Electrochemical N₂ reduction reaction (eNRR) over Cu-based catalysts suffers from an intrinsically low activity of Cu for activation of stable N₂ molecules and the limited supply of N₂ to the catalyst due to its low solubility in aqueous electrolytes. Herein, we propose phosphorus-activated Cu electrocatalysts to generate electron-deficient Cu sites on the catalyst surface to promote the adsorption of N₂ molecules. The eNRR system is further modified using a gas diffusion electrode (GDE) coated with polytetrafluoroethylene (PTFE) to form an effective three-phase boundary of liquid water - gas N₂ - solid catalyst to facilitate easy access of N₂ to the catalytic sites. As a result, the new catalyst in the flow-type cell records a Faradaic efficiency of 13.15% and an NH3 production rate of 7.69 μg h⁻¹ cm⁻² at −0.2 V_RHE, which represent 3.56 and 59.2 times increases from those obtained with a pristine Cu electrode in a typical electrolytic cell. This work represents a successful demonstration of dual modification strategies; catalyst modification and N₂ supplying system engineering, and the results would provide a useful platform for further developments of electrocatalysts and reaction systems.