Synthesis and processing of two- or three-dimensional covalent organic frameworks (COFs) have been limited by solvent intractability and sluggish condensation kinetics. Here, we report on the electrochemical deposition of poly(5,10,15,20-tetrakis (4-aminophenyl)porphyrin)-covalent organic frameworks (POR-COFs) via formation of phenazine linkages. By adjusting the synthetic parameters, we demonstrate the rapid and bottom-up synthesis of COF dendrites. Both experiment and density functional theory underline the prominent role of pyridine, not only as a polymerization promoter but as a stabilizing sublattice, cocrystallizing with the framework. The crucial role of pyridine in dictating the structural properties of such a cocrystal (Py-POR-COF) is discussed. Also, a structure-to-function relationship for this class of materials, governing their electrocatalytic activity for the oxygen reduction reaction in alkaline media, is reported.