A sol-gel electrode containing the ruthenium complex Na₃[Ru₂(μ-CO₃)₄] is used as a stable working electrode in OER while showcasing the cathodic shift and the relatively increased current in the presence of NaHCO₃.

Abstract

The Na₃[Ru₂(μ-CO₃)₄] complex is acting as a water oxidation catalyst in a homogeneous system. Due to the significance of heterogeneous systems and the effect of bicarbonate on the kinetic, we studied the bicarbonate effect on the heterogeneous electrocatalyst by entrapping the Na₃[Ru₂(μ-CO₃)₄] complex in a sol-gel matrix. We have developed two types of sol-gel electrodes, which differ by the precursor, and are demonstrating their stability over a minimum of 200 electrochemical cycles. The pH increases affected the currents and k_cat for both types of electrodes, and their hydrophobicity, which was obtained from the precursor type, influenced the electrocatalytic process rate.

The results indicate that NaHCO₃ has an important role in the catalytic activity of the presented heterogeneous systems; without NaHCO₃, the diffusing species is probably OH⁻, which undergoes diffusion via the Grotthuss mechanism.

To the best of our knowledge, this is the first study to present a simple and fast one-step entrapment process for the Na₃[Ru₂(μ-CO₃)₄] complex by the sol-gel method under standard laboratory conditions. The results contribute to optimizing the WSP, ultimately helping expand the usage of hydrogen as a green and more readily available energy source.

The two-dimensional carbon sulfide, named subunene, is primarily designed using the experimentally synthesized sulflower molecule. It exhibits a dynamical, thermal, and mechanical stability with negative Poisson's ratio. Subunene furnishes linear band dispersion, Dirac cones, degenerate massless Dirac fermions and massive fermions in the electronic band spectrum.

Abstract

In the present study, a novel and unconventional two-dimensional (2D) material with Dirac electronic features has been designed using sulflower with the help of density functional theory methods and first principles calculations. This 2D material comprises of hetero atoms (C, S) and belongs to the tetragonal lattice with P₄/nmm space group. Scrutiny of the results show that the 2D nanosheet exhibits a nanoporous wave-like geometrical structure. Quantum molecular dynamics simulations and phonon mode analysis emphasize the dynamical and thermal stability. The novel 2D nanosheet is an auxetic material with an anisotropy in the in-plane mechanical properties. Both composition and geometrical features are completely different from the conditions necessary for the formation of Dirac cones in graphene. However, the presence of semi-metallic nature, linear band dispersion relation, massive fermions and massless Dirac fermions are observed in the novel 2D nanosheet. The massless Dirac fermions exhibit highly isotropic Fermi velocities (v_f=0.68×10⁶ m/s) along all crystallographic directions. The zero-band gap semi metallic features of the novel 2D nanosheet are perturbative to the electric field and external strain.

Organic materials with Inverted Singlet-Triplet (INVEST) gaps are interesting for their potential use as photocatalytic small molecule transformations, like the entirely solar-driven water splitting reaction. However, only few INVEST emitters are thermodynamically able to split water, with first singlet excited states, S1, above 1.27 or 1.76 eV; and absorbing near solar maximum, 2.57 eV. These requirements and the INVEST character are key for achieving long-lived photocatalyst for water splitting. The only known INVEST emitters that conform to these criteria are large triangular boron carbon nitrides, with unknown synthesis pathways. With quantum-mechanical calculations using ADC(2), we describe three triangulenes. 3a is a cyano azacyclopenta[cd]phenalene derivative while 3b and 3c are cycl[3.3.3]azine derivatives. 3b has a previously undescribed disulfide bridge. Overall 3a fulfills requirements for photocatalytic four-electron reduction of water while the S1 states of 3b and 3c are likely slightly low for the two-electron reduction process. By analyzing impacts of ligands, we find that there are guidelines describing how S1-S5 energies and oscillator strengths, T1 energies and ΔES1T1 gaps are affected, requiring deep-learning algorithms for which studies will be presented by us in due time. The impact of solvation effects as well as reduced-cost ADC(2) algorithms on our findings are discussed.

Molecular imaging is the future of personalized medicine; however, it requires effective contrast agents. Hyperpolarized chemical exchange saturation transfer (HyperCEST) can boost the signal of Hyperpolarized 129Xe MRI and render it a molecular imaging modality of high efficiency. Cucurbit[6]uril (CB6) has been successfully employed in vivo as a contrast agent for HyperCEST MRI, however its performance in a clinical MRI scanner has yet to be optimized. In this study, MRI pulse sequence parameter optimization was first performed in CB6 solutions in phosphate-buffered saline (PBS), and subsequently in whole sterile citrated bovine blood. The performance of four different depolarization pulse shapes (sinusoidal, 3-lobe sinc (3LS), rectangular (block), and hyperbolic secant (hypsec) was optimized. The detectability limits of CB6 in a clinical 3.0T MRI scanner was assessed using the optimized pulse sequences. The 3LS depolarization pulses performed best, and demonstrated 24% depletion in a 25µM solution of CB6 in PBS. It performed similarly in blood. The CB6 detectability limit was found to be 100µM in citrated bovine blood with a correspondent HyperCEST depletion of 30% ± 9%. For the first time, the HP 129Xe HyperCEST effect was observed in red blood cells (RBC) and had a similar strength as HyperCEST in plasma.

Analytical methods for diagnosing the deterioration of waste batteries are reported. More specifically, the study focuses on: (1) trend analysis based on eleven key performance indicators as a method of deterioration diagnosis by fitting fifth-degree polynomial curves, and (2) comparison analysis of the second derivatives of open circuit voltage, V′′ _ocv,t and simulated open circuit, voltage V′′ _ocv,t,sim using a concept of model-in-the-loop simulation to verify the effectiveness of the former.

Abstract

We defined four major deterioration factors (electrolyte loss (EL), lithium loss (LL), lithium precipitation (LP), and compound deterioration (CD)). Then, we derived eleven key performance indicators (KPIs) for comparative analysis. After that, we fabricated three deteriorated cells for each of three deterioration factors (EL, LL, and LP) and one cell with CD (for verification) with four individual (dis)charging experiment manuals. The two major contributions of this study are the performance of 1) trend analysis to determine a suitable diagnostic metric by inspecting the eleven KPIs and 2) comparison analysis of and to verify the effectiveness of utilizing as a real-time deterioration diagnostic factor using a concept of model-in-the-loop simulation. The results show that 1) has the most conspicuous trendline tendency among the eleven comparison targets for all four major deterioration factors, and 2) the angle difference between the two trends of and lies within a minimum of 9° and a maximum of 43° (with a sscale on the x-axis and a scale on the y-axis for a clear trend line analysis). From this, we can conclude that the trendline-based real-time deterioration analysis employing may be practically applicable to a limited extent.

Fluorination of TCNQ tunes the redox potential and can alter catalytic mechanisms. Accordingly, TCNQF₄ ¹⁻ and TCNQF₂ ¹⁻ can act as catalysts for the ferrocyanide-thiosulfate reaction via the same mechanism, which differs from that found for TCNQ. CuTCNQF_n (n=0, 4) coordination polymers have sufficient solubility in water to act as catalysts via homogeneous pathways. This study challenges perceptions of insolubility being correlated with heterogeneous pathways.

Abstract

Mechanistic variation in catalysis through substituent-based redox tuning is well established. Fluorination of TCNQ (TCNQ=tetracyanoquinodimethane) provides ~850 mV variation in the redox potentials of the and (n=0, 2, 4) processes. With , catalysis of the kinetically very slow ferrocyanide-thiosulfate redox reaction in aqueous solution occurs via a mechanism in which the catalyst is reduced to when reacting with which is oxidised to . Subsequently, reacts with to form and reform the catalyst, in another thermodynamically favoured process. An analogous mechanism applies with as a catalyst. In contrast, since the reaction of with is thermodynamically unfavourable, an alternative mechanism is required to explain the catalytic activity observed in this non-fluorinated system. Here, upon addition of , reduction of to occurs with concomitant oxidation of to , which then acts as the catalyst for oxidation. Thermodynamic data explain the observed differences in the catalytic mechanisms. (n=0, 4) also act as catalysts for the ferricyanide-thiosulfate reaction in aqueous solution. The present study shows that homogeneous pathways are available following addition of these dissolved materials. Previously, these (n=0, 4) coordination polymers have been regarded as insoluble in water and proposed as heterogeneous catalysts for the ferricyanide-thiosulfate reaction. Details and mechanistic differences were established using UV-visible spectrophotometry and cyclic voltammetry.

The resistive switching behaviour of Cu₂ZnSnS₄ material on ITO substrate with three different top electrodes (Cu, Ag, and Al) and work function is demonstrated. The Ag top electrode-based resistive random-access memory device shows more stable resistive switching than the ones with Cu and Al top electrode.

Abstract

Cu₂ZnSnS₄ (CZTS) active material-based resistive random-access memory (RRAM) devices are investigated to understand the impact of three different Cu, Ag, and Al top electrodes. The dual resistance switching (RS) behaviour of spin coated CZTS on ITO/Glass is investigated up to 10² cycles. The stability of all the devices (Cu/CZTS/ITO, Ag/CZTS/ITO, and Al/CZTS/ITO) is investigated up to 10³ sec in low- (LRS) and high- (HRS) resistance states at 0.2 V read voltage. The endurance up to 10² cycles with 30 msec switching width shows stable write and erase current. Weibull cumulative distribution plots suggest that Ag top electrode is relatively more stable for set and reset state with 33.61 and 25.02 shape factors, respectively. The charge carrier transportation is explained by double logarithmic plots, Schottky emission plots, and band diagrams, substantiating that at lower applied electric field intrinsic copper ions dominate in Cu/CZTS/ITO, whereas, at higher electric filed, top electrodes (Cu and Ag) dominate over intrinsic copper ions. Intrinsic Cu⁺ in CZTS plays a decisive role in resistive switching with Al electrode. Further, the impedance spectroscopy measurements suggest that Cu⁺ and Ag⁺ diffusion is the main source for the resistive switching with Cu and Ag electrodes.

A quantum dynamics approach that combines a Smolyak scheme and curvilinear coordinates is described. It is applied to the computation of malonaldehyde tunneling splitting in full dimensionality.

Abstract

In 1963 Smolyak introduced an approach to overcome the exponential scaling with respect to the number of variables of the direct product size [S. A. Smolyak Soviet Mathematics Doklady, 4, 240 (1963)]. The main idea is to replace a single large direct product by a sum of selected small direct products. It was first used in quantum dynamics in 2009 by Avila and Carrington [G. Avila and T. Carrington, J. Chem. Phys., 131, 174103 (2009)]. Since then, several calculations have been published by Avila and Carrington and by other groups. In the present study, and to push the limit to larger and more complex systems, this scheme is combined with the use of an on-the-fly calculation of the kinetic energy operator and a Block-Davidson procedure to obtain eigenstates in our home-made Fortran codes, ElVibRot and Tnum-Tana. This was applied to compute the tunneling splitting of malonaldehyde in full dimensionality (21D) using the potential of Mizukami et al. [W. Mizukami, S. Habershon, and D.P. Tew, J. Chem. Phys. 141, 1443–10 (2014)]. Our tunneling splitting calculations, 21.7±0.3 cm⁻¹ and 2.9±0.1 cm⁻¹, show excellent agreement with the experimental values, 21.6 cm⁻¹ and 2.9 cm⁻¹ for the normal isotopologue and the mono-deuterated one, respectively.

In this investigation the dynamics of two types of bitumens with different penetration grade were tested by using dynamic shear rheometry (DSR) and Nuclear Magnetic Resonance (NMR) at unaged conditions, and upon both short- and long-term artificial aging. The gel-sol transition temperature  was found to increase with increasing the time of aging treatment. Arrhenius parameters of the viscosity were found, unexpectedly, to be correlated with those of simple liquids, suggesting that the two kinds of systems, although chemically and physically quite different, share the same basic process at the molecular level. The molecular dynamics has been then investigated by NMR Pulsed Field Gradient Stimulated-Echo (PFGSE) and relaxometry (Carr-Purcell-Meiboom-Gill, CPMG, spin-echo pulse sequence) to capture the effect of aging upon dynamics variables such as self-diffusion coefficients D and transverse relaxation times T2. The translational diffusion at T >  of the light molecular components of both types of bitumens was characterized by broad distributions of D which were found independent of the experimental time scale up to 0.2 s. Similarly, T2 data could be described as a continuous unimodal distributions of relaxation times determined both at T <  and T > .

Post-synthetic modification (PSM) with imidazole makes UiO-66-NH₂ metal-organic framework (MOF) luminescent. This enables it to detect health-hazardous pollutants such as acetone, aq. Fe³⁺, and aq. CO₃ ²⁻ by luminescence ON/OFF. This PSM MOF exhibits the highest sensitivity for pollutants among other no rare-earth element MOFs reported thus far in the literature.

Abstract

UiO-66-NH₂-IM, a fluorescent metal-organic framework (MOF), was synthesized by post-synthetic modification of UiO-66-NH₂ with 2-imidazole carboxaldehyde via a Schiff base reaction. It was examined using various characterization techniques (PXRD, FTIR, NMR, SEM, TGA, UV-Vis DRS, and photoluminescence spectroscopy). The emissive feature of UiO-66-NH₂-IM was utilized to detect volatile organic compounds (VOCs), metal ions, and anions, such as acetone, Fe³⁺, and carbonate (CO₃ ²⁻). Acetone turns off the high luminescence of UiO-66-NH₂-IM in DMSO, with the limit of detection (LOD) being 3.6 ppm. Similarly, Fe³⁺ in an aqueous medium is detected at LOD=0.67 μM (0.04 ppm) via quenching. On the contrary, CO₃ ²⁻ in an aqueous medium significantly enhances the luminescence of UiO-66-NH₂-IM, which is detected with extremely high sensitivity (LOD=1.16 μM, i. e., 0.07 ppm). Large Stern-Volmer constant, K_sv, and low LOD values indicate excellent sensitivity of the post-synthetic MOF. Experimental data supported by density functional theory (DFT) calculations discern photo-induced electron transfer (PET), resonance energy transfer (RET), inner filter effect (IFE), or proton abstraction as putative sensing mechanisms. NMR and computational studies propose a proton abstraction mechanism for luminescence enhancement with CO₃ ²⁻. Moreover, the optical behavior of the post-synthetic material toward analytes is recyclable.