Valorizing CO2 through electroreduction (eCO2RR) on copper-based catalysts may become an appealing strategy to synthesize chemicals and fuels, since some of the ca. 20 products ranging C1 to C3 that have been reported show promising selectivity. Among multi-carbon ones, ethanol, propanol, and ethylene are those with the largest potential for upscaling.1 We aim to explore the eCO2RR mechanism away from these well studied routes to answer these questions: why are only certain C3 oxygenates reported or have C4 products been so scarcely reported? In order to find the preferential routes toward C3 compounds, we combined targeted electrocatalytic experiments using C1 and C2 compounds with a DFT-based analysis of the C3 reaction network. Following this approach, we elucidate feasible routes from CO2 for the formation of the C3 backbone. We found that all predominant C3 products share the same intermediate and located a kinetic bottleneck that redirects the pathway away from propene toward 1-propanol. We also used an experimental-theoretical approach to understand C-C coupling limits that the eCO2RR on Cu-based systems can reach. Reactor engineering and high sensitivity quantification tools in combination with DFT simulations allowed us to report for the first time the formation of 1-butanol from CO2 and explain the very modest yields of C4 products ever reported.2 The pathway to form 1-butanol starts with an electrocatalytic series of steps from CO2 to acetaldehyde, which critically undergoes a chemical dimerization in solution to create the C4 backbone in the form of crotonaldehyde. This species is then electrocatalytically converted into C4 oxygenates, including 1-butanol. Notably, these phases are favoured by different chemical environments, leading to poor overall yields. All in all, our results have identified relevant frontiers and expanded the mechanistic understanding on Cu-based eCO2RR.

Expanding the mechanistic understanding on the electrocatalytic CO2 reduction: routes toward C3 and C4 compounds

ACS Spring Meeting 2021

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