Optimal Doping Ratio Research Articles

Enhancing the diffusion capabilities of oxygen ions and hydrogen protons in protonic ceramic fuel cells at intermediate temperatures through doping material and ratio adjustments

Abstract This study aims to investigate the changes in the diffusion capabilities of oxygen ions and hydrogen protons within the electrolyte materials of protonic ceramic fuel cells (PCFC) under various doping materials, doping ratios, and temperature effects. It utilizes molecular dynamics methods combined with the ReaxFF force field to analyze the reactivity and transport characteristics of oxygen ions and hydrogen protons in the BZY (Yttria-doped barium zirconates) microstructure of PCFCs. The research finds that for intermediate temperature ranges (573 K–773 K), the optimal doping ratio of Y2O3 is 13.6%, and at an operating temperature of 673 K, using MgO as a doping material for BZY can enhance the diffusion coefficient of hydrogen protons in the electrolyte, thereby optimizing the performance of PCFC.

Tuning the composition of manganese cobaltite spinel with tungsten for enhanced energy storage performance

The development of efficient and innovative energy storage devices is a necessity of the hour. Emerging nanomaterials possessing tungsten are believed to have unique physicochemical properties and their application could be extended over a wide spectrum as nanocomposite electrodes for effective high voltage energy storage applications. In the present work, a one-step hydrothermal process has been employed to prepare Tungsten (W) doped spinel oxide MnWxCo2–2xO4 (MWCO) nanostructures, where x varies from 0.01 to 0.05. The spectroscopic characterization studies proved spherical subunits embedded onto nanosheets formed by W doped bimetallic oxide with a crystalline phase. On employing the synthesized material in asymmetric supercapacitor application, it was inferred that W doping had a notable effect on the electrochemical performance. The optimized doping ratio (x=0.03) revealed an appreciable specific capacitance of 91 F g−1 at the current of 0.5 A g−1, with a retention in the capacitance of more than 80 % even after 10000 GCD cycles. Remarkable specific energy (3.17 Wh kg−1) and specific power (98 W kg−1) were also noted. Hence, the material synthesized in this study by our facile method is thought to be highly suitable as an electrode for high-performance energy storage applications.

V-Doping Strategy Induces the Construction of the CoFe-LDHs/NF Electrodes with Higher Conductivity to Achieve Higher Energy Density for Advanced Energy Storage Devices.

Doping of metal ions shows promising potential in optimizing and modulating the electrical conductivity of layered double hydroxides (LDHs). However, there is still much room for improvement in common metal ions and conventional doping methods. In contrast to previous methodologies, a hollow triangular nanoflower structure of CoFeV-LDHs is devised, which is enriched with a greater number of oxygen vacancies. This resulted in a significant enhancement in the conductivity of the LDHs, leading to an increase in energy density following the appropriate doping of V. To investigate the impact of V-doping on the energy density of the LDHs, in situ XPS and in situ X-ray spectroscopy is employed. Regarding electrochemical performance, the CoFeV-LDHs/NF electrode with optimal doping ratio exhibited a specific capacitance of 881Fg-1 at a current density of 1Ag-1. The capacitance remained at 90.53% after 3000 cycles. In addition, the constructed battery-type supercapacitor CoFeV-LDHs/NF-2//AC exhibited an impressive energy density of 124.7Whkg-1 at a power density of 850Wkg-1 and capacitance remained almost unchanged at 95.2% after 3000 cycles. All the above demonstrates the great potential of V-doped LDHs and brings a new way for the subsequent research of LDHs.

The effect of Zn doping on the structure, phase transformation and electric properties of 0.5BZT-0.5BCT materials

In the current study, an improved method of adding Zn ion doping to the 0.5BZT–0.5BCT–based films with high pyroelectric properties was designed. Under different Zn ion doping ratios, the structure, dielectric constant, phase transition relationship and other characteristics of the test product were analyzed experimentally to obtain the optimal ratio parameters. The experimental results demonstrate that the dielectric properties of the 0.5BZT–0.5BCT–xZn–based films proposed in this study can be far superior to those of other films under the optimal preparation process. The optimal dielectric properties and ferroelectric properties are obtained when the doped data are 0.008. Considering the comprehensive dielectric and energy storage capacity, the optimal doping ratio is 0.01, which can take into account dielectric data and energy storage performance. The energy storage density is 1.842 J/cm3, and the energy storage efficiency exceeds 30%. From 0 to 0.02, the properties of the material, such as the hysteresis loop and phase transition relationship are excellent. The properties of the materials studied in this study are excellent, and they are excellent candidate materials for the future application of ferroelectric materials, and provide ideas for related work.

Pd-induced polarized Cu0-Cu+ sites for electrocatalytic CO2-to-C2+ conversion in acidic medium

The acidic CO2 reduction reaction (CO2RR) offers a promising approach to mitigate CO2 reactant loss and carbonate deposition, which are challenging issues in alkaline or neutral electrolytes. However, the hydrogen evolution reaction (HER) competes in the proton-rich environment near the catalyst surface as a side reaction, reducing the energy efficiency of generating multi-carbon (C2+) products. In this work, we proposed a palladium (Pd) doping strategy in a copper (Cu)-based catalyst to stabilize polarized Cu0-Cu+ sites, thus enhancing the CC coupling step during the CO2RR while suppressing HER. At an optimal doping ratio of 6%, the Pd dopants were well dispersed as single atoms without aggregation, allowing for the stabilization of subsurface oxygen (OSub), preserving the polarized Cu0-Cu+ active sites, and reducing the energy barrier of CC coupling. The Pd-doped Cu/Cu2O catalyst exhibited a peak Faradaic efficiency (FE) of 64.0% for C2+ products with a corresponding C2+ partial current density of 407.1 mA∙cm−2 at −2.18 V versus a reversible hydrogen electrode, a high CO2 single-pass conversion efficiency (SPCE) of 73.2%, as well as a high electrochemical stability of ∼ 150 h at industrially relevant current densities, thus suggesting a potential approach for tuning the electrocatalytic CO2 performances in acidic environments with higher carbon conversion efficiencies.

Insights into nitrogen-doped BiOBr with oxygen vacancy and carbon quantum dots photocatalysts for the degradation of sulfonamide antibiotics: Actions to promote exciton dissociation and carrier migration

The strong excitonic effect significantly influences the efficiency of electron-hole pair generation. Therefore, promoting the dissociation of excitons into free charge carriers has drawn much attention. In this study, nitrogen (N)-doped BiOBr photocatalyst (BOBNC) modified with carbon quantum dots (CQDs) was synthesized via a solvothermal method. We demonstrated through photoluminescence and photoelectrochemical techniques the synergistic effect of oxygen vacancies and CQDs, facilitating exciton dissociation and charge carrier migration, consequently significantly enhancing the electron density in the material. Compared to pure BiOBr, degradation experiments revealed that the optimized doping ratio of 0.5BOBNC with CQDs increased the rate constant for sulfamethoxazole (SIZ) by 19.89 times. Furthermore, based on quenching experiments, electron spin resonance (ESR) tests, and DFT calculations, h+, O2•− and 1O2 were identified as the primary reactive species for SIZ degradation, and a photocatalytic mechanism was proposed. Additionally, the influence of various environmental factors on the photocatalytic system was investigated. In conclusion, this work not only contributes to a profound understanding of BiOBr exciton dissociation but also presents a promising photocatalytic technique for the remediation of diverse water environments.

Amino–Functionalized Multi–walled Carbon Nanotube/SPEEK Hybrid Proton Exchange Membrane for Iron–chromium Redox Flow Battery**

AbstractIn the field of iron–chromium redox flow battery (ICRFB), the optimal doping ratio of the amino–functionalized multi–walled carbon nanotube (MWCNT−NH2) blended with SPEEK as hybrid proton exchange membrane (PEM) is determined to be 2 wt % by series tests. The ICRFB single–cell containing the S/MWCNT−NH2−2 PEM was tested and compared with the Nafion 212 and original SPEEK PEMs. It is worth noting that the single–cell containing S/MWCNT−NH2–2 exhibits significantly higher coulombic efficiency (CE : 96.06 %) and energy efficiency (EE : 88.68 %) under 40 mA cm−2 than that of the Nafion 212 (EE : 82.83 %, CE : 88.9 %). Differing from the original SPEEK PEM, it also exhibits higher EE (82.04 %) than the Nafion 212 (81.09 %) at 100 mA cm−2. During the self–discharge test, the lower permeability of iron/chromium ions through S/MWCNT−NH2–2 PEM also allows for a longer self–discharge time than the other two single–cells. Additionally, the single–cell containing S/MWCNT−NH2–2 showed a smaller decay range of EE (from 82.67 % to 77.36 %) and more discharge capacity retention (48 %) than that of the Nafion 212 (EE : from 82.64 % to 75.01 %, discharge capacity retention: 18 %) after 100 cycles, which suggests that the hybrid SPEEK PEM with optimal content of MWCNT−NH2 has a great potential to replace Nafion PEMs in the large‐scale commercialization of ICRFB.

The Oxidation Performance of a Carbon Soot Catalyst Based on the Pt-Pd Synergy Effect

Pt-Pd-based noble metal catalysts are widely used in engine exhaust aftertreatment because of their better carbon soot oxidation performance. At present, the synergistic effect of Pt and Pd in CDPFs, which is the most widely used and common doping method, in catalyzing the combustion of carbon smoke has not been reported, and it is not possible to give an optimal doping ratio of Pt and Pd. This paper investigates the carbon soot oxidation performance of different Pt/Pd ratios (Pt/Pd = 1:0, 10:1, 5:1, 1:1) based on physicochemical characterization and particle combustion kinetics calculations, aiming to reveal the Pt-Pd synergistic effect and its carbon soot oxidation law. The results show that Pt-based catalysts doped with Pd can improve the catalyst dispersion, significantly increase the specific surface area, and reduce the activation energy and reaction temperature of carbon soot reactions, but excessive doping of Pd leads to the enhancement of the catalyst agglomeration effect, a decrease in the specific surface area, and an increase in the activation energy and reaction temperature of the carbon soot reaction. The specific surface area and pore capacity of the catalyst are the largest, and the activation energy of particle oxidation and the pre-exponential factor are the smallest (203.44 kJ∙mol−1 and 6.31 × 107, respectively), which are 19.29 kJ∙mol−1 and 4.95 × 108 lower than those of pure carbon soot; meanwhile, the starting and final combustion temperatures of carbon soot (T10 and T90) are the lowest at 585.8 °C and 679.4 °C, respectively, which are 22.1 °C and 20.9 °C lower than those of pure carbon soot.

Material and Antibacterial Properties of Spinel-Structure Ca-Doped ZnCo2O4 Thin Films

In the preparation of Zn(Co1−xCax)2O4 thin films with doping content ratio Cax = 0.00–0.20, analysis shows that no impurity phase is formed in spinel-structure thin films, while doping calcium reduces the grain size of the thin films and the planarization of the surface microstructure. Increasing the doping content ratio of calcium will reduce the ability of the film to absorb blue and ultraviolet light, and reduce the characteristic absorption of ZnCo2O4. The energy gap of Zn(Co1−xCax)2O4 film increases from 2.46 eV at Cax = 0.00 to 2.51 eV at Cax = 0.15. Moreover, doping Ca+2 to replace Co+3 increases the conductivity and carrier concentration, for which the optimal doping ratio is Cax = 0.07. The film resistivity decreases from 270.5 Ω-cm (undoped) to 15.4 Ω-cm (Cax = 0.07) and the carrier concentration increases from 2.54 × 1015 (undoped) to 6.25 × 1017 cm−3 (Cax = 0.07). Under ultraviolet light irradiation and in an environment without any light source, the film exhibits anti–E. coli resistance as high as 99.94% and 99.99%. Thus, P-type Zn(Co1−xCax)2O4 films can be used for antibacterial and electronic components.

Structural, optical, and electrical properties of strontium-doped tin dioxide films for high photoconductivity

In this work, tin dioxide (SnO₂) films with different concentrations of strontium (Sr) were prepared using sol-gel and immersing methods. The structural, morphological, optical, and electric properties of Sr-doped SnO₂ films were investigated for photoconductivity applications. X-ray diffraction patterns revealed a tetragonal rutile structure for the deposited films with lattice parameters (a = b = 4.726 Å, c = 3.182 Å). Adding 4.71 at.% of Sr (optimal doping ratio) into SnO2 film leads to a significant decrease in the crystallite size. Consequently, the highest electrical conductivity of Sr-doped SnO₂ films is attained at 4.71 at.%. The transmittance and optical bandgap of Sr-doped SnO₂ films exhibit a significant decrease at a high Sr doping ratio of 10.07 at.%. Additionally, the electrical conductivity of undoped SnO2 and Sr-doped SnO2 (4.71 at. %) films increases from 0.22 S/cm and 2.18 S/cm to 0.43 S/cm and 4.95 S/cm under UV-irradiation, respectively, with good consistency and repeatability. The findings of this work indicate that Sr-doped-SnO2 films are potential candidate materials for a wide range of applications, especially photoconductivity, photodetectors, and photoconductive materials.

Effect of AlN nanoparticle doping on thermophysical properties of nitrate via mechanical milling: Experimental studies and microscopic mechanisms

A compounding method based on ball milling was used to incorporate AlN into LiNO3 to effectively improve its thermal conductivity. The optimal doping ratio was determined to be 2 wt% with an increase in thermal conductivity of 112.09 % integrating the enthalpy decrease. From the perspective of molecular dynamics simulations, it is demonstrated that AlN achieves a better matching of vibrations with LiNO3 by changing its vibrational modes at the doping ratio of 2 wt% with the support of vibration density of states, overlapping energy and phonon participation ratio. When 2 wt% AlN was added, non-local vibrational modes of LiNO3 increased, which microscopically illustrated the intrinsic mechanism of 2 wt% as the optimal doping ratio. The radial distribution function was used to explain the microscopic mechanism behind the changes in the specific heat of LiNO3 concerning temperature. The reason why the enthalpy of LiNO3 would decrease after AlN added is that AlN can bind LiNO3 molecules on the surface, and LiNO3 is confined by stronger intermolecular forces, leading to a blockage of its phase change behavior. This study proposed a doping method that can uniformly disperse AlN and avoid crystallized water. It also provides a strategy for selecting the appropriate nanoaddictives for compositing in molten salts to enhance energy storage efficiency.

Theoretical understanding of defects-driven mechanoluminescence for Pr3+-doped NaNbO3/LiNbO3 heterojunctions

Mechanoluminescence (ML), which involves the emission of light under mechanical stimuli, shows great potential in various applications such as sensing, imaging, and energy harvesting. Current research suggests that the luminescence mechanism of ML is typically connected to specific defects present within the material. In this study, we focus on the investigation of ML defects in Pr3+-doped NaNbO3/LiNbO3 heterojunctions, employing a combination of experimental and theoretical approaches. Through experimental analysis, we confirmed the presence of the heterojunction and its influence on ML intensity, and the optimal doping ratio for the heterojunction in ML was established. Furthermore, we examined the influence of varying Pr3+ doping concentrations on ML behavior and a proof-of-concept was demonstrated using the X-rays charged heterostructural phosphor as a stress sensor for biological applications. The position and concentration of internal defects in the ML material were scrutinized through thermoluminescence tests employing the variable heating rate method and positron annihilation. Complementing the experimental findings, theoretical simulations were conducted to elucidate the underlying mechanisms responsible for the observed ML defects. Density functional theory calculations were employed to investigate the energy levels, charge transfer processes, and lattice distortions within the heterojunctions under mechanical stress. Theoretical predictions were compared and validated against the experimental results. The integration of experimental and theoretical approaches provides a comprehensive understanding of the ML behavior of Pr3+-doped NaNbO3/LiNbO3 heterojunctions. The insights gained from this research contribute to the development of novel ML materials and pave the way for their applications in next-generation sensing and energy conversion devices.

CuO/TiO2/MXene-Based Sensor and SMS-TENG Array Integrated Inspection Robots for Self-Powered Ethanol Detection and Alarm at Room Temperature.

In this study, a high-precision CuO/TiO2/MXene ethanol sensor operating at room temperature was prepared. The sensor exhibits excellent response value (95% @1 ppm ethanol), extremely low detection limit (0.3 ppm), fast response/recovery time (16/13 s), and remarkable long-term stability for trace detection of ethanol gas at room temperature, attributed to the p-n heterojunction formed by CuO and TiO2, as well as the rich functional groups and large specific surface area of MXene. Furthermore, a high-performance triboelectric nanogenerator (SMS-TENG) was developed through the introduction of the silicone/Mxene@silicone dual dielectric layer as the triboelectric layer, which improves the charge storage capacity of the dielectric layer and greatly enhances the output performance of the TENG. At the optimal doping ratio, the open-circuit voltage of the SMS-TENG can reach 1160 V, which is sufficient to light 720 LEDs. By combining the sensor and SMS-TENG, the resistive response of ethanol sensing is converted to a voltage response, which amplifies the response value up to 15.8 times. Finally, the designed SMS-TENGs are expected to be arrayed on an inspection robot as energy supply and combined with the CuO/TiO2/Mxene ethanol sensor to build a self-powered ethanol detection alarm system, endowing the inspection robot with the capability of self-powered ethanol detection at ppb level. This work provides an effective pathway for the intelligence of ethanol detection.

Enhanced ionic conductivity of Li1.3Al0.3Ti1.7(PO4)3 under the influence of graphene oxide

As a new type of clean and efficient energy storage device, lithium-ion batteries have been widely used in electronic products, electric vehicles, and other fields, and the accompanying safety issues are of increasing concern. Therefore, solid-state lithium-ion conductors have become a current research hotspot. This paper used graphene oxide material to design and prepare Li1.3Al0.3Ti1.7(PO4)3 solid electrolytes by the co-precipitation method and performed some relevant characterizations. The results showed that the addition of graphene oxide optimized the electrolyte structure improved the density of the powder, promoted grain growth, improved the transport path of lithium ions, and thus increased the total ionic conductivity. The optimal doping ratio was 0.5 wt%, and the total ionic conductivity reached the maximum of 2.42 × 10−4 S/cm. Compared to pure Li1.3Al0.3Ti1.7(PO4)3, the ionic conductivity increased by 154% after using the graphene oxide. It is believed that larger grains, fewer grain boundaries, and denser microstructure resulted in a less distorted migration pathway for lithium ions. Under the influence of graphene oxide, Li1.3Al0.3Ti1.7(PO4)3 exhibited better air stability than pure Li1.3Al0.3Ti1.7(PO4)3 electrolyte. The electrolyte prepared in this study showed great application potential in all-solid-state batteries.

Construction of NiCoAl-layered trimetallic hydroxides@mesoporous carbon core-shell hollow nanospheres for high-performance battery-type supercapacitors

Developing electrode materials with hierarchically porous structure and high electrochemical stability is crucial for improving the energy density of supercapacitors (SCs). Herein, the NiCoAl layered trimetallic hydroxides supported on hollow carbon shells (NCA@HCs LTHs) with various Al doping amounts is synthesized by a simple hydrothermal method. The electrode material with the optimal NCA doping ratio (mass ratio 3:2:0.3) displays a stable layered hydroxides structure and low crystallinity. Additionally, the unique 3D hollow structure not only increases the specific surface area (SSA) but also effectively prevents the agglomeration of LTHs. The synergistic interaction of these two aspects is responsible for the exceptional specific capacity and cycling performance. The optimal N3C2A0.3 @HCs LTHs exhibits a high specific capacitance of 792 C g−1 at 1 A g−1. Moreover, the constructed asymmetric supercapacitor (ASC) achieves a coulombic efficiency of 98% and retains 80% of its capacitance after 12,000 cycles at 5 A g−1. The above results show that the synergistic strategy of Al doping and hollow structure design provides new insights into improving the electrochemical performance of SCs.

Efficient heterogeneous activation of peroxymonosulfate by Ag-doped CoFe2O4 nanoparticles for sulfamethoxazole degradation

In this work, silver-doped cobalt ferrite catalysts Agx-CoFe2O4 (x = n(Ag+): n(Fe3+); x = 0, 0.02, 0.04, 0.06, and 0.08) were synthesized through the reverse co-precipitation method and employed to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation. Ag0.06-CoFe2O4 exhibited the best catalytic activity and PMS utilization efficiency, indicating the optimal silver doping ratio. The characterization results revealed that Ag doping led to the exposure of more active sites and the increase of the concentration of oxygen vacancies (OV). The effects of Ag0.06-CoFe2O4 dosage, PMS concentration, initial pH, inorganic ions, and humic acid on SMX degradation by Ag0.06-CoFe2O4/PMS system were investigated. The utilization of 0.1 g/L Ag0.06-CoFe2O4 and 0.1 mM PMS resulted in a remarkable 95.1 % degradation efficiency of 10 μM SMX in 30 min at initial pH of 5.0. Quenching experiments and electron paramagnetic resonance (EPR) analysis revealed the presence of both radical species (HO•, SO4•− and O2•−) and non-radical species (1O2) in Ag0.06-CoFe2O4/PMS system, among which SO4•− and 1O2 played a predominant role in SMX degradation. The catalytic cycle between≡CoOH+/≡CoO+ and PMS and the interaction of OV with adsorbed oxygen should contribute to PMS activation. The cycling experiments and X-ray diffraction (XRD) patterns before and after the reaction showed that Ag0.06-CoFe2O4 exhibited remarkable stability and reusability. The transformation products (TPs) of SMX were identified, and three possible degradation pathways were proposed. Most of these TPs demonstrated lower toxicity compared to SMX, as predicted by the Ecological Structure−Activity Relationship Model.

Experimental Investigation on Plume Characteristics of PTFE-Filled Carbon, Graphite, Graphene for Laser-Assisted Pulsed Plasma Thruster

This paper presents an investigation into the plume characteristics of composite propellants fabricated by polytetrafluoroethylene (PTFE) filled with different carbon additives (nano-carbon powder, graphite, and graphene) under laser irradiation in a vacuum environment. The dynamic plumes generated by the laser ablation of different modified propellant samples were captured using a high-speed camera, and the feature parameters of the plumes were extracted by image processing. The results indicated that doping carbon particles in PTFE enhanced the quality of the plasma plumes. The plume area increased up to a certain value and then stabilized, while end of plume clusters remained for a short time. Further analysis revealed that the propellant sample doped with graphene exhibited the maximum plume length and expansion rate, whereas the propellant sample doped with nano-carbon demonstrated the largest plume area. Moreover, a higher graphene doping ratio promoted greater plume length, expansion speed, and plume area. However, when the doping ratio exceeded 3%, the gain of the plume parameters gradually became saturated, and the optimal doping ratio appeared to be 5%.

Humidity sensitivity reducing of moisture swing adsorbents by hydrophobic carrier doping for CO2 direct air capture

The application of quaternary ammonium-based moisture-swing adsorbent provides an effective strategy for direct air capture (DAC) with low energy consumption of regeneration. This study optimized a fabrication method of shaped adsorbents and a hydrophobicity regulation method by doping polyvinylidene difluoride (PVDF). Characterization of the shaped adsorbents showed a desirable surface area and pore structure. Experiments of CO2 adsorption revealed that the adsorbents exhibited excellent CO2 adsorption capacity (∼0.90 mmol/g) in relative humidity (RH) range of 20 ∼ 85% was enhanced by 160% of that before doping. Meanwhile, a high CO2 adsorption rate (with a half-time of 3.6 ∼ 3.82 min) at 84.7% RH was displayed. The optimal doping ratio of PVDF was found to be 25% (QAR-25% PVDF). It can effectively release CO2 with 100% RH, and heat assistance (<60 °C) can be considered for optimal results. QAR-25% PVDF exhibited a cyclic capacity of 0.90 mmol/g after ten cycles, demonstrating its stability and reusability. DFT and microscopic characterization revealed the key role of C-F bond in promoting the hydrophobicity of adsorbents. Meanwhile, the isotherm of H2O/CO2 adsorption illustrated that doping PVDF could effectively reduce the humidity sensitivity of shaped adsorbents and improve CO2 adsorption rate significantly. Among DAC adsorbents reported previously, the adsorbents developed in this study showed higher functional group efficiency (ηQA = 0.89) at high humidity conditions. The fabrication method of shaped adsorbent provides a viable strategy for its large-scale deployment. Doping hydrophobic carriers into the adsorbent material is a simple yet effective way to reduce its humidity sensitivity, enabling it to better adapt to complex environmental conditions.

An effective copper doping strategy of Co(OH)F cathode for producing hydrogen in microbial electrolytic cells

In this study, the effective Cu doping Co(OH)F catalyst with three-dimensional network nanowires is successfully prepared by the one-step in situ hydrothermal route for Microbial Electrolytic Cell (MEC) cathode to improve the overall hydrogen production rate. The results demonstrate that the optimized doping ratio Cu-Co(OH)F exhibits a high open three-dimensional network structure and a good electrochemical hydrogen evolution activity (Tafel slope is 52.0 mV dec−1). In addition, the MEC with Cu-Co(OH)F cathode exhibits an extremely high current density of 69.2 A m−2, hydrogen production rate of 214.5 ml H2 L−1 cycle−1, and coulombic efficiency of 80.75%, which significantly improved the activity compared with undoped one. The results of density functional theory (DFT) calculations confirm that the doping of copper could regulate the electron transport rate and the Gibbs free energy to accelerate the process of hydrogen evolution, thus resulting in excellent hydrogen production in MEC.

Exploration of the oxidation behavior and doping ratio of the Si–HfO2 bond layer used in environmental barrier coatings

AbstractHafnia doping is expected to improve the performance of the silicon‐bond layer of environmental barrier coatings (EBCs) for SiC‐based ceramic matrix composites. The optimal doping ratio, distribution of HfO2, and oxidation mechanism of the bond layer have not yet been fully addressed. A prototype Si–HfO2 bond layer with a designed HfO2‐rich area was used to examine its oxidation behavior. A random dispersion model was developed to calculate the optimal HfO2 doping ratio and its appropriate distribution state. The simulation results recommended that 20–30 vol% is the optimal doping ratio, where HfO2 is well dispersed inside Si without forming networks. This enables HfO2 to react with and consume SiO2 without accelerating oxygen diffusion inside the bond layer. This was confirmed by oxidation experiments on Si–xHfO2 tablets, in which the thinnest thermally grown oxide was achieved for the 20 vol% HfO2‐doped Si tablet. Both the microstructure design and material composition selection are highly important to further boost the performance of the EBCs.