A nitrile-modified Metal-Organic Framework (MOF) membrane significantly enhances the electrochemical reduction of CO₂ to formic acid (HCOOH) by increasing local CO₂ concentration and stabilizing reaction intermediates. The MOF, UiO-66-CN, is deposited over a Bi catalyst in a Gas Diffusion Electrode (GDE), leading to a 166 mA/cm² HCOOH current density and 98% selectivity at -0.9 V vs RHE. The MOF acts as a CO₂ reservoir, increasing local CO₂ concentration by ~27-fold compared to bulk electrolyte, reaching 0.82 M. Operando infrared spectroscopy and density functional theory (DFT) simulations confirm that the MOF stabilizes intermediates and enhances catalytic activity. The strategy provides a molecular-level approach to improve heterogeneous CO₂ reduction, bringing it closer to practical implementation. The MOF membrane also facilitates dynamic CO₂ preconcentration near the catalyst surface, enabling efficient CO₂ utilization. The study demonstrates the effectiveness of MOF membranes in enhancing CO₂ reduction efficiency and selectivity, with potential applications in sustainable energy technologies. The results highlight the importance of molecular-level design in electrocatalytic CO₂ reduction and the role of MOF membranes in enabling efficient CO₂ utilization. The work presents a novel approach to enhance CO₂ reduction performance through the use of MOF membranes, offering a promising pathway for the development of sustainable energy technologies.A nitrile-modified Metal-Organic Framework (MOF) membrane significantly enhances the electrochemical reduction of CO₂ to formic acid (HCOOH) by increasing local CO₂ concentration and stabilizing reaction intermediates. The MOF, UiO-66-CN, is deposited over a Bi catalyst in a Gas Diffusion Electrode (GDE), leading to a 166 mA/cm² HCOOH current density and 98% selectivity at -0.9 V vs RHE. The MOF acts as a CO₂ reservoir, increasing local CO₂ concentration by ~27-fold compared to bulk electrolyte, reaching 0.82 M. Operando infrared spectroscopy and density functional theory (DFT) simulations confirm that the MOF stabilizes intermediates and enhances catalytic activity. The strategy provides a molecular-level approach to improve heterogeneous CO₂ reduction, bringing it closer to practical implementation. The MOF membrane also facilitates dynamic CO₂ preconcentration near the catalyst surface, enabling efficient CO₂ utilization. The study demonstrates the effectiveness of MOF membranes in enhancing CO₂ reduction efficiency and selectivity, with potential applications in sustainable energy technologies. The results highlight the importance of molecular-level design in electrocatalytic CO₂ reduction and the role of MOF membranes in enabling efficient CO₂ utilization. The work presents a novel approach to enhance CO₂ reduction performance through the use of MOF membranes, offering a promising pathway for the development of sustainable energy technologies.