Electrocatalytic reduction of CO2 over dendritic-type Cu- and Fe-based electrodes prepared by electrodeposition

The identification of the role of nano-morphology of electrodes for the reduction of CO2, particularly in determining the selectivity towards > C1 products of reduction, is still a challenge. We show here for the first time how a dendritic-type nano-morphology and related fractal dimension plays a crucial role in determining the selectivity for electrodes based on Cu and Fe. The electrodes, prepared by electrodeposition of Cu or Fe on metal substrates (Cu, Ti, Al, Fe, Fe-Cr-Ni alloy) or carbon-based gas diffusion layers (GDL), were tested in a continuous flow cell at constant potential (-1.5 V vs. Ag/AgCl) or at the onset potential of the first cathodic peak determined by cyclic voltammetry. Results showed that the dendritic-type nano-morphology influences positively not only the activity to formic acid, but especially the selectivity to gas products (i.e. CH4 and CO) and to higher carbon-chain liquid products (i.e. ethanol, isopropanol, acetic acid) when smoother edges and denser surface sites are present. Tests at the onset potential show very high total carbon Faradaic efficiency (FE) for Fe electrodeposited on GDL and Ti (about 92-95%). The lowest onset potential (-0.3 V) is observed for Cu on GDL, showing over 80% total carbon FE and almost 60% FE to formic acid.