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.

Nutrient status and pollution levels in five areas around a manganese mine in southern China

Nutrient status and pollution levels are the main factors affecting soil restoration.The nutrient status and pollution levels in five areas,an unexplored mine area(UA),an explored mine area(EA),a tailings area(TA),a reclamation area(RA)and an agricultural area(AA),around the Pingle manganese mine in Guangxi,China,were assessed in this study.The results showed that the average total phosphorus in these five areas ranged from 1.05 to 1.57 mg/kg,corresponding to grades of extremely high and high.The average total nitrogen values were 0.19,0.69,0.93,1.24 and 1.67 mg/kg in EA,TA,RA,UA and AA,corresponding to grades of very low,low,medium-low,medium-high and medium-high,respectively.The average organic matter values were 12.78,8.92,22.77,21.29 and 29.11 mg/kg in EA,TA,RA,UA and AA,which corresponded to grades of medium-low,low,medium-high,medium-high and medium-high,respectively.All these results indicated that the total phosphorus was sufficient in these areas,while the total nitrogen and organic matter were insufficient in EA,TA and RA.The available concentrations of Mn and Zn corresponded to the intermediate grade,while the values for Cu corresponded to the very low grade;these might be another factor restricting ecological reclamation.Contamination and ecological risk assessments based on the single contamination index,Nemerow multi-factor index and potential ecological risk index showed that the five tested areas around the Mn mine were considered heavily polluted and presented high ecological risk.Mn and Cd were the dominant pollutants.