main problem in the field of high temperature steam electrolysis. In this study two anode-supported solid oxide fuel cells were tested as a solid oxide electrolysis cell operating from 875 degrees C to 950 degrees C at the applied voltage of 1.5 V and 1.7 V respectively. Microstructural and chemical changes of the cell components were studied by field emission scanning electron microscope (FESEM), and X-ray diffraction (XRD) analysis before and after the electrolysis. FESEM analysis shows a delamination of anode layer from the electrolyte. Furthermore, formation of impurities like yttrium silicate at the cathode-electrolyte interface and lanthanum zirconate (LZ) at the anode-electrolyte interface were observed after electrolysis. It also reveals that lanthanum zicronate is formed only at the interfaces between anode functional layer La0.65Sr0.3MnO3-delta (LSM)/8 mol% yttria stabilized zirconia (YSZ) and electrolyte layer (YSZ) but not at the whole anode layer. Formation of LZ is attributed to the high partial pressure of oxygen at the anode-electrolyte interface while yttrium silicate is formed due to the diffusion of silica from glass sealant into the cathode layer. (C) 2014 Elsevier B.V. All rights reserved

Synthesis and characterization of Ca doped LaMnO3 as potential anode material for solid oxide electrolysis cells

There is a need for investigating new electrode materials for solid oxide electrolysis cells (SOEC) as conventional electrodes for solid oxide fuel cells (SOFC) have some limitations when they are used in SOEC mode. Sr substituted LaMnO3 (LSM) is reported to have some demerits when it is used as an anode material in SOEC. With the intention of finding new anode material for SOEC, a series of materials, where Sr of LSM was either partially or fully substituted by Ca, were synthesized via combustion synthesis method. The synthesized material was found to be phase pure with orthorhombic symmetry. Thermal expansion coefficients (TEC) of all the samples were found to be in the range of 11–12×10−6 K−1. Electrical conductivity was found to increase with increasing Ca-content for the samples where Sr was fully replaced by Ca (LCM) but the same was found to decrease with increasing Ca-content for the partially Sr substituted samples (LSCM). The materials with either partial or total substitution of Sr by Ca were used as an anode material of a coupon cell and tested in SOEC mode. These anode materials were found to be better than LSM in terms of hydrogen production. Also, LCM and YSZ did not react with each other even after a prolonged annealing of 100 h at 1000 °C

Function of Defects in NH2-MIL-125@PANI@Co3O4 Photocatalyst for Efficient Hydrogen Evolution

Defect engineering using surface linkage modification is an efficient method to tailor solar-to-chemical energy conversion performance of a metal-organic framework (MOF), albeit the nature and impact of the defects remain unexplored. The present study explored that the alteration of electronic and morphological properties due to linkage modification augments the intrinsic charge transfer in MOF but is not reflected in the overall hydrogen production activity when integrated with a cocatalyst. This is illustrated with the simply prepared judicious bulk heterostructure between defect-regulated NH2-MIL-125 and Co3O4. The study further demonstrates that the subtle use of the photosensitizer can multi-fold improve the activity while anchored onto a semiconductor surface. Several analytical methods including X-ray absorption spectroscopy revealed the unique anchoring of Co3O4 on the MOF surface that pertains to its catalytic activity. The composite Co3O4@PANI@NH2-MIL-125, without defects, showed significant spatial separation of the excited-state charge carriers thereby improving the rate of H2 evolution reaction (∼1208 μmol h-1 g-1), with apparent quantum yield of ∼3% under simulated visible-light irradiation. The separation of photogenerated charge carriers at the MOF/cocatalyst interface was unequivocally confirmed by the time-dependent emission spectra and steady-state electrochemical measurements. The photocatalytic activity is correlated with the compatible charge transfer kinetics and density functional theory calculation on the Co3O4@NH2-MIL-125 heterostructure. Further, femtosecond transient absorption spectroscopy studies revealed the initial photoexcited charge transfer from polyaniline (PANI) to hybrid PANI@NH2-MIL-125, which favorably occurs in picoseconds time scale to boost the photocatalytic activity of the system. This investigation will bestow a beneficial blueprint for structural design on MOF to precisely manipulate cocatalyst morphology and structural positions for developing an efficient photocatalyst. © 2022 American Chemical Society

Graphene-like Carbon–Nitride Monolayer: A Potential Anode Material for Na- and K‑Ion Batteries

Presently, great attention is being directed toward the development of promising electrode materials for non-lithium rechargeable batteries which have the advantages of low cost, high energy storage density, and high rate capacity for substantial renewable energy applications. In this study, we have predicted that the C₃N monolayer is a potential electrode material for Na- and K-ion batteries by first-principle calculations. The diffusion barriers are calculated to be as small as 0.03 eV for Na and 0.07 eV for K, which could lead to a very fast diffusion on the C₃N monolayer surface, implying high mobility and cycle stability for batteries. The C₃N monolayer is predicted to allow a high storage capacity of 1072 mAh/g by the inclusion of multilayer adsorption with an average voltage of 0.13 V for Na₂C₃N and 0.26 V for K₂C₃N systems, which is more promising than previously studied anode materials. All of these results ensure that the C₃N monolayer could serve as an excellent anode material for Na- and K-ion batteries

Multilayered Platinum Nanotube for Oxygen Reduction in a Fuel Cell Cathode: Origin of Activity and Product Selectivity

The practical usages of proton exchange membrane fuel cells from the economical perspective is closely related to the development of catalysts with reduced platinum loading for improved oxygen reduction reaction (ORR) activity. For this, a multilayered platinum nanotube enclosed by (111) and (100) facets has been modeled and studied for ORR activity using the density functional theory calculations. The stability of the nanotube is verified through energetic, thermal, and dynamic stability calculations. Activation barrier analysis shows that the rate-determining steps (O₂ dissociation and OH formation) are highly improved over the nanotube surface. We find that four-electron reduction pathway (for H₂O formation) is favored over two-electron reduction (for H₂O₂ formation) for the nanotube catalyst, which ensures excellent product selectivity (H₂O vs H₂O₂). The excellent catalytic activity and product selectivity of the nanotube can be attributed toward the favorable adsorption energies of ORR intermediates, as the adsorption energies of key ORR intermediates are reported to be excellent descriptors for ORR activity. Therefore, the platinum nanotube can be a potential electrode material for fuel cell and other related applications