Sorbent Mediated Electrocatalytic Reduction of Dilute CO2 to Methane

Efficient CO2 utilization is a critical component of closing the anthropogenic carbon cycle. Most studies have focused on using pure streams of CO2. However, CO2 is generally only available in dilute streams, which requires capture by sorbents followed by energy intensive regeneration to release concentrated CO2. Direct utilization of sorbed-CO2 avoids the costly regeneration step. Furthermore, the sorbent-CO2 interaction can kinetically activate CO2 and tune its reactivity to access products that could otherwise be inaccessible with direct CO2 reduction. We demonstrate that an N-heterocyclic carbene, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (DPIy), can capture CO2 from dilute streams (0.04% and 10%) to form 1,3-bis(2,6-diisopropylphenyl)imidazolium-2-carboxylate (DPICx) quantitatively. Electrocatalyst iron tetraphenylporphyrin chloride (Fe(TPP)Cl) typically reduces CO2 to CO; however, with DPICx as the substrate, the 8-electron reduced product methane (CH4) is produced with high (>85%) Faradaic efficiency and regeneration of the sorbent DPIy. In addition to the overall energy and capital advantages of integrated CO2 capture and conversion, these studies illustrate how sorbents can serve a dual purpose for both CO2 capture and chemical auxiliary to access unique products. CO2 has a spectrum of reactivity with different types of sorbents; these results reveal how sorbent-CO2 interactions can be leveraged for integrated capture and utilization platforms to access a wider range of CO2-derived products.