This study presents a novel approach to fabricate ultrathin nanosheet arrays of two-dimensional (2D) metal-organic frameworks (MOFs) on various substrates using a dissolution-crystallization mechanism. The resulting materials exhibit enhanced electrocatalytic performance for water splitting, including oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Specifically, a nickel-iron-based MOF array demonstrates superior OER performance with a small overpotential of 240 mV at 10 mA cm−2 and a turnover frequency (TOF) of 3.8 s−1 at 400 mV. The material also shows robust stability, with no detectable activity decay after 20,000 seconds. The enhanced performance is attributed to the highly exposed active molecular metal sites, improved electrical conductivity, and hierarchical porosity of the ultrathin nanosheets. The method is generic and can be adapted for other MOF materials and substrates, making it a promising strategy for electrochemical applications.This study presents a novel approach to fabricate ultrathin nanosheet arrays of two-dimensional (2D) metal-organic frameworks (MOFs) on various substrates using a dissolution-crystallization mechanism. The resulting materials exhibit enhanced electrocatalytic performance for water splitting, including oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Specifically, a nickel-iron-based MOF array demonstrates superior OER performance with a small overpotential of 240 mV at 10 mA cm−2 and a turnover frequency (TOF) of 3.8 s−1 at 400 mV. The material also shows robust stability, with no detectable activity decay after 20,000 seconds. The enhanced performance is attributed to the highly exposed active molecular metal sites, improved electrical conductivity, and hierarchical porosity of the ultrathin nanosheets. The method is generic and can be adapted for other MOF materials and substrates, making it a promising strategy for electrochemical applications.