Engineering the Artificial Carbon Cycle via Tandem Strategies and Cross-Scale Integration in Electrocatalytic CO₂ Reduction

Consumption of fossil fuels has seriously impacted the carbon cycle, creating an urgent need to develop artificial carbon cycles to mitigate climate change. While electrocatalytic carbon dioxide reduction reaction (CO₂RR) provides a promising route for converting CO₂ into value-added chemicals, the selective production of multicarbon products remains constrained by linear scaling relationships among key intermediate adsorption energies on single catalytic interfaces, as well as by mass-transport limitations under high-current-density operation. Therefore, several researchers have proposed tandem catalytic approaches to de-couple complex reaction pathways into separate and independently controllable steps either spatially or temporally. In this article we evaluate all three major types of tandem approaches: electrocatalysis-biocatalysis, electrocatalysis-electrocatalysis, and electrocatalysis-thermocatalysis. Our results indicate that the electro-biocatalyzed system using formic acid or syngas as electron carriers may overcome the kinetic barriers associated with inorganic catalysts for producing long chain molecules; the electro-electro tandem system, employing both atomic scale design of active sites and reactor engineering enables efficient production of ethylene and ethanol at > 200 mA cm^-2; and the electro-thermal integrated system, incorporating mature chemical processes, such as hydroformylation, produces high value added products such as propionaldehyde, butane and carbon nanofibers. Since our focus is on implementing tandem catalysis at large scales in industries, this study will also investigate key engineering problems related to mass transfer, electrolyte cell stability and salt precipitation at high current densities. Via specific control of the local environment around each reaction module in addition to optimizing transport mechanisms of intermediates among modules, a tandem catalysis strategy can provide a viable route for converting laboratory based CO₂RR technologies into industrially applicable technologies.