Ultra‐Fast Microfluidic Synthesis of Co‐MOF‐74 With Abundant Internal Voids for Efficient OER of Electrochemical Water Splitting

Metal-organic frameworks (MOFs) are promising electrocatalysts for the oxygen evolution reaction (OER), owing to their high surface areas, tailorable structures, and numerous potential active sites. Herein, we investigate the impact of flow velocity within microchannels on the crystallization rate and internal structures of Co-MOF-74 via an air-liquid segmented flow method. We demonstrate that a higher flow velocity enhances the frequency of collisions between the metal ions and the organic linkers, yielding Co-MOF-74 samples with improved crystallinity, and unique voids. Specifically, the A-Co-MOF-74-8v synthesized at high flow velocity, exhibits a smaller particle size, developed internal voids, and abundant accessible electroactive sites. These features facilitate efficient mass transport and gas release during electrolysis, leading to significantly enhanced electrocatalytic OER performance. In 1 M KOH, A-Co-MOF-74-8v achieves a low overpotential of 310 mV at 10 mA cm^-2, which is 42 mV lower than that of the solvothermally synthesized counterpart (ST-Co-MOF-74). This work provides key mechanistic insights and design principles for engineering highly efficient MOF-based electrocatalysts under precisely controlled microfluidic conditions.