Influence of Active Site Modification on PGM-Free Catalysts for the Oxygen Evolution Reaction in Alkaline Electrolytes

This study investigates the design, synthesis, and optimization of carbon-supported ternary Fe–Ni–Co electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. The effects of thermal treatment, particle size, composition, and metal loading were systematically evaluated through morphological, structural, and electrochemical characterization. Thermal treatment played a key role in balancing activity and durability: the baseline calcination protocol promoted optimal alloy formation and maximized initial OER activity, whereas modified treatments slightly reduced activity while significantly enhancing long-term stability. Ball milling reduced the average particle size by approximately 60%, increasing the onset potential due to partial carbon support degradation while improving mass transport and reducing the Tafel slope at high current densities. Trimetallic Fe–Ni–Co catalysts exhibited superior initial OER activity compared with bimetallic counterparts owing to synergistic interactions among the three metals, although with faster performance degradation. Nickel-rich compositions delivered the highest activity, whereas cobalt-rich and equimolar formulations showed greater stability during accelerated stress testing. Increasing metal loading proved detrimental because of particle agglomeration, highlighting the importance of active-phase dispersion. The optimized Fe–Ni–Co electrocatalysts outperformed commercial NiFe2O4, Ni/Vulcan, and IrO2, demonstrating their potential as low-cost, durable, and highly active platinum-group-metal-free (PGM-free) electrocatalysts for alkaline water electrolysis.