Boosting the oxygen reduction electrocatalytic performance of grape stem-derived N-doped activated carbons via (hydro)thermal annealing

Developing efficient and sustainable electrocatalysts for the oxygen reduction reaction (ORR) is essential for the advancement of alkaline fuel cells. In this work, nitrogen-doped activated carbons were synthesized from grape stems using urea as the nitrogen source. Porosity was developed via CO 2 activation and further enhanced by a previous hydrothermal treatment. A second thermal step at 1000 °C was employed to tune the nitrogen distribution. The combination of hydrothermal treatment and high-temperature annealing promoted an increased graphitic-to-pyrrolic nitrogen ratio, which was found to govern the overall ORR performance of the resulting activated carbons. The optimized material (CN-HGS-CO 2 -L-1000) exhibited a high surface area (782 m 2 g −1 ) and an enhanced graphitic-to-pyrrolic N ratio (2.85), translated into excellent ORR activity in 0.1 M KOH, with a half-wave potential (0.84 V) surpassing Pt/C (0.82 V vs RHE). These findings underscore the synergistic role of graphitic-N/pyrrolic-N in biomass-derived activated carbons for ORR, and provide valuable insights into the valorisation of abundant grape-processing residues into active and sustainable electrocatalysts. • Grape stems valorised into N-doped activated carbons for efficient oxygen reduction. • Sequential hydrothermal and high-temperature annealing boosts the ORR activity. • An enhanced N-graphitic/N-pyrrolic ratio improves the overall performance. • No chemical activators, pore templates, or fossil carbon sources needed.