Upcycling of polyurethane into iron-nitrogen-carbon electrocatalysts active for oxygen reduction reaction

World plastic production has increased since industrial-scale production began in the 1940s and while large amount of thermoplastic polymers can be effectively recycled and re-used, undifferentiated polymers or thermoset polymers cannot, and as a result, most of these raw materials end up in landfill or energy recovery in incinerators. The synthesis of carbon nanomaterials from conversion of waste polymers is an alternative, promising approach owing to the high added-value of these products. In particular, novel carbon materials, could translate into interesting and cheap material for the catalytic reduction of oxygen (ORR), a fundamental reaction for the production of H2O2 or in fuel cell and metal air batteries. This paper presents the synthesis of iron-nitrogen-carbon (Fe-N-C) electrocatalysts starting from a mix of polyethylene (PE) and polyurethane (PU) by adding FeCl3 as an iron source for promoting Fe-Nx sites formation. The two polymers were mixed according to a solvent assisted process employing p-xylene or with a solvent free process using a Brabender plastograph. The blend of thermoplastic and thermoset polymers was converted into Fe-N-C materials in a two-step pyrolysis, where the temperature of second pyrolysis showed to sensitively affect the chemical and textural properties of the resulting material. Depending on the temperature, and initial PE content, the surface area ranges between 195 and 479 m2 g−1, with a preferential formation of micropores. XPS analysis confirmed that the employment of PU leads to the formation of nitrogen functional groups and Fe-Nx sites, while XRD investigation in heating chamber allowed to follow the formation Fe3C, Fe2O3, γ-Fe and α-Fe with temperature rises between 700–1000°C. The new Fe-N-C catalysts were characterized by linear sweep voltammetry at ring disk electrode showing interesting activity for the ORR in both acid and alkaline electrolyte and a selectivity for H2O2 which deeply depends on the type of electrolyte as well as on nitrogen content and on the surface area of the samples.