X-ray Photoemission Spectroscopy Research Articles

Unrevealing tunable resonant excitons and correlated plasmons and their coupling in new amorphous carbon-like for highly efficient photovoltaic devices

An understanding on roles of excitons and plasmons is important in excitonic solar cells and photovoltaic (PV) technologies. Here, we produce new amorphous carbon (a-C) like films on Indium Tin Oxide (ITO) generating PV cells with efficiency three order of magnitude higher than the existing biomass-derived a-C. The amorphous carbon films are prepared from the bioproduct of palmyra sap with a simple, environmentally friendly, and highly reproducible method. Using spectroscopic ellipsometry, we measure simultaneously complex dielectric function, loss function as well as reflectivity and reveal coexistence of many-body resonant excitons and correlated-plasmons occurring due to strong electronic correlations. X-ray absorption and photoemission spectroscopies show the nature of electron and hole in defining the energy of the excitons and plasmons as a function of N or B doping. Our result shows new a-C like films and the importance of the coupling of resonant excitons and correlated plasmons in determining efficiency of photovoltaic devices.

Bismuth zinc borate- Polyacrylonitrile nanofibers for photo-piezocatalysis

This study investigates the use of an electrospun membrane composed of Bi2ZnB2O7 - Polyacrylonitrile (BBZO-PAN) for the degradation of Methylene blue (MB) dye. The membrane was fabricated using the electrospinning technique, and its structural and morphological properties were analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM). The membrane's chemical states before and after encapsulation of BBZO in PAN matrix were analyzed using X-ray photoemission spectroscopy (XPS). The optical studies revealed that the band gap of the BBZO-PAN membrane was 2.92 eV, which is lower than that of the PAN membrane (4.06 eV), due to the presence of BBZO in the PAN matrix. The prepared membrane demonstrated the capability to degrade dye under visible light irradiation via photocatalysis, piezocatalysis, and photo-piezocatalysis. The highest achieved degradation and kinetic rate constant were 82% and 8.8*10-3 min−1, respectively. The active species responsible for degradation were identified using scavenger tests for all catalytic processes. These results demonstrate the potential of the BBZO-PAN membrane for use in wastewater treatment and other environmental applications.

Investigation of the magnetic and mechanical performance of fly ash Geopolymer/BaFe12O19 nanocomposites

The magnetic and mechanical properties of a geopolymer (GeO) were improved by using composites with BaFe12O19 (BFO) nanoparticles. The composites were prepared with 0, 1, 3, and 5 wt% of BFO nanoparticles. All samples were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), vibrating sample magnetometry (VSM) and compressive strength measurements. The contribution of O 1s in all samples was observed using X-Ray photoemission spectroscopy (XPS). All composite samples exhibited ferromagnetic behavior at room temperature with large hysteresis loops and increased magnetization with higher BFO nanoparticle contents. The compressive strength values of the composites increased from 58.2 to 62.2 MPa as the BFO nanoparticle content was raised from 0 to 3 wt%. An increased strength of the GeO suggests a higher denser and more compaction due to addition of BFO nanoparticles in the voids of a N-A-S-H gel structure. The LAC values for the geopolymer composites increased with BFO powder levels.

Enhanced thermoelectric properties of porous hybrid ZnSb/EG-treated PEDOT:PSS composites

We adopt a new feasible strategy to fabricate hybrid inorganic-organic composites by soaking ZnSb in EG-treated PEDOT:PSS solution. The pristine ZnSb and the hybrid ZnSb/EG-treated PEDOT:PSS composites are characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), field emission scanning electron microscope (FE-SEM), Hall measurements, electronic transport and thermal transport. The compositing effects of this hybrid material system include a decrease in lattice constants, an increase in bulk density, and a decrease in porosity with increasing soaking days. As a result, the hybrid ZnSb/EG-treated PEDOT:PSS composite with a soaking time of 30 days has a higher power factor and lower thermal conductivity than that of the pristine ZnSb. This results in an improvement in the magnitude of zT with zT = 0.71 at 525 K.

Ultra-Sensitive and Fast Humidity Sensors Based on Direct Laser-Scribed Graphene Oxide/Carbon Nanotubes Composites.

In this paper, the relative humidity sensor properties of graphene oxide (GO) and graphene oxide/multiwalled nanotubes (GO/MWNTs) composites have been investigated. Composite sensors were fabricated by direct laser scribing and characterized using UV-vis-NIR, Raman, Fourier transform infrared, and X-ray photoemission spectroscopies, electron scanning microscopy coupled with energy-dispersive X-ray analysis, and impedance spectroscopy (IS). These methods confirm the composite homogeneity and laser reduction of GO/MWNT with dominant GO characteristics, while ISresults analysis reveals the circuit model for rGO-GO-rGO structure and the effect of MWNT on the sensor properties. Although direct laser scribing of GO-based humidity sensor shows an outstanding response (|ΔZ|/|Z| up to 638,800%), a lack of stability and repeatability has been observed. GO/MWNT-based humidity sensors are more conductive than GO sensors and relatively less sensitive (|ΔZ|/|Z| = 163,000%). However, they are more stable in harsh humid conditions, repeatable, and reproducible even after several years of shelf-life. In addition, they have fast response/recovery times of 10.7 s and 9.3 s and an ultra-fast response time of 61 ms when abrupt humidification/dehumidification is applied by respiration. All carbon-based sensors' overall properties confirm the advantage of introducing the GO/MWNT hybrid and laser direct writing to produce stable structures and sensors.

Electrostatic Self-Assembly of MXene on Ruthenium Dioxide-Modified Carbon Cloth for Electrochemical Detection of Kaempferol.

A superior composite material consisting of MXene and ruthenium dioxide-modified carbon cloth is synthesized by pulsed laser deposition and electrostatic self-assembly, which is further utilized to construct a class of novel electrochemical (EC) sensors for kaempferol (KA) detection. The carbon-cloth-based electrodes modified by ruthenium dioxide and then MXene are characterized by X-ray diffraction, scanning electron microscope, and X-ray photoemission spectroscopy. The EC process on the modified electrodes is analyzed by cyclic voltammetry, EC impedance spectroscopy, and differential pulse voltammetry. It is found that positively charged RuO2 not only possesses the remarkable electrical conductivity and electrocatalysis activity but also hampers the restacking of MXene, which accordingly enhances the exposure of the active surface area and greatly boosts the electrocatalysis activity of the entire composite. Consequently, this newly developed composite-based EC sensor exhibits a high sensitivity, selectivity, and remarkable stability to detect KA with two linear ranges of 0.06-1 and 1-15 µM. The inferred limit of detection is 0.039 µM via differential pulse voltammetry. More importantly, this novel EC sensor is found to be applicable for detecting KA in practical traditional Chinese medicines.

Deep UV transparent conductive Si-doped Ga2O3 thin films grown on Al2O3 substrates

β-Ga2O3 is attracting considerable attention for applications in power electronics and deep ultraviolet (DUV) optoelectronics owing to the ultra-wide bandgap of 4.85 eV and amendable n-type conductivity. In this work, we report the achievement of Si-doped β-Ga2O3 (Si:β-Ga2O3) thin films grown on vicinal α-Al2O3 (0001) substrates with high electrical conductivity and DUV transparency of promising potential as transparent electrodes. The use of Al2O3 substrates with miscut angles promotes step-flow growth mode, leading to substantial improvement of crystalline quality and electrical properties of the Si:β-Ga2O3 films. A high conductivity of 37 S·cm−1 and average DUV transparency of 85% have been achieved for 0.5% Si-doped film grown on a 6° miscut substrate. High-resolution x-ray and ultraviolet photoemission spectroscopy were further used to elucidate the surface electronic properties of the grown Si:β-Ga2O3 films. An upward surface band bending was found at the surface region of Si:β-Ga2O3 films. Interestingly, all the Si:β-Ga2O3 films have a very low work function of approximately 3.3 eV, which makes Si:β-Ga2O3 suitable materials for efficient electron injection. The present Si:β-Ga2O3 films with high conductivity, DUV transparency, and low work function would be useful as the DUV transparent electrode to develop advanced DUV optoelectronic devices.

Impact of La3+ doping on temperature coefficient of resistivity and peak temperature of La x Ca0.89-xSr0.11MnO3 films prepared by sol-gel spin coating method

Herein, refined LaxCa0.89-xSr0.11MnO3 (LCSMO, x = 0.65, 0.68, 0.71 and 0.74) films were prepared through the sol-gel spin-coating. The influence of La3+ content on the structural properties of LCSMO films was investigated by X-ray diffraction and Atomic force microscope, demonstrating that LCSMO films can grow well on SrTiO3 (00l) substrate. Besides, X-ray photoemission spectroscopy verified the double exchange (DE) effect was weakened with La3+ dopant. The La3+ doping and interconnected grains boundaries (GBs) led to the weakening DE effect and GBs scattering, respectively. Due to superior GBs connectivity, the resistivity of LCSMO films was less than 7.1 × 10−4 Ω·cm at low temperature of 100 K. Importantly, it is an effective control method to keep the temperature (Tk) corresponding to temperature coefficient of resistivity (TCR) at room temperature with Sr2+ content as constant in LCSMO films. At x = 0.71, the peak TCR value was found to be 8.84%/K and corresponding Tk was 283.15 K. These results are beneficial for advanced application of uncooling infrared bolometer.

Silicone Oil Tamponade Removal: Which Technique Is More Effective? An X-Ray Photoemission Spectroscopy Study.

To compare the efficacy of two surgical techniques used to remove silicone oil (SiO) emulsion tamponade after pars plana vitrectomy: triple air-fluid exchange (AFX) and balanced salt solution lavage (BSSL). X-ray photoemission spectroscopy measured silicon content of the dry residue of fluid samples taken during AFX and BSSL. Ten patients underwent AFX and five BSSL. Three fluid samples were taken per patient, and the dry residue of 10 drops per sample were analyzed. A fluid sample from a patient who never received SiO tamponade was also analyzed to set a "blank" reference sample. Patients' demographics showed no significant difference. Sample 1 of the two groups contained comparable silicon content while samples 2 and 3 of the AFX group contained significantly more silicon than that of the BSSL group (15.0 ± 0.1 and 12.0 ± 0.9 for the AFX group vs. 10.7 ± 1.4 and 5.2 ± 0.6 for the BSSL group, respectively; P < 0.05). The cumulative amount of silicon in the three successive samples was also significantly higher for the AFX group (42.3 ± 1.6 vs. 32 ± 2; P < 0.0001). The average silicon content ratio of consecutive samples was significantly higher for the AFX group compared to the BSSL group (0.90 ± 0.01 vs. 0.58 ± 0.06; P = 0.006). Triple AFX removed more silicon than triple lavage. The eye wall actively interacts with silicon emulsion retaining silicon content rather than behaving as a neutral container. Triple air-fluid exchange removed more silicon than BSS lavage. Neither technique behaved as a well-mixed box dilution, suggesting the eye walls actively retain emulsion and a dynamic equilibrium is established between silicon dispersion and the eye wall surface.

Lignocellulose biomatrix zero-valent cobalt nanoparticles: a dip-catalyst for organic pollutants degradation

Pollutant removal based on natural materials got comprehensive spread utilization because of their high efficiency in degrading toxic organic pollutants in an aqueous medium. In this work, a redox dip-nanocatalyst based on cobalt nanoparticles (Co NPs) at a size of approximately 100 nm anchored on lignocellulose biomatrix via wet impregnation was used for the degradation of model pollutants. The cobalt ions immobilized on rice husk (RH) biomass fibers were reduced to their respective zero-valent state by treatment with sodium borohydride (NaBH4). The as prepared catalyst was named as RH@Co NPs. Various analytical characterization techniques viz. Fourier transforms infrared (FTIR) spectroscopy, Field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), X-Ray photoemission spectroscopy (XPS), and X-ray diffraction analysis (XRD) were used to examine functional group analysis, morphological characteristics, stability, elemental composition, and crystalline nature of the as-prepared RH@Co nanocatalyst respectively. The catalytic properties of the RH@Co NPs were tested using different nitrophenols viz. 2-nitrophenol (2-NP), 3-nitrophenol (3-NP), 4-nitrophenol (4-NP), and dyes viz. congo red (CR), methyl orange (MO), methylene blue (MB), and rhodamine B (RB). It was found that kinetic data followed zeroth order kinetics for the degradation of model pollutants. The RH@Co showed good catalytic activity for 2-NP, 3-NP, and 4-NP with apparent rate constants (kapp) of 0.019 min−1, 0.029 min−1, and 0.0416 min−1, respectively. Similarly, in the case of CR, MO, RB, and MB dyes, the kapp was 0.067 min−1, 0.12 min−1, 0.16 min−1, and 0.085 min−1, respectively. These results present the potential application of RH@Co as a sustainable and retrievable nanocatalyst for the remediation of pollutants. Furthermore, the results are general and can be used for the reduction of other organic pollutants.

X-ray irradiation-induced ligand cleavage of a phthalocyanine derivative, tin (IV) phthalocyanine dichloride: A potential for X-ray activation of caged compounds

The X-ray dissociation of tin (IV) phthalocyanine dichloride (SnCl2Pc) was investigated using X-ray photoemission spectroscopy. The photoemission spectra of SnCl2Pc after X-ray irradiation exhibited additional components assigned as chloride ions and tin (II) phthalocyanine, as well as decomposition products from the phthalocyanine framework, indicating that X-ray irradiation induced the release of chloride ions as ligands from SnCl2Pc. Although the ligand releases were caused not by a simple cleavage between Cl-Sn bonding but by accompanying the molecular framework destruction, these reactions may robustly facilitate a novel application of X-rays to activate caged compounds in tissues.

Solid‐State Synthesis and Characterization of Mg‐Substituted P2‐Na0.70Ni0.45Mn0.55O2 Cathode Materials for Practical Sodium‐Ion Batteries

AbstractSodium ion batteries are considered as a potential alternative to existing Li‐ion batteries. Layered transition metal oxides are found to be suitable cathode candidates for Na‐ion batteries. In this study, solid state synthesis of P2‐Na0.7Ni0.45Mn0.55O2 with different Mg substitutions is reported. The synthesized materials are characterized thoroughly using X‐ray diffraction (XRD), field‐emission scanning electron microscopy (FE‐SEM), energy dispersive spectroscopy (EDS), inductively coupled plasma atomic emission spectroscopy (ICP‐AES), and x‐ray photoemission spectroscopy (XPS) analysis. SEM analysis reveals the morphology of synthesized materials to layered structure with a particle size in the range of 5–50 µm. Powder XRD shows all synthesized materials of P2 structure irrespective of Mg substitution. A spurious P3 phase is observed in 0% and 5% of Mg substituted samples which are absent in 10% and 15% of Mg substituted materials. Electrochemical performance analysis shows specific capacity reduces with Mg substitution whereas mid‐voltage reaches maximum up to 3.5 V with 10% substitution. 10% Mg substituted NMO shows a specific capacity 105 mA h g−1 in the voltage ranges of 2–4.3 V versus Na/Na+ with excellent cycling stability and rate capability.

Intrinsic resistive switching in ultrathin SiOx memristors for neuromorphic inference accelerators

Two-dimensional (2D) materials are promising memristive materials owing to their outstanding physical properties, electrical tunability and fast switching capability. However, 2D layered materials generally require sophisticated deposition techniques at the expense of limited large-scale homogeneity and high growth temperatures. Furthermore, the variability and reliability of the 2D materials based memristor should be further improved. Here, we report an intrinsic memristor based on ultrathin 2D-like nonlayered amorphous SiOx which is derived from a native oxidation process at ambient temperature. Such 2D-like memristors demonstrate low switching variability (3.7 %), nanosecond switching speed (15 ns), good endurance (>106 cycles) and high retention (>103 s at 85 °C). We verified the resistive switching mechanism via in-depth X-ray photoemission spectroscopy (XPS) analysis at different resistance states and confirmed the oxygen vacancies movement under the electric field between the SnOx reservoir layer and the SiOx layer. Moreover, Simulation results for an MNIST image classifier based on the ultrathin SiOx memristor show a high recognition accuracy of ∼ 98 %, manifesting its potential for the practical implementation of nonlayered 2D-like materials based neural network inference accelerator.

A New Approach in Prebiotic Chemistry Studies: Proline Sorption Triggered by Mineral Surfaces Analysed Using XPS.

The role of minerals in the origin of life and prebiotic evolution remains unknown and controversial. Mineral surfaces have the potential to facilitate prebiotic polymerization due to their ability to adsorb and concentrate biomolecules that subsequently can catalyse reactions; however, the precise nature of the interaction between the mineral host and the guest biomolecule still needs to be understood. In this context, we spectroscopically characterized, using infrared, X-ray photoemission spectroscopy (XPS) and X-ray diffraction (XRD) techniques, the interaction between L-proline and montmorillonite, olivine, iron disulphide, and haematite (minerals of prebiotic interest), by evaluating their interaction from a liquid medium. This work provides insight into the chemical processes occurring between proline, the only cyclic amino acid, and this selection of minerals, each of them bearing a particular chemical and crystal structures. Proline was successfully adsorbed on montmorillonite, haematite, olivine, and iron disulphide in anionic and zwitterionic chemical forms, being the predominant form directly related to the mineral structure and composition. Silicates (montmorillonite) dominate adsorption, whereas iron oxides (haematite) show the lowest molecular affinity. This approach will help to understand structure-affinity relationship between the mineral surfaces and proline, one of the nine amino acids generated in the Miller-Urey experiment.

The Effect of Key Electronic States on Excess Lithium Intercalation in Li2RuyMn1-yO3.

Excess reversible lithium storage is an alternative crucial strategy besides the expansion of redox centers to boost the capacity of layered cathodes. However, the mechanism of excess Li+ intercalation is far from being comprehended, indisputably hindering the development of layered cathodes. Herein, the comparative study of Li2RuyMn1-yO3 and Li2RuyTi1-yO3 by X-ray absorption and photoemission spectroscopies attempts to illustrate the origin. The charge transfer from Ru to Mn through TM-O π bonding interaction with the formation of O holes has been revealed in Li2RuyMn1-yO3, which originates from the inductive effect and the approaching energy level of Mn and Ru bands. The electronic state is thought to reduce the Coulomb repulsion of Li+ with the matrix, promoting excess Li+ intercalation. The results are instructive to the rational design of layered cathodes to achieve a larger reversible capacity in a wide voltage window.

Layer-resolved electronic behavior in a Kondo lattice system, CeAgAs2

We investigate the electronic structure of an antiferromagnetic Kondo lattice system CeAgAs2 employing hard x-ray photoemission spectroscopy. CeAgAs2, an orthorhombic variant of HfCuSi2 structure, exhibits antiferromagnetic ground state, Kondo like resistivity upturn and compensation of magnetic moments at low temperatures. The photoemission spectra obtained at different photon energies suggest termination of the cleaved surface at cis-trans-As layers. The depth-resolved data show significant surface-bulk differences in the As and Ce core level spectra. The As 2p bulk spectrum shows distinct two peaks corresponding to two different As layers. The peak at higher binding energy correspond to cis-trans-As layers and is weakly hybridized with the adjacent Ce layers. The As layers between Ce and Ag-layers possess close to trivalent configuration due to strong hybridization with the neighboring atoms and the corresponding feature appear at lower binding energy. Ce 3d core level spectra show multiple features reflecting strong Ce-As hybridization and strong correlation. Intense f 0 peak is observed in the surface spectrum while it is insignificant in the bulk. In addition, we observe a features at binding energy lower than the well-screened feature indicating the presence of additional interactions. This feature becomes more intense in the bulk spectra suggesting it to be a bulk property. Increase in temperature leads to a spectral weight transfer to higher binding energies in the core level spectra and a depletion of spectral intensity at the Fermi level as expected in a Kondo material. These results reveal interesting surface-bulk differences, complex interplay of intra- and inter-layer covalency, and electron correlation in the electronic structure of this novel Kondo lattice system.

Microstructural Characterization of the Sol-Gel-Derived Sr2CrReO6 Powders and Their Magnetic and Electrical Transport Properties.

The double-perovskite (DP) Sr2CrReO6 (SCRO) oxide has gained much attention due to its high Curie temperature (∼635 K), high spin polarization, and strong spin-orbit coupling, which provides promising potential for room-temperature spintronic devices. In this work, we report on microstructures of a set of sol-gel-derived SCRO DP powders and their magnetic and electrical transport properties. The SCRO powders crystallize into a tetragonal crystal structure (space group of I4/m). X-ray photoemission spectroscopy spectra verify that the rhenium ions possess variable valences (Re4+ and Re6+) in the SFRO powders while chromium ions are presented as Cr3+. Ferrimagnetic behavior was observed in the SFRO powders at 2 K, and the saturation magnetization was evaluated to be 0.72 μB/f.u. and the coercive field to be 7.54 kOe. The Curie temperature was derived from susceptibility measurements to be 656 K at 1 kOe. Such ferrimagnetic behavior stems from the Cr3-Re4+(Re6+) super exchange interaction via intervening oxygen. Electrical transport measurements revealed that the SFRO ceramic grains were semiconducting and the electrical transport process was governed by the small polarons hopping with variable ranges. The hopping paths for these small polarons are provided by the hetero-valent Re ions in the SCRO ceramics. Negative magnetoresistance (MR) was observed in the SCRO ceramics, and the plot of MR vs magnetic field (H) exhibited a butterfly-like shape. The MR (2 K, 6 T) was measured to be -5.3%, due to the intergranular magneto-tunneling effect. The present results demonstrate a unique combination of high-temperature ferrimagnetism and intrinsic semiconducting nature of the sol-gel-derived SCRO oxides, which are highly attractive for oxide spintronics.

Intra c -axis dimer hybridization and mixed valency in Mg-doped Ti2O3

We have studied the ${\mathrm{Ti}}^{3+}/{\mathrm{Ti}}^{4+}$ mixed valence state in Mg-doped ${\mathrm{Ti}}_{2}{\mathrm{O}}_{3}$ using hard x-ray photoemission spectroscopy. The Ti $2p$ spectrum for the corundum-type ${\mathrm{Ti}}_{2}{\mathrm{O}}_{3}$ revealed the ${\mathrm{Ti}}^{3+}$ configuration with strong electronic coupling in the $c$-axis Ti-Ti pairs whereas the data for the ilmenite-type ${\mathrm{MgTiO}}_{3}$ confirmed the ${\mathrm{Mg}}^{2+}\text{\ensuremath{-}}{\mathrm{Ti}}^{4+}$ charge state in the $c$-axis cation pairs. In ${\mathrm{Mg}}_{0.29}{\mathrm{Ti}}_{1.71}{\mathrm{O}}_{3}$, the Ti $2p$ spectrum hardly showed the ${\mathrm{Ti}}^{4+}$ peak, which was in ${\mathrm{MgTiO}}_{3}$ indicating that the $c$-axis pairing of the Mg is with a ${\mathrm{Ti}}^{3+}$ ion rather than a ${\mathrm{Ti}}^{4+}$ and that the ${\mathrm{Ti}}^{3+}/{\mathrm{Ti}}^{4+}$ mixed valence state is materialized within the Ti-Ti $c$-axis pairs. In ${\mathrm{Mg}}_{0.63}{\mathrm{Ti}}_{1.37}{\mathrm{O}}_{3}$, we detected the presence of ${\mathrm{Mg}}^{2+}\text{\ensuremath{-}}{\mathrm{Ti}}^{4+}$ pairs. The results indicate the important role of hybridization within the $c$-axis pairs not only in the ${\mathrm{Ti}}^{3+}\text{\ensuremath{-}}{\mathrm{Ti}}^{3+}$ configuration, but also above all in the ${\mathrm{Ti}}^{3+}/{\mathrm{Ti}}^{4+}$ mixed valence state, superseding the Madelung energy gain of the ${\mathrm{Mg}}^{2+}\text{\ensuremath{-}}{\mathrm{Ti}}^{4+} c$-axis pair formation.

Flower-like Layered NiCu-LDH/MXene Nanocomposites as an Anodic Material for Electrocatalytic Oxidation of Methanol

Direct methanol fuel cell (DMFC) technology has grabbed much attention from researchers worldwide in the realm of green and renewable energy-generating technologies. Practical applications of DMFCs are marked by the development of highly active, efficient, economical, and long-lasting anode catalysts. Layered double hydroxide (LDH) nanohybrids are found to be efficient electrode materials for methanol oxidation. In this study, we synthesized NiCu-LDH/MXene nanocomposites (NCMs) and investigated their electrochemical performance for methanol oxidation. The formation of NCM was verified through field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET), and X-ray photoemission spectroscopy (XPS) analyses. The cyclic voltammetry, chronoamperometry, and electron impedance spectroscopy techniques were carried out to assess the electrocatalytic ability of the methanol oxidation reaction. The incorporation of MXene enhanced the methanol oxidation 2-fold times higher than NiCu-LDH. NCM-45 exhibited high peak current density (86.9 mA cm-2), enhanced electrochemical active surface area (7.625 cm2), and long-term stability (77.8% retention after 500 cycles). The superior performance of NCM can be attributed to the synergistic effect between Ni and Cu and, further, the electronic coupling between LDH and MXene. Based on the results, NCM nanocomposite is an efficient anodic material for the electrocatalytic oxidation of methanol. This study will open the door for the development of various LDH/MXene nanocomposite electrode materials for the application of direct methanol fuel cells.

The Surface Structure Change of Columbite-(Fe) Dissolution in H2SO4

The mineral surface structure and ions’ interaction were of significant interest to understanding mineral dissolution and reaction. In this study, X-ray photoemission spectroscopy combined with ICP emission spectrometer was used to investigate the influence of the leaching reaction conditions of 8 M dilute sulfuric acid and 12 M concentrated sulfuric acid on the surface chemical composition, chemical (valence) state and ion distribution of Columbite-(Fe) (FeNb2O6). The binding energy of the cations (Fe, Nb) bonding with different anions (O2−, SO42−) and the ratio of Fe3+/Fe2+ oxidation–reduction provided direct understanding of Fe and Nb releasing from the mineral surface during leaching. The results showed that the binding energy of the Nb5+-O bond was much smaller than that of Nb5+-SO4, and the binding energy decreased in sequence as Nb5+-O &lt; Fe2+-O &lt; Fe3+-O and increased in sequence as Fe3+-SO4 &lt; Fe2+-SO4 &lt; Nb5+-SO4. The mineral surface reaction during the leaching could be expressed with the formula: Fe-O + H2SO4 → Fe-SO4 + H2O, Nb-O + H2SO4 → Nb-SO4 + H2O. The results also revealed that Nb dissolution from Columbite-(Fe) occurred more easily compared to Fe. Nb dissolution from the mineral was owed to the content of H+ in solution, and increasing the H+ concentration could promote the dissolution. For Fe dissolution from the mineral, the oxidation potential could play an effective role in enhancement dissolution.