Selective electrochemical reduction of CO 2 into energy-dense organic compounds is a promising strategy for using CO 2 as a carbon source. Herein, we investigate a series of iron-based catalysts synthesized by pyrolysis of Fe-, N-and C-containing precursors for the electroreduction of CO 2 to CO in aqueous conditions and demonstrate that the selectivity of these materials for CO 2 reduction over proton reduction is governed by the ratio of isolated FeN 4 sites vs. Fe-based nanoparticles. This ratio can be synthetically tuned to generate electrocatalysts producing controlled CO/H 2 ratios. It notably allows preparing materials containing only FeN 4 sites, which are able to selectively reduce CO 2 to CO in aqueous solution with Faradaic yields over 90% and at low overpotential. KEYWORDS. CO 2 reduction-electrocatalysis-iron-Fe-N-C materials-Structure-selectivity relationship.

To use water as the source of electrons for proton or CO reduction within electrocatalytic devices, catalysts are required for facilitating the proton-coupled multi-electron oxygen evolution reaction (OER, 2 H O→O +4 H +4 e ). These catalysts, ideally based on cheap and earth abundant metals, have to display high activity at low overpotential and good stability and selectivity. While numerous examples of Co, Mn, and Ni catalysts were recently reported for water oxidation, only few examples were reported using copper, despite promising efficiencies. A rationally designed nanostructured copper/copper oxide electrocatalyst for OER is presented. This material derives from conductive copper foam passivated by a copper oxide layer and further nanostructured by electrodeposition of CuO nanoparticles. The generated electrodes are highly efficient for catalyzing selective water oxidation to dioxygen with an overpotential of 290 mV at 10 mA cm in 1 m NaOH solution.