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 (“metalSA”) 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.