Polarization Resistance Research Articles

Electrochemical performance of sodium compound NaNi0.4Fe0.2Mn0.4O2 as symmetrical electrode for low temperature ceramic fuel cells

The electrochemical performance and related mechanisms of NaNi0.4Fe0.2Mn0.4O2 (NNFM) as symmetrical electrode for low-temperature ceramic fuel cells were investigated. After reduction in H2 at elevated temperature, sodium compounds including NaOH molten salt are formed in the NNFM anode, which diffuses into the GDC electrolyte, creating a composite electrolyte of “GDC-sodium compounds” with high ionic conductivity. The ionic conductivity of the “GDC-sodium compounds” composite electrolyte generated in the cell with GDC/NNFM (weight ratio 8/2) composite as the electrolyte layer reached 0.116 S · cm−1 at 550 °C. The maximum power density of the cell with the “GDC-sodium compounds” composite electrolyte reaches 273 mW · cm−2 at 550 °C. The presence of molten salt in the sodium compounds enhances the electrolyte’s ionic conductivity while also contributing to the filling of internal pores and ensuring effective fuel gas sealing. The formation of sodium compounds molten salt within the cell also significantly reduces the polarization resistance associated with the electrode reactions in the electrodes on both sides of the cell.

Effect of discharge thermal action in ECDM on electrochemical behaviours of matrix material and its recast layer in glycol-based solution

The interaction between thermal and electrochemical corrosion in the ECDM process remains unclear. This study clarifies the effect of discharge thermal action on electrochemical corrosion. Real-time temperature curves indicate that the solution temperature in the electrochemical corrosion zone increased significantly due to discharge thermal action. The corrosion resistance of the recast layer’s passive film is superior to that of the matrix due to the enrichment of Cr2O3. As the electrolyte temperature rises, the passive film thickens but shows lower polarization resistances and poorer corrosion resistance due to a loose and weak structure. The matrix material and its recast layer dissolved uniformly, resulting in a considerably flat surface in a glycol-based solution, with enhanced levelling efficiency due to discharge thermal action.

Electrochemical synthesis, physical properties and corrosion behavior of electropolymerized polyaniline films developed on 316L stainless steel

AbstractPolyaniline (PANI) films may be developed on metallic substrates by a variety of electrochemical techniques. In the present work, PANI films were electrodeposited on AISI 316L stainless steel substrates by cyclic voltammetry (CV), chronoamperometry (CA), and chronopotentiometry (CP) with the objective of comparing the efficacy of each method, based on the integrity of the developed films. Cyclic voltammetry and anodic polarization were used to determine optimal electrodeposition parameters for the development PANI films using the CA and CP methods. The structure and morphology of the coatings were characterized by scanning electron microscopy, energy‐dispersive x‐ray spectroscopy, Fourier‐transform infrared spectroscopy, and ultraviolet–visible spectroscopy. Among the evaluated techniques, CV led to the formation PANI films with the best homogeneity as well as the lowest number of defects, such as cracks or pores. Subsequently, the corrosion resistance of AISI 316L steels with and without PANI was compared in a physiological saline solution (0.9% NaCl). Potentiodynamic polarization tests indicated that the PANI‐coated samples exhibited lower corrosion current density values (0.012 vs. 0.018 μA/cm2) and lower passive current density values (0.04 vs. 0.06 μA/cm2) in comparison to the bare AISI 316L steel. Additionally, long‐term monitoring by electrochemical impedance spectroscopy revealed that PANI films consistently exhibited superior polarization resistance up to 32 days of exposure in the 0.9%NaCl solution (233,000 vs. 207,000 Ωcm2).

Zr and Y co-doped SrFe0.8Zr0.1Y0.1O3-δ perovskite oxide as a stable, high-performance symmetrical electrode for solid oxide cells

Symmetrical solid oxide cells (SSOCs), which use the same material for both anode and cathode, simplify the cell fabrication process and effectively resist carbon deposition and sulfur poisoning. In this study, Zr, Y co-doped SrFe0.8Zr0.1Y0.1O3-δ (SFZY) perovskite oxide is synthesized and evaluated its properties as an SSOFCs electrode. Density functional theory (DFT) indicates that the local state density of SFZY is lower than that of SrFeO3-δ (SFO). SFZY has good chemical compatibility with La0.8Sr0.2Ga0.83Mg0.17O3−δ (LSGM) electrolyte below cell operating temperature. Zr, Y co-doped SrFe0.8Zr0.1Y0.1O3-δ maintains structural stability in H2 atmosphere. At 750 ℃, the polarization resistance (Rp) of SFZY is 0.11 and 1.06 Ω cm2 in air and hydrogen atmosphere, respectively. During the Rp stability test, SFZY exhibits better stability than that of SrFeO3-δ in air and hydrogen atmosphere. At 750 ℃, the maximum power density of SFZY/LSGM/SFZY fuel cell reaches 420.1 and 258.31 mWcm−2 using H2 and wet C3H8 as fuel, respectively. In electrolytic mode, the current density of SFZY/LSGM/SFZY electrolysis cell reaches -0.55 A cm−2 at 1.3 V for electrolysis of pure CO2 at 750 ℃. In summary, SFZY has a great potential as SSOCs electrode.

An Electrochemical Study of the Effect of Sulfate on the Surface Oxidation of Pyrite.

Pyrite is one of the most abundant metal sulfide tailings and is susceptible to oxidation, yielding acidic mine drainage (AMD) that poses significant environmental risks. Consequently, the exploration of pyrite surface oxidation and the kinetic influencing factors remains a pivotal research area. Despite the oxidation of pyrite producing a significant amount of sulfate (SO42-), a comprehensive investigation into its influence on the oxidation process is lacking. Leveraging pyrite's semiconducting nature and the electrochemical intricacies of its surface oxidation, this study employs electrochemical techniques-cyclic voltammetry (CV), Tafel polarization, and electrochemical impedance spectroscopy (EIS)-to assess the effect of SO42⁻ on pyrite surface oxidation. The CV curve shows that SO42- does not change the fundamental surface oxidation mechanism of pyrite, but its redox peak current density decreases with the increase in SO42-, and the surface oxidation rate of pyrite decreases. The possible reason is attributed to SO42- adsorption onto pyrite surfaces, blocking active sites and impeding the oxidation process. Furthermore, Tafel polarization curves indicate an augmentation in polarization resistance with elevated SO42- concentrations, signifying heightened difficulty in pyrite surface reactions. EIS analysis underscores an increase in Weber diffusion resistance with increasing SO42⁻, indicating that the diffusion of Fe3+ to the pyrite surface and the diffusion of oxidized products to the solution becomes more difficult. These findings will improve our understanding of the influence of SO42- on pyrite oxidation and have important implications for deepening the understanding of surface oxidation of pyrite in the natural environment.

2D-3D electron transfer functions and stability of sustainable graphitic biocarbon for bipolar plate application

Biocarbon being a highly demanding renewable source of carbon is important for many applications such as soil enrichment, electronic applications, etc. In this research, sustainable waste biomass-to-energy materials conversion, kinetic, thermodynamic and electronic properties of carbonized forest biomaterials were investigated to evaluate their high-potential in bipolar plate for fuel cell application. In thermogravimetric analysis, the lignin biocarbon showed the least activation energy of 95 KJ/mol compared to 127 and 145 KJ/mol for hardwood and softwood biocarbons respectively. The crystallographic nature of carbonized ligneous and cellulosic biomaterials was also investigated, showing its intrinsic properties and exotic functionality through semi-metallic properties determined from density function theory, transmission electron microscopy and UV–Vis absorption. Finally, the electrochemical properties of bio-carbon composites were examined to prove stability and corrosion resistance comparable to metallic plates. Biocarbon composites showed high polarization resistance up to 5.96 kΩ-cm2 with non-reactive properties, favorable to use in bipolar plates as an alternative to metallic plate which is expensive and prone to corrosion. Overall, sustainable biocarbon shows its ability as a high-performance functional material alternative to expensive nanofillers as well as to enhance the attributes of the bipolar plate composite by increasing connectivity between primary filler and insulating resin.

Regulatory mechanism of N2 flow rate on structure and properties of CrAlNiYN coatings by FCVA technique

In this work, a novel CrAlNiYN coating was prepared by filter cathode vacuum arc (FCVA) technique. The evolution of the microstructure and properties of the coatings with varying N2 flow rates was systematically investigated. The results revealed that as the N2 flow rate increased from 10 to 90 sccm, the N content in the coating increased from 2.54 to 46.20 at.%, while the Ni content significantly decreased from 67.54 to 31.15 at.%. Simultaneously, the phase structure transitioned from the intermetallic compound AlNi3 to the solid solution Al(Cr)N. This transformation, along with solid solution strengthening and grain refinement, resulted an increase in hardness from 13.4 ± 0.4 to 26.6 ± 0.6 GPa. Moreover, the H/E, H3/E2 and We values also displayed a gradually increasing trend, indicating improved resistance to plastic deformation. However, the adhesion strength presented a weakening trend from HF1 to HF3. Furthermore, the corrosion current density of coatings first increased and then slightly decreased with the increase of N2 flow rate, while the polarization resistance had the opposite trend of change. Among them, the coating at 10 sccm exhibited the best corrosion resistance, with the lowest icorr of 0.150 μA cm−2 and the highest Rp of 302.1 kΩ cm2.

Porous microsphere LiNi0.8Co0.15Al0.05O2 electrode modified by Na2CO3: Enhanced performance of low temperature solid oxide fuel cells

LiNi0.8Co0.15Al0.05O2 (NCAL) has been extensively adopted as symmetric electrode for low temperature solid oxide fuel cells (SOFCs) based on oxide semiconductor electrolytes. However, the performance of NCAL electrode depend on material source, morphology and operating conditions. In this study, commercial microsphere NCAL is successfully modified with Na2CO3 by a wet chemical method. The crystal structure, surface morphology, elemental analysis, surface chemistry and electrochemical properties of NCAL modified by Na2CO3 (NCALN) are characterized by various techniques. When Na2CO3 content in NCALN is 5 wt% and 10 wt%, the CeO2 electrolyte SOFCs with NCALN symmetric electrode show significantly superior performance to that with NCAL symmetric electrode. The optimal heterostructure electrode NCALN5 exhibits a peak power density of 805 mW cm−2 and a polarization resistance of 0.237 Ω cm2 at 550 °C, which is 17 % higher and 21 % lower than those of NCAL electrode. Compared with NCAL electrode, NCALN5 electrode enhances the catalytic activities to both hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) but contributes more to ORR than HOR, especially at low temperatures. These results clearly demonstrate NCALN heterostructure composites are promising electrode materials for low temperature SOFCs.

Corrosion of Steel Pipelines in Supercritical CO2 Environments: Effects of Injection Pressure and Temperature

Combining carbon capture and sequestration with enhanced oil recovery (EOR) could potentially reduce the carbon footprint through permanent storage of carbon dioxide (CO2) at the end of the EOR operations. However, severe corrosion risks to surface facilities and pipelines come along with the benefits of CO2 injection. The present study, therefore, investigates the corrosion resulting from contact between supercritical carbon dioxide (sCO2)-saturated water and carbon steels typical of Alaska pipelines. Carbon steel was allowed to contact the corrosive environment for 72 h, while the corrosion rate was monitored using linear polarization resistance. It was found that injecting sCO2 into the test brine (synthetic Ugnu field salinity) increased the general corrosion by twofold compared to liquid CO2 owing to the solubility and the kinetics of the corrosion byproducts. The increase in sCO2 injection pressure at a fixed temperature (40°C) was proportional to an increase in corrosion rate (up to 8.83 mm/y). At a fixed pressure (12.7 MPa), increasing the temperature decreased the corrosion rate. As part of the effort to mitigate corrosion of CO2 in an sCO2 environment and to validate inhibitor performance outside of common operating conditions, the inhibiting potential of an imidazolium-based ionic liquid was also evaluated. The findings revealed inhibition efficiency up to 65% at low concentrations (up to 51 ppm) of the inhibitor. The addition of ionic liquid (IL) causes the corrosion to shift from a general type to pitting owing to a partial surface coverage. Results revealed further that ILs work better on carbon steel with low manganese concentration in the coupon steel.

Enhanced denitrification by sunlight–hematite: A neglected nitrogen flow pattern in red soil

Mineral-microbe interactions in the Earth's Critical Zone significantly influence elemental biogeochemical cycling and energy flow processes. This study addresses the key scientific question of how semiconducting minerals drive microbial nitrogen cycling. In the red soil environment, the presence of semiconducting minerals enhances the denitrification process mediated by facultative microorganisms (Pseudomonas aeruginosa PAO1) with denitrifying activity. Compared to darkness, light significantly enhanced the synergistic denitrification kinetic process of red soil and Pseudomonas aeruginosa PAO1 (1.87 times). Cyclic voltammetry shows that the P. aeruginosa PAO1-red soil synergistic system exhibits distinct redox peaks under light. The constant potential current curve and electrochemical impedance spectroscopy measurements reveal a high photocurrent density (1.0 μA/cm2) and minimal polarization resistance (102 Ω) under this condition. These findings confirm that the sunlight-red soil-P. aeruginosa PAO1 synergistic process has excellent electron generation and migration capacity, active redox reactions, and good electron compatibility. Additionally, the photoelectrons of semiconductive minerals in red soil profoundly impact the metabolic processes of microbial denitrification functional genes. Using real-time polymerase chain reaction (qPCR) gene array technology, the abundance of nitrogen metabolism functional genes in P. aeruginosa PAO1 increased by 200 % during the light-red soil synergistic process. Notably, denitrification-related genes (ureC, nirS1, gdhA, and nosZ2) were significantly upregulated. This study confirms that semiconducting minerals are involved in the nitrogen cycle pathway of microbial denitrification and supplements the theory of mineral-microbial synergistic element biogeochemical cycling in the natural environment.

New hybrid organic-inorganic conversion coating applied on the Al2024 substrate: Electrochemical, adhesion and surface study

Health problems caused by chromate conversion coatings promoted new research for discovering environmentally-friendly conversion coatings. In this study, Ti-Zr conversion coating (Ti-Zr) was deposited on the aluminum surface in the presence of nickel sulfate (Ti-Zr-Ni) and adipic acid (Ti-Zr-AA). Polarization and electrochemical impedance spectroscopy (EIS) measurements were employed to evaluate the anti-corrosion properties. Surface analysis was carried out using field emission scanning electron microscope (FE-SEM) and Atomic force microscopy (AFM). The results revealed that the Ti-Zr-Ni treatment inhibited the corrosion progression to a significant degree. The polarization resistance showed a significant increase (Rp= 58835 ohm.cm2) in Ti-Zr-Ni treatment in comparison with Ti-Zr conversion coating (Rp= 4450 ohm.cm2) and Ti-Zr-AA sample (Rp= 15058 ohm.cm2). The presence of Ni in the Ti-Zr composition, not just gave rise to the synergism but also played an important role as catalyst to further help avoiding further material degradation. Moreover, the presence of additives (nickel sulfate and adipic acid) enhanced the anti-corrosion resistance of coating by modification of surface morphology according to FE-SEM and AFM images. Anti-corrosion properties and adhesion strength of samples in a fully coated system were also investigated by EIS and pull-off tests, respectively, which revealed that the delamination of the Ti-Zr-Ni sample was lowest among others, and this sample showed better barrier performance even after 6 weeks of immersion in the corrosive environment.

Reduced Surface Area for the Oxygen Reduction Reaction in Porous Electrode via Electrical Conductivity Relaxation.

Oxygen reduction reaction (ORR) performance of porous electrodes is critical for solid oxide fuel cells (SOFCs). However, the effects of gas diffusion on the ORR in porous media need further investigation, although some issues, such as nonthermal surface oxygen exchange, have been attributed to gas diffusion. Herein, La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) with various porosity, pore radii, and gas permeability were investigated via the electrical conductivity relaxation method and analysed via the distributed of characteristic time (DCT) model. The ORR is revealed with three characteristic times, which are gas diffusion, oxygen exchange via the surface corresponding to small pores, and oxygen exchange to large pores. Gas diffusion delays the oxygen surface exchange reaction, resulting in a very low chemical oxygen surface exchange coefficient compared with that obtained with dense samples under the assumption that all the surfaces are active for the ORR. Reduced surface area is thus defined to quantitatively represent the gas diffusion effects. The reduced surface area increases with increasing gas permeability, demonstrating the importance of electrode engineering for fast gas transport. Moreover, reduced surface area is suggested for replacing the specific surface area to calculate the electrode polarization impedance via the ALS model.

The effect of glass sealing stabilization on LSM–YSZ cathode poisoning and oxygen reduction reaction processes in solid oxide fuel cell

AbstractThe perovskite structure and electrochemical activity of (La0.80Sr0.20)0.95MnO3−x–(Y2O3)0.08(ZrO2)0.92 (LSM–YSZ) composite cathode can be significantly affected by volatile boron species originated from sealing glass–ceramics. Herein, we investigate the impact of doping the varying Er2O3 content (ranging from 0 to 4%) into an aluminoborosilicate glass to mitigate boron volatilization, its interaction with the LSM–YSZ cathode and consequent effects on its electrochemical performance. The results reveal that the volatility of boron species can be significantly suppressed by introducing Er oxide into the glass network by enhancing the conversion of [BO3] to [BO4] units, thereby increasing the binding energy of boron and strengthening of the glass structure. Moreover, the electrocatalytic performance for the O2 reduction reaction on the LSM–YSZ/8YSZ/LSM–YSZ symmetric cells is studied under open‐circuit conditions in the presence and absence of glass sealants. The analyses utilizing electrochemical impedance spectroscopy (EIS) and distribution of the relaxation times (DRT) analysis indicate that the electrocatalytic performance of LSM–YSZ cathodes can be enhanced in the presence of glass with 4% Er2O3 (GE4). This enhancement in the electrocatalytic activity of the LSM–YSZ electrode for the oxygen reduction reaction (ORR) is attributed to formation of the thin layer on the electrode surface, leading to a notable reduction in the polarization resistance (Rp) from 0.81 Ω cm2 in the glass absence to 0.45 Ω cm2 in the presence of GE4. However, DRT analysis demonstrates that the prolonged exposure of the cathode to GE4 causes a deterioration in cell performance primarily due to the blocking the cathode active sites, which impedes dominant cathode processes of oxygen dissociative adsorption/desorption and charge transfer and consequently reducing kinetics of the ORR.

Performance and mechanism of triethanolamine-triisopropanolamine corrosion inhibitor to deterioration of reinforced concrete under the coupling effect of freeze-thaw cycles and chloride attack

The purpose of this study is to propose an efficient and economical organic triethanolamine-triisopropanolamine corrosion inhibitor (OTTCI) to reduce the corrosion of steel in reinforced concrete. The influence of OTTCI on corrosion of steel in reinforced concrete under the coupling effect of freeze-thaw cycles and chloride attack (FTCs-CA) were characterized by electrochemical impedance spectroscopy (EIS), dynamic electrode potential (PDP), mechanical properties (mass loss rate (M), compressive strength (fn) and relative dynamic elastic modulus value (Pi)), capillary water absorption (CWA), bubble spacing coefficient (BSC) and scanning electron microscope (SEM). The inhibition mechanism of OTTCI was also analyzed and summarized. The results displayed that the dosage of OTTCI delayed the degradation of reinforced concrete under FTCs-CA. After 150 cycles, the M value of specimens with 1.0 % OTTCI reduced by 66.31 % compared to that of specimens without OTTCI, the Pi value increased by 51.9 %, and the polarization resistance and corrosion inhibition efficiency reached 2744.19 Ω cm2 and 92.88 %, respectively. In addition, OTTCI significantly reduced the CWA value and porosity. After 150 cycles, the CWA and porosity with 1.0 % OTTCI decreased by 60.1 % and 54.54 % respectively. The capillary water absorption coefficient increased linearly with the increase of FTCs-CA. SEM tests illustrated that OTTCI inhibited the development of internal cracks and macropores in concrete and promoted the formation of hydrated calcium silicate gels and calcite. The application of this study not only provides a new method to alleviate the deterioration of reinforced concrete, but also offers theoretical and technical support for further investigate on the deterioration characteristics of reinforced concrete in harsh environments.

Corrosion kinetics of carbon steel in hydrochloric acid and its inhibition by recycling Salbutamol extracted from expired Farcolin drug

ABSTRACT Salbutamol, which has nontoxic properties, was effectively extracted from expired Farcolin and was evaluated as an inhibitor against carbon steel (CSt) dissolution in 1.0 M HCl solution. Some technologies were applied to determine the inhibition efficacy of Salbutamol such as weight loss (WL), potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). Also, FTIR, 1HNMR, and mass spectroscopy were used to clarify the structure of Salbutamol. The findings indicate that CSt can profit significantly from the recycling of Farcolin medicine and that Salbutamol may be extracted and employed as a CSt corrosion inhibitor. The efficiency of the inhibition improved with an increase in the dosage of salbutamol, polarization resistance and lowering corrosion current density, WL, and temperature. It’s reached 89.65% at a dose of 200 ppm using the EIS technology. The inhibition impact of Salbutamol was interpreted due to its spontaneous adsorption on the CSt/electrolyte interface, in accordance with Langmuir isotherm. Salbutamol was classified as a mixed inhibitor. In addition, how temperature affects the corrosion rate is considered by calculating and discussing some thermodynamic parameters.

The role of a tantalum interlayer in enhancing the properties of Fe3O4 thin films.

High spin polarization and low resistivity of Fe3O4 at room temperature have been an appealing topic in spintronics with various promising applications. High-quality Fe3O4 thin films are a must to achieve the goals. In this report, Fe3O4 films on different substrates (SiO2/Si(100), MgO(100), and MgO/Ta/SiO2/Si(100)) were fabricated at room temperature with radio-frequency (RF) sputtering and annealed at 450 °C for 2 h. The morphological, structural, and magnetic properties of the deposited samples were characterized with atomic force microscopy, X-ray diffractometry, and vibrating sample magnetometry. The polycrystalline Fe3O4 film grown on MgO/Ta/SiO2/Si(100) presented very interesting morphology and structure characteristics. More importantly, changes in grain size and structure due to the effect of the MgO/Ta buffering layers have a strong impact on saturation magnetization and coercivity of Fe3O4 thin films compared to cases of no or just a single buffering layer.

CoOX composite Pr0.4Sr0.6Co0.2Fe0.8O3-δ perovskite was used to obtain an IT-SOFC cathode with high electrocatalytic activity

The advancement and application of mesophilic solid oxide fuel cells (IT-SOFCs) rely heavily on enhancing cathode materials to achieve greater efficiency. In this paper, Pr0.4Sr0.6Co0.2Fe0.8O3-δ (PSFC) and transition metal oxide CoOx were selected as cathode materials, which not only combined the high catalytic activity of Pr6O11 but also took advantage of the structural stability and economy of Fe-based perovskite. The samples underwent analysis using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and X energy dispersion spectrometer (EDS) for structural examination. The electrochemical workstation was used to test the conductivity of the material and the stability of the cell. The results indicate that an appropriate amount of CoOX composite can effectively enhance the level of oxygen vacancies, thereby enhancing the ORR activity of the cathode. Among these composites, Pr0.4Sr0.6Co0.2Fe0.8O3-δ-CoOx-I exhibits the fastest rate of oxygen exchange at the surface and the best electrochemical performance. At 700 °C, the polarization resistance ASR of Pr0.4Sr0.6Co0.2Fe0.8O3-δ-CoOx-I is 0.0749 Ω cm2; In single-cell fuel mode with NiO-YSZ as anode, YSZ electrolyte, and GDC as cell layer, the peak power density (PDD) is 0.97W cm−2. The PSCF-CoOx composite cathode holds promise as a high electrocatalytic active material for Solid Oxide Fuel Cells (SOFCs).

Effect of Tempering Temperature on the Aqueous Corrosion Resistance of 9Cr Series Heat-Resistant Steel

In this investigation, the aqueous corrosion resistance of 9Cr series heat-resistant steel during tempering was investigated. Optical Microscopy (OM), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectrometer (EDS) were used to analyze the effect of tempering temperature on the microstructure and precipitation behavior of precipitates. The heat-resisting steel was heated to 1150 °C for 1 h, and then tempered at different temperatures between 680 °C and 760 °C for 2 h. The microstructure of the heat-resistant steel after tempering was composed of lath-tempered martensite and fine precipitates. The hardness decreased with increasing tempering temperature, ranging from HBW 261 to HBW 193. The aqueous corrosion resistance improved as the tempering temperatures increased from 680 °C to 720 °C but deteriorated at higher temperatures, such as 760 °C, which was obtained by an electrochemical corrosion performance test. The aqueous corrosion resistance was affected by the decrease in dislocation density and the decrease in Cr solution in the tempered martensite. With the increase in the tempering temperature, the aqueous corrosion potential first increases and then decreases, the self-corrosion current density first decreases and then increases, and the polarization resistance first increases and then decreases. Furthermore, the increase in corrosion resistance is attributed to the reduction in dislocation density and chromium depletion in the martensitic structure as the tempering temperature approaches 720 °C. This paper reveals the effect of tempering temperature on the corrosion resistance of 9Cr series heat-resistant steel, which is a further exploration of a known phenomenon.

Construction of a 3D spider web structure with spherical Ho2O3 wrapped by carbon nanofibers for high-efficiency microwave absorption and corrosion protection

Reasonable composition control and microstructure design are the effective ways to realize multi-functional high-performance absorbing materials. In this work, a three-dimensional (3D) spider web structure was designed by the electrospinning and high temperature carbonization technology, where Ho2O3 spheres were wrapped by carbon nanofibers. Herein, the spherical Ho2O3 were surrounded by layers of carbon nanofibers (spider silk), which were like the preys inside the spider's web. This unique bionic structure working in conjunction with the tuned components enables the as-prepared composites with improved impedance matching and enhanced loss capacity. The superior electromagnetic wave absorption performance was obtained as the minimum reflection loss of −61.37 dB at 2.90 mm and the maximum effective absorption bandwidth of 6.88 GHz (11.12–18 GHz) at 2.64 mm. At a thickness of 3.44 mm, the effective absorption bandwidth is 4.80 GHz (8–12.80 GHz), covering the entire X-band. At the same time, the composite soaked in the corrosive medium for 7 days owns a low corrosion current density (10−4 ∼10−6 A cm−2) and a high polarization resistance (105∼107 Ω), which exhibits the obvious anticorrosion ability. This work designs a specific spider web structure with high-performance microwave absorption and corrosion protection.

Characterization of A-site doped PrBaCo2O5+δ perovskites as cathode materials for IT-SOFCs

Creating highly efficient and durable cathodes persists as a formidable task in the realm of intermediate temperature solid oxide fuel cells (IT-SOFCs). Hence, we present a double perovskite oxide, Pr0.6Sr0.4BaCo2O5+δ (PS0.4BC), and its electrocatalytic activity is thoroughly investigated. The XRD test is carried out and a notable transformation in the phase structure is observed upon the introduction of Sr2+ ions into the PBC matrix. That is, the phase structure of the material changes from double perovskite structure to single perovskite structure. Through the TG and TEC test that the introduction of Sr2+ ions into the lattice can create additional sites for oxygen vacancy formation and reduce TEC values. Further verify that Sr doping can enhance the concentration of oxygen vacancies of the material. The PS0.4BC cathode material exhibits remarkably low polarization resistance, achieving an impressive value of 0.027 Ω cm2 at an operating temperature of 800 °C. Oxygen partial pressure test shows that as the oxygen partial pressure decreases, there is a notable increase in impedance, particularly evident in the low frequency region of the Nyquist plots. This indicates that the oxygen content has obvious effects on the low-frequency processes. When the oxygen partial pressure exceeds 0.05 atm, the oxygen adsorption-dissociation and diffusion process is the rate-limiting step in the ORR. However, when the oxygen partial pressure is less than 0.05 atm, the formation of lattice oxygen through the combination of oxygen ions and oxygen vacancies processes is the rate-limiting step. Compared PBC cathode material, the more pronounced changes in the high frequency arc of the PS0.4BC cathode at the same oxygen content. It shows that Sr doping significantly changes the high frequency process. After doping, the oxygen vacancy concentration increases, which facilitates the occurrence of the charge transfer process at high frequency.