The Effects of Heat Treatment on the Microstructure and Mechanical Properties of a Selective Laser Melted AlCoFeNi Medium-Entropy Alloy.

A single body-centered cubic (BCC)-structured AlCoFeNi medium-entropy alloy (MEA) was prepared by the selective laser melting (SLM) technique. The hardness of the as-built sample was around 32.5 HRC. The ultimate tensile strength (UTS) was around 1211 MPa, the yield strength (YS) was around 1023 MPa, and the elongation (El) was around 10.8%. A novel BCC + B2 + face-centered cubic (FCC) structure was formed after aging. With an increase in aging temperature and duration, the number of fine grains increased, and more precipitates were observed. After aging at 450 °C for 4 h, the formed complex polyphase structure significantly improved the mechanical properties. Its hardness, UTS, YS, and El were around 45.7 HRC, 1535 MPa, 1489 MPa, and 8.5%, respectively. The improvement in mechanical properties was mainly due to Hall-Petch strengthening, which was caused by fine grains, and precipitation strengthening, which was caused by an increase in precipitates after aging. Meanwhile, the FCC precipitates made the alloy have good toughness. The complex interaction of multiple strengthening mechanisms leads to a good combination of strength, hardness, and toughness.

Durable CO2 conversion in the proton-exchange membrane system.

Electrolysis that reduces carbon dioxide (CO2) to useful chemicals can, in principle, contribute to a more sustainable and carbon-neutral future1-6. However, it remains challenging to develop this into a robust process because efficient conversion typically requires alkaline conditions in which CO2 precipitates as carbonate, and this limits carbon utilization and the stability of the system7-12. Strategies such as physical washing, pulsed operation and the use of dipolar membranes can partially alleviate these problems but do not fully resolve them11,13-15. CO2 electrolysis in acid electrolyte, where carbonate does not form, has therefore been explored as an ultimately more workable solution16-18. Herein we develop a proton-exchange membrane system that reduces CO2 to formic acid at a catalyst that is derived from waste lead-acid batteries and in which a lattice carbon activation mechanism contributes. When coupling CO2 reduction with hydrogen oxidation, formic acid is produced with over 93% Faradaic efficiency. The system is compatible with start-up/shut-down processes, achieves nearly 91% single-pass conversion efficiency for CO2 at a current density of 600 mA cm-2 and cell voltage of 2.2 V and is shown to operate continuously for more than 5,200 h. We expect that this exceptional performance, enabled by the use of a robust and efficient catalyst, stable three-phase interface and durable membrane, will help advance the development of carbon-neutral technologies.

pH-Responsive Fluorescent Metal-Organic Framework as a Functional Nanofiller for Smart Coatings.

A zirconium-based UiO-type UiO-66-(OH)2 metal-organic framework@carbon dot composite (Zr-MOF@CD) is synthesized through a facile solvent-free thermal method. The Zr-MOF@CD exhibits pH-responsive fluorescence behavior, which emits blue fluorescence for pH < 9 at an emission wavelength of 470 nm. At pH > 9, the fluorescence color turns from blue to yellow, with the emission behavior at 535 nm. Zr-MOF@CDs can serve as functional nanofillers in the epoxy coating for the fabrication of a smart coating, which can realize coating damage warning and metal corrosion reporting. The blue fluorescence can be observed in the area of coating damage with just a minor scratch. Once the scratch is severe enough to expose the metal substrate, the cathodic reaction of oxygen reduction in the corrosion galvanic cell causes an increased pH, where the emission of yellow fluorescence can be identified. The stable fluorescence response is free from the influence of concentration, time, temperature, and the interfering substance. Zr-MOF@CDs can also serve as nanocontainers for loading with the corrosion inhibitor and realizing the repairing of metal corrosion. The development of the smart coating with dual functions of autonomous reporting and repairing holds great potential to improve the lifetime of metals in various industrial applications.

Integrated MOF-74 Coatings on Magnesium for Corrosion Control, Cytocompatibility, and Antibacterial Properties.

Biodegradable Mg and its alloys can degrade safely in vivo without toxicity. The major bottleneck inhibiting their clinical use is the high corrosion rate, which leads to the loss of mechanical integrity prematurely and bad biocompatibility. One ideal strategy is the modification with anticorrosive and bioactive coatings. Numerous metal-organic framework (MOF) membranes show satisfactory anticorrosion performance and biocompatibility. In this study, MOF-74 membranes are prepared on an NH4TiOF3 (NTiF) layer-modified Mg matrix, fabricating integrated bilayer coatings (MOF-74/NTiF) for corrosion control, cytocompatibility, and antibacterial properties. The inner NTiF layer serves as the primary protection for the Mg matrix and a stable surface for the growth of MOF-74 membranes. The outer MOF-74 membranes further enhance corrosion protection, whose crystals and thicknesses can be adjusted for different protective effects. Owing to superhydrophilic, micro-nanostructural, and nontoxic decomposition products, MOF-74 membranes significantly promote cell adhesion and proliferation, showing excellent cytocompatibility. Utilizing the decomposition of MOF-74 to generate the products of Zn2+ and 2,5-dihydroxyterephthalic acid can effectively inhibit Escherichia coli and Staphylococcus aureus, displaying highly efficient antibacterial properties. The research may shed valuable strategies for MOF-based functional coatings in the applications of biomedicine fields.

Fructus cannabis protein extract powder as a green and high effective corrosion inhibitor for Q235 carbon steel in 1 M HCl solution.

The Fructus cannabis protein extract powder (FP), was firstly used as a green and high effective corrosion inhibitor through a simple water-extraction method. The composition and surface property of FP were characterized by FTIR, LC/MS, UV, XPS, water contact angle and AFM force-curve measurements. Results indicate that FP contains multiply functional groups, such as NH, CO, CN, CO, etc. The adsorption of FP on the carbon steel surface makes it higher hydrophobicity and adhesion force. The corrosion inhibition performance of FP was researched by electrochemical impedance, polarization curve and differential capacitance curve. Moreover, the inhibitive stability of FP, and the effects of temperature and chloride ion on its inhibition property were also investigated. The above results indicate that the FP exhibits excellent corrosion inhibition efficiency (~98 %), and possesses certain long-term inhibitive stability with inhibition efficiency higher than 90 % after 240 h immersion in 1 M HCl solution. The high temperature brings about the FP desorption on the carbon steel surface, while high concentration of chloride ion facilitates the FP adsorption. The adsorption mechanism of FP follows the Langmuir isotherm adsorption. This work will provide an insight for protein as a green corrosion inhibitor.

Corrosion Behavior of the AlCoCrFeNi2.1 Eutectic High-Entropy Alloy in Chloride-Containing Sulfuric Acid Solutions at Different Temperatures.

In this work, the influence of temperature on the corrosion behavior of AlCoCrFeNi2.1 eutectic high-entropy alloy in a chloride-containing sulfuric acid solution was investigated using electrochemical measurement, X-ray photoelectron spectroscopy, and scanning electron microscopy. Results show that the passive film of AlCoCrFeNi2.1 is stable in chloride-containing sulfuric acid solutions at low temperatures, while an unstable film forms on the alloy at high temperatures. Furthermore, temperature changes the proportion of hydroxide and oxide in Fe and Cr, but it has no noticeable effect on Al and Ni, which is a significant factor on the passive behavior. L12 phase exhibits good corrosion resistance at different temperatures. Pitting occurred on B2 phase in the chloride-containing sulfuric acid solution at a low temperature of 5 °C, while pitting and dissolution take place on AlCoCrFeNi2.1 in the acid solution at room temperature and above.

Constructing nickel-iron oxyhydroxides integrated with iron oxides by microorganism corrosion for oxygen evolution.

Developing facile approaches for preparing efficient electrocatalysts is of significance to promote sustainable energy technologies. Here, we report a facile iron-oxidizing bacteria corrosion approach to construct a composite electrocatalyst of nickel­iron oxyhydroxides combined with iron oxides. The obtained electrocatalyst shows improved electrocatalytic activity and stability for oxygen evolution, with an overpotential of ∼230 mV to afford the current density of 10 mA cm−2. The incorporation of iron oxides produced by iron-oxidizing bacteria corrosion optimizes the electronic structure of nickel­iron oxyhydroxide electrodes, which accounts for the decreased free energy of oxygenate generation and the improvement of OER activity. This work demonstrates a natural bacterial corrosion approach for the facile preparation of efficient electrodes for water oxidation, which may provide interesting insights in the multidisciplinary integration of innovative nanomaterials and emerging energy technologies.

Corrosion Chemistry of Electrocatalysts.

Electrocatalysts are the core components of many sustainable energy conversion technologies that are considered the most potential solution to the worldwide energy and environmental crises. The reliability of structure and composition pledges that electrocatalysts can achieve predictable and stable performance. However, during the electrochemical reaction, electrocatalysts are influenced directly by the applied potential, the electrolyte, and the adsorption/desorption of reactive species, triggering structural and compositional corrosion, which directly affects the catalytic behaviors of electrocatalysts (performance degradation or enhancement) and invalidates the established structure-activity relationship. Therefore, it is necessary to elucidate the corrosion behavior and mechanism of electrocatalysts to formulate targeted corrosion-resistant strategies or use corrosion reconstruction synthesis techniques to guide the preparation of efficient and stable electrocatalysts. Herein, the most recent developments in electrocatalyst corrosion chemistry are outlined, including corrosion mechanisms, mitigation strategies, and corrosion syntheses/reconstructions based on typical materials and important electrocatalytic reactions. Finally, potential opportunities and challenges are also proposed to foresee the possible development in this field. It is believed that this contribution will raise more awareness regarding nanomaterial corrosion chemistry in energy technologies and beyond.

Constructing N-doping biomass-derived carbon with hierarchically porous architecture to boost fast reaction kinetics for higfh-performance lithium storage.

Active biomass-derived carbons are brought into focus on boosting high-performance lithium storage. However, their low electric conductivity and poor ion diffusion kinetics during the lithium storage reactions remain confusing topics. This study demonstrates a novel and effective strategy of dual system activation process to construct the nitrogen-doped biomass-derived carbon with hierarchically porous architecture (HNBC), which is composed of the three-dimensional porous networks connected by carbon nanorods and the flake-like edges constructed by carbon nanosheets. A large amount of nitrogen doping can improve the conductivity and facilitate the charge transfer during charging/discharging, while the hierarchically porous structure can decrease the diffusion path for lithium-ion transport, enabling fast diffusion and charge-transfer dynamics. The HNBC electrode displays a high lithium-ion storage capacity of above 1392 mAh g-1 at 0.1 A g-1 and superior stability. Moreover, the assembled asymmetric lithium-ion capacitor exhibits excellent cycling stability and delivers a high power density of 225 W kg-1 with an energy density of 186.31 W h kg-1. This dual system activation strategy may inspire the reasonable design of new-generation progressive carbon-based electrodes for high-performance lithium storage devices.

Anti-Corrosion Mechanism of Parsley Extract and Synergistic Iodide as Novel Corrosion Inhibitors for Carbon Steel-Q235 in Acidic Medium by Electrochemical, XPS and DFT Methods.

The parsley extract (PLE) was prepared using absolute ethyl alcohol. The PLE and synergistic iodide were firstly utilized as efficacious corrosion inhibitors to slow down the corrosion rate of carbon steel-Q235 in 0.5 mol/L H2SO4 solution. The anti-corrosion performance was researched by weight loss method, electrochemical tests, surface analysis and quantum chemistry calculation. Results of electrochemical and weight loss tests show that the synergetic PLE and I- exhibit the optimal corrosion inhibition efficiency 99%. The combined inhibitor displays the favorable long-term corrosion inhibition effect, and the inhibition efficiency can maintain more than 90% after 144 h immersion. The introduction of I- makes carbon steel surface with higher negative charge amount, which could be beneficial to the interaction between corrosion inhibitor and Fe atoms. The adsorption behavior obeys the Langmuir isotherm adsorption, and involves chemical and physical adsorption. On the basis of electrochemical consequences and theoretical calculation, the adsorption process and anti-corrosion mechanisms are further explored.

Direct integration of ultralow-platinum alloy into nanocarbon architectures for efficient oxygen reduction in fuel cells.

Developing efficient platinum (Pt)-based electrocatalysts is enormously significant for fuel cells. Herein, we report an integrated electrocatalyst of ultralow-Pt alloy encapsulated into nitrogen-doped nanocarbon architecture for efficient oxygen reduction reaction. This hybrid Pt-based catalyst achieves a mass activity of 3.46 A mgpt-1 at the potential of 0.9 V vs. RHE with a negligible stability decay after 10,000 cycles. More importantly, this half-cell activity can be expressed at full cell level with a high Pt utilization of 10.22 W mgPt-1cathode and remarkable durability after 30,000 cycles in single-cell. Experimental and theoretical investigations reveal that a highly strained Pt structure with an optimal Pt-O binding energy is induced by the incorporation of Co/Ni into Pt lattice, which would account for the improved reaction kinetics. The synergistic catalysis due to nitrogen-doped nanocarbon architecture and active Pt component is responsible for the enhanced catalytic activity. Meanwhile, the strong metal-support interaction and optimized hydrophilic properties of nanocarbon matrix facilitate efficient mass transport and water management. This work may provide significant insights in designing the low-Pt integrated electrocatalysts for fuel cells and beyond.

Preparation of nickel-iron hydroxides by microorganism corrosion for efficient oxygen evolution.

Nickel-iron composites are efficient in catalyzing oxygen evolution. Here, we develop a microorganism corrosion approach to construct nickel-iron hydroxides. The anaerobic sulfate-reducing bacteria, using sulfate as the electron acceptor, play a significant role in the formation of iron sulfide decorated nickel-iron hydroxides, which exhibit excellent electrocatalytic performance for oxygen evolution. Experimental and theoretical investigations suggest that the synergistic effect between oxyhydroxides and sulfide species accounts for the high activity. This microorganism corrosion strategy not only provides efficient candidate electrocatalysts but also bridges traditional corrosion engineering and emerging electrochemical energy technologies.

Microstructure and Corrosion of Cast Magnesium Alloy ZK60 in NaCl Solution.

In this work, the effects of the microstructure and phase constitution of cast magnesium alloy ZK60 (Mg-5.8Zn-0.57Zr, element concentration in wt.%) on the corrosion behavior in aqueous NaCl (0.1 mol dm-3) were investigated by weight-loss measurements, hydrogen evolution tests, and electrochemical techniques. The alloy was found to be composed of α-Mg matrix, with large second-phase particles of MgZn2 deposited along grain boundaries and a Zr-rich region in the central area of the grains. The large second-phase particles and the Zr-rich regions were more stable than the Mg matrix, resulting in a strong micro-galvanic effect. A filiform corrosion was found. It originated from the second-phase particles in the grain boundary regions in the early corrosion period. The filaments gradually occupied most areas of the alloy surface, and the general corrosion rate decreased significantly. Corrosion pits were developed under filaments. The pit growth rate decreased over time; however, it was about eight times larger than the general corrosion rate. A schematic model is presented to illustrate the corrosion mechanism.

Porous graphene based electrochemical immunosensor using Cu3(BTC)2 metal-organic framework as nonenzymatic label.

An electrochemical immunosensor for highly sensitive detection of cancer biomarkers has been developed based on the combination of a sensing platform of polydopamine modified porous graphene and a nonenzymatic label of metal-organic framework (MOF) conjugated secondary antibody. This approach achieves a wide range of linear response from 0.1 to 10 ng/mL, low detection limit of 0.025 ng/mL (at a signal to noise ratio of 3), good reproducibility and selectivity for the detection of prostate specific antigen (PSA) as a model analyte. The high performance of the immunosensor is attributed to the high surface area from porous graphene and the strong adhesion of polydopamine, allowing a high load of the primary antibody of PSA, as well as the highly electrocatalytic activity of the Cu3(BTC)2 (BTC = benzene-1,3,5-tricarboxylic acid) MOF toward H2O2 to provide greatly amplified sensitivity. In this respect, the MOF-based nonenzymatic label shows promising application for the point-of-care detection of different cancer biomarkers in clinical diagnostics.

Inhibition Effect of Three-Dimensional (3D) Nanostructures on the Corrosion Resistance of 1-Dodecanethiol Self-Assembled Monolayer on Copper in NaCl Solution.

A novel and simple method to improve the corrosion resistance of copper by constructing a three-dimensional (3D) 1-dodecanethiol self-assembled monolayer (SAM) in 3.5% NaCl solution is reported in this study. Several drops of 1% H3PO4 solution are thinly and uniformly distributed on copper surface to form a 3D nanostructure constituted by Cu3(PO4)2 nanoflowers. The anticorrosion properties of 1-dodecanethiol SAM on copper surface and on copper surface that is treated with H3PO4 solution were evaluated. Results demonstrated that 1-dodecanethiol SAM on bare copper surface exhibits good protection capacity, whereas a copper surface that is pretreated with H3PO4 solution can substantially enhance the corrosion resistance of 1-dodecanethiol SAM.

Influence of Pt and Pd Modification on the Visible Light Photocatalytic Activity of N-Doped Titania Photocatalysts.

Pd and Pt modified N-doped titania nanoparticle powders were prepared by a facile sol-gel method. Nitrogen doping and metal modification were carried out simultaneously during the preparation pro- cess. The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy and X-ray photoelectron spectroscopy (XPS). The visible light photocatalytic activities of the as prepared samples were evaluated by analyzing their effect on the photocatalytic decomposition of methyl orange (MO). The chemical state of the metal is the key factor determining the performance of metal modified N-doped titania. The Pd used to modify the N-doped titania (Pd-NT) in our study was of the PdOx(x≤2) species, which increased the absorbance in the visible light region, decreased the recombination of photo-generated electron-hole pairs, and resulted in a significant enhancement in the visible light photocatalytic activity. The Pt species used to modify the N-doped titania (Pt-NT) was mainly in the metallic state, which resulted in a decrease in the absorbance in the visible light region, and an increase in the recombination of photo-generated electron-hole pairs. Pt modification led to a deterioration in the visible light photocatalytic activity of the material.

Effect of calcination on the visible light photocatalytic activity of N-doped TiO2 prepared by the sol-gel method.

A series of N-doped TiO2 nanoparticle powders have been prepared by the sol-gel method using triethylamine as N precursor. The effect of calcination temperatures on the quality of the as-prepared samples was studied and an annealing treatment was introduced to improve further the quality of the as-prepared sample. The visible light photocatalytic activities of the samples were evaluated by decomposition of methyl orange (MO) in water. The calcination temperature plays a key role in determining the quality of N-doped TiO2 nanoparticle powders. The enhancement of calcination temperatures facilitates the crystallization of N-doped TiO2 powders and the elimination of surface organic residues, but promotes the loss of doping N and the agglomeration of nanoparticles and results in low N doping level and large particle sizes. The N-doped TiO2 sample (NT-300) calcined at 300 degrees C in air for 3 h produced the maximum visible light photocatalytic activity. The annealing treatment of NT-300 at its calcination temperature could improve the crystallinity, remove effectively the surface organic residues, keep nanoparticles in smaller size, and retain the doping N, therefore improving the visible light photocatalytic activity significantly.

Atomic force microscopy and electrochemical investigation on the corrosion behavior of carbon steel passivated by molybdate and chromate.

The effects of CrO(4)(2-) and MoO(4)(2-) ions on the corrosion behavior of carbon steel in 0.5 M NaCl solution have been studied using electrochemical measurements and atomic force microscopy. The results suggest that both ions have good inhibition effects on the general and pitting corrosion of carbon steel. At the same concentration, the inhibition efficiency of CrO(4)(2-) is higher than that of MoO(4)(2-). The passive film formed by CrO(4)(2-) is also much harder than that formed by MoO(4)(2-). The passive films formed by both ions are nonconductive.

Effects of N precursor on the agglomeration and visible light photocatalytic activity of N-doped TiO2 nanocrystalline powder.

N-doped TiO2 nanocrystalline powders were prepared by the sol-gel method using various N precursors, including triethylamine, hydrazine hydrate, ethylenediamine, ammonium hydroxide, and urea. The samples were characterized by X-ray diffraction, N2 adsorption isotherms, transmission electron microscopy, ultraviolet-visible diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activities of as-prepared samples under irradiation of visible light (lambda > 405 nm) were evaluated by photodecomposition of methyl orange. The alkalinity of N precursor was found to play a key role in the gel process. The N precursor with moderate alkalinity causes TiO2 nanoparticles to be sol-transformed into a loosely agglomerated gel. This transformation facilitates the preparation of an N-doped TiO2 powder with small nanocrystal size, large specific surface area, and high N doping level and results in high visible light photocatalytic activity. The N in TiO2 with N is binding energy at 399-400 eV may be assigned to the N-H species located in interstitial sites of TiO2 lattice which is the active N species responsible for the visible light photocatalytic activity. The N species of N 1s peak at 402 and 405 eV are ineffective to the visible light photocatalytic activity and may inhibit the photocatalytic activity. Moreover, a TiO2 nanoparticle powder with large specific area can be achieved by using urea as a template and then by using ammonium hydroxide to transform the sol into gel.