Cobalt Electrodeposition on Chars from Microwave Assisted Pyrolysis of Waste Tires: Evaluation of the Catalytic Efficiency in O.R.R
Authors: Passaponti Maurizio , Salvietti Emanuele , Giurlani Walter , Giaccherini Andrea , Rosi Luca , Innocenti Massimo 
Published: February 2020

In recent years the fossil sources dependence of our society for both fuels and essential raw materials and the global warming have led to an increasing use of renewable sources and waste valorization processes. Nowadays the outstanding increase in the number of vehicles worldwide is among the most environmental problem because of the emission of harmful pollutants and the solid wastes disposal, in particular the removal of the used tires (1). There are several technologies for tires recycling. Thermal treatments may be used such as pyrolysis: a thermal decomposition process performed at higher temperature in an inert atmosphere which allows the transformation of complex substances in simple molecules. Pyrolysis transforms starting materials into three potentially useful classes of products: char, liquid and gas. These products can be easily stored, transported and used as a source of chemicals and energy. Among several heating technologies and apparatus used in pyrolysis process, microwave assisted pyrolysis (MAP) attracted attention, in recent years, due to the considerable advantages of this technology over conventional pyrolysis process (2,3,4). The use of microwaves requires the presence of material: water, carbon, metals or materials able to absorb microwaves and releasing energy. Recently Undri et.al (5) reported the correlation between experimental conditions of pyrolysis (MAP) and some of the characteristics of char. Interesting ICP-MS analysis showed the presence of several metal. It was observed that char obtained from microwave assisted pyrolysis of waste tires showed an interesting electrocatalytic activity in the Oxygen Reduction Reaction (ORR) in alkaline medium. ORR is regarded as one of the most important electrocatalytic reactions in electrochemical energy conversion system such as fuel cells and several industrials process. In order to speed up the ORR kinetics to reach a practically usable level in fuel cell, a cathode ORR catalyst is needed. Platinum-based materials are the most practical catalyst. Nevertheless, owing to the limited reserve in nature of Platinum-group metals, and their high cost, extensive research has focused on developing alternative catalyst. To remove and replace platinum with less expensive materials it was proposed to exploit a synergic mechanism with one metal able to break the O-O bond of molecular oxygen and second metal capable in reducing the adsorbed oxygen so formed. The presence of specific metals together with a high carbon content are essential requirements for catalysts for ORR (6). Selective electrodeposition of metals such as Cobalt and Copper on chars from MAP allows a better catalytic efficiency. In particular, electrochemical analysis of Co-chars catalyst showed both onset potential (Eon) and electrons number exchange for O2 molecule similar to Platinum electrode.
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