The study presents the synthesis and characterization of a hetero-structured metal–organic framework (MOF) catalyst, Ni-BDC/NH₂-MIL-88B(Fe), for efficient oxygen evolution reaction (OER) in seawater electrolysis. This catalyst, synthesized through a solvothermal route, exhibits superior performance with a long stability of 200 hours and low overpotentials of 232 and 299 mV at 100 mA cm⁻² in alkaline freshwater and seawater solutions, respectively. The exceptional performance is attributed to the rapid self-reconstruction of Ni-BDC/NH₂-MIL-88B(Fe) to form a protective NiFeOOH layer, which prevents chlorine evolution reaction (CER)-induced dissolution. The interface interaction between Ni-BDC and NH₂-MIL-88B(Fe) forms Ni–O–Fe bonds, promoting electron transfer and lowering the energy barrier for the rate-determining step of OER. The catalyst's excellent electrochemical properties make it a promising candidate for practical alkaline seawater electrolysis.The study presents the synthesis and characterization of a hetero-structured metal–organic framework (MOF) catalyst, Ni-BDC/NH₂-MIL-88B(Fe), for efficient oxygen evolution reaction (OER) in seawater electrolysis. This catalyst, synthesized through a solvothermal route, exhibits superior performance with a long stability of 200 hours and low overpotentials of 232 and 299 mV at 100 mA cm⁻² in alkaline freshwater and seawater solutions, respectively. The exceptional performance is attributed to the rapid self-reconstruction of Ni-BDC/NH₂-MIL-88B(Fe) to form a protective NiFeOOH layer, which prevents chlorine evolution reaction (CER)-induced dissolution. The interface interaction between Ni-BDC and NH₂-MIL-88B(Fe) forms Ni–O–Fe bonds, promoting electron transfer and lowering the energy barrier for the rate-determining step of OER. The catalyst's excellent electrochemical properties make it a promising candidate for practical alkaline seawater electrolysis.