Carbon dioxide emission from fossil fuel combustion has generated an on-going debate on its impact to the global environmental and ecological systems. New carbon capture, sequestration and conversion technologies are widely pursued as potential solutions to mitigate the concerns. The electrochemical CO₂ reduction reaction (CO₂RR) to hydrocarbon fuels and chemicals using renewable electricity offers an attractive “carbon-neutral” or even “carbon-negative” mitigation strategy. CO₂ is an inexpensive carbon source and can be used as a feedstock for producing high value chemicals. Key challenges facing the current CO₂RR electrocatalysis include: a) how to improve energy efficiency by reducing the overpotentials; b) how to increase the process selectivity by enhancing a single-product Faradaic efficiency (FE); and c) how to lower the system operating cost by prolonging the catalyst stability.

Argonne National Laboratory through collaboration with Northern Illinois University recently developed a series of highly active and durable single atom catalysts (SACs) for CO₂RR prepared using a robust synthesis method over the commercial carbon support. The new electrocatalysts offer the several advantages including: a) direct conversion to C2 (C₂H₅OH and CH₃CO₂H) and C3 (C₃H₆O) chemicals in one-step electro-catalytic reaction without secondary upgrading; b) higher than 90% FE by suppressing the byproduct formation; c) high energy efficiency with the onset potential as low as 0.4 V observed for ethanol conversion; and d) good stability with no sign of activity loss during extended hours of chronoamperometry measurement.

In this presentation, we will discuss the structure-function relationship of the new SACs with particular emphasis on CO₂ to ethanol conversion. We will also share the mechanistic insight on catalysis as the catalyst transitioning from SAC to metal cluster. The catalyst performance in terms of FE, onset potential and durability will also be reported, combined with the catalyst structural properties obtained from various conventional and advanced characterization tools.

Acknowledgement: The work performed at Argonne National Laboratory is supported by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357.