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Extensive efforts are being dedicated to developing high-performance electrocatalysts for water splitting to achieve efficient and stable hydrogen production, especially under high current densities. In this study, we synthesised a CoMo microcolumn arrays (MCA)/Fe-nanowires (NWs)/nickel foam (NF) catalyst through a simple yet effective combination of hydrothermal and solution-based methods. This catalyst exhibits remarkable performance during the oxygen evolution reaction (OER), achieving a low overpotential of 425 mV at a current density of 2000 mA cm-2 and maintaining stability for 200 h at a current density of 1000 mA cm-2 in 1 M KOH. In natural alkaline seawater, the catalyst demonstrates an overpotential of 464 mV at a current density of 1000 mA cm-2, with stability extending to 250 h at a current density of 500 mA cm-2. These overpotentials are lower than that required for hypochlorite production (>490 mV). Furthermore, during alkaline full seawater splitting, the synthesised catalyst delivers a cell voltage of 1.861 V at a current density of 1000 mA cm-2, sustaining stability for 100 h at a current density of 500 mA cm-2. The heterointerfaces in the CoMo-MCA/Fe-NWs/NF structure optimise the electronic configuration, enhancing OER activity. The MCA structure and Fe2O3 NWs increase the electrochemically active surface area, providing numerous active sites and ensuring long-term durability under harsh conditions. This study suggests a promising approach for industrial-scale seawater electrolysis by engineering effective heterostructures and interfacial active sites. [ABSTRACT FROM AUTHOR]