Influence Of The Metal Center In M-N-C Catalysts On The Co2 Reduction Reaction On Gas Diffusion Electrodes

In this work, the influences of various transition metal ions as active sites in high purity metal- and nitrogen-doped carbon catalysts (in short M-N-C), where M: Mn3+, Fe3+, Co2+ , Ni2+ , Cu2+ , Zn2+, or Sn4+ in the catalyst powders, were systematically investigated for the electrochemical reduction of CO2 in the aqueous electrolyte. The almost exclusive presence of isolated M-N-4 centers as catalytic sites was determined by X-ray photoelectron spectroscopy (XPS). The catalysts were electrochemically investigated in a gas diffusion electrode arrangement in bypass mode coupled in-line to a mass spectrometer. This allowed for the nearly simultaneous detection of products and current densities in linear sweep voltammetry experiments, from which potential-dependent specific production rates and faradaic efficiencies could be derived. Postmortem XPS analyses were performed after various stages of operation on the Cu-N-C catalyst, which was the only catalyst to produce hydrocarbons (CH4 and C2H4) in significant amounts. The data provided insights into the potential-induced electronic changes of the Cu-N-C catalyst occurring under operating conditions. Our work further experimentally revealed the high affinity of M-N-C catalysts to convert CO2 to industrially relevant carbonaceous raw materials, while effectively suppressing the competing hydrogen evolution reaction. These results led to a better understanding of the role of the active sites, especially the central metal ion, in M-N-C and could contribute significantly to the improvement of selectivities and activities for the CO2RR in this catalyst class through tailor-made optimization strategies.