Exploring the Role of Activating Agents on the Electrocatalytic Activity of Grape Pomace-Derived Catalysts for the Oxygen Reduction Reaction.

The development of efficient and sustainable nonprecious metal catalysts for the oxygen reduction reaction (ORR) is central to advancing next-generation fuel cells and metal-air batteries. Fe-N-C catalysts derived from biomass have emerged as promising candidates, yet the influence of activation chemistry on the active-site formation and electrocatalytic performance remains insufficiently explored. Here, we unveil how KOH (strong base) and ZnCl2 (Lewis acid) modulate the chemical activation of wine grape pomace, a readily available agri-food residue, to generate Fe-N-C electrocatalysts through a one-step synthesis without external nitrogen precursors. KOH activation promotes extensive micro- and mesoporosity and favors the in situ development of well-coordinated Fe-Nx moieties, yielding a large electrochemically active surface area and a high ORR onset potential of 0.87 V versus reversible hydrogen electrode, comparable to leading biomass-derived Fe-N-C catalysts. In contrast, ZnCl2 activation reduced the density of active sites, resulting in diminished ORR activity. This work provides insight into how activation pathways govern porosity evolution, Fe-Nx site formation, and ORR performance. More broadly, it demonstrates the effective valorization of winemaking residues into functional electrocatalysts, offering a scalable and sustainable route for materials design in electrochemical energy conversion technologies.