The electrochemical reduction of CO2 using intermittent renewable electricity is an attractive strategy for producing value-added fuels and chemicals, but until now, it has been greatly hindered by the shortage of high-performance electrocatalysts. In this study, we have demonstrated a type of molecular-catalyst-based hybrid material by the polymerization of cobalt phthalocyanine (CoPc) on a three-dimensional (3D) g-C3N4 nanosheet-carbon nanotube support for the aqueous electrochemical reduction of CO2. The electrocatalytic results show that the obtained composite can selectively transform CO2 to CO with considerable Faradaic efficiency (FE) of 95 ± 1.8%, a turnover frequency of 4.9 ± 0.2 s-1, and excellent long-term stability over 24 h at -0.8 V vs the reversible hydrogen electrode (RHE). In comparison to the analogous hybrid electrocatalysts prepared by the drop-drying or dip-coating method, the polymeric form of the molecular catalyst immobilized on 3D carbonaceous materials with an interconnected network enlarges the electrochemically active surface area and enhances the structural and operational robustness.