Sorbent Mediated Electrocatalytic Reduction of Dilute CO2 to Methane

Abstract

Efficient CO₂ utilization is a critical component of closing the anthropogenic carbon cycle. Most studies have focused on the use of pure streams of CO₂. However, CO₂ is generally available only 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, and the sorbent-CO₂ interaction can kinetically activate CO₂ to tune its reactivity toward 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), quantitatively reacts with CO₂ from dilute streams (0.04 and 10%) to form the sorbent-CO₂ substrate 1,3-bis(2,6-diisopropylphenyl)imidazolium-2-carboxylate (DPICx). Electrocatalyst iron tetraphenylporphyrin chloride (Fe(TPP)Cl) typically reduces CO₂ to CO; however, with DPICx as the substrate, the eight-electron reduced product methane (CH₄) is produced with a high Faradaic efficiency (>85%) and regeneration of the sorbent DPIy. In addition to the overall energy and capital advantages of integrated CO₂ capture and conversion, this result illustrates how sorbents can serve a dual purpose for both CO₂ capture and chemical auxiliary purposes to access unique products. CO₂ has a spectrum of reactivity with different types of sorbents; thus, these studies demonstrate how sorbent-CO₂ interactions can be leveraged for integrated capture and utilization platforms to access a wider range of CO₂-derived products.