Combining Fe nanoparticles and pyrrole-type Fe-N₄ sites on less-oxygenated carbon supports for electrochemical CO₂...

A great challenge for electrochemical CO₂ reduction is to improve energy efficiency, which requires reducing overpotential while increasing product Faraday efficiency. Here, we designedly synthesize a hybrid electrocatalyst consisting of Fe nanoparticles, pyrrole-type Fe-N₄ sites and less-oxygenated carbon supports, which exhibits a remarkable CO Faraday efficiency above 99% at an ultralow overpotential of 21 mV, reaching the highest cathode energy efficiency of 97.1% to date. The catalyst also can afford a CO selectivity nearly 100% with a high cathode energy efficiency (>90%) at least 100 h. The combined results of control experiments, in situ characterizations and theoretical calculations demonstrate that introducing Fe nanoparticles can reduce the overpotential by accelerating the proton transfer from CO₂ to *COOH and lowering the free energy for *COOH formation, constructing pyrrole-type Fe-N₄ sites and limiting oxygen species on carbon supports can increase CO Faraday efficiency through inhibiting the H₂ evolution, thus achieving energy-efficient electrochemical CO₂ reduction to CO.