The Impact of Modification on the Stability of Catalysts for Oxygen Reduction Reaction

Vulcan XC 72R was modified in two different ways (i.g., treated by the NH₃ gas or urea). The impact of modification strategies was analyzed by correlating the structure and chemical properties of carbons with the catalytic activity and stability of corresponding catalysts. Pt clusters are homogeneously distributed through the nitrogen-doped carbon support. Electronegative nitrogen atoms create positive charge on neighbor carbon atoms. The increased interaction between the carbon support and PtCl₆^2- restrains the nucleation of platinum. N₂ adsorption-desorption results indicated that abundant of micropores were created and the proportion of micropores obviously increased from 2.8 % to 11.4 %. XPS measurement distinguished different N functionalities. Pyridinic-N and pyrrolic-N were introduced on the surface of carbon support. Pt/NC catalyst exhibits the best ORR performance among all as-prepared catalysts in 0.1 M KOH solution. Moreover, the stability of Pt/NC is superior with minor negative shift of 5 and 22 mV in half-wave potential after 3k and 6k cycles. The enhanced ORR activity and stability of NC could be ascribed to the uniform Pt distribution, which promotes oxygen adsorption and hinders the migration and agglomeration of Pt clusters.