The Study On The Catalysts Prepared By Hydrothermal-doping Nitrogen And Green Leave For Oxygen Reduction Reaction

Fuel cell attracts wide attention due to features of novel, clean, efficient and sustainable, but oxygen reduction reaction (ORR) in cathode has hindered its development. So far, platinum is still the most effective and most widely used catalyst for the ORR. However, its high price, low methanol tolerance, limited stability hinder the commercialization of this new energy systems. So it is essential to develop an efficient non-noble metal catalyst to replace platinum-based catalyst. TM-N/C catalyst is considered to be a promising alternative to Pt/C catalyst.In this work, the widely used Vulcan XC-72 was utilized as carbon source, NH3·H2O and CoCl2·6H2O were employed as nitrogen source and transition metal source. A series of TM-N/C catalysts were synthesized by an innovative direct chemical reduction combined ammonia hydrothermal method. The effects of preparation conditions on catalyst performance were discussed. LSV was used to evaluate the activity of prepared TM-N/C catalysts and to make comparisons with commercial Pt/C. Experimental result have shown that it’s effective to dope nitrogen into carbon material using NH3·H2O as nitrogen source under hydrothermal conditions. The participation of transition metal and pre-oxidation of carbon carrier played a very important role in improving the performance of catalysts. The optimal preparation conditions for the hydrothermal reaction was 180℃ and 9 h. The peak potential of prepared catalysts was approaching to commercial Pt/C catalyst.This green leaves was selected as raw materials innovatively, which is rich in chlorophyll. Then a series of leaves-based catalysts were prepared by pyrolysis the mixture of green leaves, Vulcan XC-72 and transition metals salt. The influence of the proportion of each material, heat treatment temperature and time, and transition metal species and contents on catalysts performance were investigated. And detailed characterizations were carried out to analyze the electrochemical properties of catalysts. The results have shown that it’s feasible to select the green leaves as catalyst precursor. Both the leaching out of magnesium in leaves, the adding of transition metals and carbon carrier produce positive effect on the catalytic activity. The optimal experimental condition was leaching with acid for 24h, SWA:C=1, Fe wt%= 8%,900 ℃ and 2h for heat treatment. And it was verified that Chlorophyll made a mean contribution to the catalytic activity of green leaves catalyst. The optimal catalyst made by this method was SWA+C+Fe-900-2h, which has a similar catalytic activity to commercial Pt/C catalyst, with slightly lower onset potential than Pt/C and almost equal peak potential to Pt/C under alkaline conditions. The electrons transfer number was 3.9 measured by rotating disk electrode, which belongs to 4e- pathway. The cycling stability and methanol resistance of SWA+C+Fe-900-2h were better than that of commercial Pt/C catalyst.The prepared TM-N/C catalysts by these two methods have a certain reference significance for the development of non-Pt alternative catalysts.