Showing papers by "Qiang Wang published in 2021"

Surface O2- regulation on POM electrocatalyst to achieve accurate 2e/4e-ORR control for H2O2 production and Zn-air battery assemble

Abstract: Polyoxometalate is an excellent electracatalyst for oxygen reduction reaction. Here, to enhance its selectivity towards two-electron oxygen reduction reaction, one O2− is replaced by S2−. Vulcanized polyoxometalate exhibits two-electron feature in oxygen reduction reaction. The H2O2 production rate reaches 4.48 mol gcat-1 h-1 at 0.3 V (vs. RHE) with Faradaic efficiency 83.9 %. On the contrary, pure polyoxometalate without vulcanization shows typical four-electron character in oxygen reduction reaction and can be employed as cathode material in Zn-air battery. The results imply vulcanization weakens adsorption of OOH*, impedes O-O breaking and enhances two-electron selectivity. Vulcanized polyoxometalate exhibits photothermal induced advanced oxidation process, which can degrade various organic pollutants. Compared with traditional Fenton reaction, photothermal induced advanced oxidation process shows Fe2+ free character and wide pH scope. More importantly, this work also clarifies the influence of structure on oxygen reduction reaction selectivity for polyoxometalate.

Correlation between anisotropic fractal dimension of fracture surface and coercivity for Nd-Fe-B permanent magnets

Abstract: In this work, SEM images analysis and fractal dimension calculations are performed on the fracture surfaces for N50-type with low coercivity, 30 EH-type with high coercivity, and isotropic Nd-Fe-B permanent magnets. It is discovered for the first time that the difference between the fractal dimensions of fracture surface parallel and perpendicular to the c-axis D ∥ and D ⊥ for N50-type magnet with low coercivity is large, and the difference between the fractal dimensions of D ∥ and D ⊥ for 30 EH-type magnet with high coercivity is small. However, there is almost no difference in the fractal dimension of D ∥ and D ⊥ for isotropic magnet. The correlation between anisotropic fractal dimension of the fracture surface and coercivity is revealed. The difference between the fractal dimension of fracture surface D ∥ and D ⊥ not only reflects the difference in micro morphology, but also serves as an important performance parameter to characterize the coercivity of the magnet, which provides new insights for studying the relationship between the magnetic properties and the microstructure of permanent magnetic materials.

Effects of high magnetic field annealing on FePt nanoparticles with shape-anisotropy and element-distribution-anisotropy

Abstract: The concave-cube FePt nanoparticles (NPs) with shape-anisotropy and element-distribution-anisotropy were annealed under a high magnetic field (HMF).

Experimental Study of Macrostructure and Segregation by a Novel Electromagnetic Nozzle Swirling Flow Combined with Electromagnetic Stirring in Continuous Casting

Abstract: To alleviate macrosegregation, it is the first time that an electromagnetic nozzle swirling flow is applied with a mold electromagnetic stirrer (M-EMS) during continuous casting of square and round billets. Compared with those by only M-EMS, the carbon ranges in square and round billets can be reduced to 0.022 and 0.046 pct, respectively, and the equiaxed crystal ratios are 18 and 33 pct, respectively, by using opposite nozzle swirling flow.

Macrosegregation Prediction by Evaluating Liquid Level Fluctuation in Round Billet Continuous Casting with Electromagnetic Nozzle Swirling Flow

Abstract: Under the joint action of electromagnetic swirling flow in the nozzle (EMSFN) and mold electromagnetic stirring, Liquid level fluctuation in the mold is investigated to find the optimal combination parameters for the occurrence time of the minimum macrosegregation degree in continuous casting of round billet. When the current intensity of EMSFN device is 450 A, the optimal carbon range 0.045 pct appears, after the fluctuation reaches the minimum with the current intensity at 400 A.

Flow fields control for bubble refinement induced by electromagnetic fields

Abstract: Large bubbles seriously reduce the efficiencies of the interactions between the bubbles and the molten steel, such as energy transfer, momentum transfer, mass transfer and chemical reaction. To reduce the size of the bubbles and increase the gas–liquid interface area, a novel non-intrusive method of bubble refinement was proposed, which only depends on the molten steel flow field controlled by the rotating electromagnetic field. The flow fields of the molten steel for bubble refinement were analyzed, and the corresponding bubble refinement was investigated. It was found that the molten steel formed obvious rotating turbulent flow for bubble refinement under the unidirectional rotating electromagnetic field. However, the large vortex in the center of the molten pool caused by the rotating flow made the bubbles aggregate and coalesce again, resulting in formation of larger bubbles and gas cavity. To suppress the central vortex formation and enhance the bubble refinement, the forward-reverse rotating electromagnetic field for bubble refinement was proposed. The irregular and chaotic flow occurred repeatedly because of alternating forward and reverse rotating in a short period, so that the turbulent kinetic energy and turbulent dissipation of the flow field always remained at a high level which favors bubble refinement. As a result, the bubble diameter can decrease by more than 50% compared to that without electromagnetic field. Furthermore, it is important that this non-intrusive kind of bubble refinement method completely avoids the introduction of non-metallic inclusions caused by intrusive configuration.

Three-step method with self-sacrificial Co to prepare a uniform 5 nm-scale Pt catalyst for the oxygen reduction reaction

Abstract: The catalytic activity of Pt-based catalysts for fuel cells is largely determined by the particle size and the dispersion of Pt. Normally, the electrodeposition of Pt cannot avoid a large particle size and agglomeration. For ensuring uniformity and a small size in the 5 nm scale of Pt, a three-step method was creatively applied to deposit Co first on defective mesoporous carbon (CMK-3-D) as a self-sacrificial template and as anchor points for Pt deposition. Second, we immersed Co/CMK-3-D in a mixed Pt and acid solution. Finally, the further growth of Pt was controlled by pulse reverse electrodeposition. Due to the trapping effect of defect holes from CMK-3-D, there was a small amount of nano-Co left in the catalyst carrier. The catalyst was finally composed of nano-Co and Pt nanoparticles (CoPt/CMK-3-D). The residual Co provided a large number of active sites, which promoted the excellent activity and stability of Pt due to a synergistic effect. Compared with commercial Pt/C, the specific activity of the catalyst was increased by about 2.3 times. After a 10 000 cycles test, the half-wave potential loss was only 6.4 mV. The high catalytic property of CoPt/CMK-3-D was attributed to its excellent dispersibility, small size, and the synergistic effect of the carrier and Co with Pt.