Preparation Of The Nitrogen Doped Carbon Nanosheets And Their Catalytic Performance Towards Oxygen Reduction Reaction In Acidic And Alkaline Media

Noble metal Pt/C or platinum alloy was most commonly used as the cathodic oxygen reduction reaction?ORR? catalyst for fuel cell. However, the drawbacks of Pt/C include the limited reserves, high cost and poor electrocatalytic stability. Therefore, seeking for cheap, efficient and stable non-noble metal catalyst has become one of the main goals for researches on fuel cells. At present, nitrogen-doped carbon material or nitrogen-doped carbon material-loaded transition metal nanoparticle non-noble metal catalysts, obtained through high-heat treatment, are receiving wide attentions because of their good oxygen reduction reaction catalytic activity. In this paper, simple pyrolysis was used to prepare a series of nitrogen-doped carbon nanosheets oxygen reduction catalysts and evaluate their morphology and structure characterization and electro-catalytic property. The main research contents and conclusions are as follows:1. For the first time, nitrogen-doped carbon nanosheets, prepared by improved simple high-heat pyrolysis with resource-rich and cheap corn starch and urea as raw materials, were used as the cathodic oxygen reduction reaction ?ORR? catalysts for fuel cells. The effect of pyrolysis temperature on ORR catalytic activity in sample preparation process was studied. The optimized catalysts showed excellent electro-catalytic activity comparable to commercial 20% Pt/C whether in acidic or alkaline media ?Its ORR half-wave potential-0.15V was the same with Pt/C in 0.1 M KOH?. Moreover, their methanol-tolerance and stability were better than that of Pt/C catalyst.2. The layered graphitic carbon nitride ?g-C₃N₄? derived from cheap raw materials is used as soft-template for the evolution of nitrogen-doped carbon nanosheets. This method eliminated the influence of metal impurities on ORR catalytic activity, which verified that ORR catalytic activity of nitrogen-doped carbon materials was derived from the catalytic mechanism of nitrogen-doped effect, and determined the contribution of graphite type nitrogen to ORR catalytic activity.3. The nitrogen doped carbon nanosheets wrapped cobalt nano-particle composites was prepared by simple pyrolysis. The effect of cobalt content on catalytic activity in sample preparation process was investigated. The results showed that NCN-Co-0.1 ?Co accounted for 10 wt% of C? presented the best catalytic activity, and NCN-Co-0.1 delivers better ORR activity than Pt/C catalyst ?NCN-Co-0.1 gives 35 mV more positive half-wave potential than that of Pt/C in 0.1 M KOH?, of which the ORR catalytic activity was comparable to Pt/C in 0.5 M H₂SO₄, and its methanol tolerance was better than that of Pt/C. Besides, ORR activity of NCN-Co-0.1 was significantly increased with the generation of Co-Nx structure, which confirmed that this Co-Nx structure was one of the main active points of NCN-Co-0.1.4. The nitrogen-doped carbon nanosheets wrapped Fe and Co binary metallic nanoparticle composites was preparated to improve the number of oxygen reduction activity sites, and the ORR catalytic activity of single metal Fe or Co nanoparticle loaded nitrogen doped carbon materials were compared. The experimental results showed that in acidic and alkaline medium, ORR catalytic activity of NCN-FeCo was superior to that of NCN-Fe and NCN-Co and comparable to Pt/C catalytic activity ?the half-wave potential was 70mV positive to Pt/C in 0.1 M KOH and the half-wave potential was only 40mV negative to Pt/C in 0.5 M H₂SO₄?. Besides, the methanol tolerance of NCN-FeCo and stability in alkaline electrolyte was superior to Pt/C, which determined the contribution of collaborative electronic effect between Fe and Co binary metallic nanoparticles and nitrogen in carbon nanosheets to ORR catalytic activity.5. Compared with alkaline fuel cell, the application of proton exchange membrane fuel cell in acid medium was wider. However, most non-noble metal ORR catalysts showed low catalytic activity and poor durability in acidic media now. In this paper, a series of nitrogen doped carbon nanosheets were prepared and they presented excellent ORR catalytic activity in alkaline especially acidic media, which was higher than the ORR catalytic activity of other materials reported in most literatures and of great practical value.