Synthesis of dual-doped non-precious metal electrocatalysts and their electrocatalytic activity for oxygen reduction reaction

The pyrolyzed carbon supported ferrum polypyrrole （Fe-N/C） catalysts are synthesized with or without selected dopants, p-toluenesulfonic acid （TsOH）, by a facile thermal annealing approach at desired temperature for optimizing their activity for the oxygen reduction reaction （ORR） in O2-saturated 0.1 mol/L KOH solution. The electrochemical techniques such as cyclic voltammetry （CV） and rotating disk electrode （RDE） are employed with the Koutecky-Levich theory to quantitatively obtain the ORR kinetic constants and the reaction mechanisms. It is found that catalysts doped with TsOH show significantly improved ORR activity relative to the TsOH-free one. The average electron transfer numbers for the catalyzed ORR are determined to be 3.899 and 3.098, respectively, for the catalysts with and without TsOH-doping. The heat-treatment is found to be a necessary step for catalyst activity improvement, and the catalyst pyrolyzed at 600℃ gives the best ORR activity. An onset potential and the potential at the current density of -1.5 mA/cm2 for TsOH-doped catalyst after pyrolysis are 30 mV and 170 mV, which are more positive than those without pyrolized. Furthermore, the catalyst doped with TsOH shows higher tolerance to methanol compared with commercial Pt/C catalyst in 0.1 mol/L KOH. To understand this TsOH doping and pyrolyzed effect, X-ray diffraction （XRD）, scanning electron microscope （SEM） and X-ray photoelectron spectroscopy （XPS） are used to characterize these catalysts in terms of their structure and composition. XPS results indicate that the pyrrolic-N groups are the most active sites, a finding that is supported by the correspondence between changes in pyridinic-N content and ORR activity that occur with changing temperature. Sulfur species are also structurally bound to carbon in the forms of C-Sn-C, an additional beneficial factor for the ORR.

Wear behavior of copper material removal during fluid jet polishing:A comparative study between experiment and simulation

As a crucial part in micro-electromechanical manufacture,local ultra-precision processing of highly ductile copper is expected to be realized by fluid jet polishing(FJP),which widely utilized in optical elements.Since copper exhibits different wear behavior from stiff and brittle material,there is currently no abrasive wear prediction model applicable for copper to investigate the polishing mechanism.This research reveals that the copper material removal is dominated by deformation wear rather than cutting wear through abrasive jet impact experiments and localized wear scars analysis.A three-dimensional gas-liquid-particle triphasic wear model for copper in FJP is developed by considering impact energy and wear mechanism simultaneously.Ultimately,validation assessments at various working pressures and impingement angles achieve the goodness-of-fit up to 0.92–0.97 in quantitative comparison between simulations and experimental measurements,which demonstrate the wear prediction ability of the proposed model.This investigation facilitates a better understanding of copper wear mechanism and provides theoretical guidance for FJP process optimization.

Mechanical model of nanoparticles for material removal in chemical mechanical polishing process

Chemical mechanical polishing (CMP) is the most effective method for surface planarization in the semiconductor industry. Nanoparticles are significant for material removal and ultra-smooth surface formation. This research investigates the mechanical effects of the material removal in the CMP process. The various contact states of pad, individual particle, and wafer caused by the variations of working conditions and material properties are analyzed. Three different mechanical models for the material removal in the CMP process, i.e., abrasive wear, adhesive wear, and erosive wear are investigated, with a focus on the comparison of the results for different models. The conclusions and methods obtained could potentially contribute to the understanding and evaluation of the CMP process in further work.