A New Hexagonal Cobalt Nanosheet Catalyst for Selective CO₂ Conversion to Ethanal

We report a new form of catalyst based on ferromagnetic hexagonal-close-packed (hcp) Co nanosheets (NSs) for selective CO₂RR to ethanal, CH₃CHO. In all reduction potentials tested from -0.2 to -1.0 V (vs RHE) in 0.5 M KHCO₃ solution, the reduction yields ethanal as a major product and ethanol/methanol as minor products. At -0.4 V, the Faradaic efficiency (FE) for ethanal reaches 60% with current densities of 5.1 mA cm^-2 and mass activity of 3.4 A g^-1 (total FE for ethanal/ethanol/methanol is 82%). Density functional theory (DFT) calculations suggest that this high CO₂RR selectivity to ethanal on the hcp Co surface is attributed to the unique intralayer electron transfer, which not only promotes [OC-CO]* coupling but also suppresses the complete hydrogenation of the coupling intermediates to ethylene, leading to highly selective formation of CH₃CHO.