Over the past decades, a considerable amount of work has been put into replacing expensive Pt in oxygen reduction reaction (ORR) catalysts for use in fuel cells, such as with Fe or Co and nitrogen co-doped carbon materials [1-3]. At the same time, a major environmental issue is the lack of adequate methods for repurposing or recycling waste tires. Herein, it was investigated whether waste tires could be used as a source of carbon for synthesizing ORR catalysts.

To prepare the carbon support, waste tire granules were pyrolyzed at 1000 °C for three hours in Ar. This material was then used to synthesize four non-platinum-group metal (NPGM) catalysts via dry ball-milling [2] and wet synthesis [2, 3] methods. FeSO₄∙7H₂O or Co(NO₃)₂·6H₂O salts and 2,2’-bipyridine were used as precursors. Wet synthesis required the precursors to be dissolved in water and mixed with the carbon material, after which the solution was dried. For the dry method, all precursors were mixed and ball-milled for one hour. The products of both synthesis methods were subsequently pyrolyzed at 800 °C for 1.5 h in Ar.

All materials were characterized using HR-SEM, SEM-EDX, and nitrogen sorption methods. The materials were heterogeneous and contained additives commonly present in tires as constituents of tire filler materials or residual products of tire production (Si, S, Ca, and Zn). All materials exhibited low porosity and a rather low specific surface area (S_BET = 92 to 150 m² g^-1).

Electrochemical analyses were carried out in an O₂ saturated 0.1M KOH solution using the rotating disk electrode method. Although the carbon support on its own did not show significant activity toward the ORR, the modified Co-N/C and Fe-N/C catalysts demonstrated substantially higher onset potentials (∆E_onset ~150 mV). The best electrochemical activity was achieved by the Co-N/C material synthesized using the wet method. These results show that waste tire-derived carbon materials can be used to successfully synthesize NPGM catalysts suitable for application in fuel cells.

Acknowledgements

This work was supported by PRG676 "Development of express analysis methods for micro-mesoporous materials for Estonian peat derived carbon supercapacitors" (1.01.2020- 31.12.2024), TK141 "Advanced materials and high-technology devices for sustainable energetics, sensorics and nanoelectronics" (1.01.2016−1.03.2023), and LLTKT20148 "Production of Polymer Electrolyte Membrane Fuel Cell" (10.02.2020−9.07.2021)

References

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