Electrochemical CO reduction has garnered significant interest in the conversion of sustainable energy to valuable fuels and chemicals. Cu-based bimetallic catalysts play a crucial role in enhancing CO concentration on Cu sites for efficient C─C coupling reactions, particularly for C product generation. To enhance Cu's electronic structure and direct its selectivity toward C products, a novel strategy is proposed involving the in situ electropolymerization of a nano-thickness cobalt porphyrin polymeric network (EP-CoP) onto a copper electrode, resulting in the creation of a highly effective EP-CoP/Cu tandem catalyst. The even distribution of EP-CoP facilitates the initial reduction of CO to CO intermediates, which then transition to Cu sites for efficient C─C coupling. DFT calculations confirm that the CO enrichment from Co sites boosts CO coverage on Cu sites, promoting C─C coupling for C product formation. The EP-CoP/Cu gas diffusion electrode achieves an impressive current density of 726 mA cm at -0.9 V versus reversible hydrogen electrode (RHE), with a 76.8% Faraday efficiency for total C conversion and 43% for ethylene, demonstrating exceptional long-term stability in flow cells. These findings mark a significant step forward in developing a tandem catalyst system for the effective electrochemical production of ethylene.