Hierarchically Designed Co₄Fe₃@N-Doped Graphitic Carbon as an Electrocatalyst for Oxygen Evolution in Anion-Exchange-Membrane Water Electrolysis

Anion-exchange-membrane water electrolyzers (AEMWEs) have gained considerable attention owing to their low cost and high energy efficiency, combining the advantages of alkaline water electrolyzers (AWEs) and proton-exchange membrane water electrolyzers (PEMWEs). Despite these merits, AEMWEs face challenges associated with the insufficient electrochemical activity of transition-metal-based electrocatalysts and their inferior long-term durability, particularly in electrodes for the oxygen evolution reaction (OER). To address these issues, hierarchically structured OER electrocatalysts comprising a Co₄Fe₃ core and N-doped graphitic carbon shell were synthesized in this study by pyrolyzing Co/Fe-Prussian blue analogues (PBAs)-based templates. The resulting electrocatalyst demonstrated exceptional OER activity and durability, attributed to the synergy among the abundant Co³⁺ species, the high electrochemically active surface area, a highly conductive bimetallic alloy core, and the oxygen-enriched functional groups and pyridinic N in the N-doped carbon shell. The Co₄Fe₃@N-doped graphitic carbon electrocatalyst exhibited a significantly lower overpotential (245 mV at 10 mA cm^-2) and enhanced mass transport kinetics (Tafel slope of 62.9 mV dec^-1) compared to those of a commercialized precious metal-based IrO₂ catalyst (328 mV at 10 mA cm^-2 and 95.3 mV dec^-1, respectively). In the AEMWE full cells, the electrolyzer based on Co₄Fe₃@N-doped graphitic carbon delivered a 139% higher energy efficiency and a 70 times lower performance degradation rate compared with those of the IrO₂-based counterpart. The proposed PBA-based electrocatalyst can be readily synthesized using a simple synthesis process and nonprecious-metal-based materials, presenting a promising pathway for the cost-effective commercialization of AEMWEs.