Recycling of waste automobile tires: Transforming char in oxygen reduction reaction catalysts for alkaline fuel cells

The recycling of scrap automotive tires is made difficult by a number of factors. They are composed of a complex matrix that includes hazardous materials, not to mention a gigantic annual production rate. Herein we report a novel approach tackling the recovery and valorization of chars, the least valuable by-product of waste-tire pyrolysis, through the transformation into highly efficient Oxygen Reduction Reaction (ORR) catalysts for use in alkaline fuel cells and metal air batteries. The study has been performed on chars obtained from Microwave Assisted Pyrolysis (MAP). Each sample has been characterized by metal content (ICP-MS), specific surface area (BET), porosity, crystallinity and nature of inorganic components embedded in the carbonaceous matrix (XRPD). The most promising samples exhibit an ORR onset potential of -90 mV (RHE) and a 4e- mechanism. Two main factors are found to contribute to the enhanced ORR activity. Firstly, a large specific surface area and porosity and secondly the presence of a high concentration of ZnO particles embedded within the carbon matrix.