Cr Doping Research Articles

Molecular dynamics simulation of friction in DLC films with different Cr doping levels

This study systematically investigates the impact of varying Cr doping levels on the friction properties of DLC films using molecular dynamics simulations. The results demonstrate that under identical friction velocities and load conditions, the friction force of DLC films significantly decreases when the Cr doping content reaches 16.5 %. High Cr doping levels lead to the formation of Cr atomic clusters at the interface, hindering contact and reducing the number of interface bonds. These clusters act as lubricants, filling the interface gaps and thereby reducing the friction force. Internal stress calculations indicate that Cr doping effectively reduces the average internal stress of DLC films. For DLC films with lower Cr doping levels, the friction force exhibits similar trends under different friction velocities, while films with higher Cr doping levels show a more pronounced response, with friction force increasing at higher velocities. Increasing the load significantly raises the friction force, especially for DLC films with higher Cr doping levels. Furthermore, high Cr doping levels under high loads lead to significant structural damage and adhesive wear. This study provides theoretical and technical references for optimizing the friction performance of DLC films.

Insights into the role of the Cr and rare element in improving the corrosion resistance of HRB400 rebars in simulated SO2-polluted marine environment

The present work aims to offer insights into the role of Cr and rare element (RE) in improving the corrosion resistance of HRB400 rebar in simulated concrete pore solution (SCPS) containing NaCl and NaHSO3. Electrochemical tests reveal that the increased SO2 concentration reduces the pitting potential and charge transfer resistance. However, the addition of Cr/RE significantly lowers the corrosion current density of HRB400, as confirmed by the corrosion morphology observed after immersion tests. Quantitative analysis of corrosion pits shows that SO2-induced corrosion tends to develop longitudinally, a tendency mitigated by the Cr/RE alloyed rebar. X-ray photoelectron spectroscopy (XPS) results confirm the presence of Cr and RE oxides in the oxide film and demonstrate that SO2 affects the Fe(II)/Fe(III) ratio. Cr and RE doping not only refines the microstructure and modifies inclusions but also enhances the protective properties of the oxide film on the rebar. Therefore, the combination of Cr and RE improves the durability of rebars in SO2-polluted marine environments.

Investigation on electronic and magnetic properties of Cr doped V2O5 thin films prepared by chemical solution deposition method

The present study examines the role of Cr doping on the electronic and magnetic behaviour of V2O5i.e. V2-xCrxO5 (x = 0, 0.05, and 0.10) thin films, prepared by chemical-solution deposition technique on Si (111) substrate. X-Ray diffraction technique shows the purity of the films and confirms no secondary phase formation. The atomic force microscopy was used to confirm the roughness of the films. A morphological investigation is done using High-resolution scanning electron microscopy associated with Energy dispersive X-Ray mapping of each element of the film. Fourier transform Infrared spectroscopy is utilised to identify functional groups that are present in obtained samples. The band-gap of these obtained samples is in the range of 0.8–0.6 eV, as examined by UV–Vis i.e., its value is decreasing with Cr doping. Using vibrating sample magnetometer, it is clear that samples shows ferromagnetic (FM) behaviour with saturation magnetization 0.3–0.6 μB/cc consistent with Langevin function fitting. It concludes the presence of FM behaviour of films and magnetization increases with carrier density, consistent with the carrier-induced origin of the ferromagnetism. X-ray photoemission spectroscopy (XPS) is utilised to understand its electronic properties. Core level spectra measurements suggest that V is in mixed state of 5+ and 4+. However Cr is in 3+ states. XPS and UV–Vis measurements imply that oxygen vacancies significantly contribute to the declination of the band gap and the promotion of FM-like behaviour. This discovery offers a promising pathway for engineering novel devices.

Revealing Enhanced Active Oxygen Formation by Incorporating Chromium into Nickel Hydroxide Nanosheets for Improved Oxygen Evolution Reaction.

Nickel-based oxyhydroxides have emerged as promising catalysts for the oxygen evolution reaction (OER) among Earth-abundant metals. While the incorporation of foreign elements is recognized to enhance catalytic activity, the origin of this enhancement is still debated. We synthesize and examine Ni hydroxide nanosheets, both with and without Cr doping, to elucidate the underlying enhancements. Operando UV-vis and Raman spectroscopy are employed to unravel the behavior of the catalysts. The Cr doping facilitates the oxidation of Ni, resulting in the generation of active oxygen species. The enriched active oxygen species improves OER performance through a lattice oxygen-mediated pathway in Fe-free KOH, and further contribute to the creation and increased activity of FeOxHy sites in the presence of Fe impurities. This work provides a mechanistic understanding of the performance enhancement in Ni-based catalysts through Cr doping and suggests a strategy for the design of more efficient catalysts in the future.

Utilizing Armchair and Zigzag Nanoribbons for Improved Detection of SO2 Toxicity with Graphene Biosensor

Graphene nanoribbons (GNRs), with their distinctive structural and electronic characteristics, offer significant potential for use as biosensors in the detection of sulfur dioxide (SO₂) levels. This study employs Density Functional Theory (DFT) to evaluate the sensitivity of armchair graphene nanoribbons (AGNRs) to SO₂ gas. Specifically, we investigate the influence of SO₂ molecules on the electronic and transport characteristics of both pure and Cr-doped zigzag graphene nanoribbons (ZGNRs) and Cr-doped AGNRs. Key electronic properties, including band structure, adsorption energy, and density of states (DOS), were analyzed following SO₂ adsorption. The results indicate that Cr doping leads to significant changes in the electronic properties of AGNRs upon SO₂ exposure, including alterations in the Fermi surface that result in band separation and the formation of a forbidden band. The adsorption energy of Cr-doped AGNR increased from 0.07 eV (pristine AGNR) to 0.55 eV (Cr-doped AGNR), nearly eight times higher, indicating strong chemisorption of SO₂. These findings suggest that Cr-doped AGNRs exhibit high sensitivity to SO₂, making them promising candidates for gas detection. Furthermore, this study reveals that SO₂ adsorption in the armchair direction results in a more pronounced peak-to-valley ratio compared to the zigzag direction, highlighting distinct characteristics in SO₂ adsorption behavior. These findings could facilitate the development of advanced sensors with improved sensitivity and selectivity for environmental monitoring and safety applications.

Transition metal-doped modification of lattice defects in formaldehyde catalysts − Controlling the specific surface area and mass transfer

Exploring room temperature treatment of formaldehyde (HCHO) is a crucial area of ongoing research, with transition metal catalysts showing promise for future development due to their cost-effectiveness. However, the challenge lies in the limited ability of these catalysts to activate oxygen efficiently and maintain stable catalytic oxidation of HCHO. The Mn3O4 catalyst doped with Cr, Cu, Zn, and Co was synthesized via hydrogen reduction in this study. Cr/Mn3O4 showed exceptional catalytic performance by completely converting HCHO at 30 °C and 200 ppm, while maintaining excellent stability during a 75-hour durability test. The characterization techniques revealed that the incorporation of transition metal Cr into the Mn3O4 lattice resulted in an increased number of oxygen vacancy defects on its surface, thereby significantly enhancing its ability to activate oxygen. Furthermore, Cr doping substantially augmented the specific surface area and abundance of mesoporous structures in the catalyst, which provided ample active sites and facilitated efficient mass transfer for substrate oxidation by promoting diffusion to these active sites. These enhancements ultimately led to a heightened activation of oxygen and H2O into reactive oxygen species, consequently reducing the dominance of side reaction pathways caused by intermediates occupying active sites.

Self-sacrificial hydrogen channel enhances the poisoning resistance of ZrCo-based alloy

ZrCo alloy is considered as a promising candidate for hydrogen isotope storage in nuclear fusion reactors. However, severe poisoning caused by the impurities contained in hydrogen is an inevitable issue in engineering applications. Herein, the effects of Cr-doped ZrCo with segregated the reticular ZrCr2 phase on the activation and oxidation resistance were investigated systematically. Experimental results show ZrCo0·95Cr0.05 can achieve 1.71 wt% hydriding capacity within about 37 min under 1 mol% O2 + 99 mol% H2, whereas ZrCo consumes more than 4 times (150 min) to reach the same capacity. Specifically, the improved anti-poisoning ability of the ZrCo–Cr system could be attributed to the three-step chain effect induced by Cr doping, including the hydrogenation-prone and oxygen resistance character of ZrCr2 phases, sacrificial and catalysis of in-situ formed metallic Cr clusters, and protective effects of Cr oxide layers. Hence, the active sites for rapid hydrogen absorption were obtained and inferior oxygen resistance of ZrCo substrates was alleviated through the self-sacrifice of ZrCr2 and Cr. This work not only proves the feasibility of the multi-component alloying strategy in the field of ZrCo alloy anti-poisoning modification, but also reveals that the core of the multi-component alloying strategy is to realize the modulation of the microstructure through the composition design.

Key roles of surface Cr in the NiFe layered double hydroxides for an efficient oxygen evolution reaction via adaptive reconfiguration

Cr doping is a new strategy to enhance the OER (Oxygen Evolution Reaction) performance of NiFe-LDH (NiFe-Layered Double Hydroxides) by optimizing surface states and offering a scalable production process. However, as an additive element, Cr itself has weak OER performance, so its promotion on the Ni- and Fe-active site by electron perturbation and structural stabilization in NiFeCr-LDH has been the focus. Herein, a one-step hydrothermal method is used to incorporate Cr into NiFe-LDH, systematically investigating the relationship between Cr content and the material's microstructure. The results of physical characterization show that Cr ion plays a leading role in the electron perturbation Ni/Fe-active center, which causes the increasing of Fe3+ and Ni3+ content. Furthermore, variations in Cr content resulted in the lattice stretching and morphology evolving synchronously. The optimized NiFeCr-LDH exhibited significantly enhanced OER activity and durability compared to undoped NiFe-LDH and outperformed commercial RuO2 catalysts. Additionally, a microstructure comparison was made between the initial- and long-term used-NiFeCr-LDH. The findings reveal that the material's distinctive structural evolution behavior confers it with exceptional self-adaptability to the OER reaction, which results in a consistent enhancement of activity lasting up to 12 h during long-term I-t test showing a new idea for the design of high performance NiFeCr-LDH.

Membrane‐Free Electrocatalytic Co‐Conversions of PBS Waste Plastics and Maleic Acid into High‐Purity Succinic Acid Solid

AbstractPlastic pollution, an increasingly serious global problem, can be addressed through the full lifecycle management of plastics, including plastics recycling as one of the most promising approaches. System design, catalyst development, and product separation are the keys in improving the economics of electrocatalytic plastics recycling. Here, a membrane‐free co‐production system was devised to produce succinic acid (SA) at both anode and cathode respectively by the co‐electrolysis of polybutylene succinate (PBS) waste plastics and biomass‐derived maleic acid (MA) for the first time. To this end, Cr3+‐Ni(OH)2 electrocatalyst featuring much enhanced 1,4‐butanediol (BDO) oxidation reaction (BOR) activity has been synthesized and the role of doped Cr has been revealed as an “electron puller” to accelerate the rate‐determining step (RDS) in the Ni2+/Ni3+ cycling. Impressively, an extra‐high SA production rate of 3.02 g h−1 and ultra‐high apparent Faraday efficiency towards SA (FEapparent=181.5 %) have been obtained. A carbon dioxide‐assisted sequential precipitation approach has been developed to produce high‐purity SA and byproduct NaHCO3 solids. Preliminary techno‐economic analysis demonstrates that the reported system is economically profitable and promising for future industrial applications.

Membrane-Free Electrocatalytic Co-Conversions of PBS Waste Plastics and Maleic Acid into High-PuritySuccinic Acid Solid.

Plastic pollution, an increasingly serious global problem, can be addressed through the full lifecycle management of plastics, including plastics recycling as one of the most promising approaches. System design, catalyst development, and product separation are the keys in improving the economics of electrocatalytic plastics recycling. Here, a membrane-free co-production system was devised to produce succinic acid (SA) at both anode and cathode respectively by the co-electrolysis of polybutylene succinate (PBS) waste plastics and biomass-derived maleic acid (MA) for the first time. To this end, Cr3+-Ni(OH)2 electrocatalyst featuring much enhanced 1,4-butanediol (BDO) oxidation reaction (BOR) activity has been synthesized and the role of doped Cr has been revealed as an "electron puller" to accelerate the rate-determining step (RDS) in the Ni2+/Ni3+ cycling. Impressively, an extra-high SA production rate of 3.02 g h-1 and ultra-high apparent Faraday efficiency towards SA (FEapparent=181.5%) have been obtained. A carbon dioxide-assisted sequential precipitation approach has been developed to produce high-purity SA and byproduct NaHCO3 solids. Preliminary techno-economic analysis demonstrates that the reported system is economically profitable and promising for future industrial applications.

Surface Electronic Structure of Cr Doped Bi2Se3 Single Crystals

Here, by using angle-resolved photoemission spectroscopy, we showed that Bi2−xCrxSe3 single crystals have a distinctly well-defined band structure with a large bulk band gap and undistorted topological surface states. These spectral features are unlike their thin film forms in which a large nonmagnetic gap with a distorted band structure was reported. We further provide laser-based high resolution photoemission data which reveal a Dirac point gap even in the pristine sample. The gap becomes more pronounced with Cr doping into the bulk of Bi2Se3. These observations show that the Dirac point can be modified by the magnetic impurities as well as the light source.

Insights of oxygen vacancies engineered structural, morphological, and electrochemical attributes of Cr-doped Co3O4 nanoparticles as redox active battery-type electrodes for hybrid supercapacitors

The global warming issue is spurring the development of renewable energy solutions, where supercapacitors are emerging as promising options for energy storage. Despite advancements in battery-type materials, doping is a practical approach to enhancing electrochemical performance. In this study, using the solution combustion method, we synthesized spinel Co3O4 nanoparticles doped with chromium (Cr) at 2.5 % and 5 % concentrations. The addition of Cr significantly modifies the structural, morphological, surface, and electrochemical properties of Co3O4 nanoparticles. Raman and X-ray photoelectron spectroscopy confirm that this doping method effectively regulates the oxygen vacancy defect level. Moreover, Cr dopants and oxygen vacancies modify electronic states, facilitating more accessible contact to active sites, improving electrical conductivity and more intricate redox chemistry. Notably, the 2.5 % Cr-doped Co3O4 configuration demonstrates substantially enhanced specific capacity (334.64 C g−1/92.95 mAh g−1 at 1 A g−1) and rate performance (59 %), surpassing those of 5 % Cr-doped Co3O4 and undoped Co3O4. Furthermore, the as-fabricated 2.5 % Cr-doped Co3O4//activated carbon (AC) hybrid supercapacitor (HSC) device exhibits a noteworthy energy density of 42.5 Wh kg−1 at 1295.73 W kg−1, withstanding 33.54 Wh kg−1 even at a power density of 5720.46 W kg−1. The HSC device showcases outstanding cyclic performance with 100 % capacity retention after 5000 cycles. Therefore, our work offers a viable way to improve the efficiency of hybrid supercapacitors by providing essential insights into the design of defect-engineered battery-type electrode materials.

Theoretical Study of the Multiferroic Properties of Pure and Ion-Doped Pb5M3F19, M = Fe, Cr, Al.

In a first theoretical investigation of the multiferroic properties of Pb5Fe3F19 (PFF) and Pb5Cr3F19 (PCF), we analyze their magnetic, ferroelectric, and dielectric characteristics as functions of temperature, magnetic field, and ion doping concentration using a microscopic model and Green's function theory. The temperature-dependent polarization in PFF and PCF shows a distinctive kink at the magnetic Neel temperature TN, which vanishes when an external magnetic field is applied, indicating the multiferroic behavior of these two compounds. Ion doping effectively tunes the properties of PFF and PCF. In PFF, Cr ion doping leads to a decrease in the Neel temperature TN, while Cr and Al ion doping lowers the ferroelectric Curie temperature TC. In the case of PCF, we observe the enhancement of TC by Fe ion doping and the reduction by Al ion doping. The last result coincides well quantitatively with the experimental data. Additionally, the magnetodielectric coefficient of PFF is enhanced with the increasing magnetic field.

Cr dopant mediates hydroxyl spillover on RuO2 for high-efficiency proton exchange membrane electrolysis

Simultaneously improving the activity and stability of catalysts for anodic oxygen evolution reaction (OER) in proton exchange membrane water electrolysis (PEMWE) remains a notable challenge. Here, we report a chromium-doped ruthenium dioxide with oxygen vacancies, termed Cr0.2Ru0.8O2-x, that drives OER with an overpotential of 170 mV at 10 mA cm−2 and operates stably over 2000 h in acidic media. Experimental and theoretical studies show that the synergy of Cr dopant and oxygen vacancy induces an unconventional dopant-mediated hydroxyl spillover mechanism. Such dynamic hydroxyl spillover from Cr dopant to Ru active site changes the rate-determining step from OOH* formation to O2 formation and thus greatly improves the OER performance. Moreover, the Cr dopant and oxygen vacancy also play a crucial role in stabilizing surface Ru and lattice oxygen in the Ru-O-Cr structural motif. When assembled into the anode of a practical PEMWE device, Cr0.2Ru0.8O2-x enables long-term durability of over 200 h at an ampere-level current density and 60 degrees centigrade.

Influence of chromium concentration on the structural, optical, magnetical, and thermal properties of ZnS nanocrystals

Pure ZnS and Zn1-xCrxS nanoparticles were successfully prepared using the coprecipitation method, where x represents the concentration (x = 0.00, 0.10, and 0.05). There are many analytical methods used, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and Spectroscopy of energy dispersive (EDS). The magnetism structure of the catalysts was investigated using spectrophotometry (VSM), thermogravimetric analysis (TGA), and differential thermal analysis (DTA). X-ray diffraction studies determine the nanocrystal arrangement and size of microcrystals. As seen in SEM analysis, the particles are agglomerated. The coordination of sulfur ions around zinc ions was examined using FTIR analysis. The energy band gap of the Cr-doped sample increases. Photoluminescence spectroscopy showed that the violet emission around 424 nm could be attributed to the excitation process of electrons from the low energy of the conduction band to the valence band of sulfur intermediate atoms. The front amplitude of doped ZnS nanocrystals remains constant regardless of the amount of Cr present. The results show that the ZnS nanocrystals were replaced by dilute Cr3+ ions. Cr-doped ZnS exhibits diamagnetic properties under hightemperature conditions. The results show that these materials are improved by the Cr doping process, making them suitable for many applications.

Computational Investigation on Cr-Doped Sc2CO2 MXene under Strain for Electronic Properties, Quantum Capacitance, and Photocatalytic Activity.

Sc2CO2 MXene has potential applications in energy storage and optoelectronics due to its superior structure and excellent properties. The electronic properties, quantum capacitance, and photocatalytic activity of Cr-doped Sc2CO2 under strain are studied by the density functional theory. Cr doping makes the system produce magnetism. The spin-down states of Sc2CO2-Cr under strain are direct semiconductors, while their spin-up states are indirect semiconductors. Sc2CO2-Cr under +5, -5, -3, and -2% strains in an aqueous system are suitable for cathode material. A large voltage drastically modulates the type of electrode materials. Sc2CO2-Cr under strains from 0 to +2% can perform the oxygen evolution reaction at an alkaline environment, while the Sc2CO2-Cr system under strain is a good for CO2 photocatalysis at pH 0 and 7.

Effect of Cr doping on electronic and optical properties of mono/bilayer MoTe2 nanosheets– a first-principles study

The influence of Cr-doping on mono/bilayer MoTe2 nanostructures is studied within the framework of density functional theory (DFT) since doping may be used to effectively tailor the electronic and optical characteristics in a desired manner. Chromium (Cr) seems to modify the electronic properties and energy band gap of MoTe2 considerably. At first, we confirmed the stability of the proposed structure with the support of cohesive formation energy and phonon-band-spectrum. Moreover, doping with Cr on MoTe2 produces a red shift towards far infra-red region in the absorption coefficient, thus making it suitable for far infra-red region applications. Hence, Cr doping is employed in this work. When Cr impurities are substituted in pristine MoTe2 nanostructures, the band structure gets modified. Additionally, the band gap of mono/bilayer MoTe2 nanostructures reduces from 1.143/0.74 eV for pristine MoTe2 to 0.807/0.621 eV for 8 % substitution of Cr. By examining absorption spectra, it was found that the optical characteristics of mono/bilayer MoTe2 changed significantly with doping of Cr impurities. The results of this study provide insight into the band structure, optical, and electronic attributes of mono/bilayer MoTe2 nanostructures that could be further fine-tuned for optoelectronic applications using substitution of Cr impurities.

Broadband Near-Infrared Emission from Bi/Cr Co-Doped Aluminosilicate Glasses.

Bismuth-doped aluminosilicate glass has garnered significant attention due to its unique ultra-wide luminescence properties in the near-infrared (NIR) band. Enhancing the NIR luminescence of Bi-doped glass remains challenging. To achieve Bi-doped glass with more excellent luminescent properties, a series of Bi/Cr co-doped glasses were prepared, and the optical and structural properties of the samples were observed. The results indicate that low-concentration Cr doping broadens the luminescence range of Bi/Cr co-doped glass samples. The luminescence peak of Bi in the samples is at 1230 nm, while the peak of Cr is around 804 nm. The addition of an appropriate amount of Bi2O3 can enhance the NIR luminescence of Bi and Cr in the sample, realizing the energy conversion between Bi and Cr. Bi/Cr co-doped is a novel approach for achieving broadband NIR luminescence in glass materials.

Tailoring the optoelectronic and spintronics properties of Cr-doped ZnS nanostructure thin films

This paper discusses the tailoring of the optoelectronic and spintronic of Cr3+-doped ZnS nanostructured electron beam evaporated thin films. The XRD measurements confirm the zinc blende cubic structure for the films with a preferred orientation along the (111) direction. The nanostructured features of the films were verified from the XRD and AFM results. The EDXS and XPS data show the stoichiometric chemical and electronic states of the films. Spectrophotometry measurements for the films show that the energy gap decreases from 3.67 eV to 3.43 eV as the Cr3+ increases from 0 at. % to 8.0 at.%. Such reduction of the Eg of the Cr3+-doped ZnS is attributed to the sp-d coupling. The strong PL asymmetric peak of the Cr3+-doped ZnS is observed, which is quenched and red shifted with increasing Cr doping level. Furthermore, the magnetic measurements show the occurrence of weak room temperature ferromagnetic behavior. On the other hand, the results further show that the magnetization increases with the increase of the Cr3+ dopants up to x = 0.05, then decreases with increasing the Cr doping above x = 0.05. This can be attributed to the development of the antiferromagnetic ordering.

Synergistic effects of vacancy and doping at Ge sublattices on the electronic and magnetic properties of new Janus Ge2PAs monolayer

Recently, 2D materials based on IV-V group have attracted great attention because of their interesting physical properties. In this work, Janus Ge2PAs monolayer with good stability is predicted using first-principles calculations. Our simulations assert its non-magnetic semiconductor nature with an indirect band gap of 1.11(1.75)eV obtained by PBE(HSE06)-based calculations. Further, vacancy defects and doping with transition metals (TMs = Cr and Mn) are explored in order to induce novel physical aspects. It is found significant magnetization of Janus Ge2PAs monolayer induced by Ge vacancies with total magnetic moments between 1.58 and 1.97 μB, where magnetism is produced mainly by atomic species around the defect sites. Herein, single Ge vacancy metalizes the monolayer, while the half-metallicity is obtained by creating a pair Ge vacancies. Regardless doping site, feature-rich diluted magnetic semiconductor and half-metallic behaviors are also obtained in Janus Ge2PAs monolayer by doping with Cr and Mn atom, respectively. In these case, TM impurities originate mainly the system magnetism with total magnetic moments between 2.00 and 3.03 μB. In addition, the coexistence of Ge vacancy and doping is also investigated. The calculated spin density shows an antiparallel spin orientation of Cr dopant and its neighboring atoms, meanwhile a parallel spin orientation is observed for Mn impurity and its neighboring atoms. Consequently, small total magnetic moment of 0.53 μB is obtained by the synergistic effects of doping with Cr and Ge vacancy, meanwhile the coexistence of Mn dopant and Ge vacancy generates a larger value of 4.88/4.89 μB. In all cases, the origin of electronic and magnetic properties is unraveled. Our results introduce new prospective spintronic 2D materials made from a new Janus Ge2PAs monolayer.