Recycling of waste tires by synthesizing N-doped carbon-based catalysts for oxygen reduction reaction

Currently, there are 1.5 billion waste tires (WTs) produced yearly, which has become a vital issue worldwide. In this study, we suggest to recycle rubbers and carbon black (CB) together by carbonizing rubbers in WTs. Sulfonation of WT rendered stable structure to carbonize rubbers, which are innately non-carbonizable. The following heat-treatment in Ar/NH3 atmosphere provided abundant nitrogen functional groups on resulting carbons including CB and carbonized rubbers, confirmed by X-ray photoelectric (XPS) spectroscopy and TEM micrographs. To validate them as oxygen reduction reaction (ORR) catalysts, a half-cell test in alkaline media was carried out. The N-doped catalyst with carbonized rubbers and CB exhibited a superior ORR activity to that with carbonized WTs without sulfonation and further those performance was comparable to a Pt/C catalyst. It is evident that carbonized rubbers induced higher nitrogen contents and larger electrochemical surface areas of the catalyst, which offered more active sites higher ORR activity. Therefore, we believed that the proposed approach introduced in this paper shows an effective solution to deal with WTs by envisioning alternative recycling pathway.