Interatomic Spacing Research Articles

Molecular O2 Dimers and Lattice Instability in a Perovskite Electrocatalyst.

Structural degradation of oxide electrodes during the electrocatalytic oxygen evolution reaction (OER) is a major challenge in water electrolysis. Although the OER is known to induce changes in the surface layer, little is known about its effect on the bulk of the electrocatalyst and its overall phase stability. Here, we show that under OER conditions, a highly active SrCoO3-x electrocatalyst develops bulk lattice instability, which results in the formation of molecular O2 dimers inside the bulk and nanoscale amorphization induced via chemo-mechanical coupling. Using high-resolution resonant inelastic X-ray scattering and first-principles calculations, we unveil the potential-dependent evolution of lattice oxygen inside the perovskite and demonstrate that O2 dimers are stable in a densely packed crystal lattice, thus challenging the assumption that O2 dimers require sufficient interatomic spacing. We also show that the energy cost of local atomic rearrangements in SrCoO3-x becomes very low under the OER conditions, leading to an unusual amorphization under intercalation-induced stress. As a result, we propose that the amorphization energy can be calculated from the first principles and can be used to assess the stability of electrocatalysts. Our study demonstrates that extreme oxidation of electrocatalysts under OER can intrinsically destabilize the lattice and result in bulk anion redox and disorder, suggesting why some oxide materials are unstable and develop a thick amorphous layer under water electrolysis conditions.

Geometry of plastic deformation in metals as piecewise isometric transformations

Deformation mechanisms of crystalline solids has been the subject of research for more than two centuries. The theory of dislocations dominates modern views but still has significant gaps demanding the introduction of additional concepts for the coherent quantitative description of physical phenomena. In this work, we propose a coherent geometric description of motion and deformation in crystalline solids as piecewise isometric transformations (PWIT). The latter only includes operations that, similar to interatomic spacing in crystalline lattice, do not alter distances between reference points, i.e. translations, rotations and mirror reflections. The difference between solid-body translations and plastic deformations is that the isometric transformations have discontinuities that in real-life materials realise through dislocations (termination of shifts), disclinations (termination of rotations), and twins (mirror reflections). The conceptual description of plastic deformations as PWIT can be useful for the better description of physical phenomena, proposing new hypothesis, and for developing predictive analytical models. In this paper, the use of this conceptual description enables proposing new hypothesis about the nature of such interesting phenomena in severe plastic deformation as (i) stationary ‘solid state turbulence’ stage in high pressure torsion, and (ii) rate of mass transfer (mechanically assisted diffusion) in simple-shear deformation.

Analysis of The Crystalline Phases of The Mineral Rutan By Means of The X-Ray Diffraction Technique

Objective: This work aims to analyze a sample of the mineral Rutana, composed of two crystalline phases of titanium dioxide (TiO2): rutile and anatase, using the X-ray diffraction technique. Theoretical reference: In 1914, the German physicist Max von Laue, using a CaSO4 crystal, successfully achieved the diffraction of X-rays. Crystalline solids, such as CaSO4, consist of regular arrangements of atoms with interatomic spacings of the order of 0.1 -1.0Å, that is, with the same order of magnitude as the wavelength of X-rays. Due to the periodic nature of the internal structure of the crystals, it was possible for them to act as a three-dimensional diffraction grating, providing science with a new method for indirect investigation of the internal structure of materials: the X-ray diffraction (XRD) technique. Methodology: In this technique, a finely ground crystalline powder of a material is placed in the path of a monochromatic x-ray beam. This material, composed of a large number of small crystallites, are randomly oriented. Diffraction occurs from planes of the crystallites that are oriented at the correct angle to fulfill the Bragg condition, in such a way that localized peaks of the same intensity as the diffracted beams are formed. Results and discussion: Based on the intensity, angles and width of the diffraction peaks, the mass percentages of each of the mineral's crystalline phases were obtained: rutile (62.08%) and anatase (37.92%). Research Implications: This work presents a contribution to future research related to the chemical characterization of initially unknown samples, by providing a comprehensive and representative theoretical framework related to the XRD technique. Originality/value: This study presents practical contributions to the literature related to the application of the XRD technique in the characterization of materials.

Microstructural analysis and densification of ordinary Portland cement mortars incorporated with minimal nano-TiO2: intermixing and surface coating on both fresh and hardened surfaces

The present study investigated the microstructural properties of ordinary Portland cement (OPC)-modified with minimum dosage of nano TiO2 on fresh and hardened cement mortar surfaces and intermixed samples. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) were used to analyze the morphology and hydration products of the OPC specimens doped with nanotitanium (NT).Additionally, XRD coupled with Rietveld refinement was employed to quantify the crystal phases and refine the crystal structure model through the comparison of the calculated diffraction pattern to the measured pattern. Subsequently, crystallographic analysis was conducted to evaluate the crystallographic structure and to confirm the existence of specific atoms and bonds within the crystal structure altered with NT. The findings revealed that the addition of minimal NT resulted in a more compact and denser microstructure, characterized by increased formation of calcium silicate hydrate (CSH) gel and a reduction in calcium hydroxide (CH) crystals.This led to a reduction in the porosity of the hardened coating surface, with similar improvements observed for the fresh coating and intermixed samples compared to those of the control mortar. A decrease in the lattice parameters, accompanied by an increase in the number of atoms, bonds and polyhedra in the crystal structure, led to alterations in the interatomic spacing and contributed to the densification of the cementitious matrix.The findings also showed that NT integration led to a more compact structure with shorter bond distances and smaller polyhedral volumes for the Ti samples than for the control sample. Moreover, compared with the freshly cast and hardened coating samples, the NT-intermixed samples exhibited the shortest Ti–O bond distances and the smallest polyhedral volume. Overall, the analysis presented in this study significantly contributes to the development of novel and environmentally friendly photocatalytic cementitious materials at minimal dosages.

Poly (aniline-co-aniline-2,5-disulfonic acid) / L-ascorbic acid / Ag@SiO2 / polysafranin nanocomposite: synthesis, characterization and anomalous electrical behaviour.

We report the synthesis of sulfonated copolyaniline/polysafranin/L-ascorbic acid/Ag@SiO2 fine powdered nanocomposites and investigate the influence of incorporating the dye on their conductivity. The composite was characterized via IR, UV, cyclic voltammetry (CV), electric, dielectric, SEM, TEM, TGA and DSC measurements. Microscopy images revealed intensified spherical particles that were dispersed across the entire surface, and the SiO2/Ag particles were distributed on the surface. The XRD results exhibited peaks at many 2q values, and their interatomic spacing (d) and crystallite (grain) sizes were calculated. The thermal degradation curves exhibited an interesting model of stability. The cyclic voltammogram exhibited redox peaks identical to those of the reported analogues. The d.c. conductivity of the oligomer varied from 0.06 - 0.016 (s/cm), and that of the composite varied from 0.008 to 0.016 (s/cm). The material changed from a semiconductor to a metallic material. The observed conductivity is mainly attributed to self-doping between the sulfonate groups and the charged nitrogen atoms in the polymer chains. The frequency dependence of the permittivity, ε', showed a marked effect on the frequency window under consideration. The permittivity, ε', is independent of the increase in the frequency of the oligomer and the composite. This behavior supports the non-Debye dependency by confirming the occurrence of electrode polarization and space charge effects. In conclusion, the incorporation of safranin dye with a thermally stable, highly sulfonated polyaniline derivative/Ag@SO2 nanocomposite achieved improved conductivity after heating. The d.c. conductivities are comparable to those of many commercial inorganic or organic composites, and because of their attractive electrical properties, we suggest that these materials are promising for electronic field applications.

Excellent strength-toughness combination of NiAl–30Cr composites with novel in situ composite microstructure containing NiAl matrix and Cr single-phase

Lightweight NiAl alloys are expected to replace high-density nickel-based superalloys, but their mechanical performance needs to be improved. In this work, NiAl–30Cr composites with a novel heterogeneous microstructure composed of fine NiAl matrix and Cr single-phase was successfully prepared. Nanoscale Cr particles with 15 nm in size precipitated in NiAl matrix are coherent with NiAl matrix owing to very low interplanar and interatomic spacing mismatch. Such a composite microstructure makes NiAl–30Cr exhibit high strength and high toughness. The yield strength (1207 MPa), ultimate compressive strength (2307 MPa), product of strength and plasticity (29.3 GPa%), and fracture toughness (10.76 MPa m1/2) of NiAl–30Cr increased by 96.6%, 85.6%, 55.1% and 19.7% respectively at room temperature compared to the corresponding ones of NiAl. At 1000 °C, the yield strength (144 MPa) of NiAl–30Cr was 85.9% higher than that of NiAl. Solution strengthening and precipitation strengthening were the key strengthening mechanisms at room temperature. The enhancement in toughness was attributed to grain refinement, increased crack propagation paths, weakened Ni–Al covalent bonding and coordinated deformation of Cr single-phase and NiAl matrix. By contrast, the main strengthening mechanism at 1000 °C is the solid solution Cr atoms hindering dislocation climbing and the stable interface bonding between the Cr nanoprecipitation phase and the NiAl matrix. This work provides new ideas for preparing high-strength and tough NiAl alloy.

H* Species Regulation by Mn‐Co(OH)2 for Efficient Nitrate Electro‐reduction in Neutral Solution

AbstractDuring the electrocatalytic NO3− reduction reaction (NO3−RR) under neutral condition, the activation of H2O to generate H* and the inhibition of inter‐H* species binding, are critically important but remain challenging for suppressing the non‐desirable hydrogen evolution reaction (HER). Here, a Mn‐doped Co(OH)2 (named as Mn‐Co(OH)2) has been synthesized by in situ reconstruction in the electrolyte, which is able to dissociate H2O molecules but inhibits the binding of H* species between each other owing to the increased interatomic spacing by the Mn‐doping. The Mn‐Co(OH)2 electrocatalyst offers a faradaic efficiency (FE) of as high as 98.9±1.7% at −0.6 V vs. the reversible hydrogen electrode (RHE) and an energy efficiency (EE) of 49.90±1.03% for NH3 production by NO3−RR, which are among the highest of the recently reported state‐of‐the‐art catalysts in neutral electrolyte. Moreover, negligible degradation at −200 mA cm−2 has been found for at least 500 h, which is the longest catalytic durations ever reported. This work paves a novel approach for the design and synthesis of efficient NO3−RR electrocatalysts.

H* Species Regulation by Mn-Co(OH)2 for Efficient Nitrate Electro-reduction in Neutral Solution.

During the electrocatalytic NO3 - reduction reaction (NO3 - RR) under neutral condition, the activation of H2 O to generate H* and the inhibition of inter-H* species binding, are critically important but remain challenging for suppressing the non-desirable hydrogen evolution reaction (HER). Here, a Mn-doped Co(OH)2 (named as Mn-Co(OH)2 ) has been synthesized by in situ reconstruction in the electrolyte, which is able to dissociate H2 O molecules but inhibits the binding of H* species between each other owing to the increased interatomic spacing by the Mn-doping. The Mn-Co(OH)2 electrocatalyst offers a faradaic efficiency (FE) of as high as 98.9±1.7% at -0.6 V vs. the reversible hydrogen electrode (RHE) and an energy efficiency (EE) of 49.90±1.03% for NH3 production by NO3 - RR, which are among the highest of the recently reported state-of-the-art catalysts in neutral electrolyte. Moreover, negligible degradation at -200 mA cm-2 has been found for at least 500 h, which is the longest catalytic durations ever reported. This work paves a novel approach for the design and synthesis of efficient NO3 - RR electrocatalysts.

Enhancement of second-harmonic generation in a 64° stacked WSe2/WS2 heterobilayer with local strain

Transition metal dichalcogenides (TMDs) are actively studied in various fields of optics and optoelectronics, including nonlinear optics of second-harmonic generation (SHG). By stacking two different TMD materials to form a heterobilyaer, unique optical properties emerge, with stronger SHG at a twist angle of 0° between TMDs and weaker SHG at a twist angle of 60°. In this work, we demonstrate the enhancement of SHG in a heterobilayer consisting of WSe2 and WS2 monolayers stacked at a twist angle of 64.1°, using a nanoparticle to induce local strain. The interatomic spacing of the heterobilayer is deformed by the nanoparticle, breaking the inversion symmetry, resulting in a substantial increase in the SHG of the heterobilayer at room temperature. The SHG increases depending on the polarization of the pump laser: 15-fold for linear polarization, 9-fold for right-circular polarization, and up to 100-fold for left-circular polarization. In addition, the SHG enhanced in the heterobilayer with local strain satisfies the same chiral selection rule as in the unstrained TMD region, demonstrating that the chiral selection rule of SHG is insensitive to local strain. Our findings will increase the applicability of TMD heterobilayers in nonlinear optoelectronics and valleytronics.

Influence of Nickel Percentage on Lattice Structure and Mechanical Strength in Al‐Si Alloy

Aluminum alloys play a crucial role in various industrial applications due to their low weight and favorable mechanical properties. The specific mechanical properties of aluminum alloys can be tailored through alloying and heat treatment processes to meet the requirements of different applications. This study focused on investigating the impact of Ni addition at different concentrations (0, 0.01, 0.05, and 0.1 wt. %) on the microstructure and mechanical strength of Al‐Si alloy. The evaluation was performed using X‐ray diffraction (XRD) and Vickers hardness (HV) tests. XRD analyses revealed that the Al‐Si alloy consisted of α‐Al and Si phases. Upon the addition of Ni, an intermetallic compound (IMC), Al3Ni, was identified. The presence of this IMC leads to changes in the lattice constant and interatomic spacing (dhkl). Vickers hardness (HV) measurements were performed on the samples before and after sintering. The results indicated that the highest hardness value obtained was 93 HV for the sample containing 0.1 wt.% Ni after sintering, whereas the lowest hardness value was 56 Hv for the sample without any nickel content before sintering. This increase in hardness can be attributed to the elevated temperature, which facilitated greater diffusion of nickel atoms into the aluminum lattice.

Microstructure investigation of light weight Al/Si/Ni hypoeutectic material prepared by powder metallurgy method

In this study, the researchers examined the impact of adding different percentages of nickel (0 %, 0.01 %, 0.05 %, 0.1 wt%) to an aluminum-silicon (Al-Si) alloy. Aluminum alloys are widely used in various industries due to their lightweight nature and favorable mechanical properties. The microstructure of the alloy was analyzed using X-ray diffraction (XRD) and scanning electron microscope (SEM) tests.The XRD and SEM analyses revealed that the Al-Si alloy consisted of two phases: α-Al and Si. The introduction of nickel resulted in the detection of an intermetallic compound (IMC) known as Al3Ni. This IMC caused changes in the lattice constant and interatomic spacing (dhkl). The observed distortions and densification in the microstructure were identified as indicators of increased hardness and strength in the alloys. The researchers attribute this enhancement in microstructure properties to the elevated temperature, which facilitated greater diffusion of nickel atoms into the aluminum lattice.

CHARACTERIZATION OF NANO-DOPED LIQUID CRYSTALS BY X-RAY DIFFRACTION, SCANNING ELECTRON MICROSCOPE AND OPTICAL COLORIMETRY

In this paper, the self-assembling nature of nano-doped liquid crystals is characterized using different techniques. Liquid crystals, namely 4, n-alkoxybenzoic acid (nOBA, where n = 7,8), doped with magnetic nanoparticles (Fe3O4 of size 20nm) are considered for the present study. The structural and morphological properties of nano-doped liquid crystals are determined by the techniques of X-ray diffraction and Scanning Electron Microscopy. Morphological properties like grains, grain boundaries, and crystal defects are elucidated using the scanning electron microscope technique. Structural properties such as crystal structure, grain size, inter-atomic spacing, lattice constant, and dislocation density are determined using X-ray diffraction studies. The characteristics measured from the X-ray diffraction studies are correlated using the statistical analysis of Scanning electron microscope images. This is an objective analysis of X-ray diffraction studies. In addition to these techniques, colorimetric studies of optical anisotropic liquid crystals are carried out by measuring the chromaticity coordinates and color purity. This study utilizes the polarizing optical microscope technique. Furthermore, the influence of nano dopants on the characteristics of liquid crystals with carbon chain length is also discussed.

Boosting the Catalase-Like Activity of SAzymes via Facile Tuning of the Distances between Neighboring Atoms in Single-Iron Sites.

A nanozyme with neighboring single-iron sites (Fe2 -SAzyme) was introduced as a bioinspired catalase mimic, featuring excellent activity under varied conditions, twice as high as that of random Fe1 -SAzyme and ultrahigh H2 O2 affinity as that of bioenzymes. Surprisingly, the interatomic spacing tuning between adjacent iron sites also suppressed the competitive peroxidase pathway, remarkably increasing the catalase/peroxidase selectivity up to ~6 times compared to Fe1 -SAzyme. This dramatically switched the catalytic activity of Fe-SAzymes from generating (i.e. Fe1 -SAzymes, preferably mimicking peroxidase) to scavenging ROS (i.e. Fe2 -SAzymes, dominantly mimicking catalase). Theoretical and experimental investigations suggested that the pairwise single-iron sites may serve as a robust molecular tweezer to efficiently trap and decompose H2 O2 into O2 , via cooperative hydrogen-bonding induced end-bridge adsorption. The versatile mechano-assisted in situ MOF capsulation strategy enabled facile access to neighboring M2 -SAzyme (M=Fe, Ir, Pt), even up to a 1000 grams scale, but with no obvious scale-up effect for both structures and performances.

Boosting the Catalase‐Like Activity of SAzymes via Facile Tuning of the Distances between Neighboring Atoms in Single‐Iron Sites

AbstractA nanozyme with neighboring single‐iron sites (Fe2‐SAzyme) was introduced as a bioinspired catalase mimic, featuring excellent activity under varied conditions, twice as high as that of random Fe1‐SAzyme and ultrahigh H2O2 affinity as that of bioenzymes. Surprisingly, the interatomic spacing tuning between adjacent iron sites also suppressed the competitive peroxidase pathway, remarkably increasing the catalase/peroxidase selectivity up to ~6 times compared to Fe1‐SAzyme. This dramatically switched the catalytic activity of Fe‐SAzymes from generating (i.e. Fe1‐SAzymes, preferably mimicking peroxidase) to scavenging ROS (i.e. Fe2‐SAzymes, dominantly mimicking catalase). Theoretical and experimental investigations suggested that the pairwise single‐iron sites may serve as a robust molecular tweezer to efficiently trap and decompose H2O2 into O2, via cooperative hydrogen‐bonding induced end‐bridge adsorption. The versatile mechano‐assisted in situ MOF capsulation strategy enabled facile access to neighboring M2‐SAzyme (M=Fe, Ir, Pt), even up to a 1000 grams scale, but with no obvious scale‐up effect for both structures and performances.

Effect of CuAl2 on the Microstructure and Hardness of Al-Si-xCu Alloys Produced by Powder Metallurgy

Aluminum alloys are important in many industrial applications because of their light weight and good mechanical properties. In this study, the effect of copper addition with different percentages ( 0, 0.1, 0.2, 0.3wt. %) on the microstructure and mechanical strength of Al-Si alloy were studied using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM) and Vickers hardness (Hv) tests. XRD and SEM analyses showed that the Al-Si alloy consisted of α-Al and Si phases. The intermetallic compound (IMC) CuAl2 was detected with the addition of Cu. This IMC causes a change in the lattice constant and inter-atomic spacing (dhkl). The distortion and dense of the microstructure are considered indications of the enhancement in the hardness of alloys. The Vickers hardness (Hv) was measured for the samples before and after sintering. The highest value was 28.755 Hv with 0.2wt. % Cu after sintering, whereas the smallest value was 11.643 Hv without Cu content before sintering. This improvement in hardness is attributed to the temperature that promotes the diffusion of Cu atoms into theAl lattices.

Cold-wire assisted arc direct-energy deposition of VC-strengthening 5A06 aluminum alloy: Microstructures and mechanical properties

In this study, vanadium carbide (VC) was initially introduced into the molten pool using the cold wire method to refine the deposit grains and enhance the mechanical properties of arc direct energy deposition (ADED) aluminum alloy. Next, the grain structure's evolutionary behaviors and the second phase in the VC-strengthening ER5A06 aluminum alloy deposits were investigated, and the grain refinement mechanism was determined. The findings demonstrated that the cubic Al10V phase was produced after introducing VC, and the grain structure in the middle stable region of the building wall was transformed from coarse columnar grains (with an average size of 42.3 μm) into equiaxed fine grains (with an average size of 16.4 μm). Both Al10V and VC were coherent to α-Al in terms of orientation: (020)α-Al//(444)Al10V, [101―]α-Al//[112―]Al10V, and (111)α-Al//(111)VC and [011]α-Al//[011]VC. Their interatomic and interplanar spacing misfits were lower than 5 %, facilitating the heterogeneous nucleation of α-Al during molten pool solidification. Moreover, under multiple thermal cycles of ADED, the pinning effect of VC and Al10V effectively restricted the grain growth, thus enabling the building wall to steadily maintain a uniform, equiaxed, and fine-grained structure. Due to grain refinement and homogenization, the horizontal and vertical ultimate tensile strengths of the straight wall were improved by 16.8 % and 50.2 % (351.6 and 348.1 MPa), respectively, thereby eliminating the mechanical anisotropy. This work can provide a theoretical foundation and a novel method for the fine microstructure regulation and reinforcement of ADED aluminum alloy components.

The contribution of Cr and Ni to hydrogen absorption energy in Fe-Cr-Ni austenitic systems: A first-principles study

The present study focuses on a novel hydrogen-improved strength-ductility balance in several practical Fe-Cr-Ni-based austenitic alloys that directly depends on the dissolved hydrogen content. The hydrogen absorption energy of Fe-Cr-Ni model alloys that have a face-centered cubic structure was examined using first-principles calculations to verify the contribution of Cr and Ni substitutions from Fe to hydrogen solubility in these alloys. Chromium substitution reduced the hydrogen absorption energy to a substantially greater degree than does Ni substitution, with increased Cr: Ni ratios resulting in higher hydrogen solubility. This pattern seen in the calculations supports the previously obtained experimental results in practical alloys with various Cr: Ni ratios. The pronounced reduction in hydrogen absorption energy that results from Cr substitution was mostly attributed to a decrement in the chemical effect derived from the electronic binding state rather than a mechanical effect caused by changed interatomic spacing due to these substitutions. We propose here a Cr-equivalent index to predict hydrogen solubility in Fe-Cr-Ni-based alloys that have varying Cr and Ni content.

Thermal and structural properties of polyzwitterions: Effects of monomer chemistry and salt addition

Thermal and structural properties of polyzwitterions (PZI)s comprising the sulfobetaine moiety were studied as a function of LiCl addition and variations in monomer chemistry. The polyzwitterions chosen for this study are: poly(sulfobetaine methacrylate), PSBMA; poly(sulfobetaine acrylate), PSBA; and, poly(ethyl sulfobetaine methacrylate), PESBMA. When LiCl salt is added, the Li+and Cl− ions disrupt the dipole-dipole electrostatic interaction of the PZI side groups. Fourier transform infrared spectroscopy shows that the vibrational frequencies of the symmetric and asymmetric S=O bonds increase as LiCl content increases. Structural studies by wide angle X-ray scattering show that all the PZIs are amorphous, and the average interatomic spacing, d, increases in the order: dPSBA(= 0.456±0.006nm) < dPSBMA (= 0.474±0.015nm) < dPESBMA (= 0.493±0.011nm). Upon the addition of LiCl, d-spacing for a given PZI decreases as LiCl content increases. Thermogravimetry showed that PZIs had degradation onset temperatures Td ∼ 300°C. As LiCl content increases, the onset temperature of degradation decreases suggesting that the disruption of dipole-dipole crosslinks destabilizes the polymer. All the PZIs are hydrophilic and hygroscopic, and a drying procedure was developed so that well-defined glass-to-liquid transitions could be observed in the dry solid state. PZIs without LiCl have glass transition temperatures, Tg, increasing in the order: Tg,PSBA(= 200±1°C) < Tg,PESBMA (= 204±1°C) < Tg,PSBMA (= 237±1°C). As the LiCl content increases, Tg decreases, and the liquid state heat capacity increases, in all PZIs. The specific heat capacity increment at Tg was studied for PSBA as a function of LiCl content. In PSBA, the heat capacity increment reached a maximum for molar ZI:LiCl content at and above 1:1, and its value agreed well with predictions based on an empirical bead model of polymers. Thermal data on the dry state of PZI-LiCl complexes suggest an analogy between electrostatically crosslinked, fully amorphous PZIs and semicrystalline polymers. The dipolar crosslinks confine the molecular motion of PZIs just as crystal domains confine the molecular motion of the amorphous phase in semicrystalline polymers.

Investigating the Structural Evolution and Catalytic Activity of c-Co/Co3Mo Electrocatalysts for Alkaline Hydrogen Evolution Reaction.

Transition metal alloys have emerged as promising electrocatalysts due to their ability to modulate key parameters, such as d-band electron filling, Fermi level energy, and interatomic spacing, thereby influencing their affinity towards reaction intermediates. However, the structural stability of alloy electrocatalysts during the alkaline hydrogen evolution reaction (HER) remains a subject of debate. In this study, we systematically investigated the structural evolution and catalytic activity of the c-Co/Co3Mo electrocatalyst under alkaline HER conditions. Our findings reveal that the Co3Mo alloy and H0.9MoO3 exhibit instability during alkaline HER, leading to the breakdown of the crystal structure. As a result, the cubic phase c-Co undergoes a conversion to the hexagonal phase h-Co, which exhibits strong catalytic activity. Additionally, we identified hexagonal phase Co(OH)2 as an intermediate product of this conversion process. Furthermore, we explored the readsorption and surface coordination of the Mo element, which contribute to the enhanced catalytic activity of the c-Co/Co3Mo catalyst in alkaline HER. This work provides valuable insights into the dynamic behavior of alloy-based electrocatalysts, shedding light on their structural stability and catalytic activity during electrochemical reduction processes.

Efficient removal of safranin from aqueous solution using a new type of metalated highly self-doped polyaniline nanocomposite

We report the chemical synthesis of poly(aniline-co-aniline-2,5-disulfonic acid)) and its composite containing L-hexuronic acid and metallic Ag/SiO2 nanoparticles as a new thermally stable anionic polyelectrolyte for removing safranin dye. The composite was characterized by IR, UV, cyclic voltammetry, SEM, TEM, TGA, DSC, EDXS and elemental analyses. Microscopic images exhibited intensified spherical particles dispersed over almost the entire surface. The XRD exhibited peaks of the partially crystalline material at many 2θ values, and their interatomic spacing and sizes were calculated. The cyclic voltammograms exhibited characteristic redox peaks relative to the quinoid ring transition states. The uptake rates up to 82.5% adsorption were completed within 75 min and the equilibrium time was 45 min. The isotherm of dye adsorption interprets the interaction with the adsorbent and explain the relationship between the dye removal capacity and the initial dye concentration. In the current, the Langmuir isotherm model was the optimum to interpret both the dye/copolymer and the dye/composite interactions. The uptake of safranin by copolymer/SiO2@Ag nanocomposite was well defined by pseudo second order model with rate constant K2 = 0.03 g− 1 mg− 1 min− 1 for 19 mg safranin. A comparison of safranin adsorption efficiency of the synthesized material with other reported material in the same domain suggested that the present composite has a higher adsorption rate and capacity. The ongoing research is devoted to improving the removal percentage of the dye by using 1,3,5-triazine based sulfonated polyaniline/Ag@ SiO2 nanocomposite.