Design of electrodes and processes for CO2 valorization

Nowadays the concentration of greenhouse gases is increasing, and this causes the rising up of the temperature over the time. For example, in the modern society the high consumption of fossil fuel is unavoidable to keep up the progress and this causes high CO2 emission. Different mechanisms can be exploited to mitigate the concentration of CO2 molecules in our atmosphere. Electrochemical CO2 reduction (ERC) is now taking much more attention for large-scale deployment thanks to investments and researches on renewable energies. In this project ERC was performed using a membrane based flow reactor and Cu was chosen as catalyst material because Cu is the only known metal that can catalyse CO2 in multi-carbons products with acceptable activity and efficiency. Two different Cu powders with 2 different particles diameters were used: 25nm and 50nm. For each particles diameter, six different loadings were studied: 0.125 mg*cm-2; 0.25 mg*cm-2; 0.50 mg*cm-2; 1.0 mg*cm-2; 2.0 mg*cm-2; 3.0 mg*cm-2. Moreover stability tests, with different substrate composition, were done. Chronopotentiometry (CP) was used to study the CO2 reduction reaction at constant current densities and faradaic efficiencies were calculated with High Performance Liquid Chromatography (HPLC) and Gas Chromatography (GC). Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) were performed to investigate the electrochemical properties of the electrodes. For what concern the faradaic efficiencies, the results show a similar trend for both particles size. Cu 25nm is more selective for H2 and CH4, whereas Cu 50nm is more selective for C2H4 and CO. Both particles sizes reach a maximum FE value for C2H4 at loading equal to 1.0 mg*cm-2. The stability test shows that a GDL substrate with 30% of FEPD 121 has the highest FE for C2H4 and better stability. The CV study shows similar double layer capacitance (Cdl) trend for both particles size, except for Cu loading = 2.0 mg*cm-2. Moreover at very low loading the used method fails. EIS results are coherent with the higher HER activity of Cu-25nm with respect to that of Cu-50nm at the same conditions.