Agro-food Waste as a Source for Advanced ORR Catalysts

Nowadays, the use of fossil fuels and the resulting greenhouse gas emissions have increased. Therefore, to facilitate the energy transition, it is essential to develop large-scale devices like fuel cells. However, their applicability is limited by the oxygen reduction reaction (ORR) at the cathode. This reaction must be catalyzed, and the main catalysts are typically based on platinum (Pt) or transition metals, which are either expensive and scarce or suffer from low durability.

To address these challenges, we propose the use of carbon materials such as activated carbon (AC), derived from industrial waste of the agro-food industry, making these precursors highly accessible and cost-effective. In this work, three different methods to synthesize the ACs, i.e., pyrolysis and thermal treatment with FeCl₃ or FeCl₃/ZnCl_2, were used, doping the most promising catalyst with heteroatoms (N/S) and using them as supports for a small amount of metal (Co/Ni).

These catalysts were characterized both physically,chemically, and electrochemically, and their efficiency in ORR was evaluated. Physical–chemical characterization was carried out by SEM, TEM, XRD, Raman, physical adsorption of N₂, ICP, XPS, and so on, confirming the achievement of different textures in the ACs and the success of the doping process.

The ORR performance of the catalysts was evaluated, and the electrochemical active surface area (ECSA), Tafel Slope, EIS, and durability tests were determined for the most promising catalysts. This analysis revealed a relationship between the textural properties, heteroatom content, metal support, and the improvement electrochemical properties, including charge-transfer and mass-transfer phenomena, and selectivity toward the 4-electron ORR mechanism.