Preparation And Characterization Of The Non-metal Doped And Sulfonated Carbon Nanotubes And Their Electrocatalytic Performances For Oxygen Reduction Reaction

As one of the most popular supporting materials of catalysts in low-temperature fuel cell(LTFC), carbon nanotube (CNT) receives its attention because of its unique structural andexcellent electronic properties. Many reports demonstrated that the electrochemical propertiesof carbon catalysts have been improved remarkably after sulfonating or doping differentelements such as N, P, B, I, S into the sp2hybridized carbon frameworks in carbon materials.Therefore, in this article, we focus on the effects of doping or sulfonating treatment of carbonnanotubes on electrocatalytic performance for oxygen reduction reaction (ORR).The sulfur and nitrogen co-doping CNTs (SN-CNTs) have been designed andsuccessfully prepared by the pyrolysis of N-doped CNTs (N-CNTs) with sulfur precursor. Theresult showed the as-prepared SN-CNTs have an enhanced ORR activity in both acidic andalkaline medium compared with N-CNTs in the same condition. The calculated average valueof n for the SN-CNTs in acidic media is3.42, which is higher than2.88of N-CNTs. Underalkaline solution, the average n of SN-CNTs is4, which is the same value as Pt-C (4.00) andhigher than that of N-CNTs (3.83). In contrast to the commercially available Pt-C catalyst, theresult also demonstrated that SN-CNTs exhibited an improved electro-catalytic performance,better methanol-cross tolerance and extra stability.Also, we prepared the P-doped CNTs, N-doped CNTs, and P and N co-doped CNTs bydifferent methods including chemical vapor deposition (CVD), thermolysis and hydrothermalsynthesis. The effects of preparation methods and doping elements on ORR performance havebeen evaluated in both acidic and alkaline solution. The results showed that the ORRperformances of the doped catalysts depend on the electrolyte solution and the interactionbetween doping elements.At last, we synthesized sulfonated vertically aligned CNTs (VA-CNTs) and studied theeffects of sulfonating and annealing temperature on ORR performance, improving the electrocatalytic performance of VA-CNTs for ORR.The studies on the doped and sulfonated CNTs as ORR catalysts could provide new waysto prepare alternatives of Pt-based catalysts and make a better understanding on the ORRmechanism.