Grape stalk waste-derived nanostructured electrocatalysts for oxygen reduction reaction

The development of platinum-free electrocatalysts is essential to advance the sustainability and scalability of anion exchange membrane fuel cells (AEMFCs). In this work, we present a simple and cost-effective method to synthesize nitrogen-doped carbon electrocatalysts using raw, wet grape stalks, an abundant lignocellulosic agro-industrial byproduct, without any chemical pre-treatment. The synthesis combines hydrothermal carbonization of grape stalk waste in the presence of Fe or Cu salts, mechanochemical activation with dicyandiamide (DCDA), and pyrolysis, resulting in mesoporous carbon materials enriched in pyridinic nitrogen and metal‑nitrogen coordination sites. XRD analysis additionally confirmed the in-situ formation of Fe 3 C in Fe-based samples. The resulting Fe- and Cu-based catalysts exhibit excellent oxygen reduction reaction (ORR) activity and durability in alkaline media. In particular, the Fe-based catalyst exhibits superior performance, achieving an onset potential of 0.95 V vs. RHE, a low hydrogen peroxide yield (~7%), and a Tafel slope of 53 mV/dec, attributed to the synergistic effects of Fe 3 C and N-doped carbon, as well as the high accessible surface area. Both catalysts maintain their performance after 10,000 potential cycles, with activity losses below 6%. These results highlight the potential of grape stalks as a sustainable carbon source for the production of PGM-free, high-performance electrocatalysts, contributing to circular economy strategies and the decarbonization of hydrogen-based energy technologies. • A sustainable methodology for electrocatalyst synthesis using grape stalks as precursors. • Fe and Cu enhance active site density, improving oxygen reduction reaction kinetics • Dicyandiamide increases pyridinic-N incorporation, enhancing ORR activity. • Fe N-doped carbon exhibits the best catalytic activity close to commercial Pt/C.