Electrochemical Reduction of CO₂ on Nitrogen‐Doped Carbon Catalysts With and Without Iron

Abstract

The carbon dioxide reduction reaction (CO2RR) catalyzed by N‐doped carbon materials was studied under operando conditions by on line differential electrochemical mass spectrometry and in‐line gas chromatography. Fe/NC electrocatalysts were synthesized by using a Fe+2‐impregnated pyridyl/triazine complex heat treated at 800 °C in nitrogen (Fe/NC(N2)) or ammonia (Fe/NC(NH3)) atmospheres; an iron‐free nitrogen‐doped carbon electrocatalyst (NC(NH3)) was also synthesized and included for comparison. Here, superior CO faradaic efficiencies were evidenced for NC(NH3) compared to Fe/NC(NH3), independently of the applied electrode potential; however, much larger overall catalytic activity for the promotion of the CO2RR and/or HER has been observed for Fe/NC(NH3), generating different stoichiometric ratios of syngas (CO/H2). Another important evidence is that N‐pyridinic groups, even in absence of Fe−N4 moieties and presence of high iron nanoparticles loading, play an important role as active sites for selective CO2 reduction to CO at low overpotentials.

From CO2 to Value-Added Products: A Review about Carbon-Based Materials for Electro-Chemical CO2 Conversion

“…For this case, the improvement in electrocatalytic results is related to the synergistic effect between compression stress on In 2 O 3 layer and Cu doping, so that from these parameters it is also possible to tune the CO and H 2 ratios in a wide range. Silva and co-workers [181] prepared different types of these supported catalysts: The first type consisted of catalysts that supported metal particles in a range of 150-400 nm without carbon N-doping and the second type of catalysts contained Fe particles (50-100 nm) supported on the carbon matrix doped with nitrogen in the absence of Fe-N 4 residues. The firsts showed a very low their electrocatalytic performance towards CO 2 reduction whereas the later, produce CO with a FE of 66% towards CO at a low potential of −0.6 V vs. RHE, in addition to promoting the production of H 2 , thus obtaining syngas ratios (CO/H 2 ) that can be tunable.…”

What We Currently Know about Carbon‐Supported Metal and Metal Oxide Nanomaterials in Electrochemical CO2 Reduction

“…For Fe, supported nanoparticles have been claimed to form syngas but upon a closer look, the catalyst material is a very complex one making conclusions on support immensely difficult. [34] Since there are very few publications on this category of metals, not many conclusions can be made, and therefore, the remainder of this minireview will focus on the metals that are CO 2 R active.…”

“…The synthesis method used, namely pyrolysis of metal‐tetracyanoquinodimethane compounds, could result in formation of similar mixed catalysts which has not been excluded based on the presented results. For Fe, supported nanoparticles have been claimed to form syngas but upon a closer look, the catalyst material is a very complex one making conclusions on support immensely difficult [34] . Since there are very few publications on this category of metals, not many conclusions can be made, and therefore, the remainder of this minireview will focus on the metals that are CO 2 R active.…”

Recent Advances in the Electroreduction of CO2 over Heteroatom-Doped Carbon Materials

“…Several attempts have been made to elucidate the nature of the active species actually involved in the electroreduction process, with no conclusive results having been obtained so far. Recent studies associated the high electroreduction activity of nitrogen-doped carbon materials with the presence of pyridinic functional groups [52][53][54]58,[71][72][73][74], whereas others pointed to pyrrolic N [75,76] or even both pyridinic and pyrrolic [51,77] as responsible for the good performance of these materials. Graphitic or quaternary functionalities have also been considered as the main active sites in the electroreduction process [57,62].…”