In a comparative study of the electrocatalytic CO2 reduction, cobalt meso‐tetraphenylporphyrin (CoTPP) is used as a model molecular catalyst under both homogeneous and heterogeneous conditions. In the former case, employing N,N‐dimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in a slow reaction at a high overpotential. However, upon straightforward immobilization of CoTPP onto carbon nanotubes, a remarkable enhancement of the electrocatalytic abilities is seen with CO2 becoming selectively reduced to CO (>90 %) at a low overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO2. This work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone. Heterogeneous vs. homogeneous: When cobalt meso‐tetraphenylporphyrin (CoTPP) is immobilized on carbon nanotubes, a remarkably enhanced catalytic activity in CO2 electroreduction is observed, with CoITPP− serving as the active species. The simple approach for heterogenization enables facile screening and evaluation of molecular catalysts under heterogeneous conditions.