Achieving Near‐Unity CO Selectivity for CO2 Electroreduction on an Iron‐Decorated Carbon Material

• Published in: ChemSusChem 2020-12, Vol.13 (23), p.6360-6369
• Main Authors: Hu, Xin‐Ming, Mendoza, Daniela, Madsen, Monica Rohde, Joulié, Dorian, Lassalle‐Kaiser, Benedikt, Robert, Marc, Pedersen, Steen U., Skrydstrup, Troels, Daasbjerg, Kim
• Format: Article
• Language: English
• Subjects: Carbon; Carbon dioxide; Carbon monoxide; Catalytic activity; CO2 reduction; electrocatalysis; Encapsulation; iron; Iron carbides; Iron chlorides; Nanoparticles; Porous materials; porous polymers; Pyrolysis; Reduction; Selectivity
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.202001311

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. Just encase: A porous carbon material, with atomic iron sites embedded and iron carbide nanoparticles encased, is prepared directly from a porous polymer. The atomic iron sites are active for electrocatalytic CO2 reduction, whereas the iron carbide – although not in direct contact with the electrolyte and CO2 – promotes CO2 reduction. Thus, the material exhibits near‐unity selectivity for CO2‐to‐CO conversion at a small overpotential in water.