A straightforward procedure has been developed to prepare a porous carbon material decorated with iron by direct pyrolysis of a mixture of a porous polymer and iron chloride. Characterization of the material with X-ray diffraction, X-ray absorption spectroscopy, and electron microscopy indicates the presence of iron carbide nanoparticles encapsulated inside the carbon matrix, and elemental mapping and cyanide poisoning experiments demonstrate the presence of atomic Fe centers, albeit in trace amounts, which are active sites for electrochemical CO₂ reduction. The encapsulated iron carbide nanoparticles are found to boost the catalytic activity of atomic Fe sites in the outer carbon layers, rendering the material highly active and selective for CO₂ reduction, although these atomic Fe sites are only present in trace amounts. The target material exhibits near-unity selectivity (98 %) for CO₂-to-CO conversion at a small overpotential (410 mV) in water. Furthermore, the material holds potential for practical application, as a current density over 30 mA cm⁻² and a selectivity of 93 % can be achieved in a flow cell.