Background/Objectives

The advancement of carbon dioxide (CO₂) capture technology with porous materials shows great potential to offset carbon emissions from essential human activities and finally achieve a carbon net-zero future. Challenges exist to efficiently utilize CO₂ at low concentration and subsequent selective conversion towards value added chemicals. To avoid subsequent energy-intensive separation and concentration processes, direct enrichment of CO₂ at the reactive interface becomes highly advantageous when tied with further conversion to durable chemicals. Integrated capture and conversion pathways provide essential pathways to enable transformation of CO₂ to value-added chemical species.

Approach/Activities

To address this, we have recently demonstrated new metal-free mesoporous nitrogen assembly carbons (NACs) for electrocatalytic conversion of CO₂ reduction reaction (eCO₂RR). These NACs show transition metal-like behaviors for adsorption and catalysis with unique arrangements of closely-spaced graphitic nitrogen atoms as active sites. These materials exhibit multiple functionality through different nitrogen motifs: graphitic N is responsible for adsorbing CO₂, while pyridinic N are binding sites for single transition metals (“metal_SA”) responsible for highly efficient and selective electrochemical CO₂ reduction to CO over a wide potential window with tunable current density.

Results/Lessons Learned

NAC catalysts with controlled morphology allow the surface enrichment of CO₂ and the selective conversion of CO₂ as dilute as 10 vol% was achieved. By coupling different active sites supported on or physically mixed with 3-D confined NACs, we successfully demonstrate a tandem reactive-separation process with CO as the intermediate, not only to lower the activation energy for the overall conversion but also to increase the local concentration of CO to facilitate C-C bond formation and enhance selectivity. The reaction selectivity is greatly impacted by the nature of tandem active sites and their regulated mixing with NACs.