Chromium Doping Research Articles

Effect of chromium doping on structural development and electrical properties of LaNiO3 perovskites

Effect of chromium doping on structural development and electrical properties of LaNiO3 perovskites

Effect of chromium dopant on electrospun zinc oxide nanostructure: A room temperature ethanol sensor

Nanomaterials-based gas sensors represent a ground-breaking endeavour that establishes a systematic and methodical approach to the detection of deleterious contaminants on a broad scale, particularly within the environmental and healthcare domains. In this context, we have commenced the synthesis of chromium-doped (0, 0.5, and 1 wt%) zinc oxide nanostructures through the utilization of an electrospinning technique, subsequently followed by a calcination process. The resultant chromium-doped zinc oxide nanostructures have been subjected to rigorous analysis, affirming their polycrystalline nature as well as the discernible impact of chromium dopants, as confirmed by the X-ray diffraction pattern. Interconnected irregularly shaped multi-grain particles with higher oxygen adsorption sites were confirmed by scanning electron microscope and X-ray photoelectron spectrometer. After analyzing the electrical and optical features, the fabricated sensing elements were tested for their sensing behaviour at room temperature and found to have a selective response towards ethanol vapour. Among the samples, 0.5 wt% chromium-doped zinc oxide exhibited a sensing response (S = 9.03 for 100 ppm) towards ethanol at room temperature. Additionally, the lower limit of detection was found to be 1 ppm, and the response and recovery times towards 100 ppm of ethanol are 41 & 81 s. Further, a thorough investigation into the influence of chromium dopants on the ZnO lattice has been conducted, revealing their pivotal role in augmenting the gas-sensing characteristics of the material.

Enhanced degradation of Congo-red dye by Cr3+ doped α-Fe2O3 nano-particles under sunlight and industrial wastewater treatment

Considering the increasing amount of water pollution, nanocomposite advances for the effective elimination of hazardous pollutants are still needed. α-Fe2O3, Cr0·5Fe1·5O3 and CrFeO3 nanoparticles were synthesized via an eco-friendly material synthesis i. e hydrothermal route without using any precipitating agent and were studied to remove congo-red dye using photocatalytic properties. X-ray diffraction (XRD), Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FESEM), Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS) characterizations have been performed to know about the material structure and properties of synthesized samples. High efficiency (95.2%) of degradation was achieved under sunlight using a very low amount of CrFeO3 catalyst (0.2 g/L) at a 6-pH level of dye and was confirmed using UV spectroscopy, TOC (84%), LC-HRMS. Also, the potential to degrade the CR dye was concluded from the high rate of BOD5/COD. The results showed a significant enhancement in the degradation of α-Fe2O3 from 52.3% to 95.2% in a short duration of 15 min by introducing chromium as a dopant. The doping of chromium influenced the major factors responsible for the photocatalytic activity such as the increase in range of absorbance, increased e−-h+ pair separation, improvement in the charge transfer process and active site formation which significantly enhanced the process of degradation. We found that the Cr-doped α-Fe2O3 nanomaterial could effectively remove dyes, such as congo-red, from industrial water-waste.

Cooperative phosphorus and chromium doping induced electronic and morphological dual modulation in NiMoO4 hydrate for energy-efficient urea-assisted hydrogen production

The electrochemical oxidation of urea presents a promising avenue for hydrogen production with reduced energy consumption. Therefore, developing an efficient bifunctional electrocatalyst capable of catalyzing both the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) is of prominent importance. Herein, a cooperative P and Cr co-doped NiMoO4 hydrate electrode (P/Cr60-NiMoO4) is developed as a self-supported bifunctional electrode for energy-efficient urea-assisted H2 production. Benefiting from the cooperativity of both dopants, the P/Cr60-NiMoO4 electrocatalyst exhibits remarkable performance in UOR and HER, achieving 1.33 V and 35.7 mV at 10 mA cm−2, respectively. Moreover, the utilization of P/Cr60-NiMoO4 as a dual-functional catalyst only needs 1.35 V to reach 10 mA cm−2 in 1 M KOH electrolyte with 0.33 M urea, representing a reduction of 180 mV compared to conventional water electrocatalysis devices (OER//HER systems). Theoretical calculations based on density functional theory reveal that the superior activity of the P/Cr-incorporation system can be attributed to its ability to enhance interface electron concentration, promote electron transfer, and reduce the free energy barriers associated with both UOR and HER.

Synergistic effects of low - level magnesium and chromium doping on the electrochemical performance of LiNiO2 cathodes

LiNiO2 cathode materials with magnesium and chromium doping were prepared using a simple low - cost and efficient co - precipitation and lithiation procedure. During this procedure, both magnesium and chromium form a concentrated core particle, unto which nickel hydroxide precipitates. During lithiation, the elements in question will redistribute themselves and form a homogenous mixture. Magnesium - containing materials exhibit an excellent electrochemical performance, due to phase stabilizing effects, while for chromium - containing materials, performance remains poor. Rietveld refinement reveals that there is a possible upper limit for Mg doping (~ 2.5 mol %) as a pilar dopant. Washing of the lithiated materials was explored, and it is proposed that this can improve capacity retention in prolonged cycling. However, the inevitable loss of lithium from the surface layer remains a challenge. Two sources for the chromium facilitated capacity decay are proposed, both owing to the highly irreversible redox reaction of hexavalent chromium possibly blocking lithium pathways.

Fabrication and Electrical Characterization of Cu1-xCrxO/n-Si Diodes by Sol Gel Spin Coating Method

Undoped and Cr-doped CuO thin films were deposited on n-Si substrates by sol gel spin coating method. These electrical properties of copper oxide-based heterojunction structures were examined as a function of Cr doping concentrations. The results show that a change in Cr concentration significantly affects the electrical properties of Ag/Cu1-xCrxO/n-Si diodes. The all diodes exhibit rectification behavior, as shown by their dark 𝐼−𝑉 characteristics. The crucial junction parameters such as series resistance (R𝑆), rectification ratio (𝑅𝑅), ideality factor (𝑛) and barrier height (Φ𝐵) were calculated by using 𝐼−𝑉 data. The calculated values for the ideality factor (n), which offered details about the performance of the diodes, range from 2.16 to 2.78. The highest 𝑅𝑅 value was obtained from Cu0.5Cr0.5O/n-Si diode. In addition, the capacitance-voltage (𝐶−𝑉) characteristics of the diodes were measured in the frequency range of 10 kHz and 1 MHz. The 𝐶−2−𝑉 graphs were employed to calculate the values of 𝑁𝑣, 𝐸𝑓, 𝐸𝑚𝑎𝑥, and Φ𝐵 (𝐶−𝑉). The results show that the electrical properties of Ag/Cu1-xCrxO/n-Si diodes can be controlled by various chromium doping concentration.

Efficient NH3-Tolerant Nickel-Based Hydrogen Oxidation Catalyst for Anion Exchange Membrane Fuel Cells.

Converting hydrogen chemical energy into electrical energy by fuel cells offers high efficiencies and environmental advantages, but ultrapure hydrogen (over 99.97%) is required; otherwise, the electrode catalysts, typically platinum on carbon (Pt/C), will be poisoned by impurity gases such as ammonia (NH3). Here we demonstrate remarkable NH3 resistivity over a nickel-molybdenum alloy (MoNi4) modulated by chromium (Cr) dopants. The resultant Cr-MoNi4 exhibits high activity toward alkaline hydrogen oxidation and can undergo 10,000 cycles without apparent activity decay in the presence of 2 ppm of NH3. Furthermore, a fuel cell assembled with this catalyst retains 95% of the initial peak power density even when NH3 (10 ppm)/H2 was fed, whereas the power output reduces to 61% of the initial value for the Pt/C catalyst. Experimental and theoretical studies reveal that the Cr modifier not only creates electron-rich states that restrain lone-pair electron donation but also downshifts the d-band center to suppress d-electron back-donation, synergistically weakening NH3 adsorption.

Facile Synthesis of Chromium-Doped Fe1.1Mn1.9O4 Nanoparticles and the Effect of Cr Content on Their Magnetic and Structural Properties.

In the present study, Fe1.1(CrxMn1-x)1.9O4 nanoparticles (0 ≤ x ≤ 0.5) were successfully synthesized by a combustion method, and the influence of Cr substitution on the structural and magnetic properties of the obtained nanoparticles was studied by various methods. The structural analysis revealed that the sample with x = 0 has a tetragonal structure, while all Cr-doped samples crystallize into a cubic structure. Additionally, the results of TEM show that doping with chromium leads to an increase in particle size. The magnetic hysteresis loops demonstrate the behavior typical for soft magnetic materials with low coercivity and remanence magnetization. The magnetic measurements revealed that the saturation magnetization of the obtained nanoparticles demonstrates a decreasing trend with increasing Cr content. The influence of chromium doping on the observation change in saturation magnetization is discussed. Based on the results of temperature-dependent magnetization measurements, it was found that the temperature of a magnetic transition in synthesized nanoparticles depends on Cr content.

Kinetically accelerated oxygen evolution reaction in metallic (oxy)hydroxides enabled by Cr-dopant and heterostructure

Efficient water-splitting is an underpinning technology for producing hydrogen in high-purity and enabling hydrogen economy, but it suffers from the sluggish kinetics of anodic oxygen evolution reaction (OER). Cost-efficient transition metals-based oxides/hydroxides, particularly NiFe-based double hydroxides (NiFe LDHs), have been deemed as promising OER electrocatalysts in alkaline electrolytes. However, their electrocatalytic performance still waits to be substantially optimized. Herein, we demonstrate the tremendously enhanced OER activity of NiFe LDH via a developed coupling strategies of intrinsic chromium (Cr) doping and external heterojunction engineering. Relying on the heterostructure, an in-built electric field is proved and thus the charge transfer kinetic is substantially accelerated. Remarkably, the synergistic surface electron modulation, explicitly revealed by theoretical calculation and experimental analysis, elucidates that the upward d-band center of Fe sites after doping Cr accounts for the much-enhanced OER activity, being inherited when combining with CuO substrate, while the increased empty d orbital of Ni sites after introducing CuO part interprets the activation of initially nonactive Ni sites. As a result, a low OER overpotential of 210 mV (at 10 mA cm−2) and excellent durability are achieved for Cr-NiFe LDH@CuO catalyst. Furthermore, the resultant alkaline electrolyzer also displays outstanding activity (requires a low voltage of 1.56 V at 100 mA cm−2) and good durability.

Construction and growth of black PEO coatings on aluminum alloys for enhanced wear and impact resistance

Black coatings with superior optical properties have attracted considerable attention for the surface treatment of aluminum alloys. This study focuses on the development of black coatings with superior mechanical properties on 6061Al alloy using plasma electrolyte oxidation (PEO) technique. Two different electrolytes are designed, and the effects of different electrolyte components on the microstructure, composition, growth mode, and mechanical properties of black coatings are investigated. The results show that the inward-outward growth behavior and mechanical properties of coatings are strongly influenced by the deposition originating from the electrolyte. The deposition of P– and V–containing coatings in the mixed electrolyte composed of phosphate and metavanadate proceeds easily, forming outer deposition layers with loose structures. This makes the growth of coatings largely dependent on the mode of outward growth and decreases the adhesion strength. Conversely, in the mixed electrolyte of phosphate and dichromate, the deposition of species from the electrolyte is difficult, resulting in the initial growth of coatings that relies on the oxidation of the substrate. Such a growth mode is characterized by inward growth, which endows coatings with excellent wear and impact resistance. Furthermore, the coloring mechanism is discussed, and it is concluded that the doping of vanadium (V) or chromium (Cr), especially Cr, into alumina significantly contributes to the black appearance of the coatings.

Assessment of Cr doping on TiO2 thin films deposited by a wet chemical method

Undoped and Cr-doped TiO2 thin films were synthesized by the dip-coating sol-gel process with titanium isopropoxide and chromium (III) chloride hexahydrate being used as the precursors. The chromium concentrations changed for different molar ratios, namely, 2, 4, and 8 wt.%. The samples, coated on glass substrates, were later annealed in air at 450 °C for 60 min. The influence of Cr doping on the structural, surface chemical, and optical properties of the samples was studied by several techniques, including EDS, Raman, UV–Vis, RT-PL, and XPS spectroscopies, as well as SEM and XRD. The diffraction patterns indicated that all the films displayed the anatase structure with the crystallite size decreasing with chromium doping. The same structure was confirmed by Raman spectroscopy measurements. UV–Vis absorption spectra of the samples showed a red shift of the fundamental absorption edge in the visible range following the increase of Cr doping concentration. In addition, the RT-PL study revealed that the dopant incorporation causes a decrease in the PL intensity. The EDS analysis revealed the presence of Ti, O, and Cr in the materials. Moreover, from high-resolution XPS Ti 2p spectra, titanium was found to be in the Ti4+ oxidation state evidencing the formation of TiO2, while the Cr 2p fitting analysis showed that chromium is present in the Cr (III) and Cr-metal states.

Improved optical, dielectric, and nonlinear properties of CaCu3Ti4O12 thin films by chromium doping

In the present work, the optical and dielectric properties, microstructures, and nonlinear electrical performances were systematically investigated for Ca1-xCrxCu3Ti4O12 (x = 0.00 - 0.40) thin films prepared on Pt/Ti/SiO2/Si substrates using the sol-gel method. X-ray photoelectron spectroscopy (XPS) verified that Cr3+ and Cr6+ were present in the thin films. Additionally, the content of secondary phase of titanium oxide (TiO2) increased, the grain size decreased, and the surface roughness improved with the increase in the doped content of Cr. Due to the reduced grain size and oxygen vacancy concentration, the optical energy band gap increased from 2.92 to 3.54 eV. The change in the dielectric constants (Ɛr) of the thin films followed the internal barrier layer capacitor model. Doping was found to decrease the dielectric loss (tan δ) and enhance the nonlinear properties, which was due to the presence of TiO2 secondary phase, high density, reduced grain size, incremental potential barrier height and grain boundary resistance. The Ca0.8Cr0.2Cu3Ti4O12 thin film had a high Ɛr of around 9340, low tan δ of around 0.012 at 1 kHz, nonlinear coefficient of about 4.64, and breakdown field of ca. 89 kV/mm. These results indicated that the doping of an appropriate amount of Cr could effectively modify the microstructure of CaCu3Ti4O12 thin films and improve their optical and electrical properties.

Effect of chromium doping on the structure and mechanical properties of anti-wear TiB2 coatings

TiB2-based coatings have been intensively developed due to their physical and mechanical properties, including excellent thermal stability and high hardness with good abrasion and corrosion resistance, which appear to be the most beneficial in industrial application. Previous investigations have shown that doping TiB2 with W, Ni and C can significantly reduce residual stresses and improve adhesion, making these coatings ideal on tools to machining aluminum alloys. The aim of this study was to analyze the effect of an Cr interlayer on the durability (adhesion) of the fabricated Ti1−xCrxB2 (x = 0; 0.03; 0.06; 0.10) films and determine the influence of Cr on their microstructure and mechanical properties. The structural characterization of Ti1−xCrxB2 coatings was carried out using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and atomic force microscopy. To investigate the mechanical properties, nano-scratch and—hardness tests (NST, NHT) were performed, and fracture toughness of the substrate layer systems was determined. The use of an adhesive layer of pure Cr increased the adhesion of the coatings to the substrate. It is shown that the changes in Cr content not only affect the microstructure, mainly by decreasing the crystallite size (column width), but also the texture (preferred film orientation) and phase composition. The addition of chromium also has an effect on the mechanical properties of TiB2 films by reducing their hardness and Young’s modulus and increasing their fracture toughness (KIC).

Sol-Gel Derived Chromium Doped Vanadium Pentoxide Based Nanostructured Electrode Materials for Supercapacitor Applications

Through a simple sol-gel process, chromium doped vanadium pentoxide (V2-xCrxO5-δ, where x = 0, 0.05, 0.10, 0.15 and 0.20) nanomaterials were synthesized. The XRD data confirmed the occurrence of orthorhombic crystalline structure. FTIR spectra exhibited the presence of V = O and V-O-V along with carbon di oxide and moisture in the samples.The particle diameter was found to be 146-227nm. The SEM results exhibited a sheet like structure. From the electrochemical studies, it was found that V1.95Cr0.05O5-δ electrode has exhibited a specific capacitance of 232.15 Fg−1 at the scan rate of 10 mVS−1. It can be an electrode for supercpacitors.

Sensor Performance and Structural Characteristics of CrxFe3−xO4 Ferrofluids

The CrxFe[Formula: see text]O4 ferrofluids have been successfully synthesized using natural iron sand through co-precipitation method as a voltage sensor. The use of chromium dopants is intended to increase the ferrofluids response when used as a voltage sensor. A series of characterizations were carried out to support this justification, including structure, morphology, functional groups, optical properties, and sensor performance of the CrxFe[Formula: see text]O4 ferrofluids. The increase in the Cr[Formula: see text] molar fraction has an impact on decreasing in structural parameters of the CrxFe[Formula: see text]O4 ferrofluids. Visually, the particles show an agglomeration phase by the presence of interparticle forces. The study of functional groups showed that the CrxFe[Formula: see text]O4 ferrofluids had been successfully formed, marked by the appearance of all precursor functional groups. Analysis of optical properties based on absorption shows the phenomenon of intervalence charge transfer and causes a decrease in the value of the gap energy. Interestingly, the CrxFe[Formula: see text]O4 ferrofluids sensor sensitivity shows a good and prospective response making them suitable for new sensor candidates in the future.

Exploitation of green synthesized chromium doped zinc oxide nanorods (NRs) mediated by flower extract of Rhododendron arboreum for highly efficient photocatalytic degradation of cationic dyes Malachite green (MG) and Fuchsin basic (FB)

In this work, green method to synthesize chromium-doped zinc oxide (ZnO) nanorods (NRs) using an aqueous flower extract from Rhododendron arboretum is explored. Herein, chromium-doped ZnO NRs were prepared with different amount of chromium doping, varied as 2–10%. The green synthesized products underwent substantial analysis through X-ray diffraction (XRD), spectroscopic such as ultraviolet spectroscopy(UV-Vis) and scanning electron microscopy (SEM) methods. All samples were found to have hexagonal wurtzite ZnO, with average particle sizes of 52.41, 56.6, 54.44, 53.05, and 56.99 nm, respectively, for 2, 4, 6, 8, and 10% chromium doping in ZnO NRs. The Cr-doped ZnO NRs exhibited remarkable photocatalytic degradation activity of cationic dyes under UV-light, i.e., Malachite Green and Fuchsin Basic with degradation of 99.604 and 99.881%, respectively in 90 min. The reusability tests for these green synthesized Cr-doped ZnO NRs have also been carried out, showed 9–11 cycles with 85% of degradation efficiency. In addition, the Cr-doped ZnO NRs exhibited high selectivity for cationic dyes when experiments against mixture of dyes were performed. Photodegradation kinetics followed the pseudo-first-order model. The flower-extract-stabilized chromium-doped ZnO NRs demonstrated high photocatalytic activity toward malachite green and fuchsin basic dyes, potential material for pollution remediation.

Chromium doping and in-grown heterointerface construction for modifying Ni3FeN toward bifunctional electrocatalyst toward alkaline water splitting

Exploring high-performance non-noble metal electrocatalysts is pivotal for eco-friendly hydrogen energy applications. Herein, featuring simultaneous Chromium doping and in-grown heterointerface engineering, the Cr doping Ni3FeN/Ni heterostructure supported on N-doped graphene tubes (denoted as Cr–Ni3FeN/Ni@N-GTs) was successfully constructed, which exhibits the superior bifunctional electrocatalytic performances (88 mV and 262 mV at 10 mA cm−2 for HER and OER, respectively). Furthermore, an alkaline electrolyzer, employing Ni3FeN/Ni@N-GTs as both the cathode and the anode, requires a low cell voltage of 1.57 V at 10 mA⋅cm−2. Cr doping not only modulates the electronic structure of host Ni and Fe but also synchronously induces nitrogen vacancies, leading to a higher number of active sites; the in-grown heterointerface Cr–Ni3FeN/Ni induces the charge redistribution by spontaneous electron transfer across the heterointerface, enhancing the intrinsic catalytic activity; the N-GTs skeleton with excellent electrical conductivity improves the electron transport and mass transfer. The synergy of the above merits endows the designed Cr–Ni3FeN/Ni@ N-GTs with outstanding electrocatalytic properties for alkaline overall water splitting.

Investigation of the crystal structure, electronic and optical properties of Cr-doped BaTiO3 on the Ti site using first principles calculations

In this work, we have investigated the effect of chromium (Cr) doping on the structural, electronic and optical properties of the cubic phase of BaTiO3 using first-principles calculations. Applying the GGA + U approximation, the lattice parameters as well as the band gaps of the undoped and doped phase of BaTiO3 are in fairly good agreement with the experimental data, confirming the validity of our model. Furthermore, the chemical bonding analysis underlines the ionic character of Ba–O bonds and the covalent nature of Ti–O and Cr–O bonds. Additionally, the investigation of the optical properties using the Hubbard U-potential correction provided good agreement with the experimental data in the broad energy ranges. We have also demonstrated that the substitution of chromium on the Ti site, through the calculation of both electronic and optical properties, leads to the appearance of defects close to the Fermi level, allowing the appearance of the asymmetry of the BaTi1-xCrxO3 system. As a result, the calculated total magnetic moment is 1.6038 μB, indicating that doping with Cr renders the BaTi1-xCrxO3 system ferromagnetic. Therefore, this work demonstrates that Cr-doped BaTiO3 could reasonably constitute a new class of perovskite materials for magneto-optoelectronic applications.

Chromium doping enabled improvement in alkaline seawater oxidation over cobalt carbonate hydroxide nanowire array.

The presence of chlorine species in seawater can cause severe anode corrosion, highlighting the critical need for the design of efficient and robust electrocatalysts towards the oxygen evolution reaction (OER) for hydrogen production. Herein, we present a chromium doped cobalt carbonate hydroxide nanowire array on nickel foam (Cr-CoCH/NF) as an effective OER electrocatalyst in seawater. In alkaline conditions, Cr-CoCH/NF exhibits a low overpotential of 450 mV to achieve 500 mA cm-2, surpassing that of CoCH/NF (614 mV). Additionally, it demonstrates 200 h of continuous oxygen evolution testing.

Effects of Chromium (Cr) doping on Structural, Electronic and Magnetic Properties of Barium Selenide Compound: A Theoretical Investigation

Effects of Chromium (Cr) doping on Structural, Electronic and Magnetic Properties of Barium Selenide Compound: A Theoretical Investigation