Metal-Nitrogen-Carbon Electrocatalysts for CO2 Reduction towards Syngas Generation.

Shifting syngas (an H2 /CO mixture) production away from fossil-fuel-dependent processes (e.g., steam methane reforming and coal gasification) is mandatory, as syngas is of interest as both a fuel and as a value-added chemical precursor. With appropriate electrocatalysts, such as silver-based and metal-nitrogen-carbon (M-N-C) materials, the electrochemical CO2 reduction reaction (CO2 RR) allows for the production of CO alongside H2 (from the hydrogen evolution reaction), and thus leads to syngas generation. In this Minireview, the application of M-N-C electrocatalysts for syngas generation is discussed. The mechanisms leading to different faradaic selectivities for CO are reviewed as a function of the nature of the metal, by using both computational and experimental approaches. The role played by the metal-free moieties in the M-N-C electrocatalysts is underlined. Since M-N-C electrocatalysts only recently entered the CO2 RR field (as opposed to Cu-, Ag-, or Au-based nanostructures), they have been mainly characterized in static liquid environments, in which the reaction rate is significantly hampered by CO2 -dissolution/diffusion limitations. Therefore, the design of CO2 RR electrolyzers for M-N-C electrocatalysts is addressed, and designs such as zero-gap electrolyzers with anionic membranes and humidified CO2 gas feed at the cathode are highlighted.