Plastic derived carbon nanotubes for electrocatalytic oxygen reduction reaction: Effects of plastic feedstock and synthesis temperature

Closing the resource loop by transforming plastic waste into higher value products is an important step for changing from a linear to circular economy. Using a sequential pyrolysis and catalytic chemical vapour deposition process, plastics have been successfully converted into carbon nanotubes (CNTs). Pure low density polyethylene (LDPE), polypropylene (PP) and mixed plastics (MP) were used as raw materials in the two-stage process. In the first stage, the plastics were pyrolysed at 600 degrees C. In the second stage, the non-condensable gases were converted into multi-walled CNTs over a Ni-based catalyst at two different temperatures, 500 and 800 degrees C. The influence of plastic feedstock and synthesis temperature on the performance of plastic-derived CNTs as electrode materials in electrocatalysis was investigated. The CNTs were evaluated as electrode materials for their heterogeneous electron transfer rate using a redox probe, which showed improved electrochemical behaviour. For oxygen reduction reaction (ORR), CNTs produced at 500 degrees C demonstrated superior performance compared to those produced at 800 degrees C. Influence of feedstock on electrocatalytic ORR activity of the as synthesised CNTs was marginal. Temperature was the governing factor influencing the properties of CNTs due to annealing and oxidation of edge defects generated during synthesis at higher temperatures.