Growth Of Metal Particles Research Articles

Effect of Na<sub>2</sub>CO<sub>3</sub> and CaCO<sub>3</sub> on deep dephosphorization by the direct reduction of high-phosphorus oolitic hematite

The direct reduction–magnetic separation process based on coal is considered to be one of the most important methods that can effectively utilize high-phosphorus oolitic hematite. In this study, the mechanism of the effects of CaCO<sub>3</sub> and Na<sub>2</sub>CO<sub>3</sub> on the dephosphorization of high-phosphorus oolitic hematite during the direct reduction process was investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results showed that Na2CO3 and CaCO3 reacted with Al<sub>2</sub>O<sub>3</sub> and SiO<sub>2</sub> during the direct reduction process, inhibited the generation of hercunite (FeAl<sub>2</sub>O<sub>4</sub>) and fayalite (Fe<sub>2</sub>SiO<sub>4</sub>), and promoted the reduction of metallic iron (Fe). Furthermore, the reaction inhibited the reduction of apatite and prevented the generation of FeP<sub>2</sub>. Na<sub>2</sub>CO<sub>3</sub> could change the form of phosphorus in the gangue from Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> to Na<sub>2</sub>Ca<sub>4</sub>(PO<sub>4</sub>)<sub>2</sub>SiO<sub>4</sub>. Increasing the dosages of Na2CO3 and CaCO3 in the dephosphorization agent and increasing the content of Na<sub>2</sub>CO<sub>3</sub> in the dephosphorization agent were beneficial to the growth of metallic iron particles, and increasing the dosage of Na<sub>2</sub>CO<sub>3</sub>, CaCO<sub>3</sub> in the dephosphorization agent had more significant effects on metallic iron particles than increasing the content of Na<sub>2</sub>CO<sub>3</sub> in the dephosphorization agent. The research conducted in this study is expected to provide a basis for the effective exploitation of complex and refractory iron ores.

Simulation of noble metal particle growth and removal in the molten salt fast reactor

In the Molten Salt Fast Reactor (MSFR), fuel is dissolved in a liquid salt, causing the formation and decay of fission products, such as noble metals, to be inside the salt. Noble metals have very low solubility and do not dissolve in the salt. They are known to agglomorate into particles which, in turn, diffuse, drift or sediment to interfaces such as walls, free surfaces and bubbles, where they deposit. Leveraging this in the MSFR, online or offline helium bubbling is foreseen to act as a means to extract noble metal particles from the salt. This can potentially limit strong deposition of particles onto walls (i.e., plating), preventing dangerous decay heat hotspots in the heat exchangers or other primary circuit components. In this paper, we investigate the efficiency of particle removal by helium bubbles in the MSFR using Computational Fluid Dynamics (CFD). Theoretical estimates of equilibrium particle size distributions are used as initial condition, based on previous work. CFD calculations are performed in a simplified MSFR geometry. Bubble expansion, turbulent bubble coalescence and turbulent break-up are accounted for using the poly-disperse Log-normal Method of Moments (LogMoM) model, embedded in the two-fluid framework in OpenFOAM. The CFD analyses presented in this paper, in conjunction with the developed theory of noble metal particle formation, growth and capture, will help in the understanding and optimization of the fuel cycle in the MSFR or any other molten salt reactor design. The precise knowledge of how noble metal particle populations in the salt can be controlled, and how plating of noble metal particles onto primary circuit reactor components can be reduced, contributes to safe molten salt reactor operation.

Ultrafine PtMo Nanocrystals Confined on N‐Doped Carbon Toward Efficient pH‐Universal Hydrogen Evolution Reaction

AbstractPt‐based nanocrystals with tunable electronic structure and optimized atom efficiency are essential for boosting the hydrogen evolution reaction (HER) performance and further industrial application. However, the synthesis of uniform and ordered nanocrystals is still a challenge due to the uncontrollable size growth of metal particles, restricting the active sites toward the desired catalytic activity. Herein, the synthesis of ultrafine bimetal PtMo nanocrystals on N‐doped carbon (PtMo‐NC) through an anchoring‐sites engineering strategy is reported, in which the N‐rich carbon can provide abundant sites to anchor the metal atoms and suppress the over aggregation. The PtMo‐NC catalyst exhibits superior HER performance in both alkaline and acidic conditions, delivering a smaller overpotential (80 mV and 63 mV) at a current density of 100 mA cm−2 in alkaline and acidic media. Theoretical calculations reveal that the introduction of Mo atom into Pt can reduce the energy barrier of water molecule dissociation and optimize the H intermediate absorption strength on Pt sites, thus boosting the catalytic HER performance. This study offers a universal strategy to design ultrafine nanocatalysts to achieve high‐efficiency electrocatalysis.

Extraction of ferronickel concentrate from laterite nickel ore by reduction roasting-magnetic separation using spent cathode carbon

Laterite nickel ores are the most important raw materials in nickel production, but processing laterite nickel ores with a low nickel content is difficult. Annually, the aluminum electrolysis industry produces a large amount of spent cathode carbon containing toxic substances, such as fluorine and cyanide, but a considerable amount of it cannot be effectively utilized. The purpose of the present study is to prepare ferronickel concentrates by reduction roasting–magnetic separation using spent cathode carbon as a reducing agent. Different factors affecting the agglomeration and growth of metal particles are studied. The migration of fluorine and the aggregation behavior of iron and nickel after the addition of spent cathode carbon and CaO are studied. Results show that the nickel grade in the ferronickel concentrate is 5.4 wt%, the nickel recovery rate is 84.80%, the iron grade is 67.93 wt%, and the iron recovery rate is 89.91%. Efficient recovery and utilization of nickel and iron in laterite nickel ores are realized. Waste utilization of spent cathode carbon thus provides a new method for the treatment of spent cathode carbon.

Defect-Rich and Boron-Doped Al2O3-Supported Ru Nanocatalyst for Enhanced CO2 Methanation Activity

Presently, fabricating a stable and high-performance noble metal catalyst is still a challenging task due to the easy aggregation and growth of metal particles during heterogeneous catalysis reactions. In this regard, catalyst supports always can profoundly impact the metal dispersion and electronic interaction with active metal species, thereby significantly regulating the catalytic performance of catalysts. Herein, a new strategy for fabricating boron-doped alumina support with coordinatively unsaturated penta-coordinated Al3+ (Alpenta3+) sites via a micro-liquid-film reactor-assisted coprecipitation approach was developed. Accordingly, as-formed alumina could efficiently immobilize Ru atoms via the anchoring effect of the Alpenta3+ site to construct a supported Ru catalyst for CO2 methanation. An as-constructed Alpenta3+ site-rich and boron-doped Al2O3-supported Ru nanocatalyst exhibited a better catalytic performance in CO2 methanation along with a higher methane yield of 81.2% under reaction conditions (i.e., 350 °C, 0.1 MPa pressure, and gas hourly space velocity of 6000 mL·gcat–1·h–1), compared to other supported Ru ones over commercial alumina and defect-free alumina. It was demonstrated that the high catalytic performance was closely associated with the coexistence of surface-defective Alpenta3+ sites and B–O species, thereby facilitating the accommodation of active hydrogen species on the support during CO2 hydrogenation as well as the activation adsorption of CO2 at the medium-strength basic sites originating from surface B–O–Al structures. This work provides a new strategy to construct high-performance and stable supported noble metal catalysts through engineering alumina support with special defective structures and surface modification for the applications in advanced heterogeneous catalytic systems.

Effects of CaF2 on the direct reduction of beach titanomagnetite at different temperatures

AbstractEffects of CaF2 on the mineralogical composition and microstructure of reduction products at different temperatures during direct reduction of beach titanomagnetite is investigated. In the absence of CaF2, armalcolite and a large number of small‐size metallic iron particles in reduction products at different temperatures prevented the separation of Ti and Fe. The metallization rate of reduction products was only 90.32 wt% at 1350°C. CaF2 reduced the activation energy of reduction reaction and promoted the reduction of armalcolite, further achieving the separation of Ti and Fe on the mineral phase. When 5 wt% CaF2 was added at 1250°C, the metallization rate of reduction products could reach 90.88%. The effect of CaF2 on the metallization rate was better than that of increasing temperature by 100°C. Besides, CaF2 also reduced the melting point and viscosity of the roasting system, and significantly promoted the aggregation and growth of metallic iron particles, thus optimizing the conditions for the separation and enrichment of Ti and Fe, respectively. Adding 10 wt% CaF2 promoted the growth of MgTi2O5 into a mineral with regular boundary, which created conditions for the recovery of titanium resources. By comparison, the promotion effect of CaF2 on the increasing the metallization rate of reduction products, aggregation and growth of metallic iron particles was obviously better than that of increasing the reduction temperature without CaF2. Therefore, CaF2 could also significantly reduce the energy consumption on the basis of promoting the separation of Ti and Fe.

Estimates of noble metal particle growth in a molten salt reactor

Within the H2020-Euratom project SAMOSAFER, research is currently ongoing into the Molten Salt Fast Reactor (MSFR) concept in which nuclear fuel is dissolved in a liquid salt. A major challenge in the MSFR is the online and offline treatment of salt in order to remove a plethora of fission products. Noble metals are a type of such fission products, the atoms of which are thought to coagulate into particles as a result of diffusion. Due to their low solubility, noble metal particles will deposit onto interfaces such as solid walls but also on bubbles, as was observed in the Molten Salt Reactor Experiment (MSRE) at Oak Ridge national laboratory. The relatively large interfacial area generated by bubbles makes online or offline bubbling, therefore, an interesting option to extract noble metals from the MSFR and to limit wall deposition. However, to understand the performance of the bubbling process, particle sizes must be known. Particle size distributions arise from a complex interplay of atomic formation by fission and decay, growth by coagulation and removal by interfacial deposition. In this paper, theory is developed to understand these mechanisms on a semi-analytical level, in order to provide estimates of noble metal particle growth in the MSFR. The governing partial differential equation is reduced to a set of ordinary differential equations using the method of moments, revealing the dynamics of the underlying physics. We show that large noble metal particles, up to the micrometer scale, can arise in the reactor, but only at very long operational times. Moreover, we show that the previously assumed ‘cycle time’ of noble metal particle removal of 30 s is only feasible at very high bubbling void fractions. The theory developed in this work contributes significantly to a qualitative understanding of the behavior of noble metals in an MSR. The theory can potentially help to explain certain phenomena observed in the MSRE and can assist in the future design of safe and reliable MSRs.

Multiscale Functional Metal Architectures by Antibody‐Guided Metallization of Specific Protein Assemblies in Ex Vivo Multicellular Organisms

Biological systems consist of hierarchical protein structures, each of which has unique 3Dgeometries optimized for specific functions. In the past decades, the growth of inorganic materials on specific proteins has attracted considerable attention. However, the use of specific proteins as templates has only been demonstrated in relatively simple organisms, such as viruses, limiting the range of structures that can be used as scaffolds. This study proposes a method for synthesizing metallic structures that resemble the 3D assemblies of specific proteins in mammalian cells and animal tissues. Using 1.4 nm nanogold-conjugated antibodies, specific proteins within cells and ex vivo tissues are labeled, and then the nanogold acts as nucleation sites for growth of metal particles. As proof of concept, various metal particles are grown using microtubules in cells as templates. The metal-containing cells are applied as catalysts and show catalytic stability in liquid-phase reactions due to the rigid support provided by the microtubules. Finally, this method is used to produce metal structures that replicate the specific protein assemblies of neurons in the mouse brain or the extracellular matrices in the mouse kidney and heart. This new biotemplating approach can facilitate the conversion of specific protein structures into metallic forms in ex vivo multicellular organisms.

Insight into the development of silica-based materials as photocatalysts for CO2 photoconversion towards CH3OH: A review and recent progress

High exploitation of fossil fuel energy has resulted in substantial CO2 emissions into the atmosphere, leading to severe global warming. Tremendous strategies have been developed to explore possible approaches in minimizing the content of CO2 in the atmosphere. CO2 photoconversion into CH3OH has been put forward as a promising strategy since anthropogenic CO2 is utilized to generate valuable CH3OH assisting by clean solar energy. Silica-based materials have emerged as potential candidates for photocatalysts is accredited to their mesoporous framework with a large surface area, flexible tunability pore sizes, excellent thermal stability, and capability to suppress metal particle growth. Thus, this review encompasses the current progress on applying and developing silica-based materials as photocatalysts for CO2 photoconversion into CH3OH. Apart from that, fundamental aspects of the mechanism, the factors affecting performance, and the efficiency of silica-based materials in CO2 photoconversion to CH3OH are also comprehensively highlighted. The difficulties and prospects of CO2 photoconversion into CH3OH via silica-based materials are also discussed. In general, the most recent scenarios recommended further investigation to explore these materials since CO2 photoconversion to CH3OH has not been adequately investigated in the literature.

Cobalt supported on biomass carbon tubes derived from cotton fibers towards high-efficient electrocatalytic overall water-splitting

Developing noble-metal-free electrocatalysts for high-efficiency oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is still a challenge in the energy conversion application. Herein, a new bifunctional electrocatalyst Co/BCTs is exploited via in-situ growth of metallic Co particles on/in the surface of biomass carbon tubes (BCTs) derived from available natural cotton fibers, which exhibits the outstanding electrocatalytic performance for OER, HER and overall water-splitting. It is because that the mordification effect of Co particles improves conductivity, facilitates electron transfer and activates surface of BCTs, and meanwhile the unique micro- structure and morphology of Co/BCTs can promote the molecular mass transport and shorten the molecular diffusion distance. As expected, the electrolyzer assembled by Co/BCTs-5 as electrode couple attains a very low potential of 1.40 V at 10 mA cm−2 for overall water-splitting in alkaline electrolyte. This work endows new opportunities and potential values for exploiting the high-efficiency noble-metal-free electrocatalysts originated from natural biological derived materials.

Diffusion behaviors and mechanism of copper-containing sulfide in fayalite-type slag: A key step of achieving copper slag depletion

The dissolution behaviors of copper-containing sulfide (Cu2S) in fayalite-type slag have been deeply studied through experimental research and theoretical calculations. Results show that there are three phase changes in the process of Cu2S dissolution in the fayalite- matrix: (1) the formation of metallic copper particles and ferric iron by a redox reaction; (2) the formation of a matte (Cu2−xFexS) by crystallization; and (3) chemical dissolution to form copper-doped fayalite. The formed Fe(III)-O(BO)-Si increases the content of bridging oxygen in the slag, which slows the migration and growth of metal particles. The dissolved Cu(I) substitutes at the M1 (Fe-O-Fe) site in the fayalite lattice to form the Si-O-Fe(II)-O-Cu(I)-O-Fe(III) structure or substitutes at the M2 (Fe-O-Si) site to form the Si-O-Cu(I)-O-Fe(II)-O-Fe(III) structure to obtain a copper-doped fayalite complex, and the probability is equal for Cu(I) substituting at M1 and M2. Copper-doped fayalite is the main phase causing the chemical loss of copper in the smelting slag, and is difficult to recover by traditional flotation. Through the directional modification of the copper-doped fayalite, making Cu-O-Si bond to transform into Cu-O-S bond that is easy to be leached or Cu-S bond that is easy to be reselected, which can realize the efficient recovery of copper resources from slag. These findings provide theoretical support for improving copper resource recovery in slag or reducing copper loss when producing slag during copper smelting.

Recycling of chromium sludge to promote aggregation and growth of metal during self-reduction of nickel laterite ore

Addition of stainless steel pickling sludge, which contains hazardous hexavalent chromium, to low-grade nickel laterite ore has the potential to eliminate the hexavalent chromium and promote the aggregation and growth of iron-nickel particles during reduction with anthracite. The effect of chromium sludge on the aggregation and growth of metal particles during a self-reduction process of nickel laterite ore has been studied. The detoxification effect of hexavalent chromium in the sludge was evaluated using the standard TRGS 613 leaching test. Results showed that with increasing chromium sludge addition, the size of metal particles increased. With the addition of 13.94% by mass chromium sludge the average metal particle size in the reduce ore increased from 0.42 µm to 1.38 µm while the recovery of Fe, Ni and Cr increased from 53.73%, 19.39% and 33.36% to 78.33%, 69.22% and 58.26%, respectively. It is proposed that a low melting point eutectic phase of FeS formed in the reduced products, significantly promoted the migration and aggregation of metal particles. Leaching tests indicated that the original chromium sludge released > 600 mg/kg Cr(VI) while the slag from the combined laterite and chromium sludge released less than the EPA limit of 2 mg/kg Cr(VI).

Effects of Reducing Agent on the Activity of PtRu/Carbon Black Anode Catalyst of Direct Methanol Fuel Cell

A series of PtRu/carbon black catalysts were prepared by means of deposition-precipitation and reduced by various reducing agents. NaBH4, HCHO and NaH2PO2, respectively, were used as the reduction agents. Some of the samples were reduced by various amounts of NaH2PO2 to investigate the effects of P/Pt ratios on the characteristics and activity of the catalyst. These catalysts were characterized by X-ray diffraction and transmission electron microscopy. The components of these catalysts were detected by X-ray fluorescence, X-ray photoelectron microscopy, and extended X-ray absorption of fine structures (EXAFS). The methanol oxidation ability of the catalysts was tested by cyclic voltammetry measurement. The results show that NaH2PO2 could effectively reduce the particle size of PtRu metal. It can suppress the growth of metal particles. In addition, the P/Pt ratio is crucial. The catalyst reduced by NaH2PO2 with a P/Pt ratio of 1.2 had the highest activity among all catalysts. It had the higher Pt and Ru metal contents and smaller metal particle size than the other catalysts. Its activity was 253.12 A/g, which is higher that than the commercial catalyst (Johnson Matthey H10100, 251.32 A/g).

Electrochemical quartz crystal microbalance studies on specific adsorption of nanoparticle stabilizers on platinum surface

• Phosphinate reduces mass change of adsorbate film on Pt at the double layer region. • Phosphinate suppresses reduction of Pt to zero-valent and growth of metal particles. • Citrate adsorbs on Pt and increases adsorption strength of coadsorbed oxygen. • Citrate inhibits Cu electrodeposition on Pt while phosphinate has a minor effect. • Suberate adsorbs more than citrate on Pt to prevent nanoparticle aggregation. Phosphinate and citrate ions are effective stabilizers for aqueous phase synthesis of platinum-based nanoparticles. In the present study, specific adsorption/desorption of stabilizers on platinum surface was investigated using an electrochemical quartz crystal microbalance (EQCM). Cyclic voltammetry combined with EQCM revealed that phosphinate ion reduces mass change of adsorbate film on Pt at the double layer region and it was oxidized by water and oxygen species producing anodic current above 0.2 V vs. Ag/AgCl. Phosphinate stabilizes positively charged platinum species rather than metallic species, which leads to size reduction of metal nanoparticles. Density Functional Theory calculation indicated that phosphinate adsorbs on Pt via two oxygen atoms (though coadsorbed water might change the structure) and the interaction strength increases with increasing positive charge on Pt surface. Meanwhile, citrate increased adsorption strength of oxygen on Pt in a weakly acidic condition. Electrodeposition of copper on Pt was significantly suppressed in the presence of citrate. The capping effect of citrate and oxygen on metallic surface helps dispersing nanoparticles.

Athermal Solid Phase Reaction in Pt/SiO x Thin Films Induced by Electron Irradiation.

Microelectronics based on Si requires metal silicide contacts. The ability to form platinum silicide (Pt2Si) by electronic excitation instead of thermal processes would benefit the field. We studied the effects of electron irradiation on Pt2Si formation in composite films—composed of Pt and amorphous silicon oxides (a-SiOx)—by transmission electron microscopy and electron diffraction. Pt2Si formed in Pt/a-SiOx bilayer and a-SiOx/Pt/a-SiOx sandwiched films by 75 keV electron irradiation, at 298 and 90 K. The reaction is attributable to dissociation of SiOx triggered by electronic excitation. In a-SiOx/Pt/a-SiOx sandwiched films, reflections of pure Pt were not present after irradiation, i.e., Pt was completely consumed in the reaction to form Pt2Si at 298 K. However, in Pt/a-SiOx bilayer films, unreacted Pt remained under the same irradiation conditions. Thus, it can be said that the extent of the interfacial area is the predominant factor in Pt2Si formation. The morphology of Pt islands extensively changed during Pt2Si formation even at 90 K. Coalescence and growth of metallic particles (Pt and Pt–Si) are not due to thermal effects during electron irradiation but to athermal processes accompanied by silicide formation. To maintain the reaction interface between metallic particles and the dissociation product (i.e., Si atoms) by electronic excitation, a considerable concomitant morphology change occurs. Elemental analysis indicates that the decrease in Si concentration near Pt is faster than the decrease in O concentration, suggesting formation of a Si depletion zone in the amorphous silicon oxide matrix associated with formation of Pt2Si.

Modification of Carbon Black with Hydrogen Peroxide for High Performance Anode Catalyst of Direct Methanol Fuel Cells.

In this study, high-surface-area carbon black is used to support PtRu. In order to increase the functional groups on the surface of carbon black and to have a more homogenous dispersed PtRu metal, the surface of carbon black is functionalized by H2O2. PtRu/carbon black is synthesized by the deposition–precipitation method. NaH2PO2 is used as the reducing agent in preparation. These catalysts are characterized by N2 sorption, temperature-programmed desorption, X-ray diffraction, transmission electron microscope, and X-ray photoelectron spectroscopy. The methanol oxidation ability of the catalyst is tested by cyclic voltammetry measurement. Using H2O2 to modify carbon black can increase the amount of functional groups on the surface, thereby increasing the metal dispersion and decreasing metal particle size. NaH2PO2 as a reducing agent can suppress the growth of metal particles. The best modified carbon black catalyst is the one modified with 30% H2O2. The methanol oxidation activity of the catalyst is mainly related to the particle size of PtRu metal, instead of the surface area and conductivity of carbon black. The PtRu catalyst supported by this modified carbon black has very high activity, with an activity reaching 309.5 A/g.

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TaN–(Ag,Cu) nanocomposite films were deposited by reactive co-sputtering on Si(001). The films were then annealed using RTA (Rapid Thermal Annealing) at 200–400 °C to induce the nucleation and growth of metal particles in TaN matrix and on film surface. After the surface morphologies were analyzed, the samples were tested for their antibacterial behaviors against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. It is found that the antibacterial efficiency against either E. coli or S. aureus can be much improved for TaN–(Ag,Cu), comparing with TaN–Ag or TaN–Cu films. The annealing temperature for TaN–(Ag,Cu) can be as low as 250 °C. Being annealed at this temperature, the film still shows good antibacterial behaviors against either bacterium. The synergistic effect due to the co-existence of Ag and Cu is obvious, while the films still shows good tribological behaviors.

Propagating Fe-N4 active sites with Vitamin C to efficiently drive oxygen electrocatalysis

Free transition metal ions (such as Fe 2+ , Co 2+ ) exposed on the surface of metal organic frameworks (MOFs) would be highly aggregated during the carbonization process, which is not conducive to formation of M-N X active sites, resulting in reduced electrochemically active sites. Accordingly, to effectively suppress the free metal ions on the surface of MOFs and increase Fe-N 4 active sites, Vitamin C (L (+)-ascorbic acid), with an ability to coordinate transition metals, is complexed with ferrous ions. Meanwhile, the acidity of Vitamin C can moderately erode the surface of MOFs materials, further accelerating the generation of holes and defects in the carbonized products. Compared with the control samples without introduction of Vitamin C, the iron-based (VC-MOF-Fe) catalyst, with obviously increased Fe-N 4 active sites, exhibit significantly enhanced oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performance. When used in rechargeable zinc-air batteries, the peak power density of VC-MOF-Fe (113 mW cm −2 ) is also better than that of 20% commercial Pt/C + RuO 2 . Interestingly, the function of Vitamin C also applies to the cobalt-based catalyst (VC-MOF-Co), evidencing the universality of this strategy. By introducing Vitamin C, the growth of transition metal (Fe, etc.) particles is suppressed, which significantly increases the amount of Fe-N 4 active sites in MOFs-derived catalysts, leading to a significant improvement in oxygen electrocatalytic performance. • Vitamin C suppresses aggregation of free ferrous ions on MOFs, producing more Fe-N 4 active sites. • The prepared VC-MOF-Fe catalyst exhibit significantly enhanced ORR performance in alkaline and acidic media. • It also shows improved OER performance in alkaline media. • It has high open circuit voltage and power density in the application of zinc-air batteries. • It also applies to VC-MOF-Co catalyst, which provides a new route on increasing M-Nx active sites.

Anion-Modulated Platinum for High-Performance Multifunctional Electrocatalysis toward HER, HOR, and ORR.

SummaryEfficient electrocatalyst toward hydrogen evolution/oxidation reactions (HER/HOR) and oxygen reduction reaction (ORR) is desirable for water splitting, fuel cells, etc. Herein, we report an advanced platinum phosphide (PtP2) material with only 3.5 wt % Pt loading embedded in phosphorus and nitrogen dual-doped carbon (PNC) layer (PtP2@PNC). The obtained catalyst exhibits robust HER, HOR, and ORR performance. For the HER, a much low overpotential of 8 mV is required to achieve the current density of 10 mA cm−2 compared with Pt/C (22 mV). For the HOR, its mass activity (MA) at an overpotential of 40 mV is 2.3-fold over that of the Pt/C catalyst. Interestingly, PtP2@PNC also shows exceptional ORR MA which is 2.6 times higher than that of Pt/C and has robust stability in alkaline solutions. Undoubtedly, this work reveals that PtP2@PNC can be employed as nanocatalysts with an impressive catalytic activity and stability for broad applications in electrocatalysis.

Measurement and Characterisation of Metallic Iron Particles on Coal-Based Reduction and Magnetic Separation of Refractory Titanomagnetite

Coal-based reduction followed by magnetic separation is a promising technology for processing refractory iron ores. Analysis of the size distribution of metallic iron particles is an effective approach for exploring the mechanisms of coal-based reduction. As metallic iron particles exhibit very complex shapes compared with nature ores, approaches for measuring and characterising metallic iron particles still remain unclear. In this study, the size of metallic iron particles was measured and characterised using manual point-counting by optical microscopy technics and image analysis. The effects of CaF2 as an additive on behaviour of the particle size distribution (i.e. mean size and cumulative frequency distribution) were also determined. Results indicate that CaF2 had a significant effect on the growth of metallic iron particles. When the CaF2 dosage increased from 0 to 8%, the mean size according to the area method increased from 9.03 to 16.28 μm, while the promotion effect gradually weakened and generated many fine metallic iron particles when the CaF2 dosage exceeded 8%. An increase in CaF2 dosage also led to cumulative distribution curves gradually shifting to the right mainly because F− can break the crystal structure of each phase during the carbothermic reduction of titanomagnetite and reduce the stability of the lattice structure, thus reducing the melting point and accelerating the growth of metallic iron grains. Compared to different measuring methods, the area method is a more suitable approach for measuring and characterising the size of metallic iron particles.