Confinement of metal centers is a powerful tool to manipulate reactivity and tune selectivity in chemical transformations. While aluminum as a foil is inactive for carbon dioxide reduction and shows high selectivity for the hydrogen evolution reaction, here we show that aluminum confined in a metal-organic framework (MOF), MIL-53(Al), suppresses hydrogen evolution reaction activity and enhances carbon dioxide reduction. This aluminum MOF can produce up to 40% faradaic efficiency for carbon monoxide and formic acid. This study demonstrates that the unique reaction environment created by the MOF enables changes in reaction selectivity and can impart atypical catalytic capabilities to metals.

We elucidate the role of subsurface oxygen on the production of C₂ products from CO₂ reduction over Cu electrocatalysts using the newly developed grand canonical potential kinetics density functional theory method, which predicts that the rate of C₂ production on pure Cu with no O is ∼500 times slower than H₂ evolution. In contrast, starting with Cu₂O, the rate of C₂ production is >5,000 times faster than pure Cu(111) and comparable to H₂ production. To validate these predictions experimentally, we combined time-dependent product detection with multiple characterization techniques to show that ethylene production decreases substantially with time and that a sufficiently prolonged reaction time (up to 20 h) leads only to H₂ evolution with ethylene production ∼1,000 times slower, in agreement with theory. This result shows that maintaining substantial subsurface oxygen is essential for long-term C₂ production with Cu catalysts.

We report the discovery of a quaternary ammonium surface additive for CO2 reduction on Ag surfaces that changes the Faradaic efficiency for CO from 25% on Ag foil to 97%, while increasing the current density for CO production by a factor of 9 from 0.14 to 1.21 mA/cm2 and reducing the current density for H2 production by a factor of 440 from 0.44 to 0.001 mA/cm2. Using ReaxFF reactive molecular dynamics, we find that the surface additive with the highest selectivity, dihexadecyldimethylammonium bromide, promotes substantial population of CO2 near the Ag surface along with sufficient H2O to activate the CO2. While a critical number of water molecules is required in the reduction of CO2 to CO, the trend in selectivity strongly correlates with the availability of CO2 molecules. We demonstrate that the ordering of the cationic modifiers plays a significant role around the active site, thus determining reaction selectivity. The dramatic improvement by addition of a simple surface additive suggests an additional strategy in electrocatalysis.

Electrochemical CO2 reduction (CO2R) is an attractive option for storing renewable electricity and for the sustainable production of valuable chemicals and fuels. In this roadmap, we review recent progress in fundamental understanding, catalyst development, and in engineering and scale-up. We discuss the outstanding challenges towards commercialization of electrochemical CO2R technology: energy efficiencies, selectivities, low current densities, and stability. We highlight the opportunities in establishing rigorous standards for benchmarking performance, advances in in operando characterization, the discovery of new materials towards high value products, the investigation of phenomena across multiple-length scales and the application of data science towards doing so. We hope that this collective perspective sparks new research activities that ultimately bring us a step closer towards establishing a low- or zero-emission carbon cycle.