Effect of Cobalt Speciation and the Graphitization of the Carbon Matrix on the CO₂Electroreduction Activity of Co/N-Doped Carbon Materials

The electroreduction of carbon dioxide is considered a key reaction for the valorization of CO2 emitted in industrial processes or even present in the environment. Cobalt-nitrogen co-doped carbon materials featuring atomically dispersed Co-N sites have been shown to display superior activities and selectivities for the reduction of carbon dioxide to CO, which, in combination with H2 (i.e., as syngas), is regarded as an added-value CO2-reduction product. Such catalysts can be synthesized using heat treatment steps that imply the carbonization of Co-N-containing precursors, but the detailed effects of the synthesis conditions and corresponding materials' composition on their catalytic activities have not been rigorously studied. To this end, in the present work, we synthesized cobalt-nitrogen co-doped carbon materials with different heat treatment temperatures and studied the relation among their surface- and Co-speciation and their CO2-to-CO electroreduction activity. Our results reveal that atomically dispersed cobalt-nitrogen sites are responsible for CO generation while suggesting that this CO-selectivity improves when these atomic Co-N centers are hosted in the carbon layers that cover the Co nanoparticles featured in the catalysts synthesized at higher heat treatment temperatures.