Beschreibung:
<jats:p> Pyrolysed transition metal porphyrins (MeN<jats:sub>x</jats:sub>C) were originally developed as alternative catalysts for the electrochemical reduction of oxygen (ORR). The catalytic centers were identified as base transition metal ions, integrated into graphene layers of a carbon matrix via nitrogen atoms. The carbon serves as a conductive support and influences the entire catalytic process with its variable electronic and chemical properties. Thus, this class of materials can be classified as hybrid-material between inorganic and molecular catalysts.</jats:p>
<jats:p>Meanwhile it is known that this type of catalysts are also active towards the CO<jats:sub>2</jats:sub>RR. Our presentation will show results of electrochemical studies on pyrolysed transition metal porphyrins (MeN<jats:sub>x</jats:sub>C) as catalysts for the CO2RR under variation of the metal ions (Me: Fe, Co, Ni, Sn, Zn, Cu , Mn). Their activities are determined in gas diffusion electrode (GDE) configuration using CO<jats:sub>2</jats:sub>, CO or Ar gas feeds. The product composition of the gas phase at the outlet of the cell is analyzed simultaneously by mass spectroscopy. Soluble products are analysed via ion-chromatography. It is shown that the product composition of CO2RR, as well as the respective onset potentials, partial current densities, formation rates, and Faraday efficiencies vary strongly with the type of metal ions investigated in the catalytic center. Fe-, Co- and Ni-based catalysts form predominantly CO and suppress the competing hydrogen evolution reaction. CO-formation rates of 4 mmol/(hcm<jats:sup>2</jats:sup>)at -2V NHE and 200 mA/cm<jats:sup>2</jats:sup> (Faraday efficiency close to 100%) were achieved on not yet optimized GDEs. The formation of significant amounts of hydrocarbons from CO<jats:sub>2</jats:sub> was observed only on the Cu- based material. The analysis of the potential dependence during product formation under different gases fed to the GDE allows initial conclusions about the underlying mechanisms of the CO2RR.</jats:p>
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<jats:p>Figure 1</jats:p>
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